# Thundersky Lifepo4 real world experience thread



## chamilun (Jun 17, 2008)

you might consider searching and finding specific projects that use lithium/thundersky batts. *Then invite them to share their experience(s)*. I know the guy in Australia uses them and loves em.


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## favguy (May 2, 2008)

Very good idea, I've just e-mailed everyone on the EVAlbum who are currently using TS LFP cells in completed car conversions to invite them to contribute their experiences, so hopefully we'll start to see some feedback soon 

Paul


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## favguy (May 2, 2008)

One of the EValbum guys I wrote to has kindly sent this feedback so far :

I didn't succeed in joining your group. Here in Aus we have the AEVA that you can visit. I posted just recently details of a trip I did in the forum. You may lift the following & put it in your DIYEC

Posted: 29 November 2008 at 3:35pm 
Id like to hear how our EV owners use their EVs to give us all an idea of what can & cant be done. Ill start off: 
Today I drove from Sandringham to Frankston & back, 56ks. The return trip was on the freeway about 16ks. This I did at 90ks (needing 90A @ 140V). 90Ahrs LIIon & 42Ahrs lead 144V. Once up to speed the TS held 140V. Truly amazing. Purpose was to test the LiIons 
The last time with 99Ahrs of lead I did a shorter trip and barely got home. Im thinking of selling my Honda Insight, no further use. 
David Sharpe 

I dont operate a BMS, preferring to monitor the charging process using a dig meter placed on the cell that reaches charge the fastest. When they get a bit out of balance ie some cells are not charging to 4.2V when others are, I go around each cell with an individual cell charger a modified 5V 15A computer power supply that will do 25A easily and charge to 4.2V per cell. The NG3 Zivan can charge these batteries OK but Id rather not have the final part of the cycle, 3A for one hour which is aimed at gassing wet LA cells. It should be possible to reprogramme the charger. I have a 6kW PV array here & all my driving by EV is "free". (large capital cost to setup though) 

David


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## favguy (May 2, 2008)

Another reply (& no BMS!!) :



I'm happy to tell you about our experience with our Thundersky LFP 90's...

I'm a housewife and he's an academic so neither of us knows anything about 
cars or batteries. And we haven't worried about cycles or anything. We 
just drive all day and plug in at night.

We purchased 45 cells. One was doa but that's ok as we only used 42 and 
still have 2 in reserve. We were told that a charge of over 3.8 was good so 
that's what we aim for. We have NO bms. Once a month we take the cover off 
of the battery pack, check each cell with a battery tester, and use a 
standard 6v charger to bring the 5 or 6 low cells up to 3.8v. We've been 
doing that since we started driving our car in May. Most of the cells 
charge to between 3.8 and 4.0 without any help from us and we've only ever 
had to "top up" 5 or 6 cells.

Cheers
Christie & Ray Cooksey


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## JRP3 (Mar 7, 2008)

How long have they had the pack? If they are only going to 3.8-4 volts aren't they chronically undercharging? And they are using a regular 6 volt charger to bring up the low cells? I think they are heading for an early death of their cells.


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## favguy (May 2, 2008)

I'm pretty sure that although TS cells upper voltage is 4.2v, they are 95% charged at something like 3.8v. On researching this with EVAmerica, they advised that when sourcing Zivan chargers programmed for Lifepo4 charging, Zivan recommend only charging to 95% as it minimizes stress on the cells.

EVA also advised me that another advantage of this seems to be when using a nominal 144v pack for instance, you aren't starting off with an exessive voltage as you would be at 4.2v per cell, a curtis 144v controller is OK with 171v (3.8v per cell) for the first mile or two until the cells drop near to nominal, but they shut down if you try to give them 189v!!

They've had the pack since May, used and charged daily, so early days yet and they do seem to be abusing the cells a bit!, will be a good one to watch though on two counts. Firstly at 90Ah, the constant current pull based on the cell Ah is going to be high, about 1C, with frequent bursts in excess of 2C i'd expect! Secondly add to this that they have no BMS and only check and manually balance with a very rudimentary charger once a month, if they do last even a few years with such treatment, it bodes extremely well for a setup with something like 160Ah cells and a proper BMS!

You'll also notice the first responder uses no BMS either!!! Looks like the Aussies must be big risk takers!!

Disturbing that even 1 cell turned up dead though! That's not really on, even 1 Lifepo4 cell is expensive and it could mean basic QC checking isn't done on each cell prior to dispatch, (or for the cynical amongst us, TS knowingly offload a reject or two under the guise of 2% or so failure rate bieng acceptable?! ) of course, we don't know at this time if they were bought via dealer or TS direct?

In any case I wish them well and hope they do last  I'll chase them up in 6 months I think, to see how it's going.


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## chamilun (Jun 17, 2008)

they may be never OVERCHARGING the batteries, however. It seems this is what leads to quick cell failure, meaning keeping a trickle charge on a fully charged pack, effectively overcharging them. If they are only charging to capacity and stopping, and not overcharging certain batteries, I dont see the problem

It will interesting to hear if anyone has had a lifepo4 pack die after only 1 or 2 years, early TS batteries excluded.

great thread idea, and great thread!


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## bblocher (Jul 30, 2008)

I'm of no immediate help to the thread but did purchase 45 of the 160Ah cells that should be arriving in another couple of weeks. I'll keep you posted if I get any DOA cells and experiences there after as well.


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## jwdsail (Dec 7, 2008)

thanks for starting this thread, I'll be watching it carefully 


jwd


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## ww321q (Mar 28, 2008)

bblocher said:


> I'm of no immediate help to the thread but did purchase 45 of the 160Ah cells that should be arriving in another couple of weeks. I'll keep you posted if I get any DOA cells and experiences there after as well.


At exactly what time will they be delivered ? And will you be at home ? LOL J.W.


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## JRP3 (Mar 7, 2008)

Any updates? Now that we know the cells shouldn't be charged above 3.6-3.8 I wonder what's happening with the guy who is charging to 4.2?


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## bblocher (Jul 30, 2008)

Just thought I would update on my experience. As I posted earlier I ordered some TS 160Ah batteries, charger and the BMS from ElitePowerSolutions.

I just got everything in and Elite has been responsive and helpful along the way with any questions I've had. So far two thumbs for them. They are legit.

I opened everything up and figured the first and only test I could think of was a voltage check on all cells. 41 of 45 were at 3.31 and four of them at 3.25. Voltages were +/- a few thousanths of a volt from these averages. TS docs state +/- 0.1v is normal and these were well below that.

The cells came pre strapped in groups of five with end plates and handles. I also received all the bars, bolts and locking nuts for the cells.

I still need to build the racks and get it all installed but I'll update again after the first use and so on.

I should have some pics up later tonight on the shipment showing everything.

So far so good!


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## booksix (Aug 26, 2008)

if you don't mind, how much was the entire pack/bms and what voltage are you running?


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## bblocher (Jul 30, 2008)

booksix said:


> if you don't mind, how much was the entire pack/bms and what voltage are you running?


I'm planning on 144v unless something goes wrong and I can't fit all my cells in.

I don't have the numbers in front of me right now but you can find the chargers and bms on their site. I went with the 200/24 charger and the bms for 50 cells. I paid $1.65/Ah. Pricing is based on your total Ah that you purchase. Very roughly it was like $15k out the door. The price is scary not knowing what to expect but I keep hearing a lot of people happy with the TS LFP cells and based on LA life you should easily get your money back in the long run if they are used properly.

One other thing I forget to mention. They do monthly orders towards the end of each month (they want to order in bulk to increase their profits). If you order late you have to wait for the next order before yours gets on the list. I just made the deadline ordering mine and it still took 6 or 7 weeks to arrive. I was told 5 weeks but it was over the holidays so I wasn't suprised to see some extra delay. So don't make my mistake, I ordered when I was ready for batteries and have been sitting around mostly waiting.


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## favguy (May 2, 2008)

Hi,
I'm pleased you are happy with your purchase, but you do realise the BMS you get from Elite is a monitoring system only and can't balance the cells don't you? 

You must run a proper cell balancing system in addition to what Elite have given you if you want to protect your cells from premature failure as it doesn't appear to balance at all, simply monitors!

Has anyone had a conversation with them over this, as it seems to me to be irresponsible to be selling such expensive kit without providing or advising on the need for proper cell balancing?

Don't want to be a kill joy, but when you spend as much as buying a new car just on these cells, you don't want to be screwing them up prematurely!

Paul


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## bblocher (Jul 30, 2008)

Thanks for the concern Paul. I'm building my own cell balancers actually. There are a couple ones out there you can buy that Elite provides links for but the cost is too much for something I can do myself easily. Elite has actually stated they are looking for somebody to work with and cell their balancers but I think they are, like me, looking for something cheaper.


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## JRP3 (Mar 7, 2008)

bblocher said:


> Just thought I would update on my experience. As I posted earlier I ordered some TS 160Ah batteries, charger and the BMS from ElitePowerSolutions.


I don't even see the 160 ah cells on the site.


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## bblocher (Jul 30, 2008)

JRP3 said:


> I don't even see the 160 ah cells on the site.


They won't stock them I'm guessing because of cost. Still not sure why they just don't show them with a disclaimer of the long wait. If you email them you can get a quote and they will order them for you. Strangely, however, they do show the chargers and bms system which would only be used with these larger cells


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## favguy (May 2, 2008)

Hi Brian,
I'm glad you are using cell balancers! Can I ask what voltage you are planning as the upper cut off voltage? Seems to be some debate as to the best upper voltage to use with TS cells from 3.8v to 4.2v?

Are you planning on selling your BMS at all, or are you just doing a one off for yourself? As we could all do with a more reasonably costed system I think!

Best regards

Paul


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## bblocher (Jul 30, 2008)

I'm planning on cutting off at 3.8v. Looking at the charging graphs you don't gain much capacity at all (a few more percent) by going to the maximum voltage so I figure why push them to the limit for so little gain.

I have considered selling it since there is so little out there and they are so expensive. Spending $40 a cell to balance is crazy. I'd like to see a $10/cell solutions available. We'll see, I need to finish my project first before I'd have time.


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## bblocher (Jul 30, 2008)

Just thought I'd add some more information I discovered and was pleased with. Turns out the BMS system that TS sells does more than I thought (not enough, but more). It actively will shutdown the charger when a cell reaches the highest allowed voltage. What I didn't know is that it also does over current and low voltage monitoring and sends these triggers out the same serial interface.

Not immediately but down the road I will monitor these signals with a microprocessor and take some action. For low voltage (again configurable value) you could set it up to not allow the motor to be run. This would suck to be stranded but I guess you didn't plan the trip very well. It's better than your batteries being hosed as well. You can always change the low voltage setting on the fly for an override if you desire. The second thing I was thinking was for over current (also configurable) to just cut the power to the small lead (Curtis Controller) which tells it that it's ok to turn on until the current dropped back down (which would be almost immediately).

Just some thoughts...


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## bblocher (Jul 30, 2008)

Things are going fairly well so far. Only have about 80 miles on the cells over half a dozen small charges here and there. Cells are still unbalanced so I don't want to discharge too far.

The BMS system is proving to be a bit of a pain, it's very susceptable to interference. I'm trying to isolate the issue but currently charging over 5 amps is creating problems. The computer will start sensing cells with zero volts and shut off the charger. I have an small length of high voltage line ran next to some of the BMS wiring that I'm hoping is the problem. I'll move this and try again. If not I have some head scratching to do


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## speculawyer (Feb 10, 2009)

So what does the Thundersky BMS system do? Just give you a voltage read-out for each cell? That doesn't seem to be all that useful . . . especially for $3K. 



> It actively will shutdown the charger when a cell reaches the highest allowed voltage. What I didn't know is that it also does over current and low voltage monitoring and sends these triggers out the same serial interface.


Ah . . so it can control the charger . . . is there some sort of standard interface between the BMS and charger? Or did you have to put in some glue circuitry?


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## bblocher (Jul 30, 2008)

speculawyer said:


> So what does the Thundersky BMS system do? Just give you a voltage read-out for each cell? That doesn't seem to be all that useful . . . especially for $3K.
> 
> Ah . . so it can control the charger . . . is there some sort of standard interface between the BMS and charger? Or did you have to put in some glue circuitry?


There is a standard DB9 (serial) cable connection between the two.


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## speculawyer (Feb 10, 2009)

Not sure where to put this, but this thread seemed like a good place . . 

Elithion, a BMS maker, provides a nice list of many of the different Li-Ion BMS systems available. 

They must be pretty confident of their product to advertise their competitor's products that way.


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## bblocher (Jul 30, 2008)

speculawyer said:


> Not sure where to put this, but this thread seemed like a good place . .
> 
> Elithion, a BMS maker, provides a nice list of many of the different Li-Ion BMS systems available.
> 
> They must be pretty confident of their product to advertise their competitor's products that way.


LMAO. Ok click on the Agni motors link. Then click on the "About the motor" link and watch the video.
Also the info on the Ningbo Yangming solution is in correct (I have it). There is no balancing of the cells. Monitor only.


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## speculawyer (Feb 10, 2009)

bblocher said:


> LMAO. Ok click on the Agni motors link. Then click on the "About the motor" link and watch the video.


Woah. That guy is creepy.



bblocher said:


> Also the info on the Ningbo Yangming solution is in correct (I have it). There is no balancing of the cells. Monitor only.


Yeah, I was wondering about that thing. It is expensive and gives you lots of data about the batteries . . . but it really doesn't do much besides just give you info. In the system I'm thinking of building, it will probably be the reverse . . . it will be a balancing system but it won't report any info. I'll just hope it is working properly and perhaps check up on it occasionally by manually testing the voltage on the cells.


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## JRP3 (Mar 7, 2008)

bblocher said:


> LMAO. Ok click on the Agni motors link. Then click on the "About the motor" link and watch the video.


 Yes, Cedric seems to be an odd individual, geniuses often are.


> Also the info on the Ningbo Yangming solution is in correct (I have it). There is no balancing of the cells. Monitor only.


It doesn't say there is balancing that I can see.  How are they wrong?


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## bblocher (Jul 30, 2008)

JRP3 said:


> Yes, Cedric seems to be an odd individual, geniuses often are.
> It doesn't say there is balancing that I can see.  How are they wrong?


The balancing column has a checkbox.


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## bblocher (Jul 30, 2008)

speculawyer said:


> Woah. That guy is creepy.
> 
> 
> Yeah, I was wondering about that thing. It is expensive and gives you lots of data about the batteries . . . but it really doesn't do much besides just give you info. In the system I'm thinking of building, it will probably be the reverse . . . it will be a balancing system but it won't report any info. I'll just hope it is working properly and perhaps check up on it occasionally by manually testing the voltage on the cells.


Yeah I'm building my balancing circuit as well. This with all the info from that system and I should be good


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## JRP3 (Mar 7, 2008)

bblocher said:


> The balancing column has a checkbox.


Looks like a question mark to me.


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## speculawyer (Feb 10, 2009)

bblocher said:


> Yeah I'm building my balancing circuit as well. This with all the info from that system and I should be good


How hard is it to do a balancing system? My skills are weak and I'm just trying to figure out which balancing system to buy. It is kinda annoying how they are all hard to get . . . there are no retailers . . . I'm just contacting each manufacturer one by one.


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## bblocher (Jul 30, 2008)

JRP3 said:


> Looks like a question mark to me.


Column 6 is balancing. Only one has a dash (PackTrakr) and the rest are check marks. For my setup columns 10 and 11 have a question mark though.


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## JRP3 (Mar 7, 2008)

bblocher said:


> Column 6 is balancing. Only one has a dash (PackTrakr) and the rest are check marks. For my setup columns 10 and 11 have a question mark though.


Ningbo Yangming
(no link: attack website)
Sold by Elite Power China
Zhe Jiang prov. Fancy Central. w/slaves 10,20, 30...100 Any ✓ ✓







✓ ✓ ? ? Incl.









Weird, they show as question marks on my system. Maybe I'm missing the "check" character.


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## dimitri (May 16, 2008)

Well, now that I am a happy owner of 40 TS 160AH cells, I figured I'd chime into this thread 

Last night I finished wiring up PakTrakr remotes and attempted to do first charge of the pack. Out of the box all cells had exact 3.3V and manual states that cells must be charged as they are not charged from the factory. I figured that cells must be at some SOC level between 0 and 100 and should take approx same time to charge. So I connected my brand new Zivan NG3 and flipped the power switch.

First few hours it was going as planned, but then just when I got distracted by business call for few minutes, 5 cells vent over 4V up to high limit of 4.25-4.3 V. Whole thing happened so fast I couldn’t believe it. I immediately shut off the charger and these cells settled at 3.6V within minutes. They appear just a tad warmer to touch than all the others. Man, I hope I didn’t freaking ruin them 

Those 5 cells came from same strapped group and their casing seems to have a little different shade of yellow, I think they must be from a different production batch and that is why they had diff SOC. Lesson learned, initial charge and balancing is critical to watch like a hawk.
Since those 5 cells are sequential in the pack, I will use 100 Amp car battery tester to burn off some of their charge , to bring them to same level as all others.

Hopefully I will have cell balancers soon so I can carefully balance whole pack.

From what I read, once initially balanced these cells stay pretty well balanced, so my experience today is not against TS product, just a learning curve


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## bblocher (Jul 30, 2008)

dimitri said:


> Well, now that I am a happy owner of 40 TS 160AH cells, I figured I'd chime into this thread
> 
> Last night I finished wiring up PakTrakr remotes and attempted to do first charge of the pack. Out of the box all cells had exact 3.3V and manual states that cells must be charged as they are not charged from the factory. I figured that cells must be at some SOC level between 0 and 100 and should take approx same time to charge. So I connected my brand new Zivan NG3 and flipped the power switch.
> 
> ...


I'm sure they are fine. 4.2 is still after all the manufacturers limit and if you didn't leave them slightly above for long you should be good. I'd label/mark those given cells for future tracking to see if there are long term affects after a few years or something (i.e. they are the first give to go).


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## JRP3 (Mar 7, 2008)

dimitri said:


> Well, now that I am a happy owner of 40 TS 160AH cells, I figured I'd chime into this thread


Where'd you get yours and how much were they?
What about charging the cells in parallel to balance them initially? I've read that it's supposed to work though I guess you'd need a low voltage but high amperage charger to do it.


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## dimitri (May 16, 2008)

JRP3 said:


> Where'd you get yours and how much were they?
> What about charging the cells in parallel to balance them initially? I've read that it's supposed to work though I guess you'd need a low voltage but high amperage charger to do it.


I got them from Elite Power Solutions, you can contact them for a quote, I don't want to post prices, they change too often.

Charging in parallel could work, but IMHO its not practical and not worth the trouble, plus like you said you need a 4V charger capable of at least 20 amps, unless you want to wait few days for a charge.

BTW, I balanced those 5 cells very easily last night. I used 100Amp car battery tester I got from Harbor Freight a while ago. I connected it to the string of 5 cells in question and made 5-6 burns about 10 seconds each. That burned off just enough charge for other cells to catch up once I turned the charger back on. Turns out they were not that much off anyway 
Can't burn more than 10 seconds at a time, the element gets almost white hot and starts to melt the insulation inside of the tester


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## dimitri (May 16, 2008)

BTW, I got response from Elite Power in regards to 5 cells being different. They explained that different production batches produce cells with slightly different capacity, but all over nominal capacity. E.x. some 160Ah nominal cells can actually be 166Ah or even 175Ah. Obviously it would take slightly different time for a first charge, but once fully charged and balanced in single pack, they will remain balanced as long as some balancing solution is in place.
I will be using cell balancers designed by Brian to keep my pack balanced. Contact him if you want some of those.


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## dimitri (May 16, 2008)

This weekend was fun, I got cell balancer kits from Brian and setup a small sweatshop - my wife and 10 year old son were installing components into the PCBs and I was soldering and crimping connections. 40 balancers were done in about 7 hours, everyone enjoyed it 

here are boards before heat sinks

here is final product

here are cell balancers happily LEDing on top of TS cells


Once all 40 boards were installed, I fired up Zivan NG3 charger and within few hours all cells were shining red LEDs and few minutes after that charger turned itself off. Whoo hoo, first charge is done! PakTrakr shows 144V and all cells are equally charged to 3.6V each.

Balancer kits are excellent quality and saved me lots of money on DIY vs buiyng them from someone. Every LiFePo4 cell must have one of these to avoid overcharging and allow whole pack to stay in balance long term. Brian invested his time and money into designing the PCB and working out final schematics, he also bought PCBs and parts in bulk to save more money, so he is offering remaining kits for sale on his blog and probably in "for sale" section on this forum. I highly recommend these kits, every single one worked 100% ( as long as your wife and kids don't mess up polarity on semiconductors  )


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## bblocher (Jul 30, 2008)

I did finally add something in the for sale section of this site. There is info on my blog as well.

Nothing crazy, but I just passed 250 miles on the EV over the weekend and that's just been cruising around showing friends and being bored. I can't wait for another couple weeks when the plug gets installed at work and I can start commuting in it!

I've only got about 4 or 5 charges now with the balancers in place but the voltages are much closer. Before my charger wouldn't even start backing down in amps, it would shut off because of over voltage alerts and there would be a range on my cells from 3.4-3.8 volts. I now only see a variation of about 3.59 to 3.64 or so as the charge is completing normally, no more over voltage alerts.


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## PhantomPholly (Aug 20, 2008)

Congrats, Brian!


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## JimK (Mar 21, 2009)

I also purchased the same batteries as Brian and Dimitri. Delivery is expected within the next 2-3 weeks. I will be using Brian's "Volt Blocher" cell balancer kit. This thread is a great idea and I will pitch in with my own experiences.


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## bblocher (Jul 30, 2008)

JimK said:


> I also purchased the same batteries as Brian and Dimitri. Delivery is expected within the next 2-3 weeks. I will be using Brian's "Volt Blocher" cell balancer kit. This thread is a great idea and I will pitch in with my own experiences.


Oh man another 2-3 weeks? You must have missed the ordering window? I understand them doing monthly orders to maximize their profits, but sure sucks for us if we order right after they do. Then you're looking at 2+ months for delivery.


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## JimK (Mar 21, 2009)

Brian,

My order was placed towards the end of February and the expected delivery date at that time was mid April (approx. 6 weeks). Not too inconvenienced since I still have things to work on in the meantime like fastening my battery box, rear suspension, etc.....


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## chamilun (Jun 17, 2008)

what kind of range are you guys expecting?


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## bblocher (Jul 30, 2008)

chamilun said:


> what kind of range are you guys expecting?


I was expecting about 100 mile range. Ended up getting 80 driving 55-60mph. However, I still have my original tires which are a Z rated racing type tires. I expect switching to a H rated should improve this a bit. This will be my first step in increasing range. The range is already more than I need, but I'd hate to see the project be completed so I'll always be tinkering to improve range.


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## ElectricSlide (Jan 21, 2009)

bblocher said:


> I was expecting about 100 mile range. Ended up getting 80 driving 55-60mph. However, I still have my original tires which are a Z rated racing type tires. I expect switching to a H rated should improve this a bit. This will be my first step in increasing range. The range is already more than I need, but I'd hate to see the project be completed so I'll always be tinkering to improve range.


I'm surprised at your sub 100mi range, but it must be because I'm not caring to research specs and calculate at the moment. Still a great accomplishment,though, so congrats! The surprise is based on the RAV4 EV getting 100-120mi range 10 years ago with NiMH.


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## bblocher (Jul 30, 2008)

ElectricSlide said:


> I'm surprised at your sub 100mi range, but it must be because I'm not caring to research specs and calculate at the moment. Still a great accomplishment,though, so congrats! The surprise is based on the RAV4 EV getting 100-120mi range 10 years ago with NiMH.


Any idea what the capacity of those packs were?

UPDATE:
Gotta love wikipedia. Says here the capacity was 27.4kWh. I have 23kWh in my car. It says 80-120 mile range on wikipedia, so I'm guessing that's 80 miles for 65mph or so and 120 for probably 35-45 mph. I can easily get 120 miles driving at 45 mph, the amps drop almost in half from 65-45mph.

By comparison look at the Tesla roadster which claims 220 mile range. It has a 53kWh battery!


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## JimK (Mar 21, 2009)

...and the new Tesla S is supposed to offer battery packs wit ranges up to 300 miles per charge. "Three battery pack choices will offer a range of 160, 230 or 300 miles per charge". This is one fine looking sedan that seats 7 with a projected price tag of $50K....


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## JRP3 (Mar 7, 2008)

Just remember that's $50k after your $7k govt. rebate, for the 160 mile version, and the "7 passenger" includes 2 jump seats in the trunk for kids that no one will actually use. Still a nice vehicle.


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## AndyH (Jun 15, 2008)

*LVC??!! Re: Thundersky Lifepo4 real world experience thread*

Not quite a DIY vehicle, but DIY control and monitoring of a pack of T-S cells, so I hope you don't mind. 

I have a 5000W motorcycle/scooter that uses 24 T-S 60Ah cells in series. The bike was delivered with no BMS. Cells varied WIDELY in state of charge on delivery - initial charging/balancing was rough. I'm using a 21-channel BMS board that has per cell low voltage monitoring, as well as 3.7V end of charge and 1/2 A of shunting/balancing.

Pack level low voltage cutoff (LVC) protection is not enough for any series bank of cells - we need cell-level LVC. LiFePO4 can handle significant overcharge without giving up much life - but discharging too deeply will kill a cell in short order.

Here's some data from my pack. I have a PakTrakr with three 8-cell remotes, and a Sharp Zaurus Linux PDA for data collection.





























Thunder Sky says 2.5V is the minimum for a 2000 cycle lifespan, while 2.0 is the absolute lowest the cell should go without permanent damage.

Near the end of this ride - where the cells hit their lowest points - the controller's 'pack LVC' tripped and 'pulsed' the throttle to let me know to back off. But it was already too late.

Here's a thread with the gory details:
http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=8675
Here's the BMS:
http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=5416
http://www.tppacks.com/products.asp?cat=26
Here's the bike:
http://www.rechargeablelithiumpower.com/oscommerce2/catalog/xm5000li-p-44.html

The PakTrakr reports voltage x100 (360 = 3.6V).

Bottom line - cell level LVC is the single most critical bit of data to monitor to keep LiFePO4 cells alive. Since cell end of charge is pretty close to vertical, this is something that must be automated - by the time a driver sees a 'low voltage cell' indicator light, the cell is already below the LVC point - it happens FAST!

Andy


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## peggus (Feb 18, 2008)

I can see from andys data that the impedance of the 60 Ah cells is about 3.5 mOhm per cell. 

Does anyone have data on how the larger cells perform, i.e. voltage sag at a given current. I'm trying to determine the impedance/Ah for thundersky cells. It is commonly the case with lithium cells that the higher capacity cells have higher impedance so for high performance it makes sense to parallel many smaller cells to get to the capacity you need. 

I'm wondering to what degree this is true for thundersky cells?


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## bblocher (Jul 30, 2008)

peggus said:


> I can see from andys data that the impedance of the 60 Ah cells is about 3.5 mOhm per cell.
> 
> Does anyone have data on how the larger cells perform, i.e. voltage sag at a given current. I'm trying to determine the impedance/Ah for thundersky cells. It is commonly the case with lithium cells that the higher capacity cells have higher impedance so for high performance it makes sense to parallel many smaller cells to get to the capacity you need.
> 
> I'm wondering to what degree this is true for thundersky cells?


Here is a sample set of my cells:

Internal resistance, capacity, voltage 
0.34, 166.1, 3.313 
0.31, 167, 3.313 
0.35, 166, 3.313 
0.31, 166.8, 3.31 
0.35, 166.2, 3.313 
0.31, 166.1, 3.311 
0.32, 166.8, 3.312 
0.31, 167, 3.311


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## dimitri (May 16, 2008)

I agree that LVC is critical, but I would say that overcharge control and balancing are just as critical. You say that cells handle overcharge well? My understanding is that overcharge kills them just as well.

I believe that OEM manufacturers design Lithium packs such that LVC protection kicks in well before it gets to 0% SOC, thus reducing useable energy, but at the benefit of longer pack life. Personally I agree with this approach. IMHO, instead of designing complex BMS, I'd rather set LVC at 20% SOC, well before the cliff, and also take great care to keep my pack balanced at the charging phase. This way, cells stay close enough in SOC level that 20% SOC is well above any individual cell's low voltage level.

That said, there is still a risk of ruining a cell somewhere during pack's life cycle, but I think its acceptable and manageable risk. Afterall, extra $1000 in BMS cost would buy several new cells, and they get even cheaper over time.

Granted I don't have daily experience in using TS cells just yet, so take my words with a grain of salt . I just see so many complex BMS designs, makes your head spin, which pushes some potential LiFePo4 buyers away from this technology. I think with some care and simple BMS these cells can compete with Lead Acid in total cost of ownership even today.

P.S. looking at your last graph, that one cell started to deviate from the rest pretty early in the discharge process, indicating that this cell is probably already damaged or lacks full capacity, so even with sophisticated BMS you will be stopping your whole pack short because of one bad cell. Might as well replace it now...


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## peggus (Feb 18, 2008)

Thanks, what unit is the impedance and how did you measure it?




bblocher said:


> Here is a sample set of my cells:
> 
> Internal resistance, capacity, voltage
> 0.34, 166.1, 3.313
> ...


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## speculawyer (Feb 10, 2009)

*Re: LVC??!! Re: Thundersky Lifepo4 real world experience thread*



AndyH said:


> I have a 5000W motorcycle/scooter that uses 24 T-S 60Ah cells in series. The bike was delivered with no BMS. Cells varied WIDELY in state of charge on delivery - initial charging/balancing was rough. I'm using a 21-channel BMS board that has per cell low voltage monitoring, as well as 3.7V end of charge and 1/2 A of shunting/balancing.


A 72V cycle with 60Ah cells? What kind of range does that have?


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## bblocher (Jul 30, 2008)

peggus said:


> Thanks, what unit is the impedance and how did you measure it?


These numbers are from TS during their QA cycle. They are available for all cells based off the serial numbers. I have no clue if those resistance numbers are scaled in anyway. I don't really know what is expected for these cells. I got this data to check on capacity of the cells.


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## speculawyer (Feb 10, 2009)

bblocher said:


> Here is a sample set of my cells:
> 
> Internal resistance, capacity, voltage
> 0.34, 166.1, 3.313
> ...


All of those cells have a capacity bigger than the 160Ah rating they were given? Nice. 

Edit: Oh, those are the values they tell you. Well, that is not as exciting as independent verification.


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## bblocher (Jul 30, 2008)

speculawyer said:


> All of those cells have a capacity bigger than the 160Ah rating they were given? Nice.


Correct, they "supposedly" will not allow a cell to go out if it's below the advertised rating. Dimitri got some of this batch (5 cells) and the rest were a newer batch which had all 175Ah cells (again they are "160" cells).
Maybe this variance is normal, or they are bumping them up a little so if you calculate for 160Ah capacity you'll stay further away from 0 SOC and prolong life. I'm not sure, but it seems TS is working hard to produce quality. I'll keep my fingers crossed.


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## Mesuge (Mar 6, 2008)

*Re: LVC??!! Re: Thundersky Lifepo4 real world experience thread*



AndyH said:


> Here's a thread with the gory details:
> http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=8675
> Here's the BMS:
> http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=5416
> ...


 
Hi Andy,
enjoyed your thread at EndlessO very much, incl. those videos, very nice to see all those components (BMS, TS batt., charger, scooter) put in test at once, thanks. Would you pls. post some more info about your progie for Zaurus-Paktrakr, I've had seen your original thread at EVconvert few years back, so you have perhaps made some progress on that front since then?


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## AndyH (Jun 15, 2008)

*Re: LVC??!! Re: Thundersky Lifepo4 real world experience thread*



speculawyer said:


> A 72V cycle with 60Ah cells? What kind of range does that have?


I'm getting about 45 miles if I drive it very hard - full throttle, little coasting, uphill in the wind both ways , Etc.

It's supposed to have a tested max range of 85 miles at 25mph.

I still don't have the cell-level LVC connected, and am still breaking the pack in, so can't provide better numbers yet.

Andy


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## AndyH (Jun 15, 2008)

dimitri said:


> I agree that LVC is critical, but I would say that overcharge control and balancing are just as critical. You say that cells handle overcharge well? My understanding is that overcharge kills them just as well.
> 
> I believe that OEM manufacturers design Lithium packs such that LVC protection kicks in well before it gets to 0% SOC, thus reducing useable energy, but at the benefit of longer pack life. Personally I agree with this approach. IMHO, instead of designing complex BMS, I'd rather set LVC at 20% SOC, well before the cliff, and also take great care to keep my pack balanced at the charging phase. This way, cells stay close enough in SOC level that 20% SOC is well above any individual cell's low voltage level.
> 
> ...


I agree on replacing the cell, Dimitri, and will once the pack is broken in and I'm sure it's the only weak cell. I'm documenting cell performance for the bike importer, and will use the data to support getting cells replaced under warranty if necessary. The BMS was not in place for this discharge, BTW. (The low cell charges fully and spends most of it's time in the mid-range while discharging - it broke out of the bottom near the end of a ride. That graph is actually the last 10 miles of a hard 42 mile ride.)

I suggested that LVC is most critical because it will kill a cell almost immediately. Slight to moderate overcharge (short of venting) will shorten the life, but won't do immediate damage (If you don't mind me suggesting there are different levels or definitions of damage. It's my understanding that some level of overcharge is like abnormal tire wear when the car needs shocks or an alignment, while dropping well below LVC is more similar to the tire blowing-out).

Thunder Sky, in their battery manual, give the absolute limits of their cells as 2.0 to 4.3V, but say that keeping the low side at or above 2.5V and keeping teh 4.3V upper limit will give a 2000 cycle life.

Charge and discharge limits will vary with the application. Limiting the discharge range will shorten drive time, but lengthen pack life. Hybrid cars normally don't charge higher than 80% or discharge lower than 40%, for example. Sandia Labs ran standardized tests on 10Ah 40138 cells from PSI. Keeping the cells between 2.1 and 3.65 (~100% DOD) gives 2000 cycles, while narrowing it down to 10% of capacity gives more than 8000 cycles.

This is an interesting paper on pack building and balancing. Slides 32 to 36 talk about balancing strategy. No two cells will provide exactly the same number of Ah. This means that perfectly balancing them on charge will not guarantee that the pack will discharge evenly. So...'raising' one's 'personal LVC' can give some amount of longer cell life, it still doesn't guarantee that the cells will discharge evenly. We'll always be limited to the performance of the lowest performing cell in the pack.

Andy


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## dimitri (May 16, 2008)

> We'll always be limited to the performance of the lowest performing cell in the pack.


That was exactly my point against complicating the BMS by adding cell level LVC protection. Having a PakTrakr or any other per-cell voltage monitor (which is a must for any EV pack) will quickly reveal the weakest cell in the pack. Then, all you need to do is monitor for LVC on that one cell, and set your overall pack usage range not to get close to LVC on that one cell, then the rest of the pack will just follow that one lowest cell. Over time, if this cell gets too weak, you swap it for a new one and pick the next weakest cell in the pack for monitoring.

Maybe we need to design a version of the Volt Blocher that would monitor LVC and trigger NO/NC action, but we would only need one of these boards for the weakest cell, the rest would be basic boards, so the cost doesn't rise much. Then we can route that NO/NC to the buzzer or dash light or even motor controller for action.

This is similar to what other BMSs do for LVC, but they have it on each cell, which probably triples the cost of the whole system. I think having just one such board on weakest cell should give good results.

I will definitely pursue this approach as I begin to use my pack daily, to see if it holds water.


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## dimitri (May 16, 2008)

> I suggested that LVC is most critical because it will kill a cell almost immediately.


If you think about it, this is no different in Lead Acid cells. Deep discharge kills them very quickly, and the point of no return comes very fast in EV use because discharge current is so high. In my first EV I came to my max range once on the way from work and practically limped home last half mile. Few days later the weakest cell in my pack had to be replaced ASAP since it was not holding the charge at all.

So battery management is not that different between LA and LiFePo4, keep them balanced and watch for the weakest cell...


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## JRP3 (Mar 7, 2008)

Of course with LA voltage is a better indication of SOC than with Lithium so you get more of a warning.


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## Jeff (Sep 25, 2008)

Adding LVC detection is a relatively easy add-on to a voltage clamp (shunt) circuit. It was less than $1 per channel to include precision LV detection at 2.5v
I'll post a schematic PDF link below for review. An LVR (low voltage reset) circuit asserts an opto to flag the host MCU. A local LED can be added to the circuit to visually indicate which channel is triggering the LV. Or you can strobe all to identify the channel. It wasn't important for me.

Opto 1 flags the charger to linearly reduce power when the clamp become active. Each clamp opto has it's own input to the host MCU.

Opto 2 flags the operator that one of the series cells has reported LV. All LV optos are paralleled to one input in my ebike application.

This circuit is used on many ebike packs with sixteen cells in series, one circuit for each cell.

Regards, Jeff

http://www.evbones.com/vclamp.pdf


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## AndyH (Jun 15, 2008)

dimitri said:


> If you think about it, this is no different in Lead Acid cells. Deep discharge kills them very quickly, and the point of no return comes very fast in EV use because discharge current is so high...
> 
> So battery management is not that different between LA and LiFePo4, keep them balanced and watch for the weakest cell...


In theory, Dimitri, I agree - low voltage point is important to monitor regardless of battery type. But the beauty of LiFePO4 is that they don't give a driver the 'steady slow-down' they get from lead. The flip-side of that 'strength' is that the cells fall quickly when they're done for the day.

Here's what I'm talking about. This is a 10A (1C) constant load discharge for a 36V12Ah SLA and a 36V10Ah LiFePO4 pack made from 40138 cells.










A123 cells have a more vertical drop-off after the 'shoulder', while Thunder Sky cells have a 'shallower' drop than these.

From that chart, one might assume that they would have less warning that the lithium pack was running on empty as compared to the constant slow-down the SLAs provide. Here's a LiFePO4 charge/discharge curve:










On the road - especially when one is used to lead - these cells don't give any indication that they're getting tired until the very end.

To give LiFePO4 the longest life possible, and to give the owner the best return on investment, ACTIVE cell-level LVC protection is the first order of business. Controlling discharge current and preventing overcharging are tied for second. Cell balance can be third, but that is more about giving one full range, not for preserving the pack.

LVC isn't something that clutters the battery management picture. We're talking about two functions - something to sense the voltage in each cell and something to signal the operator when the 'alarm goes off'. Look at how a group of ebikers have solved the problem - three components: A TC54 2.1V comparator, an ILD2 opto isolator, and an 820 ohm current limit resistor for the opto. It can drive a relay, it can pulse the throttle, it can pulse the brake, or it can provide electric shock to the operator's seat bottom - whatever works best. 

Andy


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## dimitri (May 16, 2008)

> Look at how a group of ebikers have solved the problem - three components: A TC54 2.1V comparator, an ILD2 opto isolator, and an 820 ohm current limit resistor for the opto. It can drive a relay, it can pulse the throttle, it can pulse the brake, or it can provide electric shock to the operator's seat bottom - whatever works best.


Andy, I am thinking of adding LVC function to my BMS, I looked at the schematics you linked above, looks very cool in its simplicity. However, they seem to take 2.1V as the cutoff point, using 2.1V comparator. Not sure if this is specific to cylindrycal cells, because according to Thundersky docs, I should use at least 2.5V or even more for LVC. I know that I need to take voltage sag into the consideration, but I think that even based on your graph above, I could use next level comparator at 2.7V and still have good LVC protection. On your 36V example it would be at 32.4V, which is about 9.3Ah for 10Ah cell, not bad.

What do you think?


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## AndyH (Jun 15, 2008)

*Lvc*

Hi Dimitri,

Yes - the 2.1V LVC was chosen for that circuit because many of the ebike folks are using A123 and PSI cells in their packs. All LiFePO4 can go down to 2.0V, but we'll get longer battery life if we keep a few 'electrons in the tank'. I agree with your idea - I'm building a new BMS board for my TS60s and using the 2.7V detector.

The volt meter and PakTrakr display will still be my primary indication of state of charge and remaining range, but the combination of pack LVC from the controller and cell LVC from the BMS board (both cutting power if/when activated) should keep me from doing something expensive. 

Andy

If you're interested in using the TC54/opto solution, contact Gary at tppacks.com - he's got a small run of LVC boards that aren't on his site yet. Each board has 24 channels and can be daisy-chained to add more channels in any combination. For our use, we can ignore the active cut-off parts on the left of the board and use the output of the optos. I don't know what the price will be.


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## dimitri (May 16, 2008)

Andy,

according to Brian who is currently using TS 160 AH cells to their full potential  its not uncommon to sag under 2.7V at 3C current, during acceleration. I drew approximate 3C line on TS discharge chart and found it to be at or under 2.7V in most of second half of discharge cycle, so cutting at 2.7V is not a good idea. I will amend my design to use 2.1V module, but use a variable resistor for final adjustment of cut off voltage, which will probably be between 2.5V and 2.6V.

I don't need Gary's boards, I will have my own PCB design, so each cell has a module on it. I think this is most appropriate for large cells.

Thanks


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## AndyH (Jun 15, 2008)

dimitri said:


> Andy,
> 
> according to Brian who is currently using TS 160 AH cells to their full potential  its not uncommon to sag under 2.7V at 3C current, during acceleration. I drew approximate 3C line on TS discharge chart and found it to be at or under 2.7V in most of second half of discharge cycle, so cutting at 2.7V is not a good idea. I will amend my design to use 2.1V module, but use a variable resistor for final adjustment of cut off voltage, which will probably be between 2.5V and 2.6V.
> 
> ...


Dimitri,

Yes - the cells will sag to 2.7 under a large load. They'll sag more deeply a few more miles down the road. That's exactly the point of LVC protection - giving immediate feedback when a cell gets close to a limit - before the pack is damaged.

This LVC circuit, when used to pulse the controller via either a brake inhibit or by pulsing the throttle, will give about 4 pulses per second if you don't take your foot off the throttle. The car will not stop in the middle of traffic, because the cell will recover quickly once the 3C load is removed, the LVC signal will stop, throttle (or controller) is released, and the controller will again respond to pedal position. If you ease-off the throttle, voltage sag is reduced and the LVC does not come into play.

In the end, you get to choose the operational limits for your pack, and that's as it should be. My interest is in reaching or beating 2000 cycles on the pack, so I'm interersted in finding the 'lines' and 'coloring' inside them. My pack management limits would be different if I was running a race vehicle with an unlimited sponsorship by a battery company. 

I'm very happy that you're including LVC protection in your management plan, Dimitri!

Andy


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## bblocher (Jul 30, 2008)

peggus said:


> Thanks, what unit is the impedance and how did you measure it?


Just an update on this. I found out those numbers from TS are in mOhms. Supposedly their tolerance level is 1 mOhm resistance.


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## speculawyer (Feb 10, 2009)

dimitri said:


> according to Brian who is currently using TS 160 AH cells to their full potential  its not uncommon to sag under 2.7V at 3C current, during acceleration. I drew approximate 3C line on TS discharge chart and found it to be at or under 2.7V in most of second half of discharge cycle, so cutting at 2.7V is not a good idea. I will amend my design to use 2.1V module, but use a variable resistor for final adjustment of cut off voltage, which will probably be between 2.5V and 2.6V.


Damn . . . this sure makes creating a good battery management system a non trivial task. One certainly doesn't want to over-discharge a battery since that could kill it thus requiring a costly replacement. But on the other hand, if you are just experiencing some transient voltage sag as opposed to real over-discharge, you wouldn't want your vehicle to just die while you are driving. Thus, a simple voltage threshold might not be a real good way of triggering low voltage cut-off. 

Then again, maybe the better way of solving the problem is designing the vehicle better such that you don't experience such sag. Perhaps adding some capacitance into the system.


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## dimitri (May 16, 2008)

Voltage sag is inevitable, no reasonable capacitor can store enough energy for even 1-2 seconds of EV energy needs.

Its not that hard to find proper LVC cutoff, just takes a bit of experimenting. At this time I decided to use 2.6V as my LVC, which would sound very annoying buzzer. I am against such approach where throttle is crippled because of potential liability and design complexity. I think that loud annoying buzzer should be enough for anyone to take a foot from the pedal and think. If not, that person is either deaf or doesn't belong in EV 

Also, LVC is not a replacement of SOC monitor, IMHO. So, SOC gauge would tell you when you are approaching point of no return way before LVC would. LVC would be a last resort protection and also indicator of failing cell.


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## dimitri (May 16, 2008)

Another thing to mention is that BMS approach is somewhat different between E-Bikes and E-Cars, based on several factors. Bikes have smaller cells and thus higher C discharge rates, so BMS must be more aggressive. And buzzer on a bike is not so effective, with a helmet and all 

Also, BMS modules for smaller packs can be done all on one PCB, but for large prismatic cells scattered across the car, individual modules per cell make more sense.


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## AndyH (Jun 15, 2008)

Let's attach a 2.7V LVC to a 'brake inhibit-like function' on the controller and take a virtual drive. Full pack, warm day, smile on the face, heading out to play for the first 20 miles on a '40 mile pack'. We're heading uphill and have it 'floored'.

IF one or more cells sag(s) to or below 2.7V: (we'll do this in slow motion) One cell drops below 2.7V. An optoisolator activates on the BMS, signaling the controller to stop feeding the motor. Power comes off. Car coasts. Cell voltage recovers to well above 3.3V. Opto de-activates. Controller feeds power to the motor. One cell sags to below 2.7V. Repeat.

Back to full speed: The driver will notice, as they continue up the hill, a 'pulse' in power delivery about 3 times per second. They check the gauges and see that they're drawing much more power than they expected. They get 'out of the throttle' a little bit.

The cells do not sag below 2.7V, the LVC stays asleep, and the drive continues.

If the driver keeps the throttle to the floor, the BMS and controller will work together to limit the current draw to keep from damaging the pack, and the driver will have the constant feedback thru both power pulses and the bouncing volt meter.

Now let's use a buzzer.

Slow motion. Full throttle, cell sags below 2.7. Buzzer sounds. Human is rocking to their favorite tunes so their reaction time is a bit up - to maybe 1/2 a second. Cell continues to sag and is now down to 1.8. Driver pulls off the throttle, cell recovers, voltage back up to 3.3V, driver gets back on the pedal and continues.

The BMS would have taken the pack off-line twice before the human reacted, and the lowest cell wouldn't have dropped below 2.7.

------

Later in the drive - say the last 10 miles of the pack's 40-mile range - is even more critical, because the pack will sag deeper with the same throttle input or load. More cells will drop below 2.7. The weakest cells in the pack will go even lower. Even with full attention on the gauges, the driver is guaranteed to take the cells down too far. Eventually, the controller's pack-level LVC will kick in, and you're back to pulsing power..and a guarantee of cell damage.

Go back up to post 53 and look at the three graphs - those are real-world end of the drive numbers from a T-S pack with NO cell-level LVC protection. There was NO indication of low cells until the controller started to pulse. Even in the pulses - the same thing that would happen if a BMS's LVC tripped - the EV had power and was in full control.

A buzzer and/or light would have been useless because there isn't enough time to react to reduce the load before the controller LVC triggers.

Bottom line -- I have damaged at least one of my cells on the FIRST FULL CYCLE of the pack because I didn't have cell-level LVC protection.


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## dimitri (May 16, 2008)

Totally agree with you that cell level monitoring/protection is a must, but I think your example of buzzer vs. throttle pulse is a little exaggerated 

You don't go from 2.7 to 1.8 in few seconds, if you do, then either its a bad cell or you are at 5% SOC, in both cases you should not be driving, especially not at 3C throttle.

And 3C loads are not typical in well designed EV, they only happen during hard acceleration and steep hills, so hitting hard bottom is an exception rather then the rule.

If your EV regularly exceeds 1-1.5 C during normal driving, then you need a bigger pack to begin with.

OK, sorry Andy, I don't mean to split hairs with you, your approach is really cool, but I will personally not recommend it to others until I try it myself


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## AndyH (Jun 15, 2008)

dimitri said:


> ... Bikes have smaller cells and thus higher C discharge rates, so BMS must be more aggressive...


According to Brian's blog, his S2000 is using 160Ah TS cells and a 500A max controller. Max pull thru the pack is just over 3C. My ride has a 100A max controller and 60Ah TS cells - 1.6C max.

Near end of my drive, I was only trying to hit 25-30 mph and was pulling cells down to 1.8V with only a .5C load - and down to 2.2V with only a .1C load! At rest the pack was not yet to the 'shoulder' of the discharge curve (but it was close).

Human reaction time - for things like hitting the brakes once a driver sees a brake light in front of them - is .6 to 1 second. It's longer when one is distracted by the radio, their date, or a cell phone. Within .6 seconds of one hearing a buzzer, an LVC will have cut power two to three times.

http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=138.0 Here's a rection time simulation - enjoy!



dimitri said:


> ... And buzzer on a bike is not so effective, with a helmet and all


What helmet?  Actually, the helmet helps - the wind in my ears at 45mph even drowns-out the loud 'turn signal' beeper - making it useless!



dimitri said:


> Also, BMS modules for smaller packs can be done all on one PCB, but for large prismatic cells scattered across the car, individual modules per cell make more sense.


I agree - different apps may require different packaging and wiring. Of my 21 cells, for example, I can immediately access the tops of only six of them. Nine are buried near the front, and others are stacked two-high in the back. I absolutely cannot use a per-cell board for my pack.

My next BMS solution may only have LVC on the bike and shunts off-bike near the charger. Packaging and heat control should be easier that way.

No sweat at all, Dimitri. I've enjoyed the conversation. Spaceba tovarich!


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## dimitri (May 16, 2008)

Andy,

I'm trying to put your experience in perspective, while looking at TS discharge graph. If you pull your cells to 1.8V at 0.5C load or 2.2V at 0.1C load, then your cells are at pretty much 100% DoD, right? That begs an obvious question, WTH are you doing driving your pack to 100% DoD?  Why not stop at say 90% or 85% DoD? 

With 21 cells of 60Ah you have about 4000Wh in the pack, right? I don't know much about bikes, but I recall reading a typical 75Wh/mile energy use, does that sound in the ballpark? That gives you around 53 miles at 100% DoD or 43 miles at 80% DoD, right? So, if you want your pack to live a long happy life, wouldn't you limit your range to 40-45 miles?

I'm just flexing my math skills here  please let me know if I am off the target or somewhere in the black at least?

Thanks


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## AndyH (Jun 15, 2008)

I took that ride with the PakTrakr installed but no cell-level BMS because I was collecting data for the company and for other owners of these bikes. The bikes arrive with no BMS and a TS charger. The cells are at varying states of charge.

The new owner follows instructions and charges the pack. Some cells come of the charger over charged while many are well below 50%. During the first full ride, some cells drop to 1. On the next charge, the high cells cook, the low cells go too low - only the cells in the middle are 'somewhat happy'. (I've got the data to prove this quick summary.)

Shunts help - as would a single-cell charger. Both can guarantee the pack is balanced when charged. Unfortunately, as I've found as as the paper I referenced earlier shows, cells don't have have the same capacity from the factory. This makes it difficult to guess exactly when our pack will hit 80% DOD. And can make it difficult to guess when a cell hits 2.5V.

Many folks seem to use a shortened range as their main management strategy - figuring that if a calculation shows a 100 mile range, that only driving 80 miles is reasonable. Unfortunately wind, temperature, altitude, and weight can have dramatic effects on range. Per the referenced paper, if one wanted to ensure their 80% DOD was a reliable stopping point, they should probably not charge all the cells to the same end of charge point - they should probably reduce the end of charge voltage for the stronger cells so that all of the cells arrive at 80% DOD together...

I'm a pilot. Airplanes fly a lot of data collection flights before they're certified. The manuals have range and power charts for a variety of flight conditions. I'm required to do the fuel calculations before departure - I know within 10% that if I fly this altitude for this long at this power level that I should land with 8.5 gallons of fuel remaining in the tanks.

The bike has a max range of 80 miles. I fully charged the bike, attached the data logger, and rode it a total of 42 miles. The data in the graphs is only the last 10 miles. Most of the pack was still at or above 80%. My best guess is that two cells were at about 85% and one was close to 100.

I hope that helps,
Andy

Your mileage may vary. Void where prohibited.


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## dimitri (May 16, 2008)

Excellent! Now everything makes sense  
Bottom line, don't use the pack that has not been initially balanced, that is something I have learned and known for long time. 

I think it is responsibility of whoever installs battery cells on the vehicle to make sure they are all fully charged and balanced. If your bikes shipped with cells all wired up, but not balanced, then its a huge quality issue and resultant dead cells should be their responsibility.



> if one wanted to ensure their 80% DOD was a reliable stopping point, they should probably not charge all the cells to the same end of charge point - they should probably reduce the end of charge voltage for the stronger cells so that all of the cells arrive at 80% DOD together...


I somewhat disagree on your point regarding balancing SOC. I think all cells must be charged to the max allowed by shunt regulators, say for example 3.8V ( just for argument sake, yours could be anything up to 4.2V ). That means all cells have equal SOC, but not equal amount of energy stored since each cell may have diff capacity. However, the overall pack capacity is equal capacity of the smallest cell in that pack, for the purpose of range estimation. Any extra energy in other cells is useless and should not be counted.

For example, if you have cells of 59, 60, 61, 62, 63 Ah in series, then your pack is 59Ah. You charge all cells to the max SOC and discharge until that lowest cell of 59Ah reaches your predetermined LVC point, but never lower than that lowest cell. 

The point is not to have all cells reach 80%DoD together, but to know when your weakest cell reaches 80%DoD, because that's the only thing that matters, and that's what defines your range.


----------



## bblocher (Jul 30, 2008)

AndyH said:


> Shunts help - as would a single-cell charger. Both can guarantee the pack is balanced when charged. Unfortunately, as I've found as as the paper I referenced earlier shows, cells don't have have the same capacity from the factory. This makes it difficult to guess exactly when our pack will hit 80% DOD. And can make it difficult to guess when a cell hits 2.5V.


I may have missed the brand of cells you're using, but TS cells come from the factory were very close in Ah capacity (unless you are mixing batches). Regardless though I agree completely with Dimitri, they should be balanced before first use.

The manufacture shows that the further you discharge these cells with each use your are greatly taking away from the life of them. So lets say you have 100Ah cells and they vary in AH(95, 102, 97, etc). You could still simply target a 80Ah discharge as maximum allowed. Some cells go slightly over some slightly less. In this case you shouldn't see a cell reach 2.5v for many years as the cells degrade.


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## AndyH (Jun 15, 2008)

dimitri said:


> Excellent! Now everything makes sense
> Bottom line, don't use the pack that has not been initially balanced, that is something I have learned and known for long time.
> 
> I think it is responsibility of whoever installs battery cells on the vehicle to make sure they are all fully charged and balanced. If your bikes shipped with cells all wired up, but not balanced, then its a huge quality issue and resultant dead cells should be their responsibility.


I agree 100%!

But if that's what you got from what I'm trying to say, then no - I'm failing to communicate! 

I'm talking about looking at managing the cells as they near end of charge. I'm trying to demonstrate that guessing is not good enough. 

Yes - I completely understand that the 91.256Ah cell should reach 80% DOD before the 92.593Ah cell - no doubt! What I want to suggest is that guessing about when one will hit 80% DOD isn't going to keep you out of trouble.

Cell level LVC will - regardless of wind, hills, regen, weight, or cell age.



dimitri said:


> I somewhat disagree on your point regarding balancing SOC. I think all cells must be charged to the max allowed by shunt regulators, say for example 3.8V ( just for argument sake, yours could be anything up to 4.2V ).


That's ok, and really this is probably thread creep. Here's my question - what's more important to you: Starting the day with a bar graph all nice and even? Or ending the trip with all the cells in the green? That's really my point.

You and Brian seem to be fixated on charge balancing - and I'm not surprised considering that you're both in the shunt state of mind.  But that's not the be-all and end-all of management.

Say you have a 2-cell pack - a 100Ah and a 200Ah. You might choose to watch the Ah display and end your drive when you've expended 80Ah.

What will your state of charge be for both cells? You have no idea. You can guess, assuming the same internal resistance profile and favorable wire lengths and connection resistance and temperature for each cell. But you really don't know - you're using an indirect method of estimating state of charge and calling it good. And down the road as the cells break in and break down, the characteristics will change - and thus the acuracy of your guess.

Do what you want to do - just make sure that, while you're assuming your pack is doing this:











That you're prepared to recognize and react - even when on the phone - when your pack decides to do this:










I'll leave it at that.

Andy


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## bblocher (Jul 30, 2008)

Well just some more updates on my experiences. The cells so far are doing as expected. I have 3,000 miles on them and I haven't noticed anything different or changing about them. I never did a capacity check myself to start with to have something like that to compare to sadly.

As far as Elite Power Solutions and the BMS charger they sell.
I've posted the email chain history as I've been trying to get the BMS bugs worked out. See my latest blog entry for details.


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## JimK (Mar 21, 2009)

Dimitri,

While waiting for my batteries which I expect to receive in the next few days, I've been reading about your LVC implementation in your cell balancers.

Did you simply modify the existing boards or have you rebuilt new boards from scratch?

Jim


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## bblocher (Jul 30, 2008)

JimK said:


> Dimitri,
> 
> While waiting for my batteries which I expect to receive in the next few days, I've been reading about your LVC implementation in your cell balancers.
> 
> ...


He built new boards from scratch.


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## tomofreno (Mar 3, 2009)

Brian,

I apologize for being off topic, but I believe you converted a late model car. Did you do anything special with the computer? Seems since there is no engine for it to control there is no reason to do anything to it.

Thanks,
Tom


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## bblocher (Jul 30, 2008)

tomofreno said:


> Brian,
> 
> I apologize for being off topic, but I believe you converted a late model car. Did you do anything special with the computer? Seems since there is no engine for it to control there is no reason to do anything to it.
> 
> ...


Although not required, I replaced the original computer with my own. The only thing that was required was to regenerate the RPM pulse so the EPS system would detect the engine was running and provide the power steering. I also added temperature monitoring for the motor and controller. Later I'd like to add some safety features such as rev limiter, fuel door safety switch, etc. Currently I'm just having too much fun driving it daily and needed a little break from the conversion but I'll get back to it eventually.


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## bblocher (Jul 30, 2008)

Wow, it's been awhile since any updates here.

I'm just about to click 7,500 miles on my cells. I use very roughly 1.25 cycles per day for the 70 mile round trip. All these hills at 65-75mph really sucks them down .

So that puts me around 130 cycles so far. It kinda puts things into perspective, even 1000 cycles is a decent amount of miles out of these cells.

Again, very rough numbers but that would mean:
1000 cycles = 57,700 miles
2000 cycles = 115k miles
etc

Just to recap on what I have (45 TS 160Ah cells). Let me know if I'm doing something looney in the math. 

So far, still good!


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## JRP3 (Mar 7, 2008)

Do you have a sense as to how much active balancing is going on during charging? In other words how out of balance does the pack get while discharging?


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## bblocher (Jul 30, 2008)

They seem to discharge at fairly consistent rates.

I have my shunting voltage just below my charger voltage. I see a few balancers turn on, and then after 15 minutes or so the charger is stepping down. When I install my new balancers, I'll set my shunt voltage to slightly above my charge voltage. This should give a better idea of balance based on how many shunt, if any, and how frequently. I'll post more on that here when I figure it out.


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## brainzel (Jun 15, 2009)

bblocher said:


> Wow, it's been awhile since any updates here.
> Again, very rough numbers but that would mean:
> 1000 cycles = 57,700 miles
> 2000 cycles = 115k miles
> etc


That would be awsome!
The SE cells (which I will use) have a rating:
70DOD%: 3000 Times or 173.100 miles or 278.500 km (following your math) ... thats a whole "car-live" 
I can't await my cell delivery


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## 86Honda (Apr 15, 2009)

JRP3 said:


> Do you have a sense as to how much active balancing is going on during charging? In other words how out of balance does the pack get while discharging?


Mine all have VoltBlochers (shameless plug) and all read 3.75 volts (or very near that) when all the red lights are lit. By the time my first red lights come on my charger is usually pushing 2 to 5 amps. At discharge all cells read 2.6 to 2.9 amps, but the pack is still new and breaking in. Therefore I am still watching the charge cycle pretty close until I get everything zeroed in.


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## JimK (Mar 21, 2009)

Brian,

I have now done over 2000 KM (1242 miles) and recently drove 92 KM (57 miles) on a charge. My resting voltage was down to 124 V from the usual 131 V after a typical daily commute of 46 KM (29 miles). 

At first, I had estimated that my range would be 100 KM (60 miles) with 40 TS LFP160 cells. Now I'm thinking the range is closer to 120 KM (75 miles).

What is the lowest resting voltage that you have gone down to so far?

If anyone else has info to pitch in, feel free.


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## dimitri (May 16, 2008)

Jim,

I doubt you would reach 75 miles, see the graph. It show's 0.5C line, so resting line is even a tad higher. So, at 124V with 40 cells your cell voltage was 3.1V, which is almost dead. If you drove couple more miles during that trip you would suddenly come to a stop.

I have same exact pack as you and the same car, and I estimate my range at 60-65 miles depending on acceleration and hypermiling. If you read my controller review thread you'd see that I got my pack to 100% DoD once. It happens very suddenly with LFP cells, due to flat discharge curve.

So far the longest trip I made on one charge was 60 miles, most of it highway, at 70-75 mph. At the end I figured I had about 5 miles left according to Paktrakr data.

IMHO, best way to gauge DoD is not with resting voltage, but how much sag you see under load, as sag increases towards the end.

Overall, Paktrakr SOC meter is quite accurate, although its not linear unfortunately, but so is fuel gauge on most ICE cars. It drops faster at the end and stays longer around the middle.


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## bblocher (Jul 30, 2008)

Yeah, resting voltage is very deceiving. I use my Kwh meter on my BMS, and I'm guessing I have a 60+ range as well at highway speeds. Furthest I've taken the car is 50 miles on a single charge I think (wish I remembered my Kwh remaining on that one). But like Dimitri said that voltage drops like a rock over just a mile of driving you can go from an ok resting voltage to a dead cell.


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## JimK (Mar 21, 2009)

Thanks for the input guys. When I took the car to 92 KM, it was by accident. It scares me to think that I was very close to fully discharged. I guess I won't be trying that again......


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## brainzel (Jun 15, 2009)

Hmmm ... so I have to cut of the power, if the voltage runs under 3,1 / 3,0 Volts?
Is there an input at the Curtis 1221C to slow down the car or would it be a "hard cut off" ?


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## dimitri (May 16, 2008)

brainzel said:


> Hmmm ... so I have to cut of the power, if the voltage runs under 3,1 / 3,0 Volts?
> Is there an input at the Curtis 1221C to slow down the car or would it be a "hard cut off" ?


No you cannot cut power at 3.0V because it sags deeper under normal driving load. You can cut power at 2.7V , which would be like 90% DoD when under load.

My LVC is at 2.7V and it worked great that one time when I was too distracted by testing Soliton1 power


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## AndyH (Jun 15, 2008)

dimitri said:


> <snip> My LVC is at 2.7V and it worked great that one time when I was too distracted by testing Soliton1 power


I'm glad you're using an LVC, dimitri, and glad that 2.7 is working for you. Nice review thread!

Andy


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## dimitri (May 16, 2008)

AndyH said:


> I'm glad you're using an LVC, dimitri, and glad that 2.7 is working for you. Nice review thread!
> 
> Andy


Thanks Andy, see , I listened to you back when we discussed the LVC feature  , some good ideas came out of that discussion....

LVC=2.7V seems to be perfect for TS cells, it kicks in just at the right time to prevent 100% DoD. I really like how it turned out...

I was showing my EV at Tampa Bay Green expo at USF campus this weekend, which was 30 miles away from my home, making it a 60 mile round trip. The car handleded 60 miles trip ( mostly highway at 70 mph ) just fine. At the end I guesstimate I had 3-5 miles left in the pack.


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## jondoh (Sep 8, 2008)

that's 2.7 volts per cell at how many C? 3C?


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## dimitri (May 16, 2008)

jondoh said:


> that's 2.7 volts per cell at how many C? 3C?


Simple BMS does not correlate current with voltage, so it will start signaling LVC event at 2.7V regardless of the current, which means that first LVC alarms will happen under heavy acceleration, when voltage sags deeper, but that is good, because it lets you know that end of charge is near, so you should slow down and get to the charging station ASAP.

In any case, once you hit 2.7V you better be close to home or charging station since you only have few minutes left to drive.


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## bblocher (Jul 30, 2008)

I just popped onto the TS site and noticed they updated the 160Ah data sheets. The numbers are quite different now for the better.

I'm curious if this applied to the older cells as they have tested further and fell comfortable relaxing the numbers, or if they have made any changes. My guess is the first case.

Differences on the 160s since I purchased them less than a year ago:
* Max charge current from 1C to 3C
* Max discharge current from 10C to 20C (impulse, constant remained at 3C)
* Cycle life 80% DOD from 1000 to 3000, and 70% DOD from 2000 to 5000!

I believe everything else is the same. The cycle life is mind blowing if they can indeed last that long. That equates to 150k to 250k miles for me! Could the batteries last longer than my car? I already have over 90k on it.


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## Sutitan (Feb 23, 2009)

> I just popped onto the TS site and noticed they updated the 160Ah data sheets. The numbers are quite different now for the better.


EVcomponents made a claim that the materials have changed a bit and that the quality has improved since the first shipment.


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## MN Driver (Sep 29, 2009)

I'm a bit excited about the numbers, granted they are a Chinese manufacturer and it would be hard to tell how accurate the numbers are without independent tests. It seems that their ratings for cycle life are based on the 0.5C charge/discharge cycle. It's hard to tell what impact we would be putting against cycle life with a 3C or 5C 10-15 second acceleration draw now and then. I remember their recommended charge current was 0.3C, now 0.5C so I feel it is safe to assume that charge/discharge is ideal at 0.5C or less which would leave for an oversized pack as far as a constant discharge rate is concerned for many but could help with reaching the extra cycles and would also mean less total cycling or less DoD per charge as well. If we can get 5,000 charge cycles under the most ideal conditions that _should_ mean that we have room to stretching the ideal conditions and still receive adequate cycle life in the end.

The following specs are what I'm most interested in, the max C draw over 15 seconds(standard duration of a hard acceleration for many people) and what voltage that would leave you at right before the 15 second amperage draw is complete. Many battery manufacturers have posted a 10 second and 1 minute max C rate, those would be useful numbers to have for pack/controller/motor planning. I'm curious about the max C draw and voltage over the same duration for a worst case temperature scenario of about -30c/-22f. I have a feeling that when it gets that cold it could be a slow start and would require heating. This problem could be solved with battery heaters and an insulated box, but I'm curious if upon unplugging the heater, leaving the house and parking at work and having the car off of the heat for 11 hours(10 hour shift, 30 min lunch break, 30 min drive to work) how warm those batteries would be with rigid foam insulation at -20f temps? Above freezing would be great, below that and we need to know some specs or have the pack heat itself off its own power to say a reasonable 50f while parked.

Have we heard back about the impulse duration of 20C? It seems to me that even with a full pack, 20C would drop us very close to the low voltage cutoff and generate heat very quickly.


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## bblocher (Jul 30, 2008)

MN Driver said:


> Have we heard back about the impulse duration of 20C? It seems to me that even with a full pack, 20C would drop us very close to the low voltage cutoff and generate heat very quickly.


I remember seeing something before when it was rated at 10C, and it was a millisecond based number (I don't recall exactly). Seems strange to go from 3C continuous to 10, now 20C sub second. I agree, we really need 15 second and 1 minute ratings to get a good sense of hard accelerating.


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## jondoh (Sep 8, 2008)

Hey Brian,

Just curious if these revised specifications can be applied to my batteries which i ordered in May '09 and received in August '09. Or exactly how old of batteries do the specifications apply?


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## CroDriver (Jan 8, 2009)

I have already posted this mail a few times but looks like no one have seen it 



> Dear Mate,
> 
> Thanks for your E-mail.My answer to your questions are as follows,
> 
> ...


This mail came direct from ThunderSky. I asked them what would happen if we exceed that claims or if we cool the batteries with big fans but I have received no reply.


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## bblocher (Jul 30, 2008)

jondoh said:


> Hey Brian,
> 
> Just curious if these revised specifications can be applied to my batteries which i ordered in May '09 and received in August '09. Or exactly how old of batteries do the specifications apply?


I honestly don't know. EVComponent might be able to get that answer. I'm not even sure how long that document has been updated. I wish when they made these changes, it changed a model or version number as well so we could track it.


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## MN Driver (Sep 29, 2009)

At this point, I'm convinced the cells are plenty capable when they come out of the crate, but for me, I'm curious how they will behave as they age, based on the cycle chart, the 8000th cycle showing 70% DoD on the chart, but it makes it appear like the gaining disadvantage over time is increased internal resistance(the charts curve looks like the 5C constant discharge curve but at 0.5C after 8000 cycles) which mimics the describes experience of those using the pre-2005 Lithium Ion Thunder Sky cells as they aged. For this reason, I plan to buy a larger Ah pack than I really need to compensate for such possible loss of amperage draw ability over time since I feel that 70% total capacity with age is less of my worries. Then again when I buy a pack, I plan on -hopefully- being able to buy the pack, 10% extra cells(4 extra cells for a 34 cell pack at this point) and use the same motor/controller/battery combo with the car I convert and if/when I decide to change cars(or if worst case scenario occurs such as a crash), to migrate this equipment to the next vehicle. If I get a pack capable of 100 miles(spendy pack or super efficient car), drive to work 30 miles round trip, charge every 2 days. 5000 cycles is 13.7 years of daily charging or 27 years of every other day charging. This is well beyond the duration that I initially ever perceiving a secondary(rechargeable) battery to possibly last, only time will tell however. 100 miles * 70% DOD = 350,000 miles. Obviously, 70% DOD will be less Ah total with 80% remaining capacity at 5,000 cycles so the real number will be less than that many miles and this would require a mighty big pack for 100 miles but we can dream. I would be thrilled to get 200,000 miles from a $10k pack. Lets see, math time, most fuel efficient gasoline car I know gets about 70mpg. 200,000 miles/70 mpg=2857 gallons, if we figure gas prices will be above $4 in 10 years we can take 2857*$4 gallon=$11,428. 35mpg is $22,856 but would likely require a bigger pack for a less efficient vehicle. I figure a donor car plus conversion could be done for around that cost. Electricity is very cheap in relation to gasoline, factor in the impact on the environment, not giving money to hostile regions of the world, not dealing with dirty engine maintenence, or whatever else is important to you for considering an EV and I think that a well planned EV conversion could perform just as well or better and last as long as a gasoline car or longer and possibly be cheaper in the long run depending on the cost of future costs of gas and electricity.

I think we've finally found the point where EVs can more than break even, even if we only get 2000-3000 cycles on a pack I don't think it would put us in the hole too much, if at all. If not now, cheaper battery costs from increased mass production, competition and improved technology over the next few years will likely make it happen if we aren't there already.




bblocher said:


> I honestly don't know. EVComponent might be able to get that answer. I'm not even sure how long that document has been updated. I wish when they made these changes, it changed a model or version number as well so we could track it.


They made that change within this week or last week because I remember looking at the specs and I'm 99% sure they still showed 4,000 cycles on every specsheet at that time when I was perusing through them. I checked every specsheet and they all show the same stats 0.5C charge, 5000 cycles 70%, same exact charts for every sheet as far as I can tell, from 40Ah all the way through 200Ah, I didn't check any of the larger cells though. It seems that all of the cells are the same composition but they just stack more 'cell sheets' in parallel inside the cells along with having larger sheets for the larger cells. I suppose the most important thing to know beyond when the specsheets changed is when the actual cell designs have changed and which specs correlate to which cells and if any of specs are related to any previous cells but just didn't have the testing to support such specs. Either way, the cells were purchased with the expectation of the older specsheets so at least you should have received something that was based on the ratings of when you bought them which must have seemed adequate to the person purchasing at the time, but of course I know we all want to know if we received the improved product and what these are really capable of which has got to be frustrating.

I viewed Jack Rickards video called Inside the ThunderSky LiFePO4 battery' that was over an hour long video and about a gigabyte to download at evtv.me http://web.me.com/mjrickard/downloads.html These cells are just stacked anode and cathode sheets connected directly to the terminals and sealed inside of the case. They don't really seem much differently packaged than the LiPolymer pouch cells except they come in a thicker stronger wrapper so to speak that need to be clamped to prevent cell swelling.



CroDriver said:


> I have already posted this mail a few times but looks like no one have seen it


I've seen that email and sometimes I forget where things were posted and it makes it hard to quote things. I'm not sure how we could extrapolate that 3 second 10C draw to 5C but I figure with 1/2 the C draw that more than 10 seconds wouldn't be a problem since they say that 3C is fine continuously as long as temperature stays in spec and you are willing to deal with some cycle life reduction. I figure that if a 3C acceleration here and there is good for a 15 second draw followed by a consistent 1C draw than that will exceed my needs for every situation I would likely come across on a regular basis but of course I can't speak for anyone else as their needs are different. I have to disagree with the 100 celcius case temperature they mentioned, that would likely murder a LiFePO4 pack. When independent company, FMA, tested A123 cells, they got decent cycle life out of the cells as long as their temperature didn't exceed 140 degrees F or 60 degrees C. Thunder Sky rates their cells at 130f/55c. I figure that as long as we don't get it hotter than that internally(not an easy measure with a thick plastic cell) then it should be fine.


----------



## bblocher (Jul 30, 2008)

I just wanted to update my current status and maybe even get some feedback.

For those who haven't checked my blog lately, I lost my first cell (completely my fault as I shorted it out for a few seconds and it died completely a couple weeks later).

Today, for the first time, I drove to work with 44 of the 45 cells. When I arrived I had a cell that got down to 2.4v resting. I'm guessing this cell has lost capacity, quite a bit but why. Is it a one cell deal, are all of my cells loosing capacity at a much higher rate than advertised?

My delima is, do I buy a few more cells and start replacing those that are getting weak, find another brand, or rethink my setup entirely. Overall, I've noticed the voltage sag really increasing lately on all cells.

I'm curious exactly where the rest of my cells stand. I think I'm going to need to charge each one seperately, and do a controlled load test to determine the capacity of each cell now before I move on. I might, first, want to move the car into the garage and charge there at nights, maybe I'm just not getting the capacity in there with the cold weather for the long hard haul up hill to work.

Comments and thoughts are most welcomed


----------



## 86Honda (Apr 15, 2009)

bblocher said:


> I just wanted to update my current status and maybe even get some feedback.
> 
> For those who haven't checked my blog lately, I lost my first cell (completely my fault as I shorted it out for a few seconds and it died completely a couple weeks later).
> 
> ...


I also lost a cell early on - it never did hold a charge well and my supplier exchanged it. I sent it to them, but don't know if they ran any tests on it. I find that the weather has a great impact on my voltage sag. 60F not so bad, 45F significant. It seems that the energy is in there, I just can't get it out fast enough, as all cells read right around 3.8 V at full charge. I have a couple of waterbed heaters for the battery packs that will be installed as soon as I get somewhat good weather and a day off together (seems rare). That, and tire rotation, radio/CD installation, space heater hookup and testing, pulling a few new front/rear lines, mounting pack heater outlets and controls, etc. (lots to do and no time).


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## jorhyne (Aug 20, 2008)

bblocher said:


> I just wanted to update my current status and maybe even get some feedback.
> 
> For those who haven't checked my blog lately, I lost my first cell (completely my fault as I shorted it out for a few seconds and it died completely a couple weeks later).
> 
> ...


What is the highest C-rate your cells regularly see?


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## dexion (Aug 22, 2009)

They hate cold. If you can warm the cells up somehow to 60F and see if you see it so bad. Insulate the battery box too if you can. I have an insulated box that I can remove the front and rear panel and expose them to outside air when it gets warm. When its cold, TS cells hate it. The new cells I got for my car (the ts cells are on my scooter 21x60ah) are (according to the engineer) specially designed for colder climates. Hopefully I will get my missing interconnects so I can finish my car conversion and test them. Its 40F here today so it would be a pretty good test this week should be 35-40F. But, I have a box heater and insulation as a backup just in case. Somewhere I read (but I cant remember where or when) that at 32F the ts cells are ok to sag to 1.4V mine sure do when they used to sag to 2.8-9 under the same load. I'm actually on the phone with him now (says they are shipping the interconnects today whoo hoo) he says they should be alot better because its a different mix. 
dex


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## bblocher (Jul 30, 2008)

jorhyne said:


> What is the highest C-rate your cells regularly see?


I have 160Ah cells on a Curtis 1231C, so they see spikes of 480, but typically I only push them around 2C on the commute. Sometimes I push them closer to 3C...but they should be able to do this all day long 

I'm thinking my problem is the temp. They are not charging fully so I'm draining them further than they should be and causing some damage. However, it's only getting into the high 50s worst case so far here in California. I'll be doing some tests in the garage with some heat applied for comparison tonight.

EDIT:
Btw, I have about 9k miles on these cells now. This is roughly 175-200 cycles.
Anybody have more miles or cycles that has done capacity checks? I'm going to capcity check mine soon, so I'll keep you posted on what I find.


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## favguy (May 2, 2008)

This does seem a worrying development Brian, lets hope it is mainly temperature related and no loss of real capacity. 

With regard to the weak cell, allowing for the chinese attitude to quality control, it's probably not to out of the ordinary to expect a couple of cells in a group of your size to fail prematurely, hopefully this is the case here and the majority of the pack will continue to perforn well for a long time yet.

Please keep us all informed, I'm sure I speak for all the EV community when I say that I for one very much appreciate the risk yourself and others take in early adoption of this new cell type. 

Best regards

Paul


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## mszhao (Oct 17, 2009)

some European customers have tested 100ah cells from Thundersky and Hipower .they found Hipower cell has higher capacity than TS.
www.haiba.net.cn
skype amymy0824
email [email protected]


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## favguy (May 2, 2008)

And surprise, surprise, you represent Hipower!!! You guys really are just too obvious!!!


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## tomofreno (Mar 3, 2009)

> some European customers have tested 100ah cells from Thundersky and Hipower .they found Hipower cell has higher capacity than TS.


 Could you supply a link to the test report? What were the sample sizes and degree of confidence?


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## dimitri (May 16, 2008)

Why would anyone care if one cell is higher capacity than the other as long as they both are at least the same capacity as marked and sold? More important tests would be voltage sag under 3C load, internal resistance, thermal stability under heavy loads, lifecycle, etc etc

Coming to a forum with statements like this really doesn't help your business, don't you see it? Most people here wouldn't pay $$$$ to someone with hotmail Email address located in another country and making bold statements without any proof.


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## JRP3 (Mar 7, 2008)

I'm not sure how great their products are since they don't seem to have cases:http://www.diyelectriccar.com/forums/showthread.php?t=37484



> we urgently need plastice or aluminium battery cases .
> first we need 2pcs,then 800pcs.
> the inner size need to be 106*18*30mm or could be a bit larger
> if anyone have finished cases pls let me know soon.and pls quote me the price.
> ...


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## MN Driver (Sep 29, 2009)

...yeah, I scratched my chin a little when I went to see their other posts too. I thought HiPower made their prismatics with cases already. I wonder if they are packing cylindricals(maybe not even the same brand) and trying to sell them as if they were natively prismatics. As usual, we will likely never hear back from those who put their ads up here trying to hijack an experience thread of people who are not disappointed at all with the brand being discussed. China manufacturers need a little help in the sales/marketing department. I personally would like to see a manufacturer come out with a 1 minute max discharge rating but it seems that we have to rely on our own testing to verify anything they say as it is anyway, but it would still be nice to see.


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## etischer (Jun 16, 2008)

bblocher said:


> Overall, I've noticed the voltage sag really increasing lately on all cells.
> I might, first, want to move the car into the garage and charge there at nights, maybe I'm just not getting the capacity in there with the cold weather for the long hard haul up hill to work.


I was wondering how much capacity you think you're loosing in cold weather. The TS data sheet shows the battery should still have about 90% of it's capacity at 
-25 deg C. Their test was done at 0.5 C though, so the battery sag you are experiencing isn't represented in the data.


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## markcycle (Nov 5, 2008)

I'm new to this forum with most of my posting being on Endless- sphere and Emoto.net. I have Been working on motorcycle motor design for the last two years. Anyway I use the same name on all the forums I'm on so you can look around for markcycle.
I have been reading this thread looking for answers to why i lost 6 of my 32 TS 40AH cell over the last 3 or 4 months after about 1500 miles

I rushed my test bike together in terms of batteries so i could start test the 600 series Motorcycle hub motor and had no cell by cell monitoring or alarm at first for maybe 500 miles, I do now and did during all my cell failures. Cell monitoring is overcharge and undervoltage alarm and shut down. Undervoltage is set to 2.1 volt currently just because at 6C I can get the batteries to spike down to 2 volts at 3C the voltage is 2.8 volts

I pull 2 to 3C as the norm and do 6C acceleration all the time. 
The cells failed in different ways all with cell by cell monitoring.
1 cell just dropped voltage at any load over .3C but didn't get hot and seemed to charge OK
1 cell got super hot and expanded out the sides (plates and straps being used) like it was going to explode during charging but was not being overvolted at the time I'm certain.
1 cell blew smoke out the vent it went from OK with cell monitoring at the time to sitting on the side of the road with smoke out the vent now that's scary (I was doing hard accelerations of 250 amps still do).
1 cell just weak to weak to call normal testing on the bench with CBA showed 20 to 25 AH capacity 

The last two were also weak but the strange thing is no noticeable heating in all the weak cells. 

It's been about 60 days since i last cleaned up all the bad cells and things seemed to be OK again. But I'm gun shy of the whole battery pack to the point I avoid the highway (3 to 4C) and am thinking of building a new pack with Headway cells

Sure I'm pushing the cells but hoped for better 

Mark


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## david85 (Nov 12, 2007)

Hi Mark, Welcome to the forum. 
Sorry to hear about your troubles.

May I ask how old the batteries are at this point? (from date of delivery)

Were you able to get any warranty service on the failed cells?


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## CroDriver (Jan 8, 2009)

markcycle said:


> Sure I'm pushing the cells but hoped for better
> 
> Mark


You're not the only one. I'm sure that this are great cells for a average EV/commuter but not fore those that are looking for performance...

I'm also working on a Headway batt pack for my car now


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## dimitri (May 16, 2008)

Mark,

TS cells are not meant to exceed 3C peaks and 1C continuous for too long, so your results are expected, you are pushing them way beyond their specs. I'm surprised you only had a few fail, but if you keep it up, they will all fail pretty soon.

Cylindrical cells are much better solution for bikes, due to high C rates.

Sorry to hear about your troubles...


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## david85 (Nov 12, 2007)

dimitri said:


> Mark,
> 
> TS cells are not meant to exceed 3C peaks and 1C continuous for too long, so your results are expected, you are pushing them way beyond their specs. I'm surprised you only had a few fail, but if you keep it up, they will all fail pretty soon.
> 
> ...


 
Realy? I thought TS was supposed to be 3C constant 5C peak?

My batteries are rated at 1C constant 5C peak though I probably will never be able to really test that. My motor will barely pass 1C floored


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## markcycle (Nov 5, 2008)

david85 said:


> Hi Mark, Welcome to the forum.
> Sorry to hear about your troubles.
> 
> May I ask how old the batteries are at this point? (from date of delivery)
> ...


The batteries are now about a year old

I did two cells were replaced under warranty (the one that smoked and the one that almost exploded) and they discounted me on six more

Mark


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## markcycle (Nov 5, 2008)

david85 said:


> Realy? I thought TS was supposed to be 3C constant 5C peak?
> 
> My batteries are rated at 1C constant 5C peak though I probably will never be able to really test that. My motor will barely pass 1C floored


I though 3C constant also so does Elite power solutions which is why they replaced them

Mark


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## JRP3 (Mar 7, 2008)

Hey Mark good to see you here, I've been following your hubmotor on ES. My guess is the repeated 6C is your problem, especially with older TS cells. The newer ones claim higher C rates but these are still only momentary pulses, I think if you're doing a few seconds at 6C repeatedly you will continue to have failures. The newer TS cells say 20C impulse current but I think that's for less than a second, they are still 3C continuous. The SE cells are 4C continuous and 12C max.


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## JRP3 (Mar 7, 2008)

Can you fit larger cells? 60ah cells might be enough to lower the C rates.


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## dimitri (May 16, 2008)

Sorry, didn't mean to stirr anything up  , but real life use of TS cells tells me not to exceed 3C and keep it close to 1C if I want them to last for more than couple of years. Plus, what's the fun in EV that can only drive for 20 min before it has to be charged? 

IMHO, street EVs should not exceed 1C cont, 3C acceleration, and if they do, then the pack is undersized.

I do agree that 6C would kill them for sure, for my 160AH that would be almost 1000 amps  , no way they can survive that for long.


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## david85 (Nov 12, 2007)

dimitri said:


> Sorry, didn't mean to stirr anything up  , but real life use of TS cells tells me not to exceed 3C and keep it close to 1C if I want them to last for more than couple of years. Plus, what's the fun in EV that can only drive for 20 min before it has to be charged?
> 
> IMHO, street EVs should not exceed 1C cont, 3C acceleration, and if they do, then the pack is undersized.
> 
> I do agree that 6C would kill them for sure, for my 160AH that would be almost 1000 amps  , no way they can survive that for long.


Nothing stirred up here, just surprised - and thankful for your insight. Didn't hear that before but I trust you more than any sales rep. Makes me wonder if mine are really that much different in terms of real world capability. I've seen the numbers revised to 2~3C constant a few months after I made my order, but I have a suspicion that they are no different than what I bought.

Oh, and the peak C rating with mine are rated for 15 seconds. I don't know if there is a general guidline for how long the "peak" rating really is, but the spec list that I recieved was the first time I ever saw an exact time duration rating for the peak C.


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## markcycle (Nov 5, 2008)

My experience sure is saying 6C -250 amps on a 40 AH cell is not good. That being said for me it was a business decision to get a bike together as fast as possible to test the MHM-600 series motor. 

I now recommend to my customers to buy 60AH cells and all have. The funny thing is now that I have weeded out the weak cells, thing seems OK and have been for weeks. I can watch the individual cell voltage and at 3C they are balanced to .1 volt and at 1C to .01 volt. At rest after the surface charge is burned off they are like perfect .001 volt. I don't mind if they die (well I do) just don't want the sudden death with smoke coming out of the bike. 

Just going to have to build a Headway pack. I'm being contracted to build a headway pack for a customer anyway, so I'll just build two.

Buy the way my real power consumption is between 
90 and 110 Watt-Hr/mile So I don't I do 3C continuously even on the parkway 60MPH @ 60 to 80 amps except up hills then 110 amps or so.

It's the 400 amp Kelly thats doing it to me allowing repeated 250 amp starts off the line so its FUN/KILL BATTERIES or LESS FUN/SAVE BATTERIES At first it I had to do repeated lock rotor starts to test the heating of the motor at close to 30KW peak. then we did the TTXGP exhibition laps at Mid Ohio race track so the batteries got tourtured. Now everytime I lower the current limit to keep the starts under 200 amps I'm just not enjoying it in the same way.

Anyway thanks for the advice and I'll keep you all posted on how the cells last or don't last which ever the case may be

Mark


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## david85 (Nov 12, 2007)

Let me get this strait. You built an electric motor cycle for the purpose of testing a (scratch built?) wheel motor, that you tested to......30kw?

30x4=120kw for an AWD setup for a 4 wheeled car. Are there any links I can look up to find out more about this?


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## markcycle (Nov 5, 2008)

david85 said:


> Let me get this strait. You built an electric motor cycle for the purpose of testing a (scratch built?) wheel motor, that you tested to......30kw?
> 
> 30x4=120kw for an AWD setup for a 4 wheeled car. Are there any links I can look up to find out more about this?


My web page is
http://www.doingitall.net/EnerTrac

You can research my user name in google markcycle 
Just getting starting with the car conversion project motor

Don't want to hijack this thread and will start a motor thread very shortly

Mark


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## Woodsmith (Jun 5, 2008)

Very interesting link there, Mark, it has caught my interest.

Currently your motor is an out runner. Is there any possibility of it being developed as a converntional motor spinning a shaft? If not, it doesn't matter, it gives me development ideas.

Should I share here, on a new thread or by pm?


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## markcycle (Nov 5, 2008)

Woodsmith said:


> Very interesting link there, Mark, it has caught my interest.
> 
> Currently your motor is an out runner. Is there any possibility of it being developed as a converntional motor spinning a shaft? If not, it doesn't matter, it gives me development ideas.
> 
> Should I share here, on a new thread or by pm?


I'll start a new thread

Mark

edit
OK started
http://www.diyelectriccar.com/forums/showthread.php?t=38486


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## jorhyne (Aug 20, 2008)

David check here for more on markcycle's motor: http://endless-sphere.com/forums/viewtopic.php?f=10&t=7718


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## Woodsmith (Jun 5, 2008)

Just read all 40 pages of that thread. Good link, thanks.


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## JimK (Mar 21, 2009)

I am also seeing reduced capacity and increased sag as the temperatures have gotten colder. North of the border, we are seeing below freezing temperatures at night and just above freezing during the day and we are nowhere near the nasty cold that comes with canadian winters. TS cells are rated at 25 celsius and their specs indicate operating temp. between -25 and 25 celsius. The obvious big unknown is how much does the cold impact the cells. From my experience so far, the effect is noticable to me and similar to what Brian and others have observed. 

When I planned my conversion I knew that my batteries (regardless of the chemistry) had to be insulated and/or heated. This was recommended by experienced people. It's a good thing that all my 40 cells are in one partially insulated box inside the trunk. Now I am thinking of improving the insulation and even adding supplementary heat to warm the trunk compartment. This can be achieved with battery blankets/warmers (ex. http://shop2.aol.ca/shop/product--catId_1002098__locale_en__productId_1849596.html) or a small area heater. When I built my box, I was low on height clearance due to the tie down bars and cell balancers so I didn't integrate the battery blankets that would heat the cells from beneath. I was also under the impression that this battery chemistry was more tolerate to high/low temperatures compared to say PbA. I might have been wrong about that and might not want to "wait and see". So, I think I will try the area heater in the meantime. This will work when I am parked and charging outside in my driveway where I can plug in a heater but like another member mentioned, it is a problem when the car is parked at work in an parking lot for many hours with no plug for power. Using the pack power will be a problem due to the already reduced range from heat usage in the car and loss of capacity from the colder temps. Looks like quite the dilemma.....

I am hearing many of you are using LVC with your cells and wanting to test the capacity of your cells. Now, I am also thinking that LVC is something I definitely need for the above mentioned reasons.

What are you using to test cell capacity?


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## JimK (Mar 21, 2009)

Just wanted to add to my previous post after I searched and found the TS manual that came with my cells. On pages 27 & 28, there are tables that indicate the standard charge/discharge voltage and current at normal temp (25C or 77F) and low temp (-35C or -31F). Here is what was stated for LFP cells:

@25C/77F: 3CA (Max.Chrg.Curr.), 4.25V (Max.Chrg.Volt.)
@-35C/-31F: 0.1CA~1.0CA (Max.Chrg.Curr.), 4.3V (Max.Chrg.Volt.)


@25C/77F: 3CA (Max.Const.Dischrg.Curr.), 2.5V (Max.Dischrg.Volt.)
@-35C/-31F: 1CA (Max.Dischrg.Curr.), 1.5V (Max.Dischrg.Volt.)

This would explain the added sag during discharge/driving.
The other thing that concerns me is the charging during low temps. The maximum current indicated in the table is 0.1~1CA. Not sure if I am interpreting this correctly. I'm beginning to think if driving in temps below freezing is worth risking damage to cells.


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## SolarJ (Sep 12, 2009)

Looks like these cells should really have temp compensated LVD and be limited to 1C or 2 C at cold temps. Do any of the current BMS do this?

--Jim


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## JimK (Mar 21, 2009)

I don't think such a BMS exists but I might be wrong. 

The ideal solution might be to better control battery temperature for the extreme cold/hot conditions. I know that Victor (metricmind) is working on something which has liquid cooling/heating for Lithium Polymer packs with integrated BMS called "smoothtalk". He also has a BMS version for prismatic cells like the thundersky cells. If and when it becomes available, it will surely be expensive......


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## JRP3 (Mar 7, 2008)

JimK said:


> If and when it becomes available, it will surely be expensive......


Yeah and with the price of lithium cells I think it makes more sense to put the money towards larger sized cells and work within their parameters. If cold reduces the range of the 100AH cells does it make sense to put money into an expensive BMS or 120AH or larger cells?


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## MN Driver (Sep 29, 2009)

There are more advantages to have larger cells, especially if the amp draw doesn't increase(same voltage). The less C draw you need to accelerate and drive, the longer you can continue to use the pack once it has aged and the internal resistence increases in the cells, especially if you can work with them until they are down to 70% capacity at 8,000 cycles as per the chart on the Thunder Sky specsheet, but take a look at the 0.5C charge curve, it looks similar to the 5C chart at normal temps when they are new. Granted 8,000 cycles is well beyond what I think anyone buying and using these cells anticipates, but sometime they will reach that condition but the more oversized the pack is and less amp-draw/capacity you will use the longer you can use it IMO. Is it expensive to oversize it? yes. How neccessary will it be? We don't know yet Will the future cost of Lithium-based chemistry cells drop or performance gain significantly between now and when it becomes an issue? It's probable, especially when you compare the cost of TS cells available now versus this date last year.

I guess I'm in the camp of oversizing it and try to use it forever, but I see advantages for cold performance and the occasional speed run that won't stress the cells out as much as a smaller pack too. LVC becomes easier because if I go with the AC50 with the Curtis AC controller because a 200Ah pack wouldn't even pull 3C when at full throttle and if I'm running low on the pack, I'm not going to be running full throttle as it is.


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## CroDriver (Jan 8, 2009)

JRP3 said:


> Yeah and with the price of lithium cells I think it makes more sense to put the money towards larger sized cells and work within their parameters. If cold reduces the range of the 100AH cells does it make sense to put money into an expensive BMS or 120AH or larger cells?


Some people also care about weight and space


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## JRP3 (Mar 7, 2008)

Yes if you need to maximize your pack capacity and use every bit of it on a regular basis then you probably do need a good BMS. But if you are like the average driver up sizing your pack by 20% or so should be achievable and probably makes the better financial investment.


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## AndyH (Jun 15, 2008)

Brian,

I think you'll find that the TS datasheets with the longer cycle life are for LiFeYPO4 cells not the prior LiFePo4. It appears that all the manufacturers are playing with different materials in the anode and cathode mixes to tweak performance.

I'm leaning more toward 'new chemistry' rather than 'loose numbers'.

Andy



bblocher said:


> I just popped onto the TS site and noticed they updated the 160Ah data sheets. The numbers are quite different now for the better.
> 
> I'm curious if this applied to the older cells as they have tested further and fell comfortable relaxing the numbers, or if they have made any changes. My guess is the first case.
> 
> ...


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## Guest (Dec 9, 2009)

dimitri said:


> Mark,
> 
> TS cells are not meant to exceed 3C peaks and 1C continuous for too long, so your results are expected, you are pushing them way beyond their specs. I'm surprised you only had a few fail, but if you keep it up, they will all fail pretty soon.


Where do you get this information????

Jack Rickard


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## JRP3 (Mar 7, 2008)

Jack, I think he was speaking to his experiences:



dimitri said:


> Sorry, didn't mean to stirr anything up  , but real life use of TS cells tells me not to exceed 3C and keep it close to 1C if I want them to last for more than couple of years. Plus, what's the fun in EV that can only drive for 20 min before it has to be charged?
> 
> IMHO, street EVs should not exceed 1C cont, 3C acceleration, and if they do, then the pack is undersized.
> 
> I do agree that 6C would kill them for sure, for my 160AH that would be almost 1000 amps  , no way they can survive that for long.


Also, check your PM's again, (you need to turn on email notification.)


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## pm_dawn (Sep 14, 2009)

Hi !

Here is a little real world report on TS LFP cells.
I have a 40s 160ah pack that I bought early this year. Got them in the end of April.
As BMS I use the Fechter/Goodrum BMS from Endless-sphere.
I got about 1A shunts and that works really good, although I hav'nt integrated the charger throttling of the BMS yet, because my inboard charger does not really like it and I would need to install an extra contactor to make it work. The car is a Renault Clio Electrique with a original pack voltage of 114V (19 Saft STM-5 100Ah NiCd blocks). 
I now run it on 128V nom pack voltage with 160ah capacity.

I have LVC set at 2,7V and I have not installed any battery heating yet.
These TS Cells does not like the cold, I can say for sure, they sag quite a lot when below 0 degC, I can easily trip the LVC with 1C load at -5 degC
even at fully charged.

I have about 2000miles on the pack now. The car got on the road in August. Guess I have done about 60-80 charge cycles. It feels pretty stable. 
Yesterday I tried to run my pack down a little further to see the range i get now in the winter. I got 116km (72 miles) all in 0 or sub 0 temperature, and the onboard display showed 146ah drawn from pack. I could perhaps have taken another 10ah but the 12v circuit was going really low since the car cuts the DCDC when low on Ah. At the en the LVC would trip at 0.5C loads. Pack voltage was never below 112v, so I might have one cell diving a little earlier than the others.

I think this is pretty good since it is winter here and I use studded M+S tires. In summer I know I can get up to about 140km (87 miles) or even more. I think I could perhaps put another 4 cells in the car to get a little more power and range. Both the charger and controller would cope. But I will see how things work out with the pack heating story and LVC.

It would be really good to get a temp corrected LVC .

Best Regards
/Per Eklund


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## dimitri (May 16, 2008)

pm_dawn said:


> It would be really good to get a temp corrected LVC .


I'm working on BMS that will do this. Your data corresponds well with data from JimK from Canada. I plan to have LVC=2.5V at 0C temp, which may still be a little too conservative, but you should be heating up the pack above freezing anyway to get decent discharge current from it.

Thanks for your great report, its very good data.


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## dtbaker (Jan 5, 2008)

so.... who has the 'real world' TS life cycle record so far? I am REALLY curious to hear from people who have been running them the longest.


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## JRP3 (Mar 7, 2008)

They haven't been around long enough to come close to their limit. I guess it's a good thing that we don't yet have reports of early pack death.


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## dtbaker (Jan 5, 2008)

yeah... only premature cell death I have been noticing is people who had 'problems' with faulty BMS/shunts draining a cell or two past point of return.


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## jondoh (Sep 8, 2008)

When counting cycles, do we count only full charges? I rarely ever seem to drain my pack past 50% DoD as I can charge at work and at school. While I typically use 70% of my pack capacity in a day, my pack rarely sees 70% DoD. I think at this rate, i should expect more than the 2000 or 3000 cycles listed in the specifications. We're talking more than 5.5 to 8+ years of service. 

Anyway, my pack is stronger now than the cell balancers have been removed (the replacement cell may have helped as well). The one new cell seems to be lower than the rest by 20 mV (0.02v). I would assume it's the stronger cell because it's newer. It's odd that it would show a slightly lower voltage. I would expect stronger cells to have higher voltage. I guess maybe that within a certain tolerance, it voltage doesn't necessarily correlate with strength or health.


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## dtbaker (Jan 5, 2008)

jondoh said:


> When counting cycles, do we count only full charges? I rarely ever seem to drain my pack past 50% DoD


I think the typical %DOD is what the 'cycles' are predicted on. In your case it will be really interesting to see how long a 50% DOD 'usual use' lasts. Too bad we'll have to wait a couple more years!

can you reply with, just to have info in this thread:
- aprox current number of cycles you have put on to date?
- current charger/bms charge curve strategy


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## jondoh (Sep 8, 2008)

I got it first up and running around this time last august. I've put on 2600 miles since. 

I figure in the 20 or so weeks i've had it, maybe 3 weeks it didn't get used so 17 x 7 cycles = 119 cycles so far.

my charger is just a simple EP-B2 from bmsbattery.com. They programmed in a profile for LiFePo but i don't know exactly what it is-- but i do know it maxes at 87.6v which equates to 3.65v per cell.

except for the one dead cell (which ev components replaced for free) i've had no issues. I'm curious to see if warmer weather will make much of a difference in performance. Right now, it's about 45 degrees outside which impacts charging and discharging. There's greater sag during acceleration and less ah during charging when cold-- maybe 15% less at around 40 degrees F, i'm guessing.


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## dtbaker (Jan 5, 2008)

jondoh said:


> my charger is just a simple EP-B2 from bmsbattery.com. They programmed in a profile for LiFePo but i don't know exactly what it is-- but i do know it maxes at 87.6v which equates to 3.65v per cell.


so... do you have a BMS, or do any type of balancing?

Do you know if your charger does a second stage at constant V, or does it just bring'em up to 3.65v and quit?


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## JRP3 (Mar 7, 2008)

jondoh said:


> Anyway, my pack is stronger now than the cell balancers have been removed (the replacement cell may have helped as well). The one new cell seems to be lower than the rest by 20 mV (0.02v). I would assume it's the stronger cell because it's newer. It's odd that it would show a slightly lower voltage. I would expect stronger cells to have higher voltage. I guess maybe that within a certain tolerance, it voltage doesn't necessarily correlate with strength or health.


Stronger may not be the best term. Generally you'll have cells with more or less overall capacity, just because it's newer doesn't necessarily mean it has more capacity. That said, a cell with larger capacity would not reach the steep end of the charge curve as soon as smaller cells, so since it's not being charged to full capacity it's voltage doesn't climb as high, so that could be why it's showing a bit lower voltage.


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## jondoh (Sep 8, 2008)

No BMS or balancers. I used to have balancers but Evcomponents recommended that i take them off (which i did) as it was suspected to have caused the one cell to die. 

The charger does appear to be a CV/CC type. After it's finished charging, it turns off completely. 

I understand it's risky to be running around without a BMS but the cells seem to stay balanced. I have a voltmeter to watch for excessive sag-- which is a pretty good indication you're at 70% DoD. I do periodically check cell voltages. There really doesn't appear to be anything in the way of a BMS that's both practical and affordable. I already feel a little burned by my cell balancers which I spent a couple hundred dollars on and the car seems to run better without them for some reason. 

I did speak to EVcomponents about a BMS and they couldn't recommend anything other than their elithion which is like $1600. This would make sense if i bought over $10000 in batteries but i spent more like $3000. For the price of the bms, i'd rather have 12 more cells.


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## JRP3 (Mar 7, 2008)

jondoh said:


> I did speak to EVcomponents about a BMS and they couldn't recommend anything other than their elithion which is like $1600. This would make sense if i bought over $10000 in batteries but i spent more like $3000. For the price of the bms, i'd rather have 12 more cells.


Exactly. The only BMS that seems reasonable would be Dimitri's Mini BMS for $12 per cell plus the main board.


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## jondoh (Sep 8, 2008)

> The only BMS that seems reasonable would be Dimitri's Mini BMS for $12 per cell



you know, i'm flat broke at the moment. I'm also leaning towards jack's way of thinking which is, more or less, BMS doesn't buy a whole lot of protection. 

Considering how quickly my other cell died, i'd have to agree that these batteries either work or they don't and I'm not seeing much in the way of balance problems yet. You have to understand, i've checked voltages a lot and I even employeed a cell log before I fried it to check voltage under load. I've employed cell balancers and right now, I'm inclined to stay BMS free until I see a real need. 

you can tisk-tisk and tut-tut me all you want, but it's my money and batteries. I even discussed the matter with EVcomponents and they're of the opinion that these lithium cells don't really need much in the way of help.


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## tomofreno (Mar 3, 2009)

> Stronger may not be the best term. Generally you'll have cells with more or less overall capacity, just because it's newer doesn't necessarily mean it has more capacity. That said, a cell with larger capacity would not reach the steep end of the charge curve as soon as smaller cells, so since it's not being charged to full capacity it's voltage doesn't climb as high, so that could be why it's showing a bit lower voltage.


 Yep, I agree, plus, did you charge that cell individually to the voltage of the other cells before adding it to the pack? Is the voltage higher both during charging and at rest? Is it higher both after discharge and after charge? Looking at this you can sort out whether it has different capacity of the other cells, just has an offset voltage, or maybe has different internal resistance. After charge the rest voltages should all be very close since the difference in voltage with Ah is very small at that end of the curve. You tend to see more difference in rest voltages below around 30% soc where the change in voltage with Ah is larger (unless you "bottom balanced" there). You may see the largest differences in voltage while charging, near the end of charge, because some cells will be at an soc where voltage rises exponentially with charge (Ah) added, and others will be at lower soc. That is typically where I see the biggest differences. They all then "relax" to rest voltages very close to each other (< +/-0.004V difference typically), even if some charged to 0.04V higher than others.


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## JRP3 (Mar 7, 2008)

jondoh said:


> you know, i'm flat broke at the moment. I'm also leaning towards jack's way of thinking which is, more or less, BMS doesn't buy a whole lot of protection.
> 
> Considering how quickly my other cell died, i'd have to agree that these batteries either work or they don't and I'm not seeing much in the way of balance problems yet. You have to understand, i've checked voltages a lot and I even employeed a cell log before I fried it to check voltage under load. I've employed cell balancers and right now, I'm inclined to stay BMS free until I see a real need.
> 
> you can tisk-tisk and tut-tut me all you want, but it's my money and batteries. I even discussed the matter with EVcomponents and they're of the opinion that these lithium cells don't really need much in the way of help.


Believe me, I agree with that completely, as most of my posts will show. My only point is that IF you want a BMS Dimitri's is the only reasonable one that I'm aware of.


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## jondoh (Sep 8, 2008)

> Yep, I agree, plus, did you charge that cell individually to the voltage of the other cells before adding it to the pack? Is the voltage higher both during charging and at rest? Is it higher both after discharge and after charge?


I did charge the replacement cell individually with a power supply set to around 3.58v and i did bring it up close to the other cells. It seem to be about 0.02 to 0.05v lower during charging but after resting, the voltage is nearly identical... maybe +/- 0.01v. I have tried to add an amphour or two since but the difference during charging remains the same. I believe the offset may be there but very small and the difference during charging may be due to lower internal resistance.


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## Guest (Jan 23, 2010)

jondoh said:


> you know, i'm flat broke at the moment. I'm also leaning towards jack's way of thinking which is, more or less, BMS doesn't buy a whole lot of protection.
> 
> Considering how quickly my other cell died, i'd have to agree that these batteries either work or they don't and I'm not seeing much in the way of balance problems yet. You have to understand, i've checked voltages a lot and I even employeed a cell log before I fried it to check voltage under load. I've employed cell balancers and right now, I'm inclined to stay BMS free until I see a real need.
> 
> you can tisk-tisk and tut-tut me all you want, but it's my money and batteries. I even discussed the matter with EVcomponents and they're of the opinion that these lithium cells don't really need much in the way of help.



You GO girlfriend. This is what I've been trying to tell these people but they all know so goddamn much from typing themselves smart that I can't get through the noise.....

Jack Rickard
http://evtv.me


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## roger (Jan 24, 2010)

Hello members, is there any experience with new Yttrium Cells from Thundersky? I´ve ordered my pack at evcomponents and will receive it in a few days. Is there any improvement in cold areas?

Roger


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## MN Driver (Sep 29, 2009)

Just noticed this morning when taking a quick look at the Thunder Sky specsheet dated 2/27/2010 that the following charge/discharge voltages have changed:

Old specs
Charge: 4.25 volts
Discharge: 2.5 volts

New specs
Charge: 4.0 volts
Discharge: 2.8 volts

Nothing else seems to have changed from the previous specsheet such as(which I'll type up for the record in case the specsheets change in the future, it will be a good past reference):
LiFeYPO4
Max charge current <= 3 CA
Max discharge current constant <= 3CA, Impulse <=20CA
Standard charge/discharge 0.5CA
Cycle life 80% DOD >= 3000 70% >= 5000
Temperature durability of case <= 200C
Operating temperature Charge/Discharge -45C-85C
Self-discharge per month <=3%
Discharge curves match the previous specsheet


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## zwmaster (Nov 23, 2009)

MN Driver said:


> Just noticed this morning when taking a quick look at the Thunder Sky specsheet dated 2/27/2010 that the following charge/discharge voltages have changed:
> 
> Old specs
> Charge: 4.25 volts
> ...


Thnx for the info.
I don't know how far the guys at EVComponents are informed but the physical dimensions are also different. This is an issue for me but will see what the EVC response will be.
For example TS-LFP100AHA:
old - 220 x 145 x 68
new - 220 x 179 x 62 or 68 confusing datasheet

Anyone with new version of TS-LFP100AHA to confirm the data?
good work MN


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## octagondd (Jan 27, 2010)

Looks like they have updated the 100AH cells to have the same cycle life as the rest of the line. Slightly higher weight and bigger dimensions.


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## PTCruisin (Nov 19, 2009)

I'm encouraged by the data, but the dimension change will cause me to redesign the battery boxes for my project. I'm glad I haven't welded anything together yet. I ordered 40+ cells from EV Components for a late March delivery so I wonder if those cells will have the new dimensions or the old (or something else) . Still lighter and smaller than the SLAs I was first going to use so I guess I shouldn't complain. Thanks for posting the update MN.


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## jtgreeson (Aug 14, 2009)

roger said:


> Hello members, is there any experience with new Yttrium Cells from Thundersky? I´ve ordered my pack at evcomponents and will receive it in a few days. Is there any improvement in cold areas?
> 
> Roger


Does anyone know how to tell if the TS batteries are the newer Yttrium type? Any certain markings or manufacture date? I had 48 delivered by EVComp. in Jan. and was just curious.

Also, they were delivered with that packing slip notice from China recommending that they be initially charged to 4.25 volts. I quote: "WARNING Before first discharge the battery, please charge it to 4.2V with the constant current of 0.1CA~0.5CA and stop until the charging current falls to 1% of the original." I believe this was posted before in these forums but I have not found a really good consensus on how to first charge and subsequently treat these cells. With the most recent info my plan (as of now) is to initially charge to 4.00 volts then keep them between 2.90 and 3.80 volts in use. Any input would be appreciated. Thanks.


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## JRP3 (Mar 7, 2008)

That sounds like a reasonable plan. As I've stated before, the initial charge recommendation of charging to 4.2 volts doesn't make sense as these cells have been tested at the factory for capacity, which means they have already been fully charged and discharged. If they really need a 4.2 volt initial charge to "activate" them, it should have already happened at the factory.


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## Frank (Dec 6, 2008)

Well I hope they haven't changed size; don't misunderstand, I want the yttrium cells but will be bummed if they changed the width. Most of my boxes are built (motorcycle project) and I'm depending on that size. 

Oh well, will someone please post if they know for sure if the size has changed?


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## icec0o1 (Sep 3, 2009)

JRP3 said:


> That sounds like a reasonable plan. As I've stated before, the initial charge recommendation of charging to 4.2 volts doesn't make sense as these cells have been tested at the factory for capacity, which means they have already been fully charged and discharged. If they really need a 4.2 volt initial charge to "activate" them, it should have already happened at the factory.


I would doubt that they test the cells at the factory for capacity. I'm pretty sure they just test them for initial voltage right after assembly and if it's within a margin, the cells are deemed good. 

The initial charge is important because it allows the lithium ions to make tunnels in the medium. That's why the current needs to be low so more tunnels are created as opposed to fewer larger ones. The voltage is high so the reaction is pushed to completion. 

I would definately follow the manufacturer's suggestions


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## JRP3 (Mar 7, 2008)

I would think they have to test capacity to make sure the cells at least meet the minumum. I've not used Thundersky but my Skyenergy cells came 
with data sheets showing the capacity of each cell, and internal resistance numbers, so they had to be fully charged and discharged at least once.


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## MN Driver (Sep 29, 2009)

JRP3, If you have the sheet handy or remember, What was the difference between the highest capacity cell and the lowest capacity cell with the Sky Energy cells? I'm curious on how close they match.


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## JRP3 (Mar 7, 2008)

Most of my cells are 110-112 Ah, four of them are 113, two are 114. This is out of a total of 34 cells, my other two are from a later batch that does not have serial numbers. The sheet also includes data for the other cells in the shipment, and most are between 110-112, nothing above 114. This is over 200 cells. Internal resistance for my cells is 0.28-0.34


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## MN Driver (Sep 29, 2009)

Those cells are matched closer than I expected, it's nice to see that you are getting an extra 10% initial capacity over spec according to the information they provide. It seems the Thunder Sky cells give a little extra capacity versus what you buy too. I'm looking to get 50+ 40Ah cells but not sure if they will fit in the application that I'd like to put them in. I know the 40Ah HiPower cells fit since they are 160mm tall but the SE's are 185mm and the Thunder Sky are 190mm. I don't know how the extra 1.1 inches will fare as it seems that I'll have roughly half an inch of clearance in the spare tire compartment where they need to fit inside, which isn't much room for the cell connections and the BMS that I want to use since I'm planning on using these around 1.5C and want somewhere between 70-80% DOD and I need to have a good idea of how many Ah I've pulled out so I'm getting the most use out of the cells without digging too far into their capacity.


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## JRP3 (Mar 7, 2008)

I've been wondering if one could make a special request, maybe for a little extra cash, to get a matched set of cells all exactly 110 or 111 ah's since most of them fall in those sizes, or whatever size you are dealing with, and maybe even closer matched resistance. It would make going BMS-less even safer.


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## Frank (Dec 6, 2008)

Frank said:


> Well I hope they haven't changed size; don't misunderstand, I want the yttrium cells but will be bummed if they changed the width. Most of my boxes are built (motorcycle project) and I'm depending on that size.
> 
> Oh well, will someone please post if they know for sure if the size has changed?


According to EV Components, they have changed the size of the 200AH cells (although the old cell size is still available with the new chemistry.) My own 100 AH cells are on-the-way so I'll be able to confirm these haven't changed when they arrive.


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## Frank (Dec 6, 2008)

I can confirm that the 100AH cells have not changed in size (at least not yet!)


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## EVfun (Mar 14, 2010)

This is an interesting thread! I have my pack of the newer Yttrium doped cells in the little 60 amp hour size that I am going to flog. 40 of them are going in the front of my '66 Datsun. That is the whole pack -- the entire conversion will be housed under the hood. 

I did want to point out one other option in BMS systems, the potted modules from EVworks in Australia. I am using those with the miniBMS control board. Mostly I'm running a mixed system because I found the miniBMS stuff after I had the other system, but check out the braided cell interconnects over at EVworks (I am using those too.)

My pack will have proper restraint end plates on the cells. The cells are in a single block, 5 cells wide across the width of the car and 8 cells deep (22.6 inches by 19.7 inches. The car will weigh about 2100 lb., about the stock weight and stock weight distribution. I'm feeding the power out with a Zilla 1k so I will have good control over the rate of abuse.


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## bblocher (Jul 30, 2008)

I posted some updated info on my TS 160Ah batteries on my blog for those interested.

http://s2kev.blogspot.com/2010/08/battery-testing.html


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## Larry D (Sep 6, 2010)

I have an interest in setting up a PV array to recharge my EV and I am considering a dual use array and that means enough PV to satisfy my Manzinita 20 amp charger with 100-390 vdc and possible draw of close to 5000 watts and grid tie when not charging the EV. The only problem is I am not real sure on the amount of PV I need to order and exactly how to switch the array for dual use. 
I would really hate to put an inverter in between PV and a charger that accepts DC to power it. 
I kinda thought you might be knowledgeable since you use 6kw pv to recharge your ev.


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## dtbaker (Jan 5, 2008)

Larry D said:


> I have an interest in setting up a PV array to recharge my EV and I am considering a dual use array and that means enough PV to satisfy my Manzinita 20 amp charger with 100-390 vdc



I do have 5kw of PV, but do not know what it would take to feed the DC to the EV batteries. I do not think your AC charger will hand DC in.... so you'd have to have some custom way to regulate the DC voltage directly (and accurately!)

I wold HOPE there is some way to tap your DC from panels just before the grid invertor, and some slick way to accurately set a 'finish' voltage and a big fat diode to prevent sucking juice OUT of the batteries.

I really don't know, I just let my PV run thru the inverter to the grid, and use a regular ac charger. I am interested though! Perhaps I can get some guidance from a local PV guy who specializes in off-grid.

One minor down-side is that if I siphon DC off before the invertor, then I don't get the REC payment from the utility company on that juice. This is not much.... but more importantly I suspect that all the extra hardware to do this would cost way more than the loss in efficiency of inverting to AC, then back thru the normal (ac) charger to DC.


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## Frank (Dec 6, 2008)

I've thought about using our PV array to charge directly in case of major grid failure also but haven't pursued it. You would need a properly rated DC transfer switch to make it happen; I would call Rich re the charger to get his input. I *think* the charger will accept just about anything as input but better to make sure....


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## PTCruisin (Nov 19, 2009)

Larry D said:


> I have an interest in setting up a PV array to recharge my EV and I am considering a dual use array...



I've had similar desires and I think the easiest way would be to configure an off-grid system with lead-acid batteries and then dump the charge from the lead-acid to the Lithium batteries. I suspect you would need some sort of PWM-type circuit to control the rate of charge transfer to the Li batteries. That would be the problem to solve.


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## sunworksco (Sep 8, 2008)

The problem of using dc is that you will need very large capacity cables for delivering current.It is much more practical to go ac-dc charger unless you are off-grid using dc battery storage for your home.
The best pv system out there is one using individual micro inverters on each pv collector.You can monitor each collector and store data history for warranty and maintenance.This is becoming the standard.
I would consider the new PVT collectors that produce dc & thermal hot water.
Regards,
John
http://pelicansolar.com/wiosun_pvt.html

http://translate.google.com/translate?hl=en&sl=de&u=http://www.solarzentrum.com/&ei=IJ6GTLfPB4O6sAOq07XbDw&sa=X&oi=translate&ct=result&resnum=1&ved=0CCIQ7gEwAA&prev=/search%3Fq%3Dsolar%2Bzentrum%26hl%3Den%26prmd%3Dv


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## dexion (Aug 22, 2009)

There are chargers (that arent very expensive) that can go dc-dc. I have a small one I use for 6amps (168VDC) (1000watts) at 110Vac for when I am out and about Its got about 300 hours on it so far. Reading the manual it also allows as an option (I havent used the feature) direct dc to dc charging as well. I paid $250 delivered. If this cheapy can do it I would think you could find a larger one that would work faster than 6amps. If your interested I can post part numbers and where I got it.


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## Sun Motors (Aug 10, 2010)

TS real world experience. I have been running 42 160aH TS cells in a 1975 914 with a 9" ADC motor and 1231 Curtis controller for about 1000 miles, usually charging at about 50 miles or 80aH. I have CellLog 8's to monitor the cells while charging and driving.

One cell has been acting strangely recently and I was wondering if anyone else sees anything similar, and maybe can say what happens next? 

When left to sit at 1/2 charge for a week or so, this cell dropped voltage somewhat, from the rest of the pack which was around 3.31 to about 3.27. When I charged it again it came back up into the pack tightly, neither the highest or lowest, and on discharge wasn't the lowest either.

The weird thing was after a couple of cycles more, on charging when nearing the shoulder when the rest of the cells were nearing 3.5v, this cell's voltage went from 3.34 to 3.17 to 3.40 and back up with the pack in a matter of minutes.

The CellLogs seem to be behaving properly otherwise, is this cell losing it? (Charging is being done at around 143v and around 11a.)


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## JRP3 (Mar 7, 2008)

Have you tried putting a different Cell log on it to make sure it's reading properly? And checked all connections? That's some strange behavior otherwise.


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## dtbaker (Jan 5, 2008)

Sun Motors said:


> TS real world experience. I have been running 42 160aH TS cells in a 1975 914 with a 9" ADC motor and 1231 Curtis controller for about 1000 miles,


I bet this is LOTS of fun!
Do you have a build thread/site, or listing in Garage to show your vehicle?



Sun Motors said:


> ... when the rest of the cells were nearing 3.5v, this cell's voltage went from 3.34 to 3.17 to 3.40 and back up with the pack in a matter of minutes.


could be as simple as a loose wire reporting a bouncing voltage, when actual is just fine. I would make SURE you don't have a long bolt in a short hole, and check connections.

Also, I am wondering why you are charging at 144v... that only averages to 3.4 v per cell, and you probably won't see the voltage start to climb until the cells hit 3.55 ?


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## Sun Motors (Aug 10, 2010)

No, the connections are good. I'll try switching the cell logs, but I don't think that is it because I have blown the fuses on the wires to the CellLogs and they show any connection problems, and the log readings have been reading fine on this cell before a few weeks ago.

I'm charging it now and that cell just went from 3.35 to 3.40v in like 5 minutes and joined the pack, which is all within 20mv of each other: it lags about 40mv behind through most of the charging then catches up in a jiffy near the shoulder. But the strange thing is I saw the voltage dropping for a while and then recovering that one time, so it must be the CellLogs, unless someone else is seeing the same thing?

I have the pack in 7 packs of 6 cells with a CellLog monitor on each or the 7 packs reading 6 cells in each. The high voltage alarm is set at 3.6v for each cell and shuts off the charger, just to be extra safe.


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## JRP3 (Mar 7, 2008)

Sun Motors said:


> I'm charging it now and that cell just went from 3.35 to 3.40v in like 5 minutes and joined the pack, which is all within 20mv of each other: it lags about 40mv behind through most of the charging then catches up in a jiffy near the shoulder.


It's possible that cell has a lower internal resistance than the rest so voltage stays low longer until it gets a bit further into the knee of the curve.


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## Sun Motors (Aug 10, 2010)

dtbaker said:


> Also, I am wondering why you are charging at 144v... that only averages to 3.4 v per cell, and you probably won't see the voltage start to climb until the cells hit 3.55 ?


The new new Russco charger barely covers the 3.3x42 pack voltage and it charges at 142-144v during the main charging time when the pack is 139-141v, then it picks up higher when the pack approaches 144. The amps output moves around from 10.5 to 12 with my connections during this time.

http://www.diyelectriccar.com/garage/cars/283

http://www.youtube.com/watch?v=_5YclCjREEc


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