# Bradley GT2 Electric Conversion



## Ocean (Dec 20, 2016)

Hi All, Merry Christmas!!! Happy New Year and Best Wishes on your Journeys...

I'm Ocean. After browsing and researching and reading several interesting threads, I'm excited to introduce myself here as I am now taking my first step into the world of EV's. I've wanted to do this for sooo long, and I finally jumped into something with style that I could afford to get started with.

I'm the proud new owner of the Bradley GT2 Electric Conversion that was recently listed on the EV Tradin' Post.

The Bradley is a sporty kit car from the 70's - early 80's. A fiberglass shell built over a VW Chassis. Overall the car is in very good condition.

The Bradley came with an 8" ADC Motor, and a pack of 15 essentially dead 8-volt LA batteries (120 volt system). The vehicle also has a relatively new Logisystems 750 Amp Controller (says 120/144volts on it), and a 15 amp on-board charger with variable amp / volt controls up to 170 volts. Nice Guages with amps to 500A and volts to 150V. Batteries were arranged in custom steel cages low in the vehicle - 9 in the back (around motor) and 6 up front. As far as I understand, re-building the pack is all that I need to do to get this baby back on the road. However, some TLC will also be involved.

So my big contemplation here is the new battery pack. My main concern is range, with a secondary desire for performance, and another primary concern for longevity of the pack. I want at least 100 miles... and 200 would be much better.

According to his page, Richard Slatin's electric Bradley GT2 at evalbum/916 weighs in at 1700 pounds with 10x 13volt NiMH batteries (130 volts nom) and has a range of about 65 miles...

So, trying to figure what my curb weight will be. I don't know what those NiMH batteries weigh, but I'm going to guess about 40 pounds per each (which would be just over half the weight of LA's in the size of a golf cart, which are usually around 70lbs each)... so that's 400 pounds of batteries in his car. Subtract that and I myself have a rolling chassis of about 1300 pounds.

So back to the battery: L-ion of some type, Of course. But how. I'm looking at 24 volt Tesla Modules. (6s @ max 4.2volts = 25.2 max voltage) I feel like 5 is not enough (25.2 x 5 = 126 max voltage of the system). 6 would give 151.2 max voltage. Now my concern: is that too much for the 8" ADC??? I don't know. Research suggest that it can handle it. It's listed as a 120 volt motor, but 120 nominal on LA's is at least 130 volts... (and it seems to be some people are out there running 8" ADC motors at 144 nominal) so... I'm thinking that about 150 max voltage would be ok. Thoughts on this???

So at 5.5 Kw per Tesla module, that would give a 33KwHour Pack (say 30 KwH conservative).... which sounds pretty good to start. The modules size (about 3" thick x 27" long x 12" high standing on edge) suggests it would fit nicely in the old battery racks (10.5 wide x 29 long x plenty vertical space in the back) - I could get 3 standing on edge together in one rack, on either side of the motor. At about 55lbs per module, I'm only adding 330 pounds to the curb weight for about 1600 - 1700 pounds.

Seems like this setup should get me at least 100 mile range. Any other estimates??? Could I expect more? What's that rule of thumb??? ev-propulsion.com/ev-calculations gave a nice formula of 250 - 300 Wh / Mile for a small car. I will say that this is a particularly small car with good aerodynamics.... so if it actually got 250 Wh / Mile that would give 30000Wh/250Wh/m = 120 miles which would be excellent. And in fact, in the long run, I can see adding another 6 in parallel (4 up front and 2 more in back) for a range of 200+ miles which would be ideal. Expensive though unless I find an amazing way to get into those batteries other than saving for a couple years...

The other possibility for me is to build my own custom pack for half the cost and 50x the work. I may be up to it. Anybody have any experience with FullRiver LifePo4 individual cells? Are they reliable to their spec is my main question. Looks like I can get large volumes of these off ebay for about 1/each (26650's) - and they are 3.3Ah x 3.2 volt nom = 10.56 call it 10Wh each. So, 3000 of those would yield a 30KwH pack... built in blocks of say 75p x 40 units in series I would then have 75*3.3 = almost 250 Ah pack at 128v nominal (148 max voltage, which I like because the volt meter goes to 150). Any ideas about how these configurations would translate to Performance on the ADC 8" motor? I would love feedback on these considerations. This pack would be a bit heavier I think than the Tesla pack, but it might have a longer life because of the difference in battery chemistry... any ideas on this???

About me: I'm an off-gridder in N. California. I've lived off grid with solar power for the last 8 years and happily married for the most recent three+. Slowly building up our little piece of paradise out here on the land, growing food and living in a permaculture lifestyle. An EV is a natural step in alignment with our values that we're looking forward too. We use Solar Energy for almost everything. I plan to build an array to charge this car. If I can charge 100 miles of range in about 3 - 4 days that would be more than enough as I typically drive less than 50 miles per week but sometimes I need to go 100. I expect a 2kw dedicated array will do it. We get lots of sun. Ultimately I would like to have the EV drive down to visit family in the bay area which is about 200 miles. That's where the range really factors in...

Cheers!!!


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## dtbaker (Jan 5, 2008)

very exciting!

If it were you.... I would ditch the Pb asap consider building up a 144v or 156v nominal Lithium battery pack. 

I don't know much about the Tesla battery packs, but the small format cells present a real challenge in the DIY world when it comes to balancing and monitoring multiple parallel/series strings. I would recommend you strongly consider large format LiFePO cells.... like the CALB for instance. In a nice 130ah size, you put 48 in series and you have a heck of a battery pack.

You'd have to re-program your charger, make sure your dc-dc can handle it, but little else would need to change. You'd want to design your racking in a couple sections to balance the weight. I'd recommend polyprop or ABS 1/4" sheets. It's easy to work with, easy to heat weld, non-conductive, etc.

enjoy!


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## Ocean (Dec 20, 2016)

Thanks Dan! Yes I'm very excited about it. I will indeed be going to lithium. goodbye SLA's. The CALB cells are pretty expensive though, and I want serious range - like 200 miles ultimately... and why not replicate the method used in a tesla pack? Tesla packs are built with hundreds of individual cells - like 74parallel x 6 series for a 24 volt 5.5Kw pack... Only difference is that I would be using LiFePo4 instead of LiCobalt or whatever their chemistry is. I think the parallel cells work to balance each other - and the parallel block could be balanced with other blocks in the series string. Right now I'm looking at TENERGY 5.5Ah cells (32650). If I stack a block of 80 in a 8x10 arrangement I believe I can fit them into the old rack (originally for the SLA's). If I build 40 of those in series I will have 3.2 x 40 = 128 nominal at about 440 Amp Hours which I think might actually get me the range I really want - about 200+ miles. Again, this vehicle was already converted and running on SLA's, so it has a pretty tough racking system built into - well balanced. If I did 45 in series it would be a 144 volt nominal pack... but I'm worried about giving the 8" ADC motor too much voltage.... Any idea about that? What's the max safe voltage to run an 8" ADC motor at? Thanks.... and Cheers!


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## dtbaker (Jan 5, 2008)

144v nominal should be fine for the motor... remember it rarely sees peak voltage.

The CALB cells are a little pricey, BUT I think you will find that fabricating, balancing, debugging hundreds of smaller cells in parallel and series will take so much more of your time and cost for reasonable BMS that you are better off with the simplicity of 45 of the large format cells in series.

I would bet that a 144v x 130ah CALB pack will get your Bradley 60-70 miles. If you step up to the 160ah or 200ah you'll be over 100 but the car will weigh more. You need to evaluate what your actual range needed is, and build to that to keep your costs down and performance up.


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## Ocean (Dec 20, 2016)

I appreciate that - I will start thinking in terms of 144 volts nominal. As far as range is concerned... I really do want 200+ miles. I know it's heavy - but really I don't think it will be any more heavy than what the car was originally carrying - 15 x 8 volt golf carts at about 70 lbs each. Performance is again secondary. Perhaps one day I will upgrade to a 9" motor. Regarding the CALB's - to get 200 miles I believe I need a 400 AH pack and that's just too expensive.

These
http://www.ebay.com/itm/NEW-Box-of-...363778?hash=item51ecc01b02:g:YPoAAOSwoi1X87JG

are looking good. that's under $5k (plus shipping) for 40s x 80p x 5.5Ah * 3.2V = 56.320KwH Pack once built.

I have much more time than money. To get 400 AH of prysmatic cells would be on the order of $18-20K. Way beyond me. Used Tesla modules (12 of them) would only be $12 - 15k - a much better deal at 250AH per module (6 x 5.5Kw Modules in Series for 133v nominal, Two strings, for a total of over 60Kw Pack)... but still way too expensive for me.

Once the blocks of 80p are built, they are installed in series just like any other. I'm not afraid of batteries. I don't see a problem building a block of 80p with appropriate bars and terminals etc. So I think BMS questions will be the same as any other large format LiFePo4 setup.

I really want 200+ mile range - 220 ideally. I really do. And if I go to 45s modules for the full 144v nominal pack, at 440 Ah... that's a 63.360KwH Pack for about $5-6k in batteries... and a lot of fab time... it's sounding pretty good. At about 117 WH / Kg that's 63360/117 = 541kg = 1194 lbs which is about 150lbs more than old lead acids which were mounted in the car originally....maybe I'll keep it down to 40s....


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## piotrsko (Dec 9, 2007)

First thing: How much energy does your vehicle use in its current configuration to go a mile?

Size your pack around that. Li batteries weigh 1/3 to 1/2 of fla depending on packaging, so there is a range boost just right there. They are a lot smaller too so you can put more in the same space.

If you are low bucks, see what is available in the local wrecking yards, use that. If you score a tesla, wonderful, otherwise leafs, VW, fiats,ETC all have a lithium pack and you can sometimes score a whole donor car for the price of a battery pack. Then you could go AC with regeneration and hvac, have a 100 + mile range right off the bat.

Your car, your conversion. My $0.02, YMMV


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## nucleus (May 18, 2012)

Ocean said:


> I appreciate that - I will start thinking in terms of 144 volts nominal. As far as range is concerned... I really do want 200+ miles. I know it's heavy - but really I don't think it will be any more heavy than what the car was originally carrying - 15 x 8 volt golf carts at about 70 lbs each. Performance is again secondary. Perhaps one day I will upgrade to a 9" motor. Regarding the CALB's - to get 200 miles I believe I need a 400 AH pack and that's just too expensive.
> 
> These
> http://www.ebay.com/itm/NEW-Box-of-...363778?hash=item51ecc01b02:g:YPoAAOSwoi1X87JG
> ...


Well, if the Tenergy batteries live up to their labeling that is a big pack for the $! 

That is a big IF. I would buy a set, get a powerlab 8 and test them through multiple discharge cycles to see if they ACTUALLY have 5.5 Ah of capacity.

You might want to check out jehugarcia on youtube, he is a little ignorant at times, but he has built multiple packs from little batteries.

I think you are on the right track with the LiFePO4 chemistry, you shouldn't need any cooling, and they are far less likely to catch on fire...

Sooner or later you will want to upgrade to AC. Brushes are a hassle and you gain efficiency and regen with an AC motor. 

You can find salvage cars on the internet, people are crashing electric cars all the time... I recently missed a rolled i3 for $4500 in my area, that would have been a steal, 170 HP transaxle plus a 24 KwH battery pack.

Interestingly, none of the OEMs seem to use LiFePO4 chemistry...

When you build your packs, I would leave access to check each battery individually so you can find any bad ones. If they reverse that can start a fire. 

I would also bottom balance every cell per EVTV.


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## Ocean (Dec 20, 2016)

Thanks... good call, I will definitely start checking my local wrecking yards. That's a really good idea.

My understanding from the previous owner is that he got about 40 mile range on a new pack of 15 x 8 volt Lead Acid's.... so, yeah. Again, I'm shooting for 200+, and I do think I can get that for the same weight in Lithium's or LiFePo4's...

Merry Christmas!!!


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## Ocean (Dec 20, 2016)

Nucleus I just saw your post as I was replying to piotrsko,

What does is mean "reverse" - in a LiFePo4 cell? it seems like you're implying that the polarity of the physical cell would "reverse" - is that possible? How???

Indeed, I too am concerned about the TENERGY cells living up to their claims, and have been thinking about how to test them. I will look into the PowerLab8. I think I did see one of jehugarcia's videos - making a VW Bus? Or was it a Powerwall? Yeah, good info there.

You are right I would like to upgrade to AC with regen eventually... although the idea of swapping the VW axle setup with something from a commercial vehicle seems a little daunting... maybe. That's all for much later. Maybe when I eventually build an electric truck...  I have high aspirations.

Also, what do you mean by: "I would also bottom balance every cell per EVTV." I was thinking that each block would balance itself when all cells are connected in parallel.... then with a series BMS once they're all in the car hooked up together.

My guess on why the big guys don't use LiFePo4 is because it's a little heavier / less power dense than Cobalt (or whatever), and since they can do thermal management fairly easily, they take the benefit of the lighter / smaller pack.

Cheers, and Merry Christmas!


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## electro wrks (Mar 5, 2012)

dtbaker said:


> I would bet that a 144v x 130ah CALB pack will get your Bradley 60-70 miles. If you step up to the 160ah or 200ah you'll be over 100 but the car will weigh more. You need to evaluate what your actual range needed is, and build to that to keep your costs down and performance up.


I haven't seen the CALB 130Ah cells listed for several years now. AIR, in a contact with CALB, they said they were discontinuing them.


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## nucleus (May 18, 2012)

See http://media3.ev-tv.me/cellcare.pdf for "Care and Feeding" of CALB batteries. 

If you haven't checked out Jack's EVTV videos, online shop, and catalog (full of nice builds), that is definitely a must.

I started at video #1 and watched them all in order, took about six months. I "watch" them while doing other things.

As to reversal, it is exactly that. 

If one battery runs out of juice before the others in the string, the power of the other batteries cause it to reverse polarity and this kills the battery. 

This is why you bottom balance so they all hit zero at the same time should you leave your lights on or whatever.

Saves batteries.

There is no need to swap your transaxle out for an AC motor, VW adapters are readily available.


I would be careful about going for too big of a battery pack, as your pack gets heavier its weight reduces your range as well.

If you consider your marginal old VW brakes and then add even more weight...

I personally think that Tesla may have screwed up using the Panasonic batteries. Yes, they their storage density is greater, but their power density is less. They also require cooling, which adds weight as well. 

In my dreams I build an aftermarket LiFeP04 pack for Teslas that allows the full HP the motors are capable of, and Elon Musk tells me how smart I am. LOL.

I am of the people who thinks that BMS's are mostly BS, big controversial subject; but I don't think you need to monitor every cell, especially with high quality LiFeP04 batteries.

Please keep us updated on your project, I used to dream about Bradley GT's when I was a kid, those sweet lines in their ads in the back of Popular Mechanics.

Nuke




Ocean said:


> Nucleus I just saw your post as I was replying to piotrsko,
> 
> What does is mean "reverse" - in a LiFePo4 cell? it seems like you're implying that the polarity of the physical cell would "reverse" - is that possible? How???
> 
> ...


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## dtbaker (Jan 5, 2008)

Nucleus has touched on the 'great debates' in the DIY world. top vs bottom balancing, and practicality/cost of BMS vs going commando.

The problems are that Li cells die horrible deaths when the voltage is too high, OR too low. 

This means you have to commit to maintaining either a top balanced system by managing the end of charge voltage and never allowing more than 80%-90% DOD for safety... or bottom balance and limit your charge cycle to never going about 80-90% 'full' to avoid overcharge on any cell.

The second part of the debate is how sophisticated you get in monitoring/managing whichever end you decide on.

These issues are why many of the EVers here still go with the large format cells in series... fewer cells to manage = fewer points of failure.


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## Karter2 (Nov 17, 2011)

Ocean said:


> My understanding from the previous owner is that he got about 40 mile range on a new pack of 15 x 8 volt Lead Acid's.... so, yeah. Again, I'm shooting for 200+, and I do think I can get that for the same weight in Lithium's or LiFePo4's...
> 
> Merry Christmas!!!


 But i dont think you have mentioned what Ahr those LAs are ?..100Ahr ?..
..or are they bigger ?
If so, they probably gave 60-80Ah max ,or 8-10 kWh available from the pack ?
Even if it were 10kWh , that means it did need 250Wh/mile average


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## Ocean (Dec 20, 2016)

Wow, Reversal. Crazy.

Hmmm... Top Balancing and Bottom Balancing.... Big consideration I suppose. I once saw a BMS system that was composed of individual modules - one for each cell. And it worked in a way that it balanced the cells by moving energy from one place to another - rather than wasting energy through heat. It had the ability to transfer I think up to 6 amps.

Found it:
www.electriccarpartscompany.com/6Am...alancing-Lithium-Battery-Balancers-Equalizers
anybody have any experience with this???

Also, I would assume that there is some ability to have a BMS system disconnect the battery once it reaches a certain critical high / low voltage - or once any of the cell blocks reach a critical high / low. I guess that's part of the BMS apart from balancing. I'm looking at a series of 40 - 45 x 3.2 volt blocks for a nominal working voltage of 120 - 144 volts.

I will say that I found some supporting documentation / test data on smaller LiFePo4 cells from TENERGY which gives me some more confidence in their product.

http://www.all-battery.com/datasheet/30069-0_datasheet.pdf

I do want a big battery but I understand as you say that more weight reduces range as well. The old pack of 15 x 8 volts was I think about 15 x 70 lbs = 1050 lbs, I definitely don't want to build a new pack weighing more than that. Less would be better. But I still want the range. Perhaps I will end up letting go of my 200 mile range aspirations. We'll see. The brakes are almost new on the car, as I understand it from the seller - so that's good. He did say the vehicle went through brakes pretty fast.

I still like the idea of using smaller 5.5 amp cells (see above link to TENERGY test data) to build blocks in the way Tesla does. All those individual cells will balance to eachother within the same block. Only problem I see there is if one fails... then what happens to the rest? Was considering how to attach them - thinking about a "fuse" wire from individual cell to bus bar (again, like Tesla does) that would blow at say 10 amps or so. Saw someone on youtube figuring that out. Even if I only build a block of 60 cells that's 60 x 5.5 = 330ah and so the system could pull about 600 amps and each cell would still see less than 10 amps (<2C) sooo....

As far as AC goes - yes, getting a motor that would adapt to the tranny seems like the best way for the long run. All in good time. Just want to get it working for now.

Thanks everyone for all the feedback.

Cheers!


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## Ocean (Dec 20, 2016)

Karter2 said:


> But i dont think you have mentioned what Ahr those LAs are ?..100Ahr ?..
> ..or are they bigger ?
> If so, they probably gave 60-80Ah max ,or 8-10 kWh available from the pack ?
> Even if it were 10kWh , that means it did need 250Wh/mile average


Good Call.
Those LA's were 183Ah at the 20 hour rate. 95 minutes @ 75 amps. Soooo... 1.5 Hours x 75 amps = 112 Ah usable... so 112Ah x 120v = 13.440 KwH Pack. But is that the useable energy of the pack? Or is it half that? I'm guessing that's the useable energy because at 40 miles that would be about 333 Wh / mile. Unless he was pulling more than 75 amps to cruise down the road. Any guess on this? I think the curb weight was about 2300 pounds with those LA's.... Curious....

-Ocean


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## hmincr (Jan 20, 2012)

Have you considered a Chevy Volt battery, They are rated at 16.5 Kwh and come as 7-- 45V @ 45 Ahr and 2- 22.5v @ 45 Ahr. The 45V are separate modules and have coolant features already built in. These are 9" long X 9" wide X 11" tall. The 22.5V are just a hair over half as long, and, the whole battery will weigh under 400 pounds. 

The 2016 and 2017 year models are 18.4 Kwh and are even lighter. The modules are 16S at 3.7 Nominal 59.2V as compared to 12S in the earlier year models. They have most of a BMS already attached and someone has hacked the system, so, it can be made functional. Parallel the 59.2V and you get 118.4V. Parallel 3 sets and you get 3 times the Ahr. which I can't remember offhand.

These are really under rated by GM. They can be bought from $1500.00 and up + S&H. I recently bought a 2017 with less than 10 miles on it, for under $1600.00 and am waiting for a shipping quote. 

I would bet a 2017 battery might get you really close to 200 miles.


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## Ocean (Dec 20, 2016)

hmincr said:


> Have you considered a Chevy Volt battery, They are rated at 16.5 Kwh and come as 7-- 45V @ 45 Ahr and 2- 22.5v @ 45 Ahr. The 45V are separate modules and have coolant features already built in. These are 9" long X 9" wide X 11" tall. The 22.5V are just a hair over half as long, and, the whole battery will weigh under 400 pounds.
> 
> The 2016 and 2017 year models are 18.4 Kwh and are even lighter. The modules are 16S at 3.7 Nominal 59.2V as compared to 12S in the earlier year models. They have most of a BMS already attached and someone has hacked the system, so, it can be made functional. Parallel the 59.2V and you get 118.4V. Parallel 3 sets and you get 3 times the Ahr. which I can't remember offhand.
> 
> ...


Wow. That's sounding really good. I like the dimensions too. The racks that were built for the 8 volt golf carts are about 10.25 wide x 29 long... easily enough (but not too much) to get three of those 45Ah units. I actually really like it. I'm going to look around...

thanks!


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## onegreenev (May 18, 2012)

Where in Northern California? Im in Northern California and if you are close enough you are welcome to come check out my VW conversion and setups. Im moving towards AC and getting away from DC but I still have my Bug that will remain DC. 

http://www.diyelectriccar.com/garage/cars/471


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## Ocean (Dec 20, 2016)

onegreenev said:


> Where in Northern California? Im in Northern California and if you are close enough you are welcome to come check out my VW conversion and setups. Im moving towards AC and getting away from DC but I still have my Bug that will remain DC.
> 
> http://www.diyelectriccar.com/garage/cars/471



Cool! I'm near Redding - about 30 miles south / south west. Where are you?


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## Ampster (Oct 6, 2012)

I just bought a Nissan Leaf pack for $1500 and plan on re configuring it for a 48Volt stationary pack for my backup Outback inverter. That was $62.50 per kWhr. I think that or a Pack from a Volt should be easily found below $100/kWhr and that beats any of the Tesla packs that I have seen or new LiFPos for that matter.


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## Karter2 (Nov 17, 2011)

Ocean said:


> Good Call.
> Those LA's were 183Ah at the 20 hour rate. 95 minutes @ 75 amps. Soooo... 1.5 Hours x 75 amps = 112 Ah usable... so 112Ah x 120v = 13.440 KwH Pack. But is that the useable energy of the pack? Or is it half that? I'm guessing that's the useable energy because at 40 miles that would be about 333 Wh / mile. Unless he was pulling more than 75 amps to cruise down the road. Any guess on this? I think the curb weight was about 2300 pounds with those LA's.... Curious....
> 
> -Ocean


 Wow ! ..183 Ahr batterys, so yes, at least that 333Wh/mile.
So that means for 200miles you will need 67kWhr useable capacity, so probably 70-75 kWh pack.!
.. That quite a bit more than a Volt pack can muster.


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## onegreenev (May 18, 2012)

Ocean said:


> Cool! I'm near Redding - about 30 miles south / south west. Where are you?


Yuba City / Marysville


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## Ampster (Oct 6, 2012)

Karter2 said:


> Wow ! .., at least that 333Wh/mile.
> .........
> .. That quite a bit more than a Volt pack can muster.


 i get 338Whr/mile in my 6,000lb. Tesla Model X. I used to get 250Whr/mile in my VW conversion. A Bradley should be sble to do the same depending on the conditions. With a 20% margin that would mean a 60kWhr pack to get a range of 200 miles. If you could get Leaf or Chevy Volt modules at $100/kWhr that would be $6000. That still compares favorably with LiFePO Prisims or Tesla packs at over $300/k/Whr. ($18.000) The biggest question is the weight for that much Lithium of any form factor on that chassis. One has to ask themselves about the concept of carrying all that weight around for the occasional 200 mile trek. Are there charging alternatives? YMMV


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## nucleus (May 18, 2012)

Ampster said:


> i get 338Whr/mile in my 6,000lb. Tesla Model X. I used to get 250Whr/mile in my VW conversion. A Bradley should be sble to do the same depending on the conditions. With a 20% margin that would mean a 60kWhr pack to get a range of 200 miles. If you could get Leaf or Chevy Volt modules at $100/kWhr that would be $6000. That still compares favorably with LiFePO Prisims or Tesla packs at over $300/k/Whr. ($18.000) The biggest question is the weight for that much Lithium of any form factor on that chassis. One has to ask themselves about the concept of carrying all that weight around for the occasional 200 mile trek. Are there charging alternatives? YMMV


The issue I see with the Volt packs is weight, according to https://media.gm.com/content/dam/Media/microsites/product/Volt_2016/doc/VOLT_BATTERY.pdf, even the new 14 KWh Volt pack is a little over 400 pounds! 

To get close to 60 KWh you are talking over 1600 pounds! Not good for a Bradley GT.

Let's compare what GM is so proud of against a home-brew pack with the identical capacity:

If you put together 44 100 Ah CALB cells you would get the same 14KWh for 330 pounds; I am confident you can build a battery box and get them strung together for less than 10 pounds. 

So a simple home-brew, high quality LiFeP04 CALB pack weighs about 15% less, AND has more than 2X the peak power (1000 A instead of 430 A).

Seriously, the OEMs are so off base with their poorly chosen chemistry and overly-engineered packs, it's silly!

P.S. I like the CALB 100 Ah cells because the have more extra capacity than the other sizes, 117 Ah on average, so you can really use all 100 Ah and still have a 15+% cushion.


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## Ampster (Oct 6, 2012)

nucleus said:


> The issue I see with the Volt packs is weight, .........., even the new 14 KWh Volt pack is a little over 400 pounds!
> ..................
> To get close to 60 KWh you are talking over 1600 pounds! Not good for a Bradley GT.
> 
> .


You make some interesting criticisms of manufacturers that have hundreds of thousands of reliable cars out there. I wouldn't own a Volt or a Leaf, but I would use their cells if I wanted a cost effective pack. The issue I see with Calbs is cost. The weight savings you are talking about is 5lbs/kWhr for a battery that costs two to three times what a used Nissan or Volt pack could cost. If 1600 lbs isn't good for a Bradley, I can't imagine 1320 lbs is that much better. The $10,000 saved could be put to a lot better uses. If the OP is really set on 200 mile range some of that savings could be put into suspension and brake enhancements. It really boils down to the OPs cost benefit analysis. There is no perfect answer.

Sent from my SM-N910T using Tapatalk


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## Karter2 (Nov 17, 2011)

> So a simple home-brew, high quality LiFeP04 CALB pack weighs about 15% less, AND has more than 2X the peak power (1000 A instead of 430 A).


 What makes you believe you can expect 1000A from a 100Ah CALB ?


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## Duncan (Dec 8, 2008)

_So a simple home-brew, high quality LiFeP04 CALB pack weighs about 15% less, AND has more than 2X the peak power (1000 A instead of 430 A)_

Umm NO
The CALB pack would be 1000A x 144v = 144Kw (if it could produce 1000amps)
Whereas the Volt Pack would be 430A x 360V = 154Kw

In practice the Volt pack can produce substantially MORE than 430 amps and the CALB pack would be sagging like a demon well before 1000 amps


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## Yabert (Feb 7, 2010)

+1 on Duncan comment.
And to add, the old chevy Volt pack only weight 336 lbs for 16 kWh when you only consider cells and plastic case (as you should consider the calb cells before you build a pack).
So that is under 300 lbs for a 14 kWh Volt pack compare to 330 lbs with Calb.

But anyhow, this is too heavy for the Ocean project. 200 miles out of an old car with a < 80% efficient drive system is a ridiculus big challenge.
100 miles + high power charger is more realistic.


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## Ampster (Oct 6, 2012)

+1 on both of the above. Their years of experience should be of value. As a side issue, perhaps on another thread, I think there is valuable knowledge to be gained that can be applied to your off grid system. Used OEM batteries are particularly suited for those applications. If you do acquire some cells and grade them, the less robust ones can be effectively be used in a stationary pack. It is not difficult to avoid a BMS in that size (48 volts) and use a simple device to give you a warning of pack imbalance, i.e. a Lee Hart Bridge. https://www.sp411.cc/showthread.php?t=192352

In addition most Inverters have low and high voltage cuttoffs to protect the pack.


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## Ocean (Dec 20, 2016)

Really appreciating all the illuminating discussion here. Awesome. After running some calculations on this page to estimate range:

http://www.evsource.com/battery_calculator.php

I have indeed come to conclude that there is a sweet spot in the 150 mile range. almost 4 miles / KwH. Over that if I had Tesla packs (they are so light at only 55 lbs per 5.5KwH pack). Just under 4 miles/KwH if I used Nissan Leaf Cells.

I like the Leaf cells because they would fit nicely (tightly) into the existing rack of the Bradley - efficiently utilizing space I could get a 36+KwH pack in there (7.6 volt, 64Ah cells, 4 in parallel x 19 series yields a 144 volt pack x 256Ah = 36.8KwH at 636 pounds. Not bad) . According to the evsource calculator, the range for this setup would be about 140 miles. That's 3.8 miles / KwH. It would be just enough for my typical needs. Includes the weight of the driver. And if that calculator is based on average builds, I'm guessing I will do pretty good with such a low profile / low drag vehicle.

Volt cells would fit too, but they are wider at the base than the top and so end up being too bulky / not enough space efficient. I couldn't fit enough of them into the car to get the range I need.

Remembering that the Bradley had special frames built into it to accommodate about 1000+ pounds of batteries.... I think the frame is plenty tough. But I do want to keep it efficient. 140 miles would solve my typical needs.... just not the occasional long range. Maybe I will end up towing an additional parallel pack to get that extra range.

So... on the lookout for a wrecked Nissan Leaf! Anyone have any leads? Anyone ever buy a complete pack from a wrecking yard over Ebay??? Any luck on that?

Anyways, thanks for all the discussion. Happy New Years!!!


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## Ampster (Oct 6, 2012)

I found a Leaf pack on Craigslist. Do your research so you know the differences between early and current packs and cells. Also there are an equal number of right and left cells in a pack.. If you buy individual cells make sure you get what you need to create the configuration you need. Since the cells nest, the alternating of rights and Lefts makes it easier to put them in series. For my stionary pack I will be paralleling groups of 5 or 6 and want to match all rights or all lefts. That term refers to which side the positive pole is on when looking at the top with the seam on the upper side.
Sent from my SM-N910T using Tapatalk


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## Ocean (Dec 20, 2016)

Ampster said:


> I found a Leaf pack on Craigslist. Do your research so you know the differences between early and current packs and cells. Also there are an equal number of right and left cells in a pack.. If you buy individual cells make sure you get what you need to create the configuration you need. Since the cells nest, the alternating of rights and Lefts makes it easier to put them in series. For my stionary pack I will be paralleling groups of 5 or 6 and want to match all rights or all lefts. That term refers to which side the positive pole is on when looking at the top with the seam on the upper side.
> Sent from my SM-N910T using Tapatalk


Thanks, Yes I am thinking about that. Right's and Left's. Similar year cells with similar "low" mileage. Hopefully all from the same pack... although I think I actually need more than one pack's worth...


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## Ocean (Dec 20, 2016)

Ampster said:


> +1 on both of the above. Their years of experience should be of value. As a side issue, perhaps on another thread, I think there is valuable knowledge to be gained that can be applied to your off grid system. Used OEM batteries are particularly suited for those applications. If you do acquire some cells and grade them, the less robust ones can be effectively be used in a stationary pack. It is not difficult to avoid a BMS in that size (48 volts) and use a simple device to give you a warning of pack imbalance, i.e. a Lee Hart Bridge. https://www.sp411.cc/showthread.php?t=192352
> 
> In addition most Inverters have low and high voltage cuttoffs to protect the pack.


When I needed to replace my 4x L-16's in my off grid system (24 volt) - I found on Ebay some Tesla-Built battery modules from a Mercedes B-Class Hybrid (3 Kwh each). They are 7Series x 3.7volt making them perfect for an off grid 24 volt setup. I got three of them in parallel. I program my Outback to bulk them up to 29.2 volts (/7 = 4.17 per cell) and float them at 28.8 (4.11 per cell) which feels pretty safe. My inverter shuts down at 22 volts (3.14 per cell).... so I'm essentially operating in the ideal 90-95% range of capacity. It's working really good.


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## Ampster (Oct 6, 2012)

The spacers are also important. They provide even pressure and prevent stress on the "sardine can” seam. Also a lot of the small busbars would be useful for a series wired pack. I will probably fabricate busbars for my 7s6p stationary pack. The cells also have 4 holes each which allows compression to some extent to keep a pack stable. The terminals are sheet metal and come off the enclosed pouch cells so there is no structural integrity. Your research may have already discovered this but the Leaf modeles are actually 2s2p in a can. The voltage of the can is a nominal 7 volts. There is a center tap for the OEM BMS and it privides a convenient place to measure voltage at the cell (2p) level.

Sent from my SM-N910T using Tapatalk


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## Ampster (Oct 6, 2012)

Ocean said:


> ..... I program my Outback to bulk them up to 29.2 volts (/7 = 4.17 per cell) and float them at 28.8 (4.11 per cell) which feels pretty safe. ......


The only thing that I would add is that I have seen some discussions that maintaining a float voltage is not good for Lithiums. I guess it depends how one defines Float. My experience with plotting the charge cycle with a CCCV charger is that once a cell reaches the Constant Voltage setpoint the current tapers as the remaining capacity declines. That may be what happens with your charge controller, in which case there is no concern. I also use an Outback inverter but use a separate charger because I am grid tied, charge my pack from the grid and need to control the timing for load shifting. Glad to see you are having a good experience with Lithiums off grid. My ocassasional wanderings onto off grid forum suggests you are on the leading edge of off gridders. 

Sent from my SM-N910T using Tapatalk


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## Ocean (Dec 20, 2016)

Ampster said:


> The only thing that I would add is that I have seen some discussions that maintaining a float voltage is not good for Lithiums. I guess it depends how one defines Float. My experience with plotting the charge cycle with a CCCV charger is that once a cell reaches the Constant Voltage setpoint the current tapers as the remaining capacity declines. That may be what happens with your charge controller, in which case there is no concern.


Interesting about the float concern. I wonder if it's about keeping the Lithiums at a constant high voltage without allowing them to cycle. I understand that they are often discharged to a low state of charge for long term storage.

In my case, I have about 1500 watts of solar (max output from the panels on a cold sunny day) - although typically I get 1.2 - 1.3 kw. That translates to roughly 43 amps at 28 volts.... slowly pushing up. The outback will push up the voltage of the pack with maximum amps available until it reaches the bulk setpoint (29.2 volts) and hold it there for about an hour (amps tapering down) - then drop amps and allow voltage to decline to 28.8. Then it will allow enough amps through to keep the batteries at 28.8 volts (floating).

However, during a cloudy day, or of course at night, there is no input, and the batteries cycle down as we use power in the house. Refrigerator is the most constant drain, plus some other small things like the internet connection, lights, computers etc.

I typically drop from 28.8 down to 26.6 over night, or about 36% of total capacity. Then the bulk cycle starts again (unless its cloudy). I have about 2-3 days of reserve capacity in this setup. And the batteries are lightly cycling on a daily basis. They rarely see any kind of intense draw - only when I use heavy tools like the air compressor or table saw - in which case they might see 150 amp draw for a few seconds, then 75 amps for several minutes.

The one thing I don't have right now is a nice way to balance the cells in these 3Kwh Tesla Packs. Each of the three packs are 7s. Last time I checked (couple months ago) the cell blocks were within 100'ths of each other. But I have concerns for the long run.

cheers!


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## Ampster (Oct 6, 2012)

I don't know if there is a difference between trickle charge and float charge, but the concept that I am beginning to recall is that it is not good for lithium batteries to stay at fully charged voltage. When a charger with a Lithium charge curve turns off it does not come back on until the voltage sags by 0.02 or 0.03 volts or more or possibly more. In your case that would be to 4.08 or 4.07. 
I have not cycled Tesla or Leaf cells but I will describe what I do with LiFePo cells and you CA decide where you want those points to be for your pack. My LiFePos have a recommended charge voltage of 3.65. I routinely set the max voltage at 3.45 and estimate that I am giving up maybe 3 or 4 percent of their maximum capacity by doing that. Within an hour or two they sag to 3.32 volts and as far as I know there is no loss of capacity in that sag. I have tested my assumption by turning the charger back on and within a couple of minutes or less the cell voltage is back to 3.45 and the cell has maybe accepted at the most 10 or 15 Watts for two minutes (.003kWhrs) for a cell that has a capacity of 480 Whrs. Interestingly they sag to 3.32 whether I charged them to 3.45 or 3.65. in the above case with my stationary pack my charger is not set to start until the voltage drops below 3.30. I hope this is helpful as one point of view about stationary packs. The Outback Power forum and other off grid forums don't have much of a knowledge base about charging Lithiums. 

As far as worrying about a BMS I have one but rarely use it for my 48 volt pack and with 8 cell banks at 24 volts you probably don't need one either especially if the cells are easy accessible. As an early warning, I might recommend a LeeHart bridge which is a simple homade device that will tell you if one half of your pack is out of balance with the other half.

Sent from my SM-N910T using Tapatalk


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## onegreenev (May 18, 2012)

Just charge your batteries to your determined final voltage then shut off the charger. No float. Float is keeping them at a specified voltage that is below the max charged voltage so your battery will continue to remain charged enough to use when needed. With the Lithium cells you don't need that function unless the cells were being discharged by something that could eventually cause the pack voltage to drop below that float so the charger will continue to charge it up. But as before, if you have something draining your pack while stationary you want that discharge to be equal among your batteries. If its not your pack will go out of balance and you will eventually destroy your cells. So Just charge and shut off. No float or trickle charge. No need with lithium. Leave nothing to drain your pack either.


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## onegreenev (May 18, 2012)

Ocean said:


> I appreciate that - I will start thinking in terms of 144 volts nominal. As far as range is concerned... I really do want 200+ miles. I know it's heavy - but really I don't think it will be any more heavy than what the car was originally carrying - 15 x 8 volt golf carts at about 70 lbs each. Performance is again secondary. Perhaps one day I will upgrade to a 9" motor. Regarding the CALB's - to get 200 miles I believe I need a 400 AH pack and that's just too expensive.
> 
> These
> http://www.ebay.com/itm/NEW-Box-of-...363778?hash=item51ecc01b02:g:YPoAAOSwoi1X87JG
> ...



I contacted the person selling the Tenergy batteries on eBay. They have 440 boxes of 80 cells each box. The prices are good but the shipping is high. But even with that I decided to get 10 cells as he had some for sale in 10 cell packs. I picked up a pack and it should be here by the 10th. I'll test them for capacity and to see for sure if these are LiFePO4 cells. I'll test for capacity and to see how well they handle fast charging and hard discharging. These 10 will net me according to the specs a single 55Ah cell if connected in parallel. Now off to find out the specs of these cells.


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## Ocean (Dec 20, 2016)

onegreenev said:


> I contacted the person selling the Tenergy batteries on eBay. They have 440 boxes of 80 cells each box. The prices are good but the shipping is high. But even with that I decided to get 10 cells as he had some for sale in 10 cell packs. I picked up a pack and it should be here by the 10th. I'll test them for capacity and to see for sure if these are LiFePO4 cells. I'll test for capacity and to see how well they handle fast charging and hard discharging. These 10 will net me according to the specs a single 55Ah cell if connected in parallel. Now off to find out the specs of these cells.



That's Awesome I really look forward to your determinations...


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## Ocean (Dec 20, 2016)

onegreenev said:


> Just charge your batteries to your determined final voltage then shut off the charger. No float. Float is keeping them at a specified voltage that is below the max charged voltage so your battery will continue to remain charged enough to use when needed. With the Lithium cells you don't need that function unless the cells were being discharged by something that could eventually cause the pack voltage to drop below that float so the charger will continue to charge it up. But as before, if you have something draining your pack while stationary you want that discharge to be equal among your batteries. If its not your pack will go out of balance and you will eventually destroy your cells. So Just charge and shut off. No float or trickle charge. No need with lithium. Leave nothing to drain your pack either.


I'm pretty sure we're on the same page here. I think I see you are saying Lithium's don't need "float" in the same way as LA's do (helps the LA's gain full charge / capacity). I get that. But I do use them continuously exactly as you mention. Here in my off-grid home system, When I say I "float" them at 28.8. What is really happening is, the charger won't push anything into them (since they will hold themselves nicely at 28.8) _Unless_ I start using them. At that point, the charger pushes energy into them as it tries to keep up with my use, trying to maintain a 28.8 level. 

So, under normal daily use, typically they reach the bulk point in the first few hours of sunlight. Then the charger goes into "float" and stops pushing energy unless the inverter draws them down below 28.8 (which I do, periodically, using chop saws, table saws, air compressors, etc... plus the refrigerator always going on) This way, the batteries are kept up near full until the end of the day, and then they are discharged overnight as I use energy after dark. If the batteries drop all the way down to 22 volts, the inverter shuts off. This being a Tesla built pack (3 x 3Kwh packs (7series ~25v) in parallel) there is no connection drawing energy from the pack anywhere except the main poles to the inverter. Again, I wonder about the need to "balance" them...

These are they:
http://www.ebay.com/itm/Tesla-24V-1...ash=item33b9cb5de2:g:1DoAAOSw3YNXaHsM&vxp=mtr


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## Ocean (Dec 20, 2016)

Ampster said:


> Glad to see you are having a good experience with Lithiums off grid. My ocassasional wanderings onto off grid forum suggests you are on the leading edge of off gridders.


Thanks... so far so good.... =)


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## onegreenev (May 18, 2012)

Ocean said:


> I'm pretty sure we're on the same page here. I think I see you are saying Lithium's don't need "float" in the same way as LA's do (helps the LA's gain full charge / capacity). I get that. But I do use them continuously exactly as you mention. Here in my off-grid home system, When I say I "float" them at 28.8. What is really happening is, the charger won't push anything into them (since they will hold themselves nicely at 28.8) _Unless_ I start using them. At that point, the charger pushes energy into them as it tries to keep up with my use, trying to maintain a 28.8 level.
> 
> So, under normal daily use, typically they reach the bulk point in the first few hours of sunlight. Then the charger goes into "float" and stops pushing energy unless the inverter draws them down below 28.8 (which I do, periodically, using chop saws, table saws, air compressors, etc... plus the refrigerator always going on) This way, the batteries are kept up near full until the end of the day, and then they are discharged overnight as I use energy after dark. If the batteries drop all the way down to 22 volts, the inverter shuts off. This being a Tesla built pack (3 x 3Kwh packs (7series ~25v) in parallel) there is no connection drawing energy from the pack anywhere except the main poles to the inverter. Again, I wonder about the need to "balance" them...
> 
> ...


In this case I see that you are just using full pack voltage from each module as it should be. I was talking about use in a vehicle where some people have devices hooked up to only a few of the cells in the pack which causes an imbalance in the cells. 

If you are starting with the Tesla modules I don't see any need to balance except to be sure each module used is balanced to each other. No need to go cell to cell as they are all pretty much going to be dead on. However if you build your own out of single cells and make modules you will need to be sure all your individual cells are bottom balanced before putting any thing together. Then just never fully charge them and you will be good to go. You will want to monitor them and have a system in place to shut down but that is usually the function of the charge controller. 

As for float from a lead acid charge controller? You will need to know that the float won't put more power into the pack unless the pack is used and the voltages go below the minimum float. Just be sure all the components play well. I understand that the home backup would be in constant use and no matter, if you use lithium you should always bottom balance and stay off the extreme top of the charge voltages. You really don't loose much in the way of capacity really. Just when the charger is just about done be sure no single cell or module is above the maximum voltage allowed by the manufacturer. Once you know those parameters then it should be pretty much a set and forget except for an occasional visual check of voltages and condition. 


Pete


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## Ocean (Dec 20, 2016)

onegreenev said:


> In this case I see that you are just using full pack voltage from each module as it should be. I was talking about use in a vehicle where some people have devices hooked up to only a few of the cells in the pack which causes an imbalance in the cells.
> 
> If you are starting with the Tesla modules I don't see any need to balance except to be sure each module used is balanced to each other. No need to go cell to cell as they are all pretty much going to be dead on. However if you build your own out of single cells and make modules you will need to be sure all your individual cells are bottom balanced before putting any thing together. Then just never fully charge them and you will be good to go. You will want to monitor them and have a system in place to shut down but that is usually the function of the charge controller.
> 
> Pete


Indeed. I can imagine why some would do that (attach to individual batteries within a pack) - but it's obvious to me that's a bad idea precisely for the reason you gave - causing imbalance in the pack. I'm still not sure what I will end up with for the Bradley...

I did look into "Bottom Balancing" - seems to make sense... dropping all cells down to the bottom of the voltage range and letting them rest there until they are all stable / equal at the base of the range.

I do really like the Tesla modules they are made so nicely.... =)


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## Jayls5 (Apr 1, 2012)

Nucleus, I'm going to respectfully disagree with your criticism of OEM lithium packs.

There's nothing inherently inferior about some of the chemistries they are using, and a lot of their overbuilt pack designs are to ensure they last to warranty regardless of harsh use and climate. 

I've seen those large size LiFePO4 cells, and their voltage sag is terrible under high load. With my LiCoO2 LIPO, I'm getting under 0.2v sag per cell at 8C.

On a personal level, I wouldn't opt for a fancy BMS. I'd just take that extra money and put that into batteries, and run them in a safe charge/discharge range of use.


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## Ampster (Oct 6, 2012)

The simplest way to balance a group of cells is to string them together in parallell. Physics insures that they will all be at the same voltage. It was inevitable that the bottom balance theory would show up here, but it is not necessary to do them individually. After I tested my 48 used 160AmphourThundersky's individually for capacity I wasn't going to spend another 10 days or more balancing them. Since they were going to be in a 16s3p configuration I just put all 48 cells in parallel for a few days and then assembled them into a 48 volt pack. 

Sent from my SM-N910T using Tapatalk


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## onegreenev (May 18, 2012)

Ampster said:


> The simplest way to balance a group of cells is to string them together in parallell. Physics insures that they will all be at the same voltage. It was inevitable that the bottom balance theory would show up here, but it is not necessary to do them individually. After I tested my 48 used 160AmphourThundersky's individually for capacity I wasn't going to spend another 10 days or more balancing them. Since they were going to be in a 16s3p configuration I just put all 48 cells in parallel for a few days and then assembled them into a 48 volt pack.
> 
> Sent from my SM-N910T using Tapatalk


It works to a degree. I'd do that for fast equalization but then do a fine bottom balance.


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## Ampster (Oct 6, 2012)

onegreenev said:


> It works to a degree. I'd do that for fast equalization but then do a fine bottom balance.


I am not sure what you mean by a fine bottom balance? Electrically I don't think there is any difference between discharging one cell to 2.5 volts or a hundred cells in parallel to 2.5 volts except it will take longer and maybe more discharge current. You can't draw any conclusions about an individual cell's capacity doing that but that is not the purpose of bottom balancing anyway. Running an individual cell through a charge/discharge cycle is the only way to measure capacity.

Sent from my SM-N910T using Tapatalk


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## onegreenev (May 18, 2012)

Ampster said:


> I am not sure what you mean by a fine bottom balance? Electrically I don't think there is any difference between discharging one cell to 2.5 volts or a hundred cells in parallel to 2.5 volts except it will take longer and maybe more discharge current. You can't draw any conclusions about an individual cell's capacity doing that but that is not the purpose of bottom balancing anyway. Running an individual cell through a charge/discharge cycle is the only way to measure capacity.
> 
> Sent from my SM-N910T using Tapatalk


I put over 60 cells in parallel to do this before and up to a point it works. There is still an imbalance among the cells when you do this but it does get them real close. What I mean by fine balance is to take each cell after you do this and discharge them further with a device that can take them to a stable charge and one where you can do this consistently so they are better balanced. 

If you choose to only do the parallel way of balancing just be aware they are not fully balanced. My trick for a solid balanced pack works great. 

If you do the parallel balance, leave them for a month. As the cells get closer to being in balance the process goes a whole lot slower.


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## dtbaker (Jan 5, 2008)

onegreenev said:


> I put over 60 cells in parallel to do this before and up to a point it works. There is still an imbalance among the cells when you do this but it does get them real close.


I can totally back you up on this onegreenev.... whether you are top OR bottom balancing, if you are doing a long string in parallel they will not be completely balanced (because of voltage drop along the string).

In my case I top balanced an entire pack, taking the time to make a temp wiring harness to put the entire pack in parallel. I connected + and - at opposite ends hoping to minimize the drop and set the power supply for 3.65v and left it for a week. It got things close, but after I had cells installed in car, I checked balance at end of charge, and still had to tweak a few cells, draining a couple with a resistor to get them all within .02v at end of charge.

This does open up the great top vs bottom debate.... but people need to understand that final balancing has to be done per cell whether it is manual or with an active shunt BMS. 

I chose top balancing mostly because chargers all assume top balance to control and end their charge cycle, and as long as you check the top balance on all cells at end of charge once in a while, nothing further is required. The danger is if I ever approach 95=% DOD, I'd be likely to lose cells. I use a Zilla controller that watches pack voltage, gives warnings, and goes into limp mode at a desired low pack voltage to keep me from over-discharge on any given cell.

There is another camp that protect against over discharge by bottom balancing, but rely on a BMS to end charge 'prematurely' as soon as the first cell hits max voltage.... requiring a reliable BMS and active control to stop the charge and prevent over charge on any individual cell while maintaining the bottom balance.

The thing to understand is that you have to choose between top and bottom balancing.... you can't have both. Your choice determines how you use your charger and whether you use a BMS and how you use it.


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## Ampster (Oct 6, 2012)

I have not seen any empirical data and there are no laws of physics that support your opinion. I do agree that it takes time but I am not sure that anything more than a few days. It all depends on the initial voltage difference. The bigger the differences the higher the current until they equalize. Here is the formula:
I =(V1-V2)/(R1-R2)
Where I equals Current, V equals Voltage and R equals internal resistance

I defy any Voltmeter to be able to get to this level of accuracy. 
I now understand what you define as fine balance. I am glad you have the time to do that needless extra step. For others who don't have that luxury I offer this to save some time and let physics be your friend. Think of voltage in parallell cells like water that seeks its own level. If you don't believe me ask the guru, Jack Rickard. 

My apologies to the original poster for this hijack. I can't stand statements that fly in the face of simple physics, and I feel an obligation to at least let other readers know. Pete has a lot of experience but opinions are just opinions. I prefer to use science as my friend.


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## dtbaker (Jan 5, 2008)

Ampster said:


> I have not seen any empirical data and there are no laws of physics that support your opinion.



I don't wanna hijack the thread into the 'great debate' either... but do want to point out that the key issue specific to Lithium cells that IS supported by physics is that the resting voltage of a lithium cell does not give you any idea of its actual state of charge.

i.e. two cells connected in parallel may indeed level at a resting voltage of 3.2v, but that does NOT mean they are either top or bottom balanced or at the same state of charge.

This builder is trying to choose his battery layout, and choosing between these two different approaches determines the BMS strategy, charge control and initial top or bottom balance techniques.

I'm not saying one way is better than the other, just that cell level initial balancing and 'fine tuning' is important whichever way you choose.


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## Ampster (Oct 6, 2012)

dtbaker said:


> I don't wanna hijack the thread into the 'great debate' either... but do want to point out that the key issue specific to Lithium cells that IS supported by physics is that the resting voltage of a lithium cell does not give you any idea of its actual state of charge.
> 
> i.e. two cells connected in parallel may indeed level at a resting voltage of 3.2v, but that does NOT mean they are either top or bottom balanced or at the same state of charge........I'm not saying one way is better than the other, just that cell level initial balancing and 'fine tuning' is important whichever way you choose.


 I don't disagree about your statement regarding SOC. That is because no two cells will have the exact same capacity. Close perhaps but not the same. My point is about whether the voltage is equalized not whether SOC was the same. I think you would agree if you took them both or all 60 paralleled to 2.5 that they would both be balanced somewhere near the lower end of their capacity. I value your experience as well and anyone can use any technique they want. I am just trying to point out a time saving technique supported by science.


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## onegreenev (May 18, 2012)

Ampster said:


> I have not seen any empirical data and there are no laws of physics that support your opinion. I do agree that it takes time but I am not sure that anything more than a few days. It all depends on the initial voltage difference. The bigger the differences the higher the current until they equalize. Here is the formula:
> I =(V1-V2)/(R1-R2)
> Where I equals Current, V equals Voltage and R equals internal resistance
> 
> ...



Not opinion. Fact. I DID put cells in parallel and they were still OFF. They were close but still off. I originally did my MG Midget Pack exactly that way. All in parallel till balanced by their own accord. The cells were still around 3 volts each when I did this but figured that once all were looking to be in balance they would be in balance according to the thinking like water in a pan where it will level it self. It does not. If I had started with cells that were already at like 2.4 volts then it would be reasonable to assume that they would all be good because the end voltage cut back for my controller would be well above that voltage. I lost two cells due to over discharge and reversing them. They were not properly bottom balanced. Since then I take each to 2.4 volts. Not 2.41 or 2.42 or any thing like that. 2.4 volts after a long rest. 

So when you did your parallel setup I assume you just disconnected them and put them into a pack expecting them to be balanced. But I left mine disconnected after letting them sit for over three weeks connected. After disconnecting them they all changed voltage. Some were the same but not all of them. Not the same is not balanced. 


If this way of balancing were top dog then Jack would not have used a setup to bottom balance single cells for the entire pack. its a great way to get the pack to a closer balance. Not a great balance. Fact. Not opinion. Opinion would be from someone NOT doing the actual procedure. 

Ive done this with my Leaf Modules and yes, its a pain in the butt but for the safety of your investment its a minor annoyance. Cut corners and you will loose cells. Or you can have an imbalanced top and bottom and just never go above or below the safe range. That you can do. 

Pete


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## Ampster (Oct 6, 2012)

onegreenev said:


> Not opinion. Fact. I DID put cells in parallel and they were still OFF. They were close but still off. I originally did my MG Midget Pack exactly that way. All in parallel till balanced by their own accord. The cells were still around 3 volts each when I did this but figured that once all were looking to be in balance they would be in balance according to the thinking like water in a pan where it will level it self. It does not. If I had started with cells that were already at like 2.4 volts then it would be reasonable to assume that they would all be good because the end voltage cut back for my controller would be well above that voltage. I lost two cells due to over discharge and reversing them. They were not properly bottom balanced. Since then I take each to 2.4 volts. Not 2.41 or 2.42 or any thing like that. 2.4 volts after a long rest.
> 
> So when you did your parallel setup I assume you just disconnected them and put them into a pack expecting them to be balanced. But I left mine disconnected after letting them sit for over three weeks connected. After disconnecting them they all changed voltage. Some were the same but not all of them. Not the same is not balanced.
> ...............
> ...


Again, my apologies to the OP for this hijack. I think I used the wrong term. Instead of "balanced" I should have said equalized to the same voltage by putting them in parallel. I don't bottom balance and I selectively turn on a BMS when I want to see a chart of the 16 celll group voltages. I use a Lee Hart bridge to tell me if there is a difference in voltage between the two halves. Yes I have observed different deltas of the cell groups depending on the SOC of the pack. I believe that is what DT Bakers point was about SOC

I never "balanced" my thunderskys in my stationary pack. After assessing that they ranged between 145 Ahrs and 163 Ahrs I put them all in parallel for a couple of days, then assembled them into a 3p16s pack. Now my pack looks like sixteen 450 approximate Amphour buddy cells. Anytime I have seperated the 3 buddy cells they have always been the same voltage. Like any Lithium pack there is going to be some drift and that is what you were describing. Some of that apparent drift may be caused the resistance of the connection The cell has no memory of how it got to an equal voltage. Therefore the drift could not have been different because it was discharged to a voltage by a load individually connected or to a load that it shared in parallel. The physics are the same. My stationary pack is never even close to being discharged 50% and I only charge them to 3.40 volts so they are never at the top or never near the bottom. They do cycle cycle daily between 3 to 5 kWhrs for a 20 kWhr pack.

Yes it is a fact that you lost two cells. Perhaps those were the two that you parallelled together or maybe it was two others. You didn't say why you only parallelled those two so it would be hard for me to conclude what the cause of two cells was except those were possibly the weakest and they hit the bottom first. That would be the explanation of the physics of cell discharge. It would also support your opinion that they were not properly balanced. From a pure cause and effect logic it was that the pack was discharged too close to the bottom that killed those cells. Yes "proper" bottom balancing might have saved those but overdischarge was the cause. 

Again, my apologies, I just want to make sure the physics of paralleling two cells is not misunderstood. I offered bulk paralleling as a time saving method of getting a large number of cells to the same voltage. That is all.

N.B. the equation cited a few posts above was for the current flowing between two batteries in parallel. The following formula properly states the relationship of multiple cells in parallel. 
V = V1=V2=V3...=Vn


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## Ocean (Dec 20, 2016)

I really am enjoying this dialogue. It's eye opening and I think offering lots of useful information for myself and other readers as well.

So far I've settled on the idea of 6 x Tesla modules (~22.2 volts nominal x 6 = ~133 volts nominal system).... it's about the same price as Leaf modules if I get those individually. Unless I find TWO complete Leaf packs (because one is not enough... I would still need an additional 6 - 10 kw of cells).... so... saving my pennies!!!

Either way I'm sure I will do the basic "parallel equalization"... I imaging letting them sit like that for a few days until I cannot measure any more amperage moving between the packs (or cells). Perhaps I will then drain them down to a low state of charge (like 2.7 volts per cell)... while in parallel. This it would seem will get me a pretty good bottom balance.

But it's going to be a while. I've got a lot of pennies to save!

cheers!
-Ocean


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## nucleus (May 18, 2012)

Duncan said:


> _So a simple home-brew, high quality LiFeP04 CALB pack weighs about 15% less, AND has more than 2X the peak power (1000 A instead of 430 A)_
> 
> Umm NO
> The CALB pack would be 1000A x 144v = 144Kw (if it could produce 1000amps)
> ...


Good catch, I mixed up amps and power, but CALB CA cells will do 10C no problem, and sag less than any other chemistry...


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## nucleus (May 18, 2012)

*chemistry comparisons*



Jayls5 said:


> Nucleus, I'm going to respectfully disagree with your criticism of OEM lithium packs.
> 
> There's nothing inherently inferior about some of the chemistries they are using, and a lot of their overbuilt pack designs are to ensure they last to warranty regardless of harsh use and climate.
> 
> ...


What brand of large LiFePO4 cells? 

What brand of LiCo02 cells?

Have you tested at higher discharge rates?


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## nucleus (May 18, 2012)

onegreenev said:


> Not opinion. Fact. I DID put cells in parallel and they were still OFF. They were close but still off. I originally did my MG Midget Pack exactly that way. All in parallel till balanced by their own accord. The cells were still around 3 volts each when I did this but figured that once all were looking to be in balance they would be in balance according to the thinking like water in a pan where it will level it self. It does not. If I had started with cells that were already at like 2.4 volts then it would be reasonable to assume that they would all be good because the end voltage cut back for my controller would be well above that voltage. I lost two cells due to over discharge and reversing them. They were not properly bottom balanced. Since then I take each to 2.4 volts. Not 2.41 or 2.42 or any thing like that. 2.4 volts after a long rest.
> 
> So when you did your parallel setup I assume you just disconnected them and put them into a pack expecting them to be balanced. But I left mine disconnected after letting them sit for over three weeks connected. After disconnecting them they all changed voltage. Some were the same but not all of them. Not the same is not balanced.
> 
> ...


I have had the same exact experience Pete.


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## nucleus (May 18, 2012)

Ampster said:


> Like any Lithium pack there is going to be some drift


This is where I disagree - the packs I have worked with: ZERO DRIFT!

(once we took off the BMS)

This "drift" you speak of, and those of us who don't run BMS's don't see, what is the science of it?


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## Ampster (Oct 6, 2012)

nucleus said:


> ......,.
> This "drift" you speak of, and those of us who don't run BMS's don't see, what is the science of it?


The science in practice is that it is difficult to manufacture cells with the exact same kWhr capacity and internal resistance. That is why some cells last longer and why some break down quicker when over charged. Ion exchange does have some random behaviors. I would guess that is why even good quality prism LifePOs are actually several pouch cells in parallel. The law of averages masks the differences. 

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## onegreenev (May 18, 2012)

nucleus said:


> This is where I disagree - the packs I have worked with: ZERO DRIFT!
> 
> (once we took off the BMS)
> 
> This "drift" you speak of, and those of us who don't run BMS's don't see, what is the science of it?


The issue is to define drift. Maybe they can define it for you.


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## Ampster (Oct 6, 2012)

DT Baker alluded to it when he said the same resting voltage did not equal the same SOC. Pete described it earlier when he said those two cells were "off". In other posts Pete has described it as unstable voltage at the top and the reason one can only bottom balance. 
What I call "drift" is any difference in voltage (delta) between cells. If you take two cells and plot them in a charge discharge cycle there will be voltage differences at the SOCs along that curve. In a pack i have observed different deltas depending on the SOC of the pack. I have not seen drift as something that continues unless a cell is weak or lost capacity then over time the delta has increased for that cell. Near the bottom it is lower than the others and near the top it it higher than the others.

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## onegreenev (May 18, 2012)

Drift. Is an ACTION. Drift denotes movement. If the battery is sitting yet changing in capacity and voltage it is drifting. Drifting usually is taken as a slow process. Not that the cells are different voltages yet fully charged. 

The issue I mention is not all batteries will be the same capacity. Being what may all cells within a pack are different capacities for some reason or another. Usually just because the process of building is not exact. These differences are minute. If they are more than minute you might not be able to get away with that. 

Lets say I have two cells. One is 10.1Ah and the other is 10.3Ah. If I charge them as a single cell the 10.3 cell will run longer. Voltages are really pretty much the same. Put them in parallel and charge them together. The 10.1 Ah battery will fill first before the 10.3Ah battery fills. As the battery charges to the top the voltage increases because it requires more voltage to push more into the battery. No other reason. So when the 10.3Ah cell reaches its peak voltage the 10.1 Ah cell may be at 3.8 volts and the 10.3Ah cell is at 3.55 volts. The low AH cell reached its peak but when you remove the current both will settle to the same voltage. If the cells were bottom balanced they will both have exactly the same capacity when the charge is done. The higher Ah cell will not be using .2Ah because the low capacity will not allow that. 

If you top balance both cells you will have a problem on the bottom of the discharge. The low capacity cell will reach the cutoff before the higher capacity cell. 


This difference either on the top or bottom is NOT drift. It is just a difference in capacity. 


Bottom balanced and charged to 3.55 volts average in series will result in a pack that when near empty will be exactly the same voltage and capacity when empty. So off the top after you begin to use your cell your voltage will still be the same. 


If you happen to have a cell that is 10Ah and the other 8Ah then you might have an issue but if bottom balanced you will still have the same capacity in each cell. The low capacity cell limits the top charge cutoff and the high capacity cell will not be using 2Ah. I'd change the cells to better match the capacity.


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## onegreenev (May 18, 2012)

Batteries. 

I just received my Tenergy LiFePO4 5.5Ah cells for testing. They are larger than the 18650 cells. They do have a cardboard sleeve over the cell but should be shrink wrap. Time to set up the discharge testing for these cells. I have the ability to do 40 amp charge or discharge and to log it all on my computer. I'll post graphs and post my results. Need to bring in my 12 LiFePO4 100Ah pack for charging and discharging these little cells.


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## nucleus (May 18, 2012)

*Re: Testing Tenergy LiFePO4 5.5Ah Cells*



onegreenev said:


> Batteries.
> 
> I just received my Tenergy LiFePO4 5.5Ah cells for testing. They are larger than the 18650 cells. They do have a cardboard sleeve over the cell but should be shrink wrap. Time to set up the discharge testing for these cells. I have the ability to do 40 amp charge or discharge and to log it all on my computer. I'll post graphs and post my results. Need to bring in my 12 LiFePO4 100Ah pack for charging and discharging these little cells.


If they match their claimed specs they would be a breakthrough. 

I eagerly await your results!


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## onegreenev (May 18, 2012)

*Re: Testing Tenergy LiFePO4 5.5Ah Cells*



nucleus said:


> If they match their claimed specs they would be a breakthrough.
> 
> I eagerly await your results!


If they ditch that high shipping cost, yes. They seem to be of good quality build. Now to look into making a spot welder for these. I don't really want to solder them. Just too messy.


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## Ampster (Oct 6, 2012)

Okay then, apparently I used the wrong term. My statement several posts above should have read, ".....There is going to be some difference in capacity." I think we all agree then, and you and nucleus do observe differences in capacity. A BMS or bottom balancing cannot fix that.


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## onegreenev (May 18, 2012)

Ampster said:


> I think we all agree then, and you and nucleus do observe differences in capacity. A BMS or bottom balancing cannit fix that.
> 
> 
> Sent from my SM-N910T using Tapatalk


Correct. 

Also trying to squeeze out every last mili amp hour is a waste of time. Just build a larger pack if you need more. Bottom balance, then stay off the bottom and stay off the top and use the usable Ah within those two extreme points and you will be a happy camper and your cells will be happy. Its pretty simple. If you can, build one of those Lee Hart Battery Bridge devices and let that help. Be sure to wire it up so it completely shuts off so not to bring in an artificial drain on the battery pack. If you have a dumb charger or dumb controller you will need a way to control the shutting off of each. Most have smart chargers and many have smart controllers that will allow you to limit current and voltages to the point of not being able to over discharge the pack. But if not a simple BMS may help. I can only recommend the Orion. It has gobs of functions and will help protect your pack if you need. I know of a few folks with them. I don't have the need, neither does he, but he feels better.


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## electro wrks (Mar 5, 2012)

As an indicator of the complexity of the BMS issue and the dangers associated with battery use, read through (if you can stand it!) this patent granted to Tesla last month: http://patft.uspto.gov/netacgi/nph-...=50&s1=9529048.PN.&OS=PN/9529048RS=PN/9529048

I'm guessing this is related to the ever increasing charge rates available at newer charging stations. It's something to think about if DIY vehicles are going to use these newer charging stations.


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## Ampster (Oct 6, 2012)

onegreenev said:


> ......... If you can, build one of those Lee Hart Battery Bridge devices and let that help. Be sure to wire it up so it completely shuts off so not to bring in an artificial drain on the battery pack. If you have a dumb charger or dumb controller you will need a way to control the shutting off of each. .......


My stationary pack is cycled about 15% every day so I am not concerned about the negligible draw of Lee Hart bridge. The purpose of using it is to warn me if the pack got out of balance during those cycles. It would defeat my purpose if I turned it off. Far many installations it probably does make sense to turn off anything connected to the pack but my inverter is powered by the pack so I can't do that or it would not give me backup power. I do have a voltage controlled relay that turns on the charger every evening if pack voltage drops below my set point. I use a Meanwell power supply for charging and and the voltage controlled relay shuts of the charger when my set voltage is reached.


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## Ampster (Oct 6, 2012)

electro wrks said:


> .........
> 
> I'm guessing this is related to the ever increasing charge rates available at newer charging stations. It's something to think about if DIY vehicles are going to use these newer charging stations.


It is very simple really:
"A computer-implemented method for detecting an exceptional charge event for an energy storage system having a plurality of series-connected battery elements,........."
LOL, Of course the irony with Tesla is if the invention is really good they won't patent it, but rather shroud it in secrecy.


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## onegreenev (May 18, 2012)

Ampster said:


> My stationary pack is cycled about 15% every day so I am not concerned about the negligible draw of Lee Hart bridge. The purpose of using it is to warn me if the pack got out of balance during those cycles. It would defeat my purpose if I turned it off. Far many installations it probably does make sense to turn off anything connected to the pack but my inverter is powered by the pack so I can't do that or it would not give me backup power. I do have a voltage controlled relay that turns on the charger every evening if pack voltage drops below my set point. I use a Meanwell power supply for charging and and the voltage controlled relay shuts of the charger when my set voltage is reached.


If the system is never off then my comment is moot. A Lee Hart Bridge is a low power draw. Not sure how low but if its going to be off line for some time like in a bad storm for days and you deplete your pack to the point it shuts off then you might want it off so it does not drain until you have power back and charging back. But like I said its moot if the system is always cycling and never off for any length of time.


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## Ocean (Dec 20, 2016)

onegreenev said:


> Batteries.
> 
> I just received my Tenergy LiFePO4 5.5Ah cells for testing. They are larger than the 18650 cells. They do have a cardboard sleeve over the cell but should be shrink wrap. Time to set up the discharge testing for these cells. I have the ability to do 40 amp charge or discharge and to log it all on my computer. I'll post graphs and post my results. Need to bring in my 12 LiFePO4 100Ah pack for charging and discharging these little cells.



Indeed, thank you for checking into this. Very interested to see your results. The shipping is definitely an issue. I know they will combine shipping.... and my question would be: how many do I need to order so as to get free shipping on all of them??? Still. Very interesting.


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## nucleus (May 18, 2012)

It occurs to me that these even if good aren't really a breakthrough because they aren't making them anymore as far as I can tell.

The shipping costs are likely a result of the regs with shipping lithium batteries, nevermind that the LiFePO4 are very safe.

If you were going to build a car with these your best bet could be to rent a uhaul and pick them up yourself.


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## onegreenev (May 18, 2012)

Im thinking backup house battery pack. But for a vehicle it may be a perfect fit for an idea I have for the VW platform.


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## Ampster (Oct 6, 2012)

onegreenev said:


> Im thinking backup house battery pack. .....


Asuming the capacity is as advertised a pack of those cells would cost $90per kWhr. That compares favorably with individual Nissan Leaf cells at $200per kWhr


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