# Cycle Life Testing of Thundersky Cells



## nimblemotors (Oct 1, 2010)

Has anyone done any cycle testing, beyond the published specs of .3c ?

Jack Murray
Nimble Motorsports


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## BatMan (Mar 1, 2011)

I've been warned from colleagues that I'd be lucky to get 200 cycles, and that was at 0.1-0.2C. 

They did find a vendor that guaranteed 1000 cycles with fast charge, but can't remember the name off the top of my head.

Mike


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## EVfun (Mar 14, 2010)

So what brand of Lithium batteries do you sell BatMan?


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## nimblemotors (Oct 1, 2010)

How can any battery company guarantee cycle life??
There is no possible way to determine the number of cycles at the cell level. You would have to sell a fully engineered pack to offer a warranty that isn't just hype and marketing. Otherwise, a battery company would go broke in a hurray, but maybe they don't plan to be around after the sale anyway.



EVfun said:


> So what brand of Lithium batteries do you sell BatMan?


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## nimblemotors (Oct 1, 2010)

So it appears nobody has done any cycle life testing on Thundersky cells.
I find that quite amazing, given the cost of these cells, the cycle life actually determines how much the cells are worth. At $10k-$20k a pack, that is a lot of cash based on faith and battery salesman claims.

So I'm going to be doing cycle tests, I have to believe you will want to see the results, would you pay $5 to see them? I'd like to propose that I raise a collection for the tests, let's say $500, so 100 people at $5 would cover it, any less I don't publish, you get the $5 back or whatever donation has been given.

The plan is to charge them at 1c, discharge at 3c to empty, and just keep doing it is until they are dead. This takes a long time to run and destroys the cells. At 1c charge, 1 hour to charge, 20 minutes to discharge, time to rest say 10 minutes, so a cycle takes 1.5 hours. That is 16 cycles a day, 480 cycles a month. So to test the claimed 3000 cycles will take almost over 6 months of 24/7 testing. 

Another set of parameters will take longer, if discharge is only .5c, it will take 3 hours to do one cycle, so 12 months of 24/7 testing.
And if one tests only discharge to 80% or 70%, another set of cells to destroy and test hardware to build and keep running.

You see this is a significant investment in time and energy to run these tests, and make sure they work property over such a long time frame.
I don't think it is unreasonable to get some financial support to do the tests.


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## T1 Terry (Jan 29, 2011)

I'm interested in the 3C claims, in each direction. A suggestion, the cell discharge is used to recharge a large percentage of the other cell on test. 3 cells will need to be tested at 70% discharge and 3 cells at 80% discharge. The charging and discharging will need to be done via a controlled method with digital recording equipment so charts can be seen as far as voltage sag, and recharging trends indicating changes to internal resistance. The question is, do you have the facilities to carry out this sort of testing?

T1 Terry


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## nimblemotors (Oct 1, 2010)

Certainly the charge/discharge will be controlled and recorded and equipment to do it properly will be built. I have some ultracaps I planned to use to store the discharge and then put it back in, but I could use a second battery as well to toggle the flows and test two at once, will probably complicate the setup, but maybe not too much.

I finally got my cells today. I tore apart one of them to see what's inside, and was thinking I could take some sub-cells out to test smaller Ah, but while the insides are grouped into 20Ah assemblies with 40 .5ah cells,
they are not individually sealed, so its really just one battery, can't take them apart with integrity. I did construct a single .5ah cell, it discharged nicely to power a flashlight bulb. 



T1 Terry said:


> I'm interested in the 3C claims, in each direction. A suggestion, the cell discharge is used to recharge a large percentage of the other cell on test. 3 cells will need to be tested at 70% discharge and 3 cells at 80% discharge. The charging and discharging will need to be done via a controlled method with digital recording equipment so charts can be seen as far as voltage sag, and recharging trends indicating changes to internal resistance. The question is, do you have the facilities to carry out this sort of testing?
> 
> T1 Terry


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## MN Driver (Sep 29, 2009)

nimblemotors

Very interesting, it makes me want to buy a 40Ah battery to pull a sheet and do a capacity test and then if I could find a thermal imaging camera to test it at 10C and see how warm it got and where it gets hot. It seems that the high discharge A123 pouches get hot towards the terminal while the rest of the battery seems to stay cold. It would be interesting to see if we find any hot spots in a single sheet pair or whatever the capacity a single set tests to.


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## DIYguy (Sep 18, 2008)

nimblemotors said:


> So it appears nobody has done any cycle life testing on Thundersky cells.
> I find that quite amazing, given the cost of these cells, the cycle life actually determines how much the cells are worth. At $10k-$20k a pack, that is a lot of cash based on faith and battery salesman claims.
> 
> So I'm going to be doing cycle tests, I have to believe you will want to see the results, would you pay $5 to see them? I'd like to propose that I raise a collection for the tests, let's say $500, so 100 people at $5 would cover it, any less I don't publish, you get the $5 back or whatever donation has been given.
> ...


Here's some advice... don't tell anyone if you do the testing.


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## nimblemotors (Oct 1, 2010)

DIYguy said:


> Here's some advice... don't tell anyone if you do the testing.


I don't get it, you being facetious? 

I'm working on the test hardware, trying to figure the best way to do it.

I have a motor controller I built to run my electric outboard that could handle 48v and 200 amps, I sold my sailboat a long time ago, so I can repurpose it for this testing. 3C for a 40Ah battery is 120amps.

It looks like I will need about 70 of my 2600F caps to hold the discharge, but I'm not certain if that will work, because of the voltage mismatch between battery and caps


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## DIYguy (Sep 18, 2008)

nimblemotors said:


> I don't get it, you being facetious?
> 
> I'm working on the test hardware, trying to figure the best way to do it.
> 
> ...


Actually, I wasn't. Lots of people have invested lots of $ and time to post information of value on this site. Comments like "so 100 people at $5 would cover it, any less I don't publish, you get the $5 back or whatever donation has been given" rub me the wrong way.
You don't publish? Look buddy, do it or don't do it. But if you do it and don't share it.... it may not go over so well. So, my advise is...if that's your game... don't tell anyone. Or, like the rest of the people on this site....share your information.


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## nimblemotors (Oct 1, 2010)

I share plenty of information, I'm sharing how I'm going to run these tests.
You can then build and buy the parts and run them yourself.
Seeing as nobody has, what could be the reason? 



DIYguy said:


> Actually, I wasn't. Lots of people have invested lots of $ and time to post information of value on this site. Comments like "so 100 people at $5 would cover it, any less I don't publish, you get the $5 back or whatever donation has been given" rub me the wrong way.
> You don't publish? Look buddy, do it or don't do it. But if you do it and don't share it.... it may not go over so well. So, my advise is...if that's your game... don't tell anyone. Or, like the rest of the people on this site....share your information.


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## DIYguy (Sep 18, 2008)

nimblemotors said:


> I share plenty of information, I'm sharing how I'm going to run these tests.


 oh,...well, that's rocket science. 



nimblemotors said:


> Seeing as nobody has, what could be the reason?


It's a conspiracy. Everyone secretly knows that these cells only get 500 cycles. We all work for the Chinese on commission. When they sell to "the people who don't really know", we all get some good $$ . So ...shhhhhh.


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## DavidDymaxion (Dec 1, 2008)

One thought is to get Headway or A123 or similar cells. You could then do much higher currents, and get ~4 times as many cycles in the same time. The cost would be much cheaper, for both the cells and the equipment.


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## brainzel (Jun 15, 2009)

Jack Rickard did some testings but not over such a long period of time.
I have to say that I am skeptical that your collected data will fit the interest of all the 100 donors.

I would support the meaning of DIYguy, I blowed up some things, I got the wrong parts, replaced others and all of these experiences I would give to the community for free, because they helped me for free.

If anyone is so grateful and full of overwhelming gratitude, he could donor my project via PayPal ... if not, no problem.
I do it for hobby, not for dollars


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## F16bmathis (Jun 6, 2008)

Its not scientific and half of it is for Lead acid, but my trucks been running over two years, 10400+ miles, mostly highway, which means high amps with my Zilla, but I track evey bit of juice pushed in, and so it gives cycles also. Just got the Thundersky's in Oct 10?

www.evalbum.com/1752 There's a picture of my excel chart.

I haven't bought gas since early Dec 2010!


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## nimblemotors (Oct 1, 2010)

Rickard just published data obtained from Thundersky.
He did do 400amp tests that killed a cell.

No one needs to run these tests to get a EV working, which is why they are not done. It is usually a university or national lab that does these kinds of tests, funded by your tax dollars. 
In my opinion, knowing how to treat these cells to make them last is very important information. If you and the useless DIYGUY don't think $5 is worth finding out, then so be it. I will know how to make my EV last a long time. 



brainzel said:


> Jack Rickard did some testings but not over such a long period of time.
> I have to say that I am skeptical that your collected data will fit the interest of all the 100 donors.
> 
> I would support the meaning of DIYguy, I blowed up some things, I got the wrong parts, replaced others and all of these experiences I would give to the community for free, because they helped me for free.
> ...


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## nimblemotors (Oct 1, 2010)

I am interested in the Thundersky cells specifically (Calb appear to be essentially the same) these are a bit different than the headway and certainly the A123. But really when testing the C rating, it takes just as long to do 2ah as 200ah, it is just that 2ah is a lot less current, 6amp vs 600amps, a lot easier to deal with. I've got 40Ah cells which is the smallest thundersky makes, so 3C is 120amps for 20 minutes.

I don't see much issue draining the cell into the ultracaps, but charging the cell back from them will be the harder part. I will need to have a DC-DC conversion to constainly raise the voltage level up to the charge voltage. Not so simple for just 2-4volts. 




DavidDymaxion said:


> One thought is to get Headway or A123 or similar cells. You could then do much higher currents, and get ~4 times as many cycles in the same time. The cost would be much cheaper, for both the cells and the equipment.


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## DIYguy (Sep 18, 2008)

nimblemotors said:


> Rickard just published data obtained from Thundersky.
> He did do 400amp tests that killed a cell.
> 
> No one needs to run these tests to get a EV working, which is why they are not done. It is usually a university or national lab that does these kinds of tests, funded by your tax dollars.
> In my opinion, knowing how to treat these cells to make them last is very important information. If you and the useless DIYGUY don't think $5 is worth finding out, then so be it. I will know how to make my EV last a long time.


Careful there sunshine. Personal attacks only demonstrates a weak argument. There is a vendor section if $ is your game..


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## Jan (Oct 5, 2009)

Useless diyguy.


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## Lordwacky (Jan 28, 2009)

I would be happy to make a small donation to cover some of the cost assocated with testing these batteries, but I think it is going to cost most then $500 to do it correctly. 

but I'm with DIYguy.... if you do the testing you might as well give out the information. Becasue if you don't, the chances are one of your donors will, in fact I would insist that the information be made available if I were to donate.


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## david85 (Nov 12, 2007)

Lets see if this can continue without the personal barbs, ok?

Having done my own public testing a few years back, I am glad to see some one offering to do it again. Although what is more likely, is people who can afford a little risk will buy anyway and share what they know.


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## brainzel (Jun 15, 2009)

Don't get me wrong, the idea is perfect and I'm curious to see the results. I personally won't pay for something, I don't know whose benefit.

Further the time span is wide and I don't know if I could use the results or if the project ends by 90% because you run out of time or pleasure.

My suggestion was serious to make it and hope that someone will donor your investigation after looking at your hopefully great statisitcs.
That's only my way, I didn't want to convert you or expose you.


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## DIYguy (Sep 18, 2008)

Jan said:


> Useless diyguy.


Thanks buddy... lol


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## nimblemotors (Oct 1, 2010)

It will absolutely cost more than $500 to do these tests, I'd charge minimum $5,000 to do them for someone else. 
If you read what I proposed, the donations are returned unless the $500 is reached, no data is published until then. 
I'm documenting the testing process here.



Lordwacky said:


> I would be happy to make a small donation to cover some of the cost assocated with testing these batteries, but I think it is going to cost most then $500 to do it correctly.
> 
> but I'm with DIYguy.... if you do the testing you might as well give out the information. Becasue if you don't, the chances are one of your donors will, in fact I would insist that the information be made available if I were to donate.


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## nimblemotors (Oct 1, 2010)

Thought I'd post a video of the motor controller I'm planning to use for the tests. It has 4 100v-220amp mosfets (http://parts.digikey.com/1/parts/1016072-mosfet-n-ch-100v-220a-isotop-ste250ns10.html) in a full-bridge setup to run the outboard in both forward and reverse. I use a LT1161 driver chip (http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=LT1161ISW%23PBF-ND) to drive the mosfets.
This has a watercooled heatsink, which was added later, if you take notice the burn marks on the case... 

The microcontroller is one of my R/C transeivers, that uses a MSP430 1122 micro (http://focus.ti.com/docs/prod/folders/print/msp430f1122.html)
The outboard could be controlled via a wireless link, although I never got the wireless steering part done before the sailboat was sold.

I use a DC-DC converter to provide the power for the controller, which was originally a board I created for power-over-ethernet to send 24v up a tower to power 9v equipment.

This controller has no current sensing or voltage monitoring, all that will need to be added. I'm going to use a AllegroMicro 758 current sensor (http://www.allegromicro.com/en/Products/Part_Numbers/0758/).

So next is to reconfigure the mosfets add the current and voltage sensing, and figure out how to do the charging.


http://www.youtube.com/watch?v=LFbRP-wft5w


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## hipowerkevin (Jan 14, 2010)

nimblemotors said:


> Thought I'd post a video of the motor controller I'm planning to use for the tests. It has 4 100v-220amp mosfets (http://parts.digikey.com/1/parts/1016072-mosfet-n-ch-100v-220a-isotop-ste250ns10.html) in a full-bridge setup to run the outboard in both forward and reverse. I use a LT1161 driver chip (http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=LT1161ISW%23PBF-ND) to drive the mosfets.
> This has a watercooled heatsink, which was added later, if you take notice the burn marks on the case...
> 
> The microcontroller is one of my R/C transeivers, that uses a MSP430 1122 micro (http://focus.ti.com/docs/prod/folders/print/msp430f1122.html)
> ...


Dear nimblemotors,

Very interesting...It will tell us the real life of batteries.
In lab people always use "simulate age testing", accelerate it's aging to calculate results.

However, in EV application, here are some more need to consider.
Consistent of cells in battery pack, is very important. asume if two cells have different discharge curve, it means in same SOC condition, they have different discharge currents, they would effect lifetime. If in very large discharge, total battery pack already nearly fully discharging, maybe some of cells have already over-discharged, over-discharge would definitely effect the life time, this situation would be avoid.

Life cycle test would be very value in energy storage area, like solar, wind system or so. modest charge / discharge environment would fully show battery's life time.

I want to say, the key parameter to decide life time, is the formula of battery chemistry and control way of Factory in production. To have fair result, you also need do sample pick up, like 2 from 200 cells in random.

Kevin Tang
[email protected]


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## nimblemotors (Oct 1, 2010)

I've reconfigured the circuit of the motor controller into a simple DC-DC boost circuit. Only use two mosfets, and moved the motor negative wire directly to ground. So basically, I have a simple Boost DC-DC circuit, where the diode in the circuit is a mosfet which is used to discharge the cell into the capacitors. To charge the cell, the negative mosfet is used to PWM the inductor to ground and boost the DC to charge the cell.


Cap+ ----Inductor--+---[ DischargeFet ]----+--- Cell +
| -----
| cap ---
BoostFet | 
| | 
Cap- -------+----------------------------------+------ Cell -

Unfortunately, the boost DC-DC is not working. The parts are hooked up using alligator clips, so this might be an issue. I don't know what size inductor should be used to do 2v to 3.6v. The ones I've tried do nothing.
Any suggestions?


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## bruceme (Dec 10, 2008)

Interesting thread on testing. For some more real-life info... I'm running 44 x 100Ah TS LifePO4's for over a year now. I commute every day I can and run about 45% discharge each way with a recharge at work. Controller caps current at 250amps (2.5C) and typical cruise is 60-100A (40-60mph). I run miniBMS to top balance. I've done ~200 cycles so far, no sign of anything ugly, all cells are operating normally.

-Bruce


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## JRoque (Mar 9, 2010)

nimblemotors said:


> How can any battery company guarantee cycle life??
> There is no possible way to determine the number of cycles at the cell level...


Hi. They test their products before shipping. They've come up with a design that they test to gather data. They then publish a set of parameters that you must follow if you want to get a certain number of cycles out of the batteries. If you keep the charge/discharge rates and temperatures as specified, you'll get the number of cycles printed in the datasheet.

"Testing" the cells to ensure they do yield the specified number of cycles, destroys them. We have to accept and trust the manufacturer... or have them guarantee their product will perform as spec'd. The most we consumers can do is quality control check of a batch of cells, scarifying a small sample and trust the rest in the pack will behave the same way.

JR


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## nimblemotors (Oct 1, 2010)

It turns out that the LT1161 mosfet driver can't even come close to handling 20khz pwm frequency that is needed for a DC-DC boost.
I'm going to use another driver chip that is high-speed.

However, I've been thinking it might actually be better to discharge into the caps, and when charging back reconfigure them into a higher voltage configuration. So for example 40 connected in parallel that are charged to 2v, then switch them to 10 parallel 4 serial, to get an 8v to then pwm to charge the cell. I'd need 12 switches capable of handling 120amps.
Don't really want to go buy them, I have two EV200 contactors, only need 10 more... isn't it possible to create a solid-state switch using two mosfets? Then I'd only need 24 of them.. but I could repurpose them.




nimblemotors said:


> I've reconfigured the circuit of the motor controller into a simple DC-DC boost circuit. Only use two mosfets, and moved the motor negative wire directly to ground. So basically, I have a simple Boost DC-DC circuit, where the diode in the circuit is a mosfet which is used to discharge the cell into the capacitors. To charge the cell, the negative mosfet is used to PWM the inductor to ground and boost the DC to charge the cell.
> 
> 
> Cap+ ----Inductor--+---[ DischargeFet ]----+--- Cell +
> ...


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## JRoque (Mar 9, 2010)

nimblemotors said:


> However, I've been thinking it might actually be better to discharge into the caps, and when charging back reconfigure them into a higher voltage configuration. So for example 40 connected in parallel that are charged to 2v, then switch them to 10 parallel 4 serial, to get an 8v to then pwm to charge the cell. I'd need 12 switches capable of handling 120amps.
> Don't really want to go buy them, I have two EV200 contactors, only need 10 more... isn't it possible to create a solid-state switch using two mosfets? Then I'd only need 24 of them.. but I could repurpose them.


Hey. Got a schematic of your idea? I seem to be thinking you want to switch some caps between serial and parallel at 20kHz using contactors. Are you planing on building a charger or load (or both) for testing cells?

JR


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## nimblemotors (Oct 1, 2010)

I tried to show a schematic, but the text version doesn't really work.

The design is to discharge the cell into a supercap bank, using the motor controller to pwm the discharge at the C3 rate of 120amps. The cell is discharged down to 2v, so the caps will have a max of 2v, essentially charged from 1v to 2v. Now I need to charge the cell to 3.6v from the 2v caps. I configured a DC-DC boost circuit to do this, but it didn't work and eventually found out why, the mosfet driver chip can't do high speed switching required for a DC-DC boost circuit. I'm going to try a driver chip that does handle 20Khz. But even still, this is not a highly efficient DC-DC conversion. I think it would be more efficient to reconfigure the caps from parallel to serial to boost the input voltage and then pwm them down to the charge voltage, so when they decay from 2v to 1v, I still have 4v input,
and the parallel-serial switch is done once per cycle.

Jack



JRoque said:


> Hey. Got a schematic of your idea? I seem to be thinking you want to switch some caps between serial and parallel at 20kHz using contactors. Are you planing on building a charger or load (or both) for testing cells?
> 
> JR


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## GizmoEV (Nov 28, 2009)

nimblemotors said:


> I tried to show a schematic, but the text version doesn't really work.


Try the HTML tag "quote" feature that looks like <> in the button bar of the edit window. Note the difference below, both in a Courier New font.




> --------------
> | |
> |  |
> \ /
> ...




```
--------------
|            |
|            |
 \           /
  \         /
   \       /
    -------
```


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## Coulomb (Apr 22, 2009)

nimblemotors said:


> I configured a DC-DC boost circuit to do this, but it didn't work and eventually found out why, the mosfet driver chip can't do high speed switching required for a DC-DC boost circuit.


Huh? Why does a DC-DC boost circuit require 20 kHz? I'm sure that 8 kHz will do fine, or possibly even lower if needed.


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## Tesseract (Sep 27, 2008)

nimblemotors said:


> ...However, I've been thinking it might actually be better to discharge into the caps, and when charging back reconfigure them into a higher voltage configuration.... .


No, ditch the supercaps. Use a battery pack of 4-6x more voltage than the cell/battery under test for the charge/discharge reservoir.

This way when discharging the test battery/cell at, e.g., 3C you are charging the reservoir pack at, e.g., 3/4C or 1/2C. And vice versa. You could use cheap lead-acid batteries for the reservoir pack and keep a small float charger on them to make up for the losses in the charge/discharge process.

At a current level of 100-200A you probably don't want to go much higher than 20kHz for the switching frequency. 

Also, you really want to use a bidirectional buck/boost converter. This means a half-bridge switch with level shifted or floating gate drive on the high side. Easy enough to find driver chips that can do this - a level shifted high side driver plus a ground referred low side driver in one package. Fairchild part number FAN7392 is an example of one such chip, but Microchip, IRF, ON Semi, etc., all make them.

The inductor needs to use a core material that saturates softly. Iron powder is ok, proprietary materials like MPP are even better. "CWS Bytemark" is a good place to get onesy-twosy orders of transformer and inductor cores.


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## nimblemotors (Oct 1, 2010)

Discharging into other batteries will destroy them just like the test battery. The caps last 500,000 cycles, won't even dent their lifetime, and they have almost no resistance so they are very efficient. 
They battery would have to be at lower voltage to accept the discharge so it must be a non-lithium, unless I boosted the discharge, which just isn't efficient, having to do it when charging is at least only half the time.
We hope this cell goes 3,000 cycles, that is a lot of total energy moved,
what 360kw ?




Tesseract said:


> No, ditch the supercaps. Use a battery pack of 4-6x more voltage than the cell/battery under test for the charge/discharge reservoir.
> 
> This way when discharging the test battery/cell at, e.g., 3C you are charging the reservoir pack at, e.g., 3/4C or 1/2C. And vice versa. You could use cheap lead-acid batteries for the reservoir pack and keep a small float charger on them to make up for the losses in the charge/discharge process.
> 
> ...


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## Tesseract (Sep 27, 2008)

nimblemotors said:


> Discharging into other batteries will destroy them just like the test battery. The caps last 500,000 cycles, won't even dent their lifetime, and they have almost no resistance so they are very efficient.


Have you actually calculated how much capacitance you'll need to absorb the energy from a single LFP cell? I'm guessing you haven't otherwise you probably wouldn't find the supposed near-infinite lifetime of the supercaps all that attractive anymore.

The energy storage (in Joules, or Watt-Seconds) of a capacitor is 0.5*C*V²; the energy storage of a battery in Joules is V*Ah*3600. A 40Ah LFP cell holds approximately 461kJ (if discharged completely) whereas two 2.7V/2000F Maxwell "Boostcap" supercapacitors in series (which halves the capacitance) will only hold 0.5*1000*3.2*3.2 Joules, or 5120J. 

In other words, it will take 90 of those supercapacitor pairs (180 total!) to hold the charge from a single 40Ah LFP cell. I've seen those particular supercaps for as little as $30 each, surplus, but that'd still be some $5400 worth.... You can go through a lot of lead-acid batteries, or even LFP cells, for that kind of coin.


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## Inbred_Weasel (Aug 6, 2010)

Why not just discharge your test cell through a resistor? As you already indicated, this will consume about 360kWh of electricity over 3000 cycles. Around here (~$0.10/kWh) that will cost $36.00 from the grid. Probably a bit more to account for charging efficiency, but you're still likely to be under $50.00 in electricity. But your setup will be quite a bit simpler, and you won't have to tie up thousands of dollars worth of supercaps for the months it will take to complete this test. 

Also consider that you're going to be destroying a ~$50.00 cell, so using ~$50.00 in electricity to do so seems almost poetic.


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## nimblemotors (Oct 1, 2010)

Are you trying to be helpful, or just being an asshole?




Tesseract said:


> Have you actually calculated how much capacitance you'll need to absorb the energy from a single LFP cell? I'm guessing you haven't otherwise you probably wouldn't find the supposed near-infinite lifetime of the supercaps all that attractive anymore.
> 
> The energy storage (in Joules, or Watt-Seconds) of a capacitor is 0.5*C*V²; the energy storage of a battery in Joules is V*Ah*3600. A 40Ah LFP cell holds approximately 1.38MJ (if discharged completely) whereas two 2.7V/2000F Maxwell "Boostcap" supercapacitors in series (which halves the capacitance) will only hold 0.5*1000*3.2*3.2 Joules, or 5120J.
> 
> In other words, it will take 270 of those supercapacitor pairs (540 total!) to hold the charge from a single 40Ah LFP cell. I've seen those particular supercaps for as little as $30 each, surplus, but that'd still be some $16k worth.... You can go through a lot of lead-acid batteries, or even LFP cells, for that kind of coin.


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## EVfun (Mar 14, 2010)

Was that your attempt at snark, or just being an asshole? Tesseract just gave you an honest estimate of how much capacitance would be required and roughly what that would cost. 



nimblemotors said:


> Are you trying to be helpful, or just being an asshole?


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## GizmoEV (Nov 28, 2009)

EVfun said:


> Was that your attempt at snark, or just being an asshole? Tesseract just gave you an honest estimate of how much capacitance would be required and roughly what that would cost.


Ditto! It was a very helpful and honest reply. Why would you think otherwise?


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## nimblemotors (Oct 1, 2010)

ya know, not really much use even engaging in discussions here.

Previously I posted:
"It looks like I will need about 70 of my 2600F caps to hold the discharge, but I'm not certain if that will work, because of the voltage mismatch between battery and caps "

but mr. helpful didn't bother to even read the thread, and notice that I have 70 2600F caps, in fact, I have 150 of them, so the cost isn't an issue, i have them already. It is certainly possible I miscalculated the number needed, but mr. helpful didn't correct that number before. It appears to me his numbers are wrong, 

"The energy storage (in Joules, or Watt-Seconds) of a capacitor is 0.5*C*V²; the energy storage of a battery in Joules is V*Ah*3600. A 40Ah LFP cell holds approximately 1.38MJ (if discharged completely) whereas two 2.7V/2000F Maxwell "Boostcap" supercapacitors in series (which halves the capacitance) will only hold 0.5*1000*3.2*3.2 Joules, or 5120J. "

The battery is 3v * 40 * 3600 = 432000 joules. The voltage is going to sag at 3C.
I don't need two caps in series, they will be charged from 0-2v.
.5 * 2600 * 2v^2 = 5200 joules, 432000/5200 == 83 caps. 

what I actually asked for help with. making a solid state switch from mosfets, mr. helpful didn't answer, i.e. what I actually wanted help with.
so maybe mr. helpful is not the right reference.




EVfun said:


> Was that your attempt at snark, or just being an asshole? Tesseract just gave you an honest estimate of how much capacitance would be required and roughly what that would cost.


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## Tesseract (Sep 27, 2008)

Well... this was unexpected. Yes, it appears I made a bizarre error (which I will correct in the original post) when I calculated out the energy content of a 40Ah LFP cell. The number I came up with is 3x too high - ie, correct for a 120Ah cell - but I have no idea how I got there. Oh well, that's why I like to put the actual equation I use in my explanations so that it is possible to check my work.

I am also sorry I didn't read the whole thread - but that's mainly because if I had known that you were rude to DIYguy I wouldn't have chosen to respond in the first place. Which segues nicely into the rather obvious point that I am under no obligation to answer your specific questions here. I choose to reply to a post, or I choose not to, and that's that.


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## JRoque (Mar 9, 2010)

nimblemotors said:


> Are you trying to be helpful, or just being an asshole?


Awww dude. Really? The man does this for a living and has taken the time to read your question, done calculations and posted a reply. Even if he got it all wrong - and he didn't - don't you owe him a bit of respect for at least trying? You're acting like you're entitled to get help and you're not. If someone gets part of your plot wrong, correct them, say thank you and please to see if they try again. Wouldn't you expect the same?

JR


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## ElectriCar (Jun 15, 2008)

This guy is officially an idiot, drunk or a drunken idiot. Either way I apologize FOR him. Sorry guys...


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## david85 (Nov 12, 2007)

nimblemotors said:


> Are you trying to be helpful, or just being an *asshole*?


Thats two.

Only need more.


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## ufomoracesnorscanov (Feb 23, 2015)

This thread stopped 3 years ago... after all the debate and drama and angst and collar tugging, did someone get 1000 runs from their thundersky lifepo?

who got 200 cycles prior to some errors, and who got 400 and who got 800 from them??

please inform us because there isn't currently any reliable info on thundersky batteries, all i can see is that they prices are 1/4 of what they were in 2008 on these products, and that there hasn't been a stampede from everyone to get them...

Are they basically sound or are they totally bad batteries? i can get 12v 20ah cells of them for 150 dollars 130 euros in the EU now, seems quite interesting.


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## Sunking (Aug 10, 2009)

ufomoracesnorscanov said:


> This thread stopped 3 years ago...


Thundersky batteries went bankrupt 4 years ago. Why would anyone want a 4 year old dead battery? Could it be because no one has ever seen or heard of a Thundersky Battery with 400 cycles?


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## ufomoracesnorscanov (Feb 23, 2015)

Oh thanks... i figured that the trade name had continued by the companies new owners, synopoly. 

Because i have found these batteries that have some kind of similar technology, perhaps they are winston?

http://www.ev-power.eu/LiFePO4-small-cells/LiFePO4-High-Power-Cell-3-2V-20Ah.html?cur=1


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## T1 Terry (Jan 29, 2011)

ufomoracesnorscanov said:


> This thread stopped 3 years ago... after all the debate and drama and angst and collar tugging, did someone get 1000 runs from their thundersky lifepo?
> 
> who got 200 cycles prior to some errors, and who got 400 and who got 800 from them??
> 
> ...


Thundersky became Winston Battery Company and Sinopoly after a serious split within the management team. Sinopoly bought the rights to also build the LYP formula cells that were originally the brain child of Winston Chun, the head of Winston Battery Company. I have 4 yrs cycling (by the end of June 2015) on a 24/7 basis from a pack of Thundersky/Winston cells. The pack is half the old Thundersky LFP and half the newer Winston LYP chemistry, all 90Ah cells and 4 of each type in parallel to build a 720Ah @ 12v nom house power battery pack.

Now, I have never heard of 20Ah cells from any of these companies, 40Ah is the smallest I have seen so a link to the 20Ah cells would be very much appreciated.

T1 Terry


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## ufomoracesnorscanov (Feb 23, 2015)

Oh nice that you have a kushdi battery of that kind, it's from suizhong zhengguo new energy technology, distributed in EU by someone that has titanate lithium batteries, the specifications are detailed and they quote 2000-3000 cycles, i figure they are okay, except heavy compared to a 18650 cell.

http://www.ev-power.eu/LiFePO4-small-cells/LiFePO4-High-Power-Cell-3-2V-20Ah.html?cur=1


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## T1 Terry (Jan 29, 2011)

ufomoracesnorscanov said:


> Oh nice that you have a kushdi battery of that kind, it's from suizhong zhengguo new energy technology, distributed in EU by someone that has titanate lithium batteries, the specifications are detailed and they quote 2000-3000 cycles, i figure they are okay, except heavy compared to a 18650 cell.
> 
> http://www.ev-power.eu/LiFePO4-small-cells/LiFePO4-High-Power-Cell-3-2V-20Ah.html?cur=1


Thanks, that link is not for Thundersky/Winston/Sinopoly cells, they look like GBS cells rebadged and GBS don't have a very good rep at all as far as maintaining capacity

T1 Terry


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## ufomoracesnorscanov (Feb 23, 2015)

http://files.ev-power.eu/inc/_doc/attach/StoItem/2098/GWL-LFP020Ah-Product-Spec.pdf

if you see the company standards paper on the last page, it sais the name of the factory that makes them.


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## ufomoracesnorscanov (Feb 23, 2015)

Oh sorry that was the wrong reference http://www.ev-power.eu/docs/web/2014/GWL-ZG-LFP020AH-Spec.pdf

I found that one and figured they were related. the rugged one is indeed GBS perhaps ill check it out.


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## kennybobby (Aug 10, 2012)

T1 Terry said:


> ... I have 4 yrs cycling (by the end of June 2015) on a 24/7 basis from a pack of Thundersky/Winston cells. The pack is half the old Thundersky LFP and half the newer Winston LYP chemistry, all 90Ah cells and 4 of each type in parallel to build a 720Ah @ 12v nom house power battery pack....
> T1 Terry


This is a good data point, thanks for sharing. Is this a solar installation? What is a typical discharge/charge cycle for your pack, current draw, etc. if you would care to share some details i'm sure others would like to hear also. kb


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## Sunking (Aug 10, 2009)

T1 Terry said:


> The pack is half the old Thundersky LFP and half the newer Winston LYP chemistry, all 90Ah cells and 4 of each type in parallel to build a 720Ah @ 12v nom house power battery pack.


Why would you make a 12 volt house battery? 12 volts is for toys and RV's. Home power systems are 48 volts and higher for the same reason EV's use high voltage. 

Would you build a 12 volt EV?


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## onegreenev (May 18, 2012)

I agree that 48 volts would be best. Still looking for a lithium based 48 volt charge controller. Most homes would need 48 volts. However some folks will build small out cabins off grid and utilize the components from an RV which would need to be 12 volts. Nothing wrong with that. Im looking into doing just that. But for the home I will want 48 volts.


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## prensel (Feb 21, 2010)

onegreenev said:


> I agree that 48 volts would be best. Still looking for a lithium based 48 volt charge controller. Most homes would need 48 volts. However some folks will build small out cabins off grid and utilize the components from an RV which would need to be 12 volts. Nothing wrong with that. Im looking into doing just that. But for the home I will want 48 volts.



Did you look at the MorningStar MPPT Tristar 60 charge controller ?
It's programmable so easy adapted to Lithium.


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## pm_dawn (Sep 14, 2009)

Hi !

I have Thunder sky batteries from early 2009 in my car.
The car has been on the road since mid 2009.
40 pcs of 160ah, The car has run about 22000 miles or 35000km.
I would say that I have atleast 500 full cycles on them.
They still work but the sag is bad.
They have been mistreated some so I cannot tell if they are fading because of age or cycles. They have been charge in subzero(Centigrade) temperature.

The lowest capacity is down at 130ah. and I have two cells fail shorted.


Regards
/Per


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## Sunking (Aug 10, 2009)

onegreenev said:


> I agree that 48 volts would be best. Still looking for a lithium based 48 volt charge controller.


Don't hold your breath waiting for one. The only one out there is made by Genasun and really hard to call them made for LFP batteries. The largest is 10 amps for a 12 volt marine toy system.

The big issue and will be for a long time to come is Lithium just is not competitive and ready up against FLA batteries. You can sort of make some of the solar charge controllers work with LFP, but you really have to know what you are doing and requires some additional equipment and modifications to equipment to make it half arse work.


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## pdove (Jan 9, 2012)

pm_dawn said:


> Hi !
> 
> I have Thunder sky batteries from early 2009 in my car.
> The car has been on the road since mid 2009.
> ...


Most likely from subzero charging.


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