# Testing Sinopoly Cells



## skooler (Mar 26, 2011)

Hi All,

I recently purchased some Sinopoly 60AH (B) cells for testing, the idea being that the results can be shared with the rest of the community.

The cells recently landed but I dont have the equipment to test them and I'm also quite busy at the moment so Jozzer (steve from jozztek) and electricmini (http://www.supralectrix.com/Supralectrix/The_Electric_Beast/The_Electric_Beast.html) have kindly offered to test the cells.

*Question*
What tests would everyone like to see?

*Test 1*
Well it's not really a test, more of an accident...

I'm using 4 of these cells as my accessory battery and accidently let them run flat. All cells were below 1v, one wouldnt register a voltage on my meter. 

All of the cells have bounced back well, are holding a charge and staying in balance with eachother.

So on this occasion, they have handled overdischarge quite well 

We will keep this thread updated with results.

Cheers,

Mike


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## Ziggythewiz (May 16, 2010)

The only reasonable test I can think of is voltage sag at various C levels up to max.

The unreasonable tests of course would be for cycle life at various C and DOD levels.


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## MN Driver (Sep 29, 2009)

I'm interested in the voltage sag of these 60Ah-B cells as I'm planning to use them on my conversion(if I can manage to actually get them in the US early next year from a distributor for a cost resonably similar to other LiFePO4 cells sources here).

I'm looking for voltage sag data at 1C, 2C, etc up to 10C. I might be pulling up to 10C(600amps) for a very short period with a Soliton Jr but only if their voltage sag is reasonable. FWIW CALB rates their smaller(under 70Ah cells) at 10C for 10 seconds, which assumes they were not hot to start with and are treated gently right after to allow time to cool. I'm thinking these cells probably can handle similar for short periods if they don't sag too badly. Sinopoly rates all their cells to 5C for 15 seconds but doesn't rate them differently from their largest cells to the smallest when the smallest will have better performance(less sag) and by their nature can handle more current. I'd like to see it quantified, if you're willing to have them tested them that way for us.


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## DavidDymaxion (Dec 1, 2008)

I find it quite amazing that Jack Rickard (and myself in limited testing) find that batteries stay so well balanced after a bottom balance.

It would be surprising to me that lithium batteries are so well matched they stay perfectly in step. One theory I have is lithium might have a self balancing effect. Some rigorous testing this way could be a great data point for the BMS debate.

You could do it something like this:

Discharge all batteries to the lower knee ~2.5V.

Put 1/2 the capacity into 1/2 of the batteries (30 Ahr into a 60 Ahr battery).

Charge and discharge in series 10 or 20 times, making sure no battery goes overvolt or undervolt.

If there is a self balancing effect, the batteries will start to get closer (you'd get more and more Ahr out as you swung between the high voltage cutoff when any cell hits it, and low voltage cutoff when any cell hits LVC). This would be a point for the anti-BMS crowd. OTOH, if the batteries stayed the same or diverged and delivered less and less capacity, this would be a point in favor of having a BMS.


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## Ziggythewiz (May 16, 2010)

DavidDymaxion said:


> if the batteries stayed the same or diverged and delivered less and less capacity, this would be a point in favor of having a BMS.


Don't you mean in favor of doing a proper balance?


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## rwaudio (May 22, 2008)

DavidDymaxion said:


> I find it quite amazing that Jack Rickard (and myself in limited testing) find that batteries stay so well balanced after a bottom balance.
> 
> It would be surprising to me that lithium batteries are so well matched they stay perfectly in step. One theory I have is lithium might have a self balancing effect. Some rigorous testing this way could be a great data point for the BMS debate.
> 
> ...


That's an interesting point of view, however a "successful" outcome (IE if there was some self balancing, or that's what the test results appeared to show) it would only prove that the cells DON'T stay balanced.

I would much prefer cells that stayed where I put them, top balanced, bottom balanced etc.


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## electricmini (Oct 21, 2008)

skooler said:


> Hi All,
> 
> I recently purchased some Sinopoly 60AH (B) cells for testing, the idea being that the results can be shared with the rest of the community.
> 
> ...


Ok guys,

Bearing in mind I only have 1 cell at the moment....

I have an embedded microcomputer board (VM1 from Microrobotics) and various add-ons for it (relays, temp sensor, etc). It has built-in 12bit AtoD converters, but I also have some higher-resolution chips lying around in the office that I could use, for digitizing cell voltage.

I also have a spare Emeter (aka Link10) with the RS232 option, so I can log
parameters such as voltage, current, Ah put in/drawn out, etc. as each test progresses.

Finding & building a suitable load for a single 3.x V lithium cell might be fun,
especially if some of you want 10C discharge curves 

I do have a variety of resistors, heatsinks, coathangers-in-buckets-of-water, contactors, and big power supplies here so I'm pretty sure we can get fairly close to a useful set of discharge curves, even if they don't maintain an exact xC discharge current during the entire run.
(since the Emeter will compute Ah each time it spits out a block of data, i.e. once per second, a varying load current doesn't matter so much)

Myself, I'm interested in the voltage sag vs discharge current
(i.e. "internal resistance" of the cell), to see if they might be good for the Supra.

My initial thoughts are that the computer board would control whether the cell is being charged/discharged/resting and would also capture the Emeter's output into a text file on a SDcard for later analysis.
The computer would constantly check for:
Cell undervoltage ( < 2.8 V ), terminate discharge if cell drops below this threshold
Cell overvoltage ( > 3.8 V ), terminate charge if cell rises above this threshold
Cell temperature ( 0'C < cell 'C < 40'C ), terminate discharge/charge if outside this range
Total Ah removed/replaced ( 60Ah ), terminate discharge/charge if total Ah from Emeter is outside sensible spec for cell
Discharge time/Recharge time, terminate if stage is taking too long

Comments?

Richard


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## MN Driver (Sep 29, 2009)

"Finding & building a suitable load for a single 3.x V lithium cell might be fun,
especially if some of you want 10C discharge curves 

I do have a variety of resistors, heatsinks, coathangers-in-buckets-of-water, contactors, and big power supplies here so I'm pretty sure we can get fairly close to a useful set of discharge curves, even if they don't maintain an exact xC discharge current during the entire run.
(since the Emeter will compute Ah each time it spits out a block of data, i.e. once per second, a varying load current doesn't matter so much)

Myself, I'm interested in the voltage sag vs discharge current
(i.e. "internal resistance" of the cell), to see if they might be good for the Supra."

It isn't as tough as you make it out to be, you can get one of these which is designed to pull 500 amps for a few seconds and you're set. You need a different meter to get accurate amperage and another meter for accurate voltage since these meters aren't too accurate but the answers you get are plenty close with one of these. To reach 10C, you'd need two of them.
http://www.harborfreight.com/500-amp-carbon-pile-load-tester-91129.html


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## 3xe-electric-cars (Jun 7, 2012)

We use also Sinopoly cells in some series conversions.
Our engineers are very satisified with the "self balancing" effect. It lets our battery pack to be charged faster and discharged deeper.
When I will get exact test results from technical department I will share it with you.


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## DavidDymaxion (Dec 1, 2008)

Ah, just one cell, that's different. I'd like to see Voltage vs. time for various current levels. Keep ramping up the current levels until a dead short or the cell vents (taking all due safety precautions, of course).

On the now theoretical self-balancing thing:



ZiggytheWhiz said:


> Don't you mean in favor of doing a proper balance?


Excellent point, it could be the magic is in bottom balancing and starting 1/2 way out of balance wouldn't work.



RWAudio said:


> DavidDymaxion said:
> 
> 
> > If there is a self balancing effect, the batteries will start to get closer (you'd get more and more Ahr out as you swung between the high voltage cutoff when any cell hits it, and low voltage cutoff when any cell hits LVC). This would be a point for the anti-BMS crowd. OTOH, if the batteries stayed the same or diverged and delivered less and less capacity, this would be a point in favor of having a BMS.
> ...


It could prove they don't stay balanced, but if they kept getting closer and closer, and then stayed bottom balanced, that would show the cells tends towards a bottom balanced state automatically. It just seems amazing to me that cells can stay close when bottom balanced, by charging and discharging with exactly the same efficiency for every cell. It seems more likely there would be something that tends to push them together.

I'm aware of bottom balanced batteries staying together. Most of the BMS systems actively top balance every charge cycle. Is there someone that has top balanced and showed the cells stayed together without a BMS? Maybe bottom balancing is a more natural state for staying together?


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## Ziggythewiz (May 16, 2010)

I plan to top balance mine when I get em...maybe I should take up a collection...


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## octagondd (Jan 27, 2010)

DavidDymaxion said:


> I find it quite amazing that Jack Rickard (and myself in limited testing) find that batteries stay so well balanced after a bottom balance.
> 
> It would be surprising to me that lithium batteries are so well matched they stay perfectly in step. One theory I have is lithium might have a self balancing effect. Some rigorous testing this way could be a great data point for the BMS debate.


I don't know that lithium itself has a self balancing effect, but here is my theory about possible self balancing with bottom balanced packs and no bms:

Batt A 100 AH capacity
Batt B 110 AH capacity

Charge 1 - Batt A reaches full charge (100AH) and slightly over before Batt B gets there due to voltage. Batt A is slightly overcharged, but not much degradation of capacity. Batt B is undercharged (91% capacity)

Discharge 1 - Batt A is at 20 AH remaining, (80AH removed), 80% DOD. Batt B is at 20AH remaining, (80AH removed), 82% DOD.

The key here is DOD% of current capacity and the load during charge or discharge. As cycles continue, the smaller cells do get overcharged a bit, but the degradation of capacity is not as great because it is at a very low amperage. The large cells are being degraded at a greater rate because they have large loads on them when at a greater DOD%.

Does this make sense?


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## Ziggythewiz (May 16, 2010)

No, that doesn't make sense. They're bottom balanced, so when everyone is at a high % DOD the smaller cells will be the highest DOD.

The only way self balancing would work is if, as you mentioned, the cells getting higher are slightly damaged which causes them to not charge quite as quick.

I don't think self balancing is really possible. I think some people make exagerations, such as "The drift is so low, I think they're getting closer!" Well, that's not possible, because you balanced them, so the difference was 0. Anything else, plus or minus, is straying from that 0. You can say the drift is so small it's not an issue, which is great, but to say it goes the other way is just wrong.


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## rwaudio (May 22, 2008)

DavidDymaxion said:


> Ah, just one cell, that's different. I'd like to see Voltage vs. time for various current levels. Keep ramping up the current levels until a dead short or the cell vents (taking all due safety precautions, of course).
> 
> On the now theoretical self-balancing thing:
> 
> ...


My A123 8S3P pack that runs my chargers is top balanced and has stayed "in balance" for hundreds of shallow cycles that gradually take the battery down to empty. IE discharge 4Ah, charge 2Ah, discharge 4Ah, charge 2 Ah etc. I don't know if those are the numbers but it gradually empties the battery while doing shallow charge/discharges. When it's low I turn on a 27.2v power supply that charges it back up, I chose the low voltage because I can't fully charge the pack or sometimes it won't regen discharge properly from the cells being tested.

To fully qualify the pack it's made of 3P groups that have been tested and grouped to equal the same total capacity per group. Top balanced (which is virtually bottom balanced as well with the exception of 1 cell group that is lower than all the rest) I don't charge that high on a regular basis or I wouldn't be able to regen discharge but the cells are always the same at the top and always the same relationship on the bottom. The "low" cell group doesn't get lower or higher it has simply stayed in the same relationship to the rest.

A123's aren't Sinopoly but it's the only long term reference that I have, perhaps it's useful info anyway.


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## octagondd (Jan 27, 2010)

Ziggythewiz said:


> No, that doesn't make sense. They're bottom balanced, so when everyone is at a high % DOD the smaller cells will be the highest DOD.
> 
> The only way self balancing would work is if, as you mentioned, the cells getting higher are slightly damaged which causes them to not charge quite as quick.


They are bottom balanced which means the largest capacity cells never fill up to 100%, so they are actually the most out of line, voltage and DOD% wise, after you charge. Exaggerate the example and do the Jack Rickard stick test. Say you have a 100AH cell and a 150AH cell. When you bottom balance, and then charge to a specific voltage, the smaller cell will reach 100 AH and 100% charge, or 0%DOD, the large cell will reach 100AH and 66% charged, or 33%DOD. As you discharge, the difference gets smaller, but you are pulling 200-300amps from a cell which is at a greater DOD than the smaller cell. My theory is that this "damages" the larger cell at a faster rate which lowers its capacity and the cells self balance.


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## DavidDymaxion (Dec 1, 2008)

RWaudio: Thanks for that data point, it's good to know lithium can stay matched when top balanced, too.

On the self-balancing thing again:

It could also be that lower state of charge cells accept charge more efficiently -- it doesn't require a damage mechanism (although damage well could be what is occurring) -- just a "less full, so more accepting" mechanism.

Also, a self balancing effect would obviously be small if the cells were bottom balanced and well matched.

Anyway, I don't know of anyone claiming a self balancing effect, it is just a hypothesis of mine that I'd be interested in seeing proved or disproved. It's on my list of things to do...

I can think of various self balance mechanisms (these are total speculation, I don't know if they are true!):


Maybe low cells have more resistance, so heat up a bit more, and the heat makes it charge more efficiently. Perhaps heat would make it deliver power more efficiently, too (to a point!)
Charging is mildly endothemic, maybe that slows down acceptance of charge for cells charging faster
Maybe it's statistical, emptier cells have more "sites" to accept charge, so accept more than fuller cells.
Again, all just speculation! It has been interesting to see how the "conventional" wisdom on lithium has shifted. I like what Bill Dube said about lithiums, something like "Forget everything you think you know about batteries."



Ziggythewiz said:


> ... The only way self balancing would work is if, as you mentioned, the cells getting higher are slightly damaged which causes them to not charge quite as quick.
> 
> I don't think self balancing is really possible. I think some people make exagerations, such as "The drift is so low, I think they're getting closer!" Well, that's not possible, because you balanced them, so the difference was 0. Anything else, plus or minus, is straying from that 0. You can say the drift is so small it's not an issue, which is great, but to say it goes the other way is just wrong.


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