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11-02-2004 04:47 PM  13 years agoPost 1
pigs dont fly

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Hi everyone

My Tp2100's seem to take on less power during recharge than before only about 1750'ish mah from 9v cut off, they have about 25-30 cycles on each. I was wondering if my cells are out of balance? Does anyone know a good way to balance lipos? i.e. TP2100 G2 with no connectors except the main one.
Thanks
E

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11-02-2004 06:12 PM  13 years agoPost 2
playfair

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Try discharging them after a flight at a lower current then the heli draws; Perhaps 1 amp (or even less?)

If you have a Triton or similar, keep the cutoff at 9v. This will more deeply discharge the cells, yet stay above the minimum "load voltage".


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11-02-2004 08:02 PM  13 years agoPost 3
Rob_T

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The only way to balance lipos is to have the extra connectors or have balancing circuits built into the pack. Unfortunately TP does not do this yet.

To check the balance, the proper way is to measure the voltage of each cell at the end of charge. There should be no more than 10mv difference between any 2 cells. You can check the balance without actually adding connectors, but you do need to cut through the heatshrink to do it. Replace the heatshrink afterwards.

I've added JST connectors for balancing to 1 of my packs. To balance, I just charge it as a 1 cell pack through each of the JSTs (so 3 separate charges). I only did this because the pack got damaged by being over discharged (by a faulty Schulze charger), and balancing it allowed me to continue using it, although the capacity is now reduced to about 1700mah from 2100mah. Most of the time I still charge it as usual through the deans connector.

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11-03-2004 02:40 PM  13 years agoPost 4
pigs dont fly

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Many thanks for the help guys

Rob I will do the same as you did, can you just tell me how you wired the JST's, is it just a case of stripping the heatshrink away, and using 3 JST's, solder one on each cell, plus to plus neg to neg and nothing else? Then just charge one cell each untill they are all the same.
Thanks
E

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11-03-2004 10:41 PM  13 years agoPost 5
Rob_T

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Yes, that's pretty much it. The + and - of each JST goes to the + and - of a cell. You can check that you have done it right by measuring the voltage at the JSTs- you should read about 3.7 to 4.2V depending on the state of charge of the battery. Because of the way the cells are series connected you'll find that you end up connecting the +wire from one JST to the -wire of a different JST in 2 places. Thats correct, so dont worry about it!

My pack had the cell-to-cell connections made by crimping the cell tabs together with a crimp that seemed to be made of steel. This was very difficult to solder and I ended up having to use a non-electrical flux to get it to solder right. If you have to do this, you must then clean off all traces of flux so that it doesnt corrode the joint. Proper electrical flux is non corrosive, but I couldn't get a good joint using it.

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11-04-2004 09:27 AM  13 years agoPost 6
pigs dont fly

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Cheers Rob, I will be going to my LHS this PM to get myself 6 JST's and do both packs. Many thanks once again.
Rgds
E

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11-05-2004 01:55 PM  13 years agoPost 7
pigs dont fly

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Changed my mind, I was thinking about this last night, I will open the packs enough to probe the tabs, then DISCHARGE each cell down to a set voltage (above 3v of course) using a motor or a resistor, then recharge the whole pack and check voltage again, I think this way ie a second check after main charge, I can then tell if theres any cell damage as the cells would be out of balance again if there was. This way I end up with a pack the same weight as I started with and dont have to do any soldering.
E

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11-05-2004 08:45 PM  13 years agoPost 8
Rob_T

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A better variation on that idea is to just charge the cells one at a time while you have the heatshrink open. You can do this with a charge lead with clips at the end rather than the usual deans or JST. Just make sure you dont short anything out! (Clips with insulated boots over them...)

Lipos need to be balanced at full charge. Balancing by discharging doesn't balance out the capacity difference between cells. (It's better than doing nothing, but its not really the right way to do it...)

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11-06-2004 02:19 AM  13 years agoPost 9
pigs dont fly

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Cheers Rob, I have just checked my cells..had to fix the digital voltmeter first..didnt charge them at all, I just pulled them out the box and checked them..anyways the cells are 4.15, 4.13, 4.14 for one and 3.60, 3.60, 3.69 for the second pack. I will make up a set of crocodile clipped charge leads in the morning.

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11-06-2004 05:36 AM  13 years agoPost 10
iskoos

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your first pack looks good. You can't expect to see the very same voltage for each cell all the time. I would work on the second pack instead.

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11-06-2004 09:14 AM  13 years agoPost 11
Rob_T

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The first pack is almost fully charged and does show more than the desired 0.01v spread between cells, so will benefit from balancing, but is not yet at the point where I would expect to really notice any loss of capacity from being out of balance.

The second pack looks like it is empty. Voltages when empty dont tell you much about how well balanced the pack is when full. You should recharge the second pack before trying to make any judgements about the state of balance. (Being nearly empty exagerates and voltage difference resulting from different cell capacities).

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11-06-2004 03:57 PM  13 years agoPost 12
pigs dont fly

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Thanks, I will charge them now and measure them again. I'm having problems locating some crocodile clips, but hopefully should be able to knock something together.
E

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11-06-2004 08:49 PM  13 years agoPost 13
pigs dont fly

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Ok then, after charge

pack 1
4.17, 4.18, 4.16

pack 2
4.18, 4.16, 4.18

So this confirms that both sets do need balancing, based on that >0.01v out rule, mentioned earlier.
Can I asks if this is correct, C rate? I think the C rate I should use to recharge 1 cell is: 1C ie TP2100/3= 0.7a @ 3.7v.
Thanks again
E

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11-07-2004 12:15 AM  13 years agoPost 14
ericfly

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Hi Pigs,
1C is 1C regardless of number of cells so for a 2100mAh its 2.1Amps.
Obviously you still have to set your charger for the number of cells you are charging (volage) but you don't have to change the current setting if you still want to charge at 1C.

I think that the only way you can balance packs is by charging each cell separately.

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11-07-2004 05:58 AM  13 years agoPost 15
iskoos

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You DO NOT need to balance any of those packs. They are just fine. They are within 0.02v of each other and this is acceptable. There is really no rule of thumb like 0.01v. It would be good to have 0.01v or even 0.00v difference but what you have is just fine. You are being too conservative if you want to see 0.01v difference between cells.

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11-07-2004 05:00 PM  13 years agoPost 16
pigs dont fly

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Hi there folks, my newbe voyage into cell balancing continues
Thanks ericfly for the info on C, I assumed that the total amps would be divided by 3, like the volts, I guess I forgot how they are wired..doh
And as per iskoos, for the 0.02 variance, I dunno, I understand what u mean re its only 0.02 out, but Im such a perfectionist Im still gonna have a go, it cant hurt. I thought I would charge each cell up to 4v then do the whole pack together for the rest, is this correct or should I just charge each cell to its max?
Thanks
E

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11-08-2004 12:07 AM  13 years agoPost 17
Rob_T

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To balance you need to finish by charging each cell individually. To speed things up, you can charge the whole pack to about 12.4V, then finish of each cell all the way to 4.2V per cell.

The figure I quoted earlier of 10mV spread is one I've seen quoted on RR before and is achievable, but I just checked FMA's website and they only say to balance within 100mV. Based on that your packs are within acceptable balance already.

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11-08-2004 03:17 AM  13 years agoPost 18
iskoos

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Rob_T kind of told you what I meant. You really don't need to worry about balancing till you see the voltage difference of 0.1 or greater between cells. That means if one cell is 4.2v and the other one 4.1v, then you should think of balancing them. But if one cell is 4.2 while the other 4.15v for example, you are okay. The difference in this example (again this is just an example) is 0.05v and this is considered acceptable. In your case, you only got 0.02v difference. This is even smaller than 0.05v. So you are good. However I understand the feeling of being perfectionist because I have the same thing. Go ahead and balance your pack; it wouldn't hurt, but I bet you after first cycle, you will measure the same voltage difference or very close between cells. I got 2 lipo packs, and I always measure between 0.01-0.05v difference and this is okay.

Hope it is clear now.

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Zoom › Lipo Cell Balance help!
11-08-2004 01:55 PM  13 years ago •• Post 19 ••
pigs dont fly

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Many thanks for all the help guys, I'm still looking for some tiny crocodile clips so havent done the deed as yet, did find some larger ones but they were too chunky to poke through the holes in the heatshrink (I dont want to hack the TP's up too much). I guess this little exercise is still usefull. At least I now understand a bit more about whats happening with my packs under the heatshrink Just wish they would take a better charge as they are only doing about 1750-1800mah even with a deep discharge to 9v at 0.1a. I guess Ive damaged them both by flying without a lipo alarm.
Thanks again
E

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11-08-2004 06:31 PM  13 years agoPost 20
iskoos

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I have TP1320 and I was putting average of 1200mah into it. This was for the first 10-15 cycles and now(I have about 25 cycles) it reduced to 1150mah. Couple times I discharged it down to 9.0v and charged it to see the capacity and it only put 1270mah.
By looking at it, I wouldn't expect more than 1800 for the TP2100 pack.

I don't know why is that. When I had the stock evoflight 1600mah pack, I would easily put 1600+

I use Triton charger and my ESC cut off is set to 8.6v. However I don't wait till cut off occurs.

We should ask other TP owners to make sure of this.

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