Balancing Lipo packs

[SpEEdyBL]

How many of you are balancing your packs and how often? Kokam seems to be strictly enforcing balanced packs. It's it really that necessary for the cells to be balanced so precisely or is kokam just trying to sell their products? The fact that a cell in a pack could suddenly become damaged early lifespan worries me. In fact, tcolsen just lost one of his cells. 1.) I don't want to spend $120 on a brand new lipo pack and lose a cell soon after because I didn't buy the $40 accessory that allows maintain warranty. 2.) I don't to baby my pack (watch over it and test cell voltage) during all of its existance.

One of the main reasons for wanting to go lipo was for a longer lifespan and less rest time between charges. Now I'm hearing that unless lipo's are perfectly balanced, theres a risk of one cell leaving the safe voltage range of 2.5-4.2 volts is too high. Now I guess you can't charge your pack without letting it cool because the outside cells which will cool down faster will charge differently and therefore imbalancing the cells. I don't want to wait the recommended 1 hour to cool before I recharge my pack, and I don't want to balance the cells by hand every other time I use the pack.

I have the Duratrax ice

My favorite option is the kokam cellpro 3200 3s unless I have to buy the $40 cpm in order to maintain warranty.

The PQ 4400s are next although they don't seem to handle enough amps, (they drop below 3 volts at 60 amps) and they dont fit into my car without mods.

Otherwise, pair of gp2200 or 3300/3700 packs can charge in as little as 30 minutes. In fact I'm quite happy with the fact that my current gp3300s have held up quite well for an entire 1-1.5 years.

[Rtsbasic]

If you try and charge a GP3300 or GP700 pack in half an hour your gonna kill its runtime pretty fast..thats what, 6.5-7 amps, and doing a pair of packs in series, so not going to peak correctly anyway.

I personally would get the balancer, your going to spend big $$ on a battery, and just spent big $$ on a charger, why not put in a little more and ensure your cells stay balanced. Its akin to a discharge tray/equaliser for NIMH packs, no point buying top of the line packs if your not going to look after them.

Just a thought, but you may be better off with something like 6000mah packs so you can run 2 heats without re-charging, but that depends on the vehicle your running it in.

[tcolesen]

How often one should balance a Lipo pack depends upon how much the cells will become out of balance by. 0.05v imbalance is the maximum safe value, since a cell becames unstable at 4.25v, and generally shoulnd't be allowed to go this high.
Usually, a Lipo pack's cells will stay relatively in balance as long as the cells' have near the same IR to each other. Several manufacturers do "match" Lipo packs by the data sheets provided with each cell. Two of these manufacturers are MaxAmps and TP.

I end up balancing my packs whenever I charge them. The main reason for this is that they are older packs, and as the cells get older, variations from cell to cell will be greater. The current pack I am using is a Maxamps 3s 3300mah that lost a cell over the summer, and was a 4s pack, but I rebuilt it to 4s. This pack stays pretty well in balance, with a maximum cell voltage variation of about 0.08v. Considering that I bought this back in March or February, that isn't too bad.
I have another MaxAmps 3s 4500mah pack that I built back in January. This pack tends to not stay in as well of balance, but it has also been used more, and harder than the other one.
My most recent pack is made up of low-cost 2000mah 10C cells, which I put into a 4s2p configuration for 4000mah. At $96 for all 8 cells, it was a good deal. A few weeks ago, I lost one of the parallel blocks. Something like this has to be expected at some stage or another, especially since these cells were not specially picked by IR or anything like that. Pretty soon I will turn this pack into a 3s 4000mah. BTW, the cells for this pack were bought in mid May, and have been used pretty heavily, and have heated up more than any other Lipos of mine, but have been within the temp range.

For balancing, there are a couple of options. The cheapest and most time-consuming way is what I do; manual balancing. What I do is I charge the pack up until it finishes CC charge mode, monitoring the voltage of each cell the whole time. If the cells are pretty badly imbalanced, I will stop the charge sooner. After this, I manually charge each cell in the pack. This does take a while, but it ensures good balance.
The other way is to buy a balancer. This is a more foolproof and time-saving way to balance Lipos. They can be bought for as little as $25 (Astroflight "Blinky" 6s balancer, or Hyperion 5s balancer), or for more, like TP's TP-205 for ~$60 that can do 5s Lipo. If it weren't for the fact that I am scrounging money so that I can buy a new Lipo pack, or that at 16 years I have school but no job, I would have a balancer.

The Duratrax ICE is an excellent Lipo charger, in fact it is the one that I use.
The CPM that you can get for the CellPro pack is basically a balancer, just specified for the CellPro packs.
Waiting for a Lipo to cool down after use shouldn't take too long. The nice thing is that you don't have to wait for it to cool down after charging (it won't get warm).
PQ4400s seem overrated in that they don't seem to be able to handle their given amp rate. Whether they need to heat up first to be able to deliver amps at their rated current, I do not know.

P.S. - 2.5v really is too low for the safe range of a Lipo. 3v is much better, and for the newer cells like TP Prolites, 3.2v is even better.

[glassdoctor]

Quick reply:

Just a thought to keep in mind about the Kokams. They are in general very tolerant of over/under charge abuse, as lipos go. That's one of the good things about the latest "heavy" type cells.

And it seems that a big reason they are stressing the balance issue is for the high rate charging. This is where it becomes more critical that the pack is balanced. Their new balance system with their new charger can do a 3c charge. At high rates of charge things can go wrong much easier.

Also I recall how strongly ThunderPower used to preach that their packs don't need balance taps and how rare it is that they get out of balance. They have backed off that now. They have a balancer and their packs have taps.

[tcolesen]

Even though Kokams are more tolerant, that does not mean that their overall life won't be reduced by something like overcharge or overdischarge. At high C rate charging, a cell's voltage will jump much more quickly than 1C, so a cell could easily exceed 4.2v if the pack is out of balance.

TP matches their cells well enough to almost eliminate the need for a balancer, but there is nothing better than knowing that your pack (especially an expensive TP one) will be as safe as it can be.

BTW, TP is coming out with their 5 and 10 cell chargers that will be able to communicate with the TP balancers. These chargers will allow higher than 1C charging for TP Prolite packs. When there is an imbalance, the balancer will work with the charger to lower the charge rate until the cells are balanced. The balancer's data can even be displayed on the chargers screen!

[scoob]

i've run one of my TP8000 packs quite a bit for the last 6 months without balancing and it's still in great shape, holds 7900mah and no puffing. I may get the TP balancer anyway though just for piece of mind. It's only $60 bucks and the packs are expensive.

[tcolesen]

When a pack isn't pushed hard, it is less likely to go out of balance. This is because any abnormalities in a cell are more likely to be increased as they are pushed harder (as temperature goes up).

[SpEEdyBL]

That's good to know. Anybody hear anything on the cellpro 4s charger? Kokam mentions it but doesn't seem to advertise. I'm not interested in the skyvolt 6s, which requires an adaptor and is very expensive (can't find it any other place than kokam's site). At first I would use my ice, and maybe swap over the the cellpro 4s charger if it's available in 4-5 months. It would be nice to have 35 minute cycles of 15 minutes runtime and 20 minutes charging. Not that I'm holding anything against the Ice. The ice is an amazing charger.

About the cellpro node connector. I looked at the manual for the 3200 20c 3s pack and there is a diagram of the wires and the indiviual cells they connect to. However, kokam doesn't want you do stick pins in the slots, which is required to check/charge individual cells. Is that really a bad idea?

[tcolesen]

As long as you know what you are doing, sticking "pins" in the slots isn't a bad idea. I think they are worried about shorting it out, but if you are careful that won't be a problem.