dischage rates for dummys

[steveo]

i was doin some reading in another forum, i wanted to use a single 5s 4000mah maxx amp batt, its discharge rate is 48 amps constant, i run ib 3800 two 6 cell packs in series so two 30amp become 60 amps, so should i run a 2s and 3s in series to get 96 amps continous, or do i not have clue about this type of stuff

i would lke to save weight with the 5s and run it in the center of the truck
my set up is going to be a 10xl mgm speedo, some one told me the 5s would work very well, but i started to read that forum and got scared

[coolhandcountry]

The only way you double the discharge rate is run the batts in parrellal. If you run series it is no better than the weakest battery.

[BrianG]

And it's not advisable to run NiMH/NiCD in parallel. Only Li seems to be acceptable for parallel running AFAIK.

[Serum]

Why is that Brian?

the only downside is the weight, otherwise it should be okay if you used proper balanced cells.?

If it's good for 48amps you can get 900watts.

Not sure how much the motor would pull, to get twice the current capacity you would need two of these packs in parallel (as already mentioned).
Another option is getting packs which can deliver more current / amps safely. This would be lighter too.

[coolhandcountry]

Originally Posted by BrianG

And it's not advisable to run NiMH/NiCD in parallel. Only Li seems to be acceptable for parallel running AFAIK.

I am curious as to why you say this. The weight and area the batts take up is the main reason why like rene stated. To get twice the capacity you have to add 12 cells to a 12 cell system for 24 cells total. That is alot of weight. If you go that route just get lower kv motor and run in series for it would be more efficent.

[squeeforever]

Exactly, otherwise Dynamite probably would have never made that chassis for 4 battery packs.

[BrianG]

From various places and some manufacturers. From what I've read, the issue was mostly with cell mismatch near the end of the cell life. It was also recommended to use matched cells so there is very little to no current flow between the cells. Also, if you do want to parallel, it is best to parallel individual cells instead of creating a series pack and putting it in parallel with another series pack. Any cell mismatches would be amplified in two series packs put in parallel.

I had a bunch of 2500mAh AA cells lying around a while back, so I though I'd try to parallel two for greater capacity. I charged them all and paired them up so there was little mismatch, but even so, there was up to ~0.05v between most pairs. Not a big deal at first glance. However, I made a 7.2v pack and it never seemed to have the capacity of a 7.2v pack with series cells only (of the same type) multuplied by 2. For example, if I was getting 2A for 70 minutes on the series pack, I would expect 2A for 140 minutes on the paralleled pack. It was close, but not quite. I got maybe 90-95% of the expected capacity. I can only guess that the cell mismatches caused the strong cell in each pair to either be undercharged by a little, or overcharged the weaker cell and I lost some capacity. Mybe the test would have come out better using GP cells or something, but I didn't want to waste the time to find out.

So, in a nutshell, it probably won't hurt anything as long as the cells are pretty close to start with, but it looks like you get better results with a single cell of the capacity you want instead of paralleling. Also, at or near the end of the cell life, any mismatches even between individual cells may get worse.

[SpEEdyBL]

You can parallel ni-mh cells when running them, but not when charging them. The problem is that the paralleled nimh cells may peak at different voltages. As soon as a nimh cell peaks, the voltage wont go any higher. Meanwhile, if one of the cells has not peaked and it's voltage rises above that of the other (peaked) cell, it (the non-peaked cell) will send current to the peaked cell, and over charge it. And because the non-peaked cell is sending current, it, itself will take even longer to peak. Sorry if this is confusing. It's late at night.