Technical multiple LiPo pack question

[Kiwi]

If I was to install a battery configuration made up of 4 packs.

Two packs of 6S 4900 and two packs of 6S 4000.

Would the 4 pack arrangement draw down equally from all packs or would the smaller packs take a beating. I know I need to have one of each in parallel thats not the question however.

To my way of thinking they will all drain at an equal voltage and thus the capacity is not critical per pack.

Why would I want to do this?? Well I have the 4900's but if for some reason (IMAC EVENT) I need a bit more security on duration I can also use my other 6S 4000 MaH packs to give me a bit more gas in the tank.

Is this an acceptable configuration or am I missing something.

[bodywerks]

Never tried it to be honest. But I would imagine that the voltage drop of the 4000 will be greater than that of the 4900, and if the voltage drops then it can't push the amps as well as the 4900. I would think that if you were to burn, say, 6000ma total it wouldn't be 3,000 from each pack, but more like 2400 from the 4,000 and 3600 from the 4900. I don't see why this would be a problem. It is obviously not an ideal situation but I don't see how it could hurt the batteries.

[sweetpea]

The downside is, the higher capacity will tend to carry most of the load and the total capacity will be slightly less than the sum of the individual capacities. The one with the lower internal impedance will tend to take more of the load. If your battery has a capacity of 100AH and the the other one still had 45AH, then in parallel you will get something less than 145AH, but it will help and it will work.

When the lower one eventually drains, it will drag the higher one down but this happens whenever two batteries are in parallel and one dies, the only difference here is it is going to happen sooner than it would had they both been the same.



The bottom line is the batteries in parallel provide more power - never less - than either one on its own - it just may not be the "ideal" way to do it.

[tkilwein]

charge-top off all of them and then use them for short test-run time as you have indicated.
Then charge each one indivdually and see the charge put in each one.
That will tell you how it will work with the existing packs.
As the internal resistance and battery heath in general changes over time this will change how they discharge when used in your setup.

[Judge]

How are you connecting the packs?

(6S 4,000 + 6S 4,000) and (6S 4,900 + 6S 4,900) in parallel = 12S2P @ 8,900 mAh

or a

6S 4900 + 6S 4000 in series = 12S1P @ 4,000 mAh??

[Kiwi]

Judge,

This was the idea.

I can get a good flight in on the 4900 packs just horsing around having fun but to get in two Sportsman sequences would be really tight if at all possible.

Thus for just buggering about the 4900 or 5000 packs are fine. When I need a bit more duration I piggy back the 4000 packs into the system.