What happens to discharge rate if you run in parallel? - RC Groups
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Sep 27, 2005, 08:58 AM
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What happens to discharge rate if you run in parallel?

If I connect a 11.1v lipo with a 6C discharge ratein parallel to a 11.1v lipo with a 10C discharge rate will I get 16C?
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Sep 27, 2005, 09:28 AM
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No you will get a puffed battery.
When discharging two batteries in parallel the dischage need to be the same rate on both batteries and same mAh.
So what will happen if you discharge the pack as 16 C the 6C will be discharging at 8C
If you run two batteris in parallel they need to be the same mAh and the same C rate.
Now if you have two 1500 mAh that are 8C, now they become 3000 mAh at 8C.
Sep 27, 2005, 09:33 AM
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No. For one thing it's not a brilliant idea to parallel different types of packs but if you do you add the *calculated currents* together but NOT the *C rate*.

Assuming both packs are the same size, at 6C a 1000mAh pack will give 6A. A 10C 1000mAh pack will give 10A. So in total you have about 16A. But by putting two 1000mAh packs in parallel you've made a 2000mAh pack so 16A is 8C not 16C.

If one was 1000mAh at 6C and the other was 1500mAh at 10C you'd have a total of 21A available and a 3000mAh pack so that would be 7C not 16C.

Sep 27, 2005, 12:34 PM
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podavis's Avatar
When the smaller battery begins to poop-out it's current output will begin to drop as if it's seeing a larger resistance at whatever voltage the larger battery can sustain. From the point of view of the smaller battery it doesn't know the larger battery is even there, all it knows is that the resistance is dropping at some voltage well above 3 volts per cell. .

The internal resistance of the 6c battery partly means it has a higher internal resistance that will throttle it so that it doesn't put-out as many amps as the 10C battery it's in parallel with, but you probably shouldn't bank on it, or as suggested, you might overheat it. Perhaps you might try a current output half way between the calculated ideal combination of the two batteries and twice the current capability of two times the smaller battery. This will take advantage of the throttling effect but be conservative, but do short runs at first and check the temperature of both batteries after every run. I always check my batteries to see how warm/hot they get anyway. I plan to try this myself at some point. I have a ammeter and will be able to compare the current sharing between the batteries.

Last edited by podavis; Sep 27, 2005 at 12:46 PM.
Sep 27, 2005, 02:28 PM
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So basically the 6C battery is worthless.

The only thing I could do is buy another "junk" 6C pack and get a 2600 mah 6C battery? That seems like a waste.

Or buy another 2000 mah 10C battery and get a 4000 mah 10C combination?

Do I have this correct?
Sep 27, 2005, 02:33 PM
"$$Crashable Income$$"
So basically the 6C battery is worthless.


go with trying to get another 10c 2000mah pack make a 3s2p pack.
fly the 6c pack on a slowstick or something, it isent EXACTLY worthless.
Last edited by maux; Sep 27, 2005 at 02:40 PM.
Sep 27, 2005, 03:46 PM
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It's perfectly possible to run unequal size or different type packs in parallel. It's been discussed many time in the Battery and Charger forum and many experiments have been performed.

As podavis correctly says they will sort out the current between them with the smaller or lower C-rated one providing less than half the total current and the larger or higher C-rate (lower impedance) version providing more than half the current.

The catch is that you have to understand a few things like the difference between Current and C-rate to use this information safely. Like so many things in this fairly technical hobby if you don't understand the basics the only safe advice is to stick with IDENTICAL packs which are completely predictable.

Sep 27, 2005, 05:52 PM
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podavis's Avatar
Originally Posted by slipstick
... Like so many things in this fairly technical hobby if you don't understand the basics the only safe advice is to stick with IDENTICAL packs which are completely predictable.

I get carried away some times and forget that I have 25 years of engineering to lean on. I just downloaded a couple of etec discharge charts to figure out a way to use the charts to define the safe operating region. I know it's sure to already have been done in the batteries forum, but I'll understand it better if I do it for myself.

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