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Thread: series batteries not discharging evenly

  1. #1
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    Default series batteries not discharging evenly

    I have 2 Gens ace 7000mah 50c batteries in series in my MG29. I am having some inconsistent power fluctuations when running, and when i charge the packs, one always takes 30% less, at least.

    Anyone run into this before?

  2. #2
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    How old are they? What do the individual IR readings looks like from one pack to another?
    Vac-U-Tug Jr (13mph)

  3. #3
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    They are brand new, and I have not temp checked them yet. but will on next run

    It seems to be the left side battery

  4. #4
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    Something is definitely wrong. If they were within 1% I would not be too concerned, but 30% is far too much. Have you cycled then individually? I would not run them together until checking with the maker.


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  5. #5
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    "IR" means Internal Resistance. It is a great measure of the health of the battery. It is not temperature... Most good charger can measure this parameter when the batteries are hooked up. You'll want to measure it both, before and after charging. If the IR changes greatly, then there is something definitely queer going on in the cell. This is a strong indication of troubles in the carbon conductor. That should match with a higher temp reading after running the boat.

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    Are you sure they are in series and not parallel?

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    Quote Originally Posted by Doby View Post
    Are you sure they are in series and not parallel?
    The stock MG29 ESC is wired with series connections.
    Vac-U-Tug Jr (13mph)

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    Just want to make sure no "mods" were done.

  9. #9
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    no mods done to wiring. can i check the IR with a fluke multimeter?? set to ohms

  10. #10
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    So I just did a run all the way down to LVC and the batteries both were even this time. But they only accepted 4200 mahs charge a piece on 7kmah batteries. lowest voltage cell was 3.89V's, highest cell was 3.95V's. I am wondering if the ESC has an issue. maybe over heating??
    Last edited by Drkrieger; 07-22-2017 at 04:56 PM.

  11. #11
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    How are they being charged? Details please.

    The ESC cannot make one pack worse than the other. 2s packs or 3s?
    Nortavlag Bulc

  12. #12
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    If the ESC LVC is operating correctly it was not what shut down the boat, the voltage was still high. If the ESC has a high temp sensor, it is more likely that is why the boat stopped.


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  13. #13
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    If a cell or two collapses its voltage under high current, the ESC will hit the LVC. The only way I know to test for bad cells is the load test them on a bench setup. Then measure all the cells with a DMM while under load. I got a bench mounted air propellor for such purposes. Your right, ESC doesn't cause the problem, it's a battery problem.

  14. #14
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    If the cells in a series string are coming out that much different, then there is a difference in the resistance from cell to cell. Internal Resistance (IR) can only be measured by a charger that has that function. You need that. Next, there can be one of the battery connectors that is performing poorly. All connectors need to have the same tightness when engaging them. If loose, they should show signs of heat. You can measure the temp of each connector right after a run with an Infared Temp Meter and check for any reading warmer that the others. Between temp checks and using the functions on your charger, you should be able to determine the problem...

  15. #15
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    .013 vs .004 ohms IR between 2 cells on one battery. the other that i run in that pair is .005 and .007. Both of the other pair is .005 and .003.

    What is a good reading, and how far apart can they be?

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