Battery Failing Under Load?

Batteries, Chargers, and Battery Management Systems.
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BonesNis
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Battery Failing Under Load?

Post by BonesNis » Dec 04, 2017 11:10 pm

I have a 50V Triangle Pack 22.0 Ah 25R with about 20 cycles on it. When charged 85%, it powers my mid drive while on a bike stand (rear wheel off the floor and no load) with no issues. The mid drive works perfectly with no error codes from the controller and nothing out of the ordinary on the Cycle Analyst.

When the mid drive is under load (with me riding the bike) the mid drive sputters and operates very intermittently and eventually stops running. This has happened on two occasions. The first time, I thought that perhaps the battery was overcharged for the controller and when I drained the battery by running the bike on a bike stand, the mid drive motor worked when I rode it and lasted 4 rides (approx 100 kms). The bike sat over the weekend and when I went to ride it with the battery at 85%, the mid drive motor sputtered again and would not run.

This time no amount of draining the battery would work. Very confusing in that it works perfectly when there is no load, but when there is a load, it doesn't work.

Could this be a battery issues. Again, no error codes on the controller or issues on the Cycle Analyst. Any suggestions would be greatly appreciated. Thanks.

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amberwolf
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Re: Battery Failing Under Load?

Post by amberwolf » Dec 04, 2017 11:32 pm

Battery is probably not balanced, so a cell falls below LVC and it's BMS then cuts out. When the voltage bounces back up after the BMS removes the load, the BMS turns back on and reapplies the load, motor starts back up and the cycle then repeats (stutters). To fix this you'd fully charge the pack and leave it on the charger until it is balanced; if teh BMS does not have individual LEDs for each cell you'd have to measure teh voltages of each one or leave it on the charger for potentially days (or longer) depending on how bad the imbalance is.

The controller could also be hitting it's own LVC because of the votlage sag under load. To fix this, if the battery is not the problem, you'd need to change the controller's LVC to match the battery.

Or it could be a limit on the CA being hit (current, voltage, power, etc).

If none of the limit flags on the CA are showing, you could try disconnecting the CA from the system and directly connect everything together, so that would avoid the possibility of the CA causing the issue. If it tehn operates normally, you can investigate teh various CA limits and settings and find and fix the issue.


It could also be a bad connection in the power wires from the battery to teh controllr or controller to motor, etc., which would basically cause a low-voltage condition under load like a bad or unbalanced cell would.

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dogman dan
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Re: Battery Failing Under Load?

Post by dogman dan » Dec 09, 2017 7:54 am

Hard to say what you mean by sputters. But it could be something else. In particular, you might have a very bad connection to the motor on the main phase wires.

Once I had a cut wire, that I just kept failing to see, where the wire rubbed a tire. I had two good wires, but the third motor wire was cut down to just two strands big as a thread.

Unloaded, the motor worked great. only needed a fraction of an amp then. But ask it to pull 15 amps, and those two strands could not do that. so then it ran on only two phases, doing what I call motor stutter. Sometimes a motor will run fine on just two phases, but don't try to ride it under load. chunka chunka chunka, and it barely rolls at all.

Since yours runs fine when the battery is full, ( or does it now?) your problem may be entirely battery related. It could be a broken wire to the bms, just out of balance, or even a cell died. But look a good hard look at all your wiring too. 95% of all e bike problems are a plug or a wire not connected right. This could include the battery wire, causing a voltage drop to your system, which then shuts itself off. ( controller low voltage cutoff, or your CA can be doing it if you have it set high)

To fill and balance your battery, charge full, unplug, let sit half an hour. then replug, and charge more. if it won't restart, ride around the block and then recharge. When the green on the charger light turns on, your bms will be discharging any cells that are slightly overcharged, then in half an hour, it can then restart and fill the low cells a bit more. It could take many repeats to get the battery fully balanced. Its balanced when the battery holds full voltage, or very close to it, after you unplug and wait half an hour. If your pack can't hold 58v or more, and keeps dropping to lower than 58v with no improvement each try, then your battery has an actual problem. Ideally, a new battery would balance well, and hold 58.8v for at least a few hours. In reality, it might be full as it gets at less, but not less than 58v.

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