Low Voltage Cut out?

[getzbuzy]

Hey everyone,

I'm looking for some advice.

I have a 14s, 15ah li-ion pack, and within the last week my setup has been cutting out. My CA2 will show the voltage dropping quickly, when I release the throttle my regen breaking kicks in and it will power back up. This has never happened in the past 15 months of running this battery pack. It appears that all my connections are ok and nothing is loose, but I haven't given a "thorough" inspection. All seems to be running well regardless of amps drawn, which is typically between 30 and 40, as long as my charge is above 51 volts. However, once I drop below 51 volts, I will randomly loose all power if I let it pull 30amps or more. As long as I stay around 20amps only, it's fine.

The pack uses samsung 25r cells with max continuous current of 40A, and has a "very robust BMS, that can deliver around 40A continuous, but much more for extended bursts."

I use a 40A 12 FET IRFB4110 INFINEON CONTROLLER (MOTOR WITH HALL SENSORS)

I have my CA2 limited to 40Amps.

Currently the pack has 2500 amp hours on it, which would mean it has been "cycled" approximately 167 times since it was purchased in May of 2015. Nonetheless, I've charged it (variably between the 90% charge and the 100% charge) between 300-400 times I would guess. Nearly everyday except during the winter months. The actual battery cycle count on my CA2 has never properly worked.

Cycle Life of the pack is estimated at 500-700 cycles (to 80% Retained) with 100% Charge and 100% discharge cycles. Cycle life is extended (possibly doubled) by charging to 90% and limiting discharge to 90%"

I am hard on my setup. I run full throttle always, but I always pedal a going up hills, as well as when taking off from a complete stop. I always stay within the limitations of the system, which for my setup means I use between 1700 and 2000w in short bursts when accelerating, and usually run continuous between 1000w and 1500w when Im up to speed. I usually pull between 30 and the max 40 amps regardless.


It is also definitely worth mentioning that about 8 months ago I melted my anderson pp connection from the battery to my controller, and I was sent a much more heavy duty connector which I had to solder myself.....and my soldering skills definitely aren't anything amazing.

If my "sub-par" solder job weakened over these last 8 months then maybe it can't handle the high amps???

Any other ideas??

Any insight would be helpful.

 

[dogman dan]

If it is your soldering, the solder joint would be heating up noticeably. but if it's actually so bad it's separated, then you could get an actual shut off.

 

[MadRhino]

You have to first diagnose the reason why the voltage is dropping faster than usual. It could be the battery itself, or it could be that your bike is pulling more current due to electric or mechanical reasons.

Mechanical reasons are easy to diagnose. So check that first, everything is free to spin normally.

Battery should be tested for each cell individually, making sure that all the cells are about equal at both full charge and discharged levels.

Electrical reasons for dropping your battery voltage faster than usual are many. First thing to check is power usage at rest, for you want to make sure there is no short. Next comes resistance check, measure impedance of each motor phase between each other (and motor axle where there has to be no continuity at all), measure impedance of each wire line to find weak connector or damaged wire. After all that is checked and OK, you are into controller (or BMS) malfunction.

 

[getzbuzy]

You have to first diagnose the reason why the voltage is dropping faster than usual. It could be the battery itself, or it could be that your bike is pulling more current due to electric or mechanical reasons.

Mechanical reasons are easy to diagnose. So check that first, everything is free to spin normally.

Battery should be tested for each cell individually, making sure that all the cells are about equal at both full charge and discharged levels.

Electrical reasons for dropping your battery voltage faster than usual are many. First thing to check is power usage at rest, for you want to make sure there is no short. Next comes resistance check, measure impedance of each motor phase between each other (and motor axle where there has to be no continuity at all), measure impedance of each wire line to find weak connector or damaged wire. After all that is checked and OK, you are into controller (or BMS) malfunction.

Thanks for your reply. The voltage isn't dropping faster than normal. Once I am depleted below 51 volts, I risk my setup shutting down if I draw too many amps. By the time I deplete to 47 volts, that risk is much higher. And by "risk drawing too many amps," I mean that drawing 20amps is safe and it will not shut off, but drawing 30 amps will inevitably shut the system down.

When the occurance happens I lose power to the motor, and my CA display will go dim and over about a 2 second period it will show, for example, 48volts....30volts....23volts....

At this moment, I release the throttle and let my regen brakes kick in. All of a sudden the CA goes back to a strong backlight, and volts are back to normal.

Also, once the occurance happens, it is guaranteed that if I draw close to 30amps again at all, the same occurance will repeat itself over and over until I recharge.

 

[jbalat]

I have the same controller and same issue.
It's happening more lately I believe because of the colder weather.

I know when I hit lvc the voltage readout drops like you say, it's just the bms shutting down and capacitors discharging as someone mentioned above.

My setup is 84v full charge and low voltage cutout at around 66volts. If I power up a hill I can watch the voltage drop to 70v and if I apply more throttle it drops to 69, 68 depending on amp draw. Sometimes lvc can occur at 70v since it only takes one of the cells to hit under 3.4v and the whole system shuts down.

It's normal for the internal resistance of the cells to get worse during the cold so you will see a bigger voltage drop.