what does it mean when the LVC function stops working like it should?

Hi ESFMs,

I've been riding my 48v 35ah pack for just a little over a year. The other night on my way home I experienced something I've only experienced one other pack.

I knew I was running a little low on batterry, and so I was expecting to hit the low voltage cutoff near the end of my ride home.

Normally, when it happens, my power stays on but I can't activate the throttle for a few seconds. I usually just half throttle the rest of the way (usually that last 500 meters) so to stay above the LVC point (which I think it's around 41v but I like to stay in 42v or above for good measure)

Anyway, what's started happening is that my entire pack just shuts down. No power at all and when I go to disconnect and reconnect the battery it doesn't respond. It takes several minutes before this pack decides to provide power again.

Would this be an issue with the cells or more likely the bms?

Clinton

there are usually 2 limits, the "soft off" where it recovers in voltage and if that happens fast enough the bms simply enables the output again. if the recovery does not happen in the set timespan the bms usually goes into a hard lock and only renables the output once you hook up a charger.

it might be a sign the pack is wearing out or you are pushing it too hard.

Yes as a pack wears (loses Ah capacity) the voltage drop correlating with a given SoC becomes earlier and earlier in the discharge cycle.

Starting out with a larger Ah pack will stretch out that deterioration, stopping discharge at average say 30% SoC can be double the cycling lifespan of going lower.

ClintBX said:

Normally, when it happens, my power stays on but I can't activate the throttle for a few seconds.

Click to expand...

That is the *controller* LVC. (not the battery or BMS LVC)

Anyway, what's started happening is that my entire pack just shuts down. No power at all and when I go to disconnect and reconnect the battery it doesn't respond. It takes several minutes before this pack decides to provide power again.

Click to expand...

That is the battery's BMS's LVC.

Would this be an issue with the cells or more likely the bms?

Click to expand...

Probably the cells, just getting unbalanced over time as they age, and/or because of quality / matching issues.

Leave the pack on the charger for several hours, days, or weeks, and it will probably rebalance them. If not (or if you don't want to leave it on charge), then you'd have to open it up and measure the voltage of each cell group, and list them all here in order. There's a lot of battery troubleshooting threads that explain this sort of troubleshooting if you poke around.

If it isn't a balance issue, then it's just old cells losing capacity.

amberwolf said:

ClintBX said:

Normally, when it happens, my power stays on but I can't activate the throttle for a few seconds.

Click to expand...

That is the *controller* LVC. (not the battery or BMS LVC)

Anyway, what's started happening is that my entire pack just shuts down. No power at all and when I go to disconnect and reconnect the battery it doesn't respond. It takes several minutes before this pack decides to provide power again.

Click to expand...

That is the battery's BMS's LVC.

Would this be an issue with the cells or more likely the bms?

Click to expand...

Probably the cells, just getting unbalanced over time as they age, and/or because of quality / matching issues.

Leave the pack on the charger for several hours, days, or weeks, and it will probably rebalance them. If not (or if you don't want to leave it on charge), then you'd have to open it up and measure the voltage of each cell group, and list them all here in order. There's a lot of battery troubleshooting threads that explain this sort of troubleshooting if you poke around.

If it isn't a balance issue, then it's just old cells losing capacity.

Click to expand...

Thanks for clarifying that. I understand now, about the 2 LVCs. And yeah, I suspect a few unbalanced cells as my to charge has been dropping several decimals over the past few months. I think one lost 0.5v.