bafang bbs02b - battery drops to 0% after throttle use in 7, 8, 9 assist?

[Netrider101]

Hi all, I’m a new bafang bb02b 750w owner.

While riding, the battery dropped from about 25% to 0% under load from using the throttle.

This issue happened both when I first used a friend’s bike, which tempted me to get my own. I used the throttle, probably with PAS on 9, in a high gear uphill, all not recommended which I now know.

It happened again on my own setup yesterday, slightly different scenario, hit the throttle on a slight incline with PAS on 7 in about a middle gear.

Battery instantly dropped to 0% from around 23%.

After 5 minutes of pedalling at PAS setting 1, it recovered to 4%, slowly back up to 15%, but then at the next hill it dropped down to 0%

The fact that I was just about able to make it up the hill, make me wonder if is was still giving some very minimal amount of assist, to compensate from the additional weight/resistance of the bafang kit.

I have two questions really.

1.) when the battery drops like this, is this a sign of a fault or temporary overload?

2.) at 0% in these conditions is the motor still giving some sort of assist?

Thanks in advance

 

[Member 4888]

Charge the battery to 85% capacity and don't ever discharge under 20% capacity. Don't expect to drag race on an empty tank.

 

[Canva Krusho]

Charge the battery to 85% capacity and don't ever discharge under 20% capacity. Don't expect to drag race on an empty tank.

Great information, thanks.

 

[Deleted member 4845]

What you are seeing is called voltage sag. Very common.

Voltage sag increases as the battery nears end of capacity. Voltage sag increases as batteries age. Sag to this degree indicates a low AH-capacity battery, especially if new or nearly-new.

It is a sign of overload, could also be considered a "fault". Not a designed-in feature.

Both the controller and the in-battery BMS have an LVC, or low voltage cutoff. As long as you have not triggered either of those, then motor is still getting some power. Once an LVC is triggered, all battery output is ended. You have to turn off and on again, ideally after charging.

 

[Member 4888]

Great information, thanks.

De nada!

 

[Jeffb]

Hi all, I’m a new bafang bb02b 750w owner.

While riding, the battery dropped from about 25% to 0% under load from using the throttle.

This issue happened both when I first used a friend’s bike, which tempted me to get my own. I used the throttle, probably with PAS on 9, in a high gear uphill, all not recommended which I now know.

It happened again on my own setup yesterday, slightly different scenario, hit the throttle on a slight incline with PAS on 7 in about a middle gear.

Battery instantly dropped to 0% from around 23%.

After 5 minutes of pedalling at PAS setting 1, it recovered to 4%, slowly back up to 15%, but then at the next hill it dropped down to 0%

The fact that I was just about able to make it up the hill, make me wonder if is was still giving some very minimal amount of assist, to compensate from the additional weight/resistance of the bafang kit.

I have two questions really.

1.) when the battery drops like this, is this a sign of a fault or temporary overload?

2.) at 0% in these conditions is the motor still giving some sort of assist?

Thanks in advance

It is just a momentarily indicator of current battery. If you were to put a voltage meter on your car battery at it showed 14.5 volts and then crank the engine the meter would show around 9 or 10 volts. When you stop cranking the voltage returns to normal. Point is that the meter is not accurate when battery is under high load. It is only accurate when in a level state.
Now if you were to put a amp meter on the battery it would show 0 amps. Then crank the motor it will show amps being used. Just opposite of each other.
I don't see a concern when you say you see this when at 25% power. I would expect this result of 0 volts when pressing throttle. It doesn't mean there is no power it's just the physics of how the meter is displaying voltage. Voltage measurements when reading capacity are done with no load applied.