Power cuts out under load

[smarmstrong]

Hello,

I'm new to the forum and the concept of e-biking , looking forward to the experience, but it's becoming more complicated that I envisaged and I could do with some assistance getting my 'rig' working.

I have a 500w geared motor conencted to chain, and a LifePo4 24v 20ah Battery which came earlier this week from China, my problem is that when it's wired and I test it with the bike off the ground everything's fine, but as soon as I put any load on the bike, slight braking or riding the Battery cuts out.

To reset I disconnect the power and re-attach and the same thing happens again.

I've tested the battery and it's pumping out 28v, so I can only think it's something to do with the BMS, but how can I confirm this and correct it.

Any help would be appreciated.

 

[Tiberius]

Cutting out like that is likely to be either the controller or the battery BMS.

The controller may have a low voltage cut out (LVC) point that is set for a particular battery type. If the battery voltage falls below this it cuts out to protect the battery. Controllers often also have circuits to limit the battery current but that appears as a reduction in throttle opening rather than a cut out.

BMS circuits inside the battery vary in what they do. Almost all will monitor for LVC, some will also monitor for overcurrent. They also vary in how they react. Some will have a FET switch to disconnect the battery; some will signal to the controller to turn off.

We'd need to know more about the battery, controller and motor to comment further. But 500 W at 24 V is just over 20 A. At low speed or stationary, the motor could be calling for 40 A if you open the throttle under load. The battery could well be complaining.

Nick

 

[torrent99]

Cutting out like that is likely to be either the controller or the battery BMS.

The controller may have a low voltage cut out (LVC) point that is set for a particular battery type. If the battery voltage falls below this it cuts out to protect the battery. Controllers often also have circuits to limit the battery current but that appears as a reduction in throttle opening rather than a cut out.

BMS circuits inside the battery vary in what they do. Almost all will monitor for LVC, some will also monitor for overcurrent. They also vary in how they react. Some will have a FET switch to disconnect the battery; some will signal to the controller to turn off.

We'd need to know more about the battery, controller and motor to comment further. But 500 W at 24 V is just over 20 A. At low speed or stationary, the motor could be calling for 40 A if you open the throttle under load. The battery could well be complaining.

Nick

And it's one of those cheap duct tape LiFePO4s you see on Ebay, my money will be on the BMS. Many of these duct tape BMS circuits have proved inadequate in the past. (The Ping BMSs excluded)

 

[Beeping-Sleauty]

And it's one of those cheap duct tape LiFePO4s you see on Ebay, my money will be on the BMS. Many of these duct tape BMS circuits have proved inadequate in the past. (The Ping BMSs excluded)

... i second that,

if switching off & switching back on solves the problem, the problem will be the BMS, contact your supplier and ask for a new board 30 amps min. you will have to solder the new one into place, bit fiddly - but fairly easy if you have some solder tape, ensure the connections by number and not by the colour coded wire as these can vary.

 

[smarmstrong]

Thanks for help on this, I'll contact battery supplier and see what he comes back with.

 

[Tiberius]

It would be worth monitoring the battery voltage as you slowly increase the load. Then you could tell what the voltage sag was, whether it was the controller or battery cutting out, what the cut out voltage was, etc.

Nick