Strange bms readings

[Dale101]

Hi
Hope someone can help my battery wouldnt charge so i did a bms reset that fixed the problem it charged to 58v but it also measures 24v when the battery is switched off...is this a sign that the bms is toast?? i pulled the multi plug and pluged in the charger for 10 seconds to reset tge bms
Regards Dale

 

[4πr^2]

What is 'switched off'? How are you measuring? and what are you measuring with?

If 'switched off' means an electronic / mosfet switch and you are measuring with the battery out of the bike or disconnected (completely unloaded, or in an open circuit) and you are using a digital volt meter, then it's possible you could see 24 volts across an open / 'turned off' mosfet. But you might also read a few volts if you hold one volt meter lead in the air and stick the other one in the ground. They are just that sensitive and 'volts' alone don't really mean much.

If you have some way to test the battery under load - either still in the bike, or by hooking up an oldschool hot plate, incandescent light bulb, etc, you may find that the 24V goes down to essentially zero.

If the bike is still 'on' even though the BMS is 'OFF', then yes, you may have blown a mosfet and it is stuck in an 'on' state.

If dealing with mechanical relays or contactors, those are harder for electrons to sneak across, though I have still seen it happen on some old relays which had a vaporized metal film built up inside. They can show a few volts on a sensitive DVM, but with no effective power / current flow.

 

[Dale101]

What is 'switched off'? How are you measuring? and what are you measuring with?

If 'switched off' means an electronic / mosfet switch and you are measuring with the battery out of the bike or disconnected (completely unloaded, or in an open circuit) and you are using a digital volt meter, then it's possible you could see 24 volts across an open / 'turned off' mosfet. But you might also read a few volts if you hold one volt meter lead in the air and stick the other one in the ground. They are just that sensitive and 'volts' alone don't really mean much.

If you have some way to test the battery under load - either still in the bike, or by hooking up an oldschool hot plate, incandescent light bulb, etc, you may find that the 24V goes down to essentially zero.

If the bike is still 'on' even though the BMS is 'OFF', then yes, you may have blown a mosfet and it is stuck in an 'on' state.

If dealing with mechanical relays or contactors, those are harder for electrons to sneak across, though I have still seen it happen on some old relays which had a vaporized metal film built up inside. They can show a few volts on a sensitive DVM, but with no effective power / current flow.

Hi im testing the discharge ports, what i mean as of is tge on/off switch on tge bike turn it on it measures right with my voltmeter turn it off its still measuring 24v ..regards

 

[amberwolf]

Fets are imperfect switches and leak tiny amounts of current, so there are "ghost" voltages on the output of a pack that isn't hooked up to a load. If you had it connnected to the controller, there would probably be no voltage present, as the controller would drain the tiny current making the ghost voltage.

 

[Dale101]

Fets are imperfect switches and leak tiny amounts of current, so there are "ghost" voltages on the output of a pack that isn't hooked up to a load. If you had it connnected to the controller, there would probably be no voltage present, as the controller would drain the tiny current making the ghost voltage.

Hi amberwolf
Thanks for your reply id read about ghost voltage before but couldnt get my head round it, basically if hook the battwry back up to my bike with the battery switched off and put it under load ,the battery would then go down to zero and stay there if ive understoid you corretly ...i will try this thank you ...do you think a new on/off switch would be a good idea too? This really helps as i was worried id damaged my BMS...
Regards