SW900 display does not stay on

[Tucuman]

I assembled a bike with a 500 Watt gearless hub, a 36 Volt 12 Amp hour battery, a generic controller, and a SW900 display.
It worked fine for a couple of months until today: I was returning home with an almost empty battery and suddenly there was a short weak cracking sound, error 10 appeared on the display, and the motor stopped working.
I charged the battery, measured the voltage and all seems to be OK. However, when I tried to turn on the display pressing the central button it lighted up normally just for a moment and died. Pressing the button a second time does nothing. If I turn off and on the battery then then the display lights up again for a second and dies. Could anyone help me please on how to fix this problem?

 

[E-HP]

If I turn off and on the battery then then the display lights up again for a second and dies. Could anyone help me please on how to fix this problem?

Can you measure the battery output voltage before you turn it off and on again, to eliminate the possibility that the battery BMS is tripping?

 

[Tucuman]

Thank you E-HP:
I took the battery off the bike and measured at the connectors: 40V or 0V depending on the On/Off switch position. Does this answer your question?

 

[E-HP]

Thank you E-HP:
I took the battery off the bike and measured at the connectors: 40V or 0V depending on the On/Off switch position. Does this answer your question?

Sort of. The test is to see if when the issue occurs, and you don't shut off the battery switch, is the output still 40V. It's likely a controller issue, but this test will eliminate the possibility that it's the battery tripping. Also, is it correct to assume that when the display lights up, then goes dark, that the bike no longer functions?

 

[Tucuman]

Sorry, I do not understand the meaning of "battery tripping". Since the incident, the bike no longer functions and the display has the behavior I described. The battery appears to behave normally: It charged in the usual 4 hour time. The final voltage measured with the battery off the bike seems to be normal and the LEDs on the battery case light up showing full charge independently of the On/Off switch position. Do you need a voltage reading with the battery mounted on the bike? I do not know how to measure that.

 

[E-HP]

Sorry, I do not understand the meaning of "battery tripping". Since the incident, the bike no longer functions and the display has the behavior I described. The battery appears to behave normally: It charged in the usual 4 hour time. The final voltage measured with the battery off the bike seems to be normal and the LEDs on the battery case light up showing full charge independently of the On/Off switch position. Do you need a voltage reading with the battery mounted on the bike? I do not know how to measure that.

Sounds like the battery is fine. When you heard the noises, were they coming from the display or controller? Many times you can run a controller that normally uses a display and run it without one. Looking at the wiring diagram for your display, the red pin ("Power Positive" battery positive) can be jumped to the blue wire ("Controller's electric door lock") to turn on the controller without the display connected. That will determine if your controller still works, or partially works, vs being dead, or if getting a new display may fix the issue.

 

[Teeman]

Hello, I had the same problem, it always seems do it after I charge the battery to full, I keep the battery on for 24 hours, the next day the bike works fine again.

 

[Tucuman]

Thank you E-HP for your detailed answer, which might be quite useful in the future. Meanwhile, suddenly the problem disappeared just as described by Teeman! As for the short noise, it probably came from the controller, certainly not from the display.

 

[E-HP]

Thank you E-HP for your detailed answer, which might be quite useful in the future. Meanwhile, suddenly the problem disappeared just as described by Teeman! As for the short noise, it probably came from the controller, certainly not from the display.

A lot of controllers that run on 36V can also run on 24V. Some autodetect the battery voltage, and on others it's parameter set by the user. Per the SW900 manual, P03 appears to be the voltage selection. Make sure that's not set to 24V. If letting the voltage drain a bit fixes your issue, the controller could think it's working with a 24V battery, and the fully charged 36V is above the high voltage cutoff (for a 24V battery) and shuts down.

 

[Tucuman]

A lot of controllers that run on 36V can also run on 24V. Some autodetect the battery voltage, and on others it's parameter set by the user. Per the SW900 manual, P03 appears to be the voltage selection. Make sure that's not set to 24V. If letting the voltage drain a bit fixes your issue, the controller could think it's working with a 24V battery, and the fully charged 36V is above the high voltage cutoff (for a 24V battery) and shuts down.

The parameter P03 was originally set to 36V and still keeps this value.