Bafang Display showing incorrect battery voltage - down 3 volts on display.

[Tom@WashDC]

I had a Luna/Bafang 860C display on my Luna/Bafang BBSHD. It went bad a few days ago. Would not turn on, spoke with LunaCycles support, ended up buying a new 860C display from Luna. The new display Voltage readout consistently shows 51.2V on a battery that is charged to 54.7V according to my multimeter.

I ran this test on two separate batteries, each reading a full charge of 54.7V on the charging ports and the discharge ports.
When I place the batteries on the bike, turn on the Bafang display, the voltage reading is 51.2V for both batteries.

I rode the bike yesterday. When finished riding the display read 44V, my multimeter says the battery was 47V. The same 3V difference.

I ran a continuity test on the battery cradle pins to the motor case and bike frame to look for a ground short to the frame. No issues.
I also ran a continuity test on all of the pins coming out of the wiring harness to the display, throttle, and brakes, to see if there was a ground short to the frame or motor case. No issues.

I've sent video to Luna.

Any thoughts?

Voltage Test: https://streamable.com/87ec1s

 

[JRA]

I would say that knowledge is power. So knowing this discrepancy you could just allow for the error. However it is not known if it will kick off the LVC with still 3v remaining of battery which would be a PITA. Hopefully it will get resolved.

 

[JES2020]

I had a Luna/Bafang 860C display on my Luna/Bafang BBSHD. It went bad a few days ago. Would not turn on, spoke with LunaCycles support, ended up buying a new 860C display from Luna. The new display Voltage readout consistently shows 51.2V on a battery that is charged to 54.7V according to my multimeter.

I ran this test on two separate batteries, each reading a full charge of 54.7V on the charging ports and the discharge ports.
When I place the batteries on the bike, turn on the Bafang display, the voltage reading is 51.2V for both batteries.

I rode the bike yesterday. When finished riding the display read 44V, my multimeter says the battery was 47V. The same 3V difference.

I ran a continuity test on the battery cradle pins to the motor case and bike frame to look for a ground short to the frame. No issues.
I also ran a continuity test on all of the pins coming out of the wiring harness to the display, throttle, and brakes, to see if there was a ground short to the frame or motor case. No issues.

I've sent video to Luna.

Any thoughts?

Voltage Test: https://streamable.com/87ec1s

On some controllers / displays, you can select several different algorithms to display the voltage, each having varying degrees of accuracy. I'm sure if this is the case Luna will advise.

 

[JES2020]

I would say that knowledge is power. So knowing this discrepancy you could just allow for the error. However it is not known if it will kick off the LVC with still 3v remaining of battery which would be a PITA. Hopefully it will get resolved.

edit

 

[Tom@WashDC]

Yeah, I have no problem living with the display error as long as my Low Voltage /cutoff does not rob me of the 3 Volts. While I'm waiting for a resolution, I will try running the battery down to where it cuts out, and check the Voltage of the battery.

 

[m@Robertson]

I have a Luna DPC-18 that consistently reads 1 volt too much. It happens. And on that bike I have a second display for a second motor and that one reads correctly, so I've never felt a need to mess with it. 3v sounds a bit much, though.

 

[Tom@WashDC]

I have a Luna DPC-18 that consistently reads 1 volt too much. It happens. And on that bike I have a second display for a second motor and that one reads correctly, so I've never felt a need to mess with it. 3v sounds a bit much, though.

Luna sent me another new display. Same problem, reading 3.5V less than the battery. I borrowed a friends DCP-18 Bafang Display and had the same problem. I presume this is a controller issue now.

 

[rich c]

What quality of multimeter do you have? If it's a Harbor Freight special, I suggest you find a couple of people with quality meters and cross check your meter. Ignore that if you have something like a Fluke.

 

[Tom@WashDC]

I used two different multimeters. One old analog, and one digital. Both reading the same.