Bafang brake sensor signal voltage over 40V?

[meddler]

Hello all, new member. BBS02B user for nearly two years and love it.

I've been toying with the idea of upgrading to hydraulic brakes with integrated cut offs such as Tektro HD-E350 and doing some research. I know this would require some conversion of the Higo connectors from three pin on the loom to two pin etc.

I've been checking my brake sensor pin outs to ensure they correspond with what they should be according to sources on the internet.

I'm getting ground on pin 8 which is good, 4.8v on pin 6, and over 40v on pin 4 where I was expecting to get a signal voltage of 5v or less?

What is more interesting is that I get this voltage even when the main battery is disconnected and removed from the bike. It must be coming from my 850C display?

Can anyone help me out here?

 

[TommyCat]

Hi meddler,
And welcome to the forum!

and over 40v on pin 4 where I was expecting to get a signal voltage of 5v or less?

I agree with your expectation and from description would find this high voltage reading highly unlikely if the bike is working properly at this time.
No offense, but are you sure it wasn’t 4 volts? Is the battery in your meter weak? Using the ground on pin 8 for the test?
The display does get full battery voltage, but wouldn’t maintain it for longer than the controller’s capacitor charge holding capability of a few minuets, if that. And certainly not on the low brake signal wire.

Thats an interesting one.



Regards,
T.C.

 

[meddler]

Hi meddler,
And welcome to the forum!



I agree with your expectation and from description would find this high voltage reading highly unlikely if the bike is working properly at this time.
No offense, but are you sure it wasn’t 4 volts? Is the battery in your meter weak? Using the ground on pin 8 for the test?
The display does get full battery voltage, but wouldn’t maintain it for longer than the controller’s capacitor charge holding capability of a few minuets, if that. And certainly not on the low brake signal wire.

Thats an interesting one.



Regards,
T.C.

Hi T.C. thanks for the welcome

Yes absolutely sure, ~40.1V. Meter is good and using pin 8 for ground.

If I disconnect the main battery and try to power up my 850C display as I normally would when switching the bike on, the display will briefly come on for a second before shutting off again completely. At this point, I get 0V on pin 4 until I connect the main battery again then it goes back up to about 40V.

Also, I run a peripheral light kit which plugs into the main loom (front light with integrated horn, rear light with brake light ) - if I try to use any of these with the main battery disconnected they will work for a split second before dying, and again at this point I get 0V on pin 4. If I connect main battery again they all work and I get about 40V on pin 4. Of note here - the brake light comes on briefly when I pull either brake lever, even with main battery disconnected and display switched off.

It's as if the main battery is charging the secondary battery in the display to about 40V with just enough residual capacity to last a second so.

My existing brake cut offs (3 pin sensors, magnetic type on original hydraulic brakes) work just fine with this signal voltage around 40V.

I'm happy with my plan to splice in 2 pin red Higo connectors in my existing main loom to replace the 3 pin yellow orange type, and happy with determining the correct pin out for sensor/ground. I'm just stumped why I'm getting 40V on the signal wire!

 

[TommyCat]

Thank you for double checking and providing more detail and clues!

I'm very familiar with the battery phenomenon as you described as I encountered it with my present 2018 model, 52v, GA ceil bottle battery.
I liken it to a BMS bleed thru of less than nominal voltage, when the switch is in the "off" position. And though somewhat annoying and perhaps a miniscule waste of power. I don't think the source of your excessive voltage on the brake signal wire.

What does seem a bit suspicious, is the interaction between your peripheral light kit and the braking actuation.
Perhaps a temporary disconnection of the lighting kit would verify this as the source of the voltage contamination.

But at the very least, I would encourage you to take a current reading that is needed when sinking this higher voltage signal to ground.
For reference my Magic Pie V5 controller puts out a 3.1 vdc signal that requires .27mA when shorted to ground to deactivate the motor.
It would be wise to verify if your new brake reed switches (?) can handle the current that you see now, before you install them.

I'm just stumped why I'm getting 40V on the signal wire!

It's got my hair up. If you would like to pursue this further, I would be very interested in helping.


For future reference.

 

[meddler]

TommyCat, thanks for the reply. I apologise though, I didn't read it before I embarked on the work.

The good news is, all appears ok. I spliced in the two pin red Higo connectors into the existing loom and get normal operation of the brake cut off when the brake lever is pressed. No other adverse symptoms noted.

 

[TommyCat]

Sounds great, thanks for the update! Hope it stays that way.


Cheers,
T.C.