Brake sensor wiring - again.

[ccihon]

I have seen several threads her and elsewhere regarding adapting 2-pin brake sensors to 3-pin Bafang (BBSHD) connectors. I still am unclear about my specific situation. My question is really to ask owners of Tektro HD-E350 brakes what the actual switch function of the lever sensor is - normally open or normally closed? The Tektro's I am adapting currently have "SM-2Y" connectors on them. I don't have the set in hand yet.

I need to change the connector on a set of HD-E350 hydraulic brakes to adapt the exist SM-2Y two-pin connector to a bafang mid-drive that is cabled for three-pin brake sensors. I know that the existing bafang levers short two of the pins with the brakes applied. Do the Tektro levers short the two connectors, and are normally "open" when the brake is in the un-engaged state? I know what two wires need to be shorted to lock out the brakes on the bafang. My concern is that the SM-2Y connector on the Tektro levers is "normally closed" rather than "normally open" if that makes sense.

 

[E-HP]

Measure the resistance and you’ll know. You should have zero ohms when the lever is actuated.
Normally open vs closed can be confusing with brake cutoffs. Relative to the switch itself, many/most cutoff switches are normally closed and in the”normal” position when the lever is engaged and when the brake lever isn’t engaged, they are actuated/open.

 

[AGS]

Don’t plug a 2 pin red brake connector into a 3 pin yellow Bafang socket or you will blow the 5v regulator in the controller.

Here is the wiring diagram for a BBSHD.

Shorting pins 6 and 8 in the brake connector will blow the controller.

 

[ccihon]

Don’t plug a 2 pin red brake connector into a 3 pin yellow Bafang socket or you will blow the 5v regulator in the controller.

Here is the wiring diagram for a BBSHD.

Shorting pins 6 and 8 in the brake connector will blow the controller.

View attachment 355360

The levers supplies with my bbshd, which I will not be using, actually short the other two pins, 4 and 8, when brakes pulled. The red wire connected to 6 appears unused.

 

[TommyCat]

If you carefully reread AGS‘s post, you’ll see that you’re both on the same page.
With the goal to make sure you don’t get the 5vdc power supplied to the brake cable inadvertently mixed up with the brake signal and/or ground when making connections to your new brake switch.

Please keep in mind the mirroring of pin labels when changing between male and female sides… (just a general precautionary note)


Regards,
T.C.

 

[d8veh]

Brake switches are very simple. When the brake signal wire is high (5v), the motor gives power. When it's low (0v) power is cut.

The signal wire is held up by a resistor, so it rests at 5v. When you operate the brake, it has to be shorted to ground to cut the power.

 

[ccihon]

For those stumbling on this in future - the answer is the Tektros have two wires, regardless of the way the plug is configured - the two wires are generally blue and black, and are open until the brakes are engaged (normally open switch). For the Bafang three pin connector, you want to connect the blue to signal, and black to ground pins 4 and 8 from the diagram above. - Harness colors may vary.