LED Brake Light Wiring

[bullfrog]

I am looking for help in wiring 12 volt LED brake lights into the Magic Pie brake switch circuit.
I have a 36 volt 16ah battery, so have considered using a 36v to 12v voltage reducing converter to power the LED
brake lights. To switch on the brake lights I want to install a normally open relay with the control circuit connected
 in series with the hand brake switches. When the hand brakes are applied the control citcuit would open causing
the 12v contacts to close and power the brake lights.
To me this sounds OK, but I think I will need to use a 5 volt 5 pin mini relay and don't know if I need back EMF
protection for the speed controller. Has anyone had any experience with fitting 12 v LED brake lights with the
hand brake sitches?

[MonkeyMagic]

Hi Bullfrog

If you not running regen, and just want to use the brake levers solely for the rear LED brake light(going through your voltage regulator), then you will probably be fine without the relay altogether providing your LED brake light does not draw say, more than say 1amp .

If you are running regen, then you could use your voltage converter to provide a constant 12+ to the relay coil and the LED brake light. Then connect the brake lever switch side to the relay coil GND(-) connection. Since the Magic Pie uses GND as the brake signal, this will allow you to connect your brake relay as you intend providing you have a voltage converter from the same battery - or if using a different battery connect the GND wires together.

Although, why go to all that trouble.... If you are handy with electronics - I would inspect the LED brake light for how its connected inside. You may be able to simply change the input resistance to a higher value so it switch directly from the brake lever without any converter (with battery+ constantly connected to the LED brake light, then use the brake lever to switch GND)

Have a look inside the brake light, check how many LED's and how they are connected in circuit..... Hopefully its just using a single resistor for up to 15v use you can swap out

[Bikemad]

I recommend fitting a diode into the existing brake switch signal wire to prevent any chance of high voltage going back up the wire and possibly damaging the controller.

I have attached two circuit diagrams below showing alternative methods of running the 12V LED from the 36V battery.

Here are a couple of very useful LED related links:
LED series/parallel array wizard
Using the LM317T with LED lighting

I realize this post might be a little bit late, but hopefully it will still be of some use.

Alan