Controller on/off switching question

The switching wire on my Lyen 18 FET controllers are fed from the battery voltage which varies from around 30V to 80V depending on how the bike is set up, but is there any way to switch the controller on and off using a lower switching voltage? I was thinking that using a Cree led light supply would be handy so 7.2V / 8.4V. Or possibly 12V?

yes you can.

you can use a 12V source for the circuit current but you will have to bypass the input and tie directly to the 12V rail inside the controller.

you can use a DC-DC converter but it is hard to find higher than 40V DC converters so using the internal voltage regulator would be easier. or you can carry a separate 12V battery capable of delivering the needed current at the 12V for the duration.

if you use a wide range of input voltages then you can change the input power resistor for each voltage. or have a switch selectable input power resistor for the different input voltages. use about 54mA for the idle circuit current. the risk is on the low input side where the power resistor is large and the input voltage low so that the input to the 12V regulator is too low so the mosfet drivers cannot properly turn on the mosfets.

the opposite is where the input power resistor is small and the input voltage is high so the input to the regulator is so high that it pulls the 12V rail way high and that damages the mosfet drivers too.

Sadly I'm a build circuits kind of guy not a design kind of guy. An add on kind of circuit would be the best option until (or if) the controller designs evolve to include this as an option. It looks like a separate supply will be the way for me to go, thanks.

if you use a battery for the 12V then you should be certain that the battery will still produce 12V+ when it reaches the LVC. you don't wanna have a battery that is 12V at full charge as the current source for the circuit current. it would draw down well below the minimum needed as it discharged and 15-18V on the 12V rail is not gonna damage anything.