Shunt booster switch (more amps at button press)

[jimmyhackers]

yet another weird one here....

name kinda rounds up what i want.....i just need to know the "how to"

basically in my controller....and most as i assume, there's a shunt wire (3 in my case) that has a set resistance and from this it decides how many amps its going to send to my motor.

one of the wires seems to be nicked in several places. i guess this was a "factory" way of calibrating the controllers amp output.

googling ive seen many people get more amps/torque by simply beefing up these wire shunts with solder or thicker wire to give them more amperage.

this all seems to work soundly but its very..... uneasily reversible.

hence me wanting to find a way to change the controller output amperage at the flick of a switch.

so going back to that nicked shunt wire, if i solder on a wire to either side of the nicks and put a switch in parrallel......
will it work?

or is it not that simple?



theres the guts.

thanks in advance for the help
jim

 

[Drunkskunk]

Good thinking, but bad idea. Those "wires" are actually resistors. if you add a switch across those resistors, well, electricity takes the path of least resistance. It would ignore the resistors and flow across the switch, bypassing the current sensor part of the circuit. The poor switch will see full unregulated current and melt the first time you go full throttle. (battery's voltage ÷ the resistance of the motor windings, so probably 300+ amps)

But there is another way!

Those shunt resistors are really just a sensor for the controller to read the current. On that board there is a trace that leads back to the chip; that black postage stamp thing. Along that trace should be a tiny surface mount resistor tied to either ground, or the 5 volt source. the combination of the shunt and the surface mount resistor makes a voltage divider and gives the chip a stable voltage to read. ... more information that you need probably, but that voltage is how it decides how much current is going through, and when the voltage it senses along that trace changes past a certain point, the chip over rides the throttle to limit the current.

Putting a switch and another resistor across that surface mount resistor will do what you want. Or do it with a pot and a switch, so you can dial in exactly how much boost you want. With a couple resistors and a 3 position switch from an Infineon controller, you could even make your own version of the 3 position switch.

I think it was Ypedal who wrote a thread on doing it to Infineons. That used to be a sticky, I think.

 

[Gregory]

There is some ideas in the Post your circuit and schematics thread that may help.

 

[d8veh]

You have to be careful about adding any external wire to the shunt. I tried adding a loop to change the reistance, but the controller wouldn't work like that. It must have been generating interference or something like that. I tried coiling it in every way to counter that, but still it did not work.