Introduction: Quick and Dirty - Use a 2-Wire Throttle on a 3-Wire Scooter Motor Controller

I recently embarked on a project to upgrade my 24v SLA powered Razor scooter to a 36v lithium ion battery.

Nothing too special, just a new controller, a new battery (that I salvaged out of a dead hoverboard) and that was about it. Or so I thought.

I didn't buy a new throttle for the new motor controller and when I realised My throttle only had 2 wires and the new controller had three, I was a bit stuck.

Here's how I fixed it (temporarily).

You're going to need 3 resistors, a 3-pin plug, along with a soldering iron and some insulation.

Step 1: Basic Circuit

The 3-wire throttles use a hall effect sensor in the grip. The motor controller sends it circa 5v and depending on how hard you have your throttle on, it sends back a voltage in the range of 0.85v to 4.0v.

0.85v - Zero throttle.

4.0v - Full throttle.

I think some motor controllers also check for the presence of this 0.85 volts on startup, so if it's not present, the controller won't work.

Anyway, the 2-wire throttle is just a simple switch. On or Off. To simulate the 3-wire circuit using a 2-wire throttle, I've used a simple voltage divider that allows my 2-wire throttle to at least be present on controller startup and when you turn the throttle on, sends the 4.0v signal to go! Fast.

My motor controller actually sends 4.65v (not 5v), so the resistance values i've used are based on that lower voltage.

This is the circuit I used is shown, with some resistor variants. I used 2% resistors to try and keep it fairly accurate - it's also what I had in the box.

Step 2: Wiring the Throttle

The image here shows how I wired-in the resistors at the 3-pin connector.

Using a bit of insulation to make sure none of the wires cross.

Works like a charm - either full-on or full-off. That can put a heavy strain on the motor, controller and battery, so please keep that in mind. When my new 3-wire throttle controller arrives, I'll swap it out, but at least I've been able to ride while I wait.