'78 Spitfire Electric Conversion: Pot Box

Electric vehicles are throttled via the motor controller, and to tell the motor controller how much power to deliver you use a Pot (Potentiometer) Box. It is a variable resistor designed to connect to the existing throttle cable from the accelerator pedal. For my car, I bought the PB-6 Pot Box. Its resistor ranges from 0 to 5k Ohms (standard among controllers), and it includes a micro switch for additional control/protection.

Just a note for you EV converters out there - the price on the Pot Box (and any EV component for that matter) varies widely among vendors. Definitely shop around.

Here's where I'm going to put it. There is a sharp turn for the accelerator cable which I don't like, but it is in a very clean place and the cable itself will be very short.

There was a bracket there for a hose going through the firewall that I removed. I think the hose was for the heating / ventilation system - I'll have to work on that later. The screw on the right held the bracket in place and a support for cabling underneath.

There is enough clearance underneath the Pot Box for the right screw to not be a problem so I'm leaving it in. Time to drill a few holes.

I also need to cut the accelerator cable back. The cable actually consists of several pieces - an inner steel cable that slides back and forth, a smooth plastic sheathing enclosing the cable, a segmented metal sheathing enclosing the plastic, and then a shiny blue sheathing making it all look pretty. The segmented metal was pretty tough, but my Dremel easily took care of it.

I added two eye hooks purchased from Home Depot - one to help hold the accelerator cable in place and the other to hold a backup spring for the Pot Box. The Pot Box is spring loaded, but just in case that spring fails I've added an additional backup. It is required in some countries - I don't know if it is in the U.S. but seems to be a good precaution nonetheless.

Looks pretty darn good. I also made a few adjustments to the other end of the cable. The floor pedal had nothing holding it up other than the cable, and I didn't want the weight of the pedal to drag on the Pot Box. Another spring should take care of that.

This picture actually has the pedal slightly depressed. You can see the accelerator cable connected to the pedal itself - pretty freaking simple and cool. For those of you installing a Pot Box and having trouble getting full throttle - it wasn't perfect on my first shot. I had to adjust the throw length of the pedal and my attachment of the cable to the Pot Box arm to get a full swing.

The final product with no power.