Step 7: Controller

Picture of Controller
The controller is an important part of the electric car conversion.

The controller is a solid-state electronic box that controls the power (speed) between the batteries and the motor.

My controller is a Curtis 400 amp peak PWM controller designed for use with series-wound motors. It can run on 48-72 volts.

The higher amperage your controller is, the better your acceleration will be. The higher voltage, the better top speed and efficiency of the car.

Also, keep in mind that amperage is also what defines range in a battery. Capacity is marked in Amp Hours, but draining a battery at double the amps will give you LESS than half the run time! Having a controller running higher voltage will use LESS amps to do the same amount of work.

What's this mean? Buy the highest voltage controller you can afford! 48 volt controllers are cheap, as they are used in so many golf carts. 100V+ controllers get expensive real fast.

My 72V controller seemed to be a good compromise of cost and efficiency. I bought it slightly used on E-Bay for $300.

Follow the schematics available through the controller manufacturer to connect the batteries to the controller and motor with heavy gauge cabling, such as welding cable, with solid, heavy-duty lug terminals on the end.

The controller requires a 0-5Kohm potentiometer as a "throttle". This could be as simple as a $3 Radio Shack part, or as fancy as a purchased, specialty part such as a Curtis PB-6

I split the difference and installed a 0-5K pot inside a free-from-the-junkyard forklift throttle control.

Run the gas pedal cable to the potentiometer, so that when your foot is on the gas, it sends a variable signal to the controller.

Update! I later switched over to running an Open ReVolt motor controller. It's the same one you can find here on Instructables at http://www.instructables.com/id/Homemade-100-HP-Motor-Controller-for-an-Electric-C/
That controller is good for up to 144V and 500amps.
Ben19822 years ago
Ah, of course. I didn't even think about it being front wheel drive. Love it.
Ben19822 years ago
I like what you've done with this conversion. To reduce weight and save power, couldn't the transmission be eliminated if a driveshaft ran from the motor to the rear differential?
bennelson (author)  Ben19822 years ago
This is a front-wheel-drive car, so there is no rear differential. The differential is built into the transmission in the front, which is as good of a reason as any to keep the transmission.

On rear-wheel drive cars, there are setups where builders will put a high-power, high-torque motor onto a short driveshaft and straight to the rear differential. Makes for sun little dragsters!
would this controller work
for a go cart conversion? I cant afford any other controllers.
bennelson (author)  jimmerforpoy3 years ago
YES! I would LOVE to see that controller in a go cart!

That's the controller that's in my car right now.
How much did it cost you? Was it very hard? Thanks you are very helpful!
bennelson (author)  jimmerforpoy3 years ago
It's a bit of work to do it all yourself, but if you get the kit, the electronics are sort of "paint by number". Check out http://www.paulandsabrinasevstuff.com/

ll the costs, help, and info are right there.
jpwhite3 years ago
Im new to this and have a golf cart that I want to learn the basic workings of electric cars on. Im an engineer, but lack some of the electrical knowledge, but a quick learner....I would like to start with understanding the controller what it means to run at 144v or 72v, sizing the controller etc...I would be glad to chat outside of this forum to "get up to speed" Your videos are very informative...
boyaka5 years ago
you don't want to over volt the motor very bad
i didn't see you say anthing about that
bennelson (author)  boyaka5 years ago
 This motor has no problems at all running over-volted.
I have run it as high as 144V with no trouble at all.

Heat might be a problem with a smaller motor. This one is very beefy. Solid and well built. No trouble whatsoever.

In general though, if you are overvolting a motor - keep an eye on it and the temperature.
I am curious that you have not mentioned the average range of the car?
I have been considering either a car or motorcycle conversion.
Also have you considered converting your headlight to H.I.D. projectors? They pull less power and the other light bulbs to led?
How do you shift the 5 speed with no clutch; that wasn't mentioned?
Cars top speed on the 72v or the 144v your tried it at?
bennelson (author)  menahunie4 years ago
For shifting, you just shift - it's really not that complicated.
The top speed at 72V is 45mph and 75 mph at 144v.

I also have a motorcycle that I converted to electric.

HID headlights are expensive. The lights I have already work fine.
The tail and turn signal lights are LED.

The exact range of the car has been kinda hard to nail down. My original estimates were 30 miles at 144V, and 20 miles at 72V.

Real world driving has been a bit less than that. I am driving on USED batteries. The limiting factor is the worst battery in the string. I finally got a small battery monitor that shows the voltage of each battery individually. That will help me track down the worst battery, and trade it out for a better one.
i been hunting a diy site on how to build electic cars and i have seen that if you overvolt without advancing the motor it will start arcing to the brushes
i have heard storys of people destroying their motors