Picture of Homemade 100 HP Motor Controller for an Electric Car
This instructable explains how to build your own 100 HP (peak) motor controller for use in an electric car or motorcycle conversion.  It can take any voltage up to 144v, and the peak current is 500 amps.  The cost of the components is a few hundred dollars, which means you can save over $1000 by putting one together yourself.   At 144v, you can expect a top speed of around 75 MPH in a car. 
Check out  http://ecomodder.com/forum/open-revolt-open-source-dc-motor-controller.html
if you want to read about the whole story!

Experience in soldering is important.  If you want to really keep costs down, a mill is helpful, but that work can be outsourced to a local metal shop.

Step 1: Get/Make a power board and control board.

You are going to need a control board and etched power board.  The power board needs to be at least 3 ounce copper.   Ebay is a good place to look for heavy cheap copper clad PCB.  For example:

You could print the picture from this link and somehow transfer it onto a piece of heavy blank PCB, and etch it with a dremel if you have a ver y steady hand.  The dimensions are 8"x6".  This link also has the G-code that you can use to etch with a CNC mill or you could give the G-code to a machine shop.

Picture 2 and 3 below is an example of an early power board I made with a Dremel.

You can get a control board from me or you can make the control board in your favorite PCB layout software using the schematic here::
And here are some pictures of the PCB layers:

A predone control board is Picture 1.

Pictures 7 and 8 are the power board top and bottom.  The 8 solder spots are just where vias were added.

Once you have the 2 boards, you can go to step 2. 
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MichaelL186 days ago

There are several links that are broken in the instructable above. Files may last forever on the internet, but they don't stay in the same location ;)

You can download the various files for several versions of the controller here


And if you'd like to take a look at the rest of the wiki as well ...



TEXACA13 days ago
lkeerthan1 month ago

Hi! I'm a part of FS hybrid team, your instructable/blog is a invaluable source for amature and students like me

I have a query, in your motor controller how did you isolate the 12V and the high voltage side?

We have a kelly contoller (which has the problem having common ground), any solution / way to isolate the grounds other than an 12V isolated DC-DC converter run from the low volatge side?

Awaiting your response

Thank you in advance

afbcom4 years ago

Just a thought, you could eliminate a lot of voltage spike issues by mounting the controller as close to the motor as possible. Any time the length of the wire between the motor controller exceeds the diameter of the wire, the collapse current becomes significant. Since Vpeak = di/dt, and you have a peak current of ~500 amps, if your switching time is <1ms which I'm guessing it is, this will result in a spike of 500 000 volts! These voltage spikes can damage the control circuitry. This is assuming that you are having voltage spike issues to begin with. Regardless it is typically a good idea to mount the power control board as close as possible to the motor.

MPaulHolmes (author)  afbcom4 years ago
I've done some voltage spike tests, and at 500amp, the spikes are about 20 or 25v, so it's not too bad. I'm using 200v components, so at 144v, I'm still a fair distance away from danger. The nice thing is, under heavy current, the battery pack voltage sags, so the net result is that the voltage spikes are about 20 or 25v above like 135v in the worst case.
Hello Paul, I was looking to adding 6 more batteries to my EV. So do i just need to change the speed controler & charger ?? And by the way would you sell a controler ??

To clarify - 500KV spikes are real but only open loop, where the input impedance is very high. You are are clamping the spikes to 25V with your protection circuit.


Not that I doubt you, but where are you measuring the spikes. The ones that I am referring to is the reverse against the driving fets from the motor and supply cables to it. If you're getting results around 25 volts then you have done a damm good engineering job and kudos to you sir.


ps awesome response time
MPaulHolmes (author)  afbcom4 years ago
Hi afbcom! I measured the voltage spikes from drain to source of the mosfets. Every time the mosfet turns off, the voltage from drain to source goes from nearly zero to full pack voltage, and it wants to keep going past pack voltage. I also use some polypropylene metal film capacitors to help snub the spikes. My friend in Phoenix has a video of the spikes on his oscilloscope. I'll find it. When I tested it in my car, I just used a peak voltage detector (like a crab trap. but instead of crabs, it traps electrons. haha):
I can't see exactly where you're connecting your measurement probe, but it is necessary to connect both the probe and the ground as closely as possible to the place you're actually measuring, because inductance is playing a huge part in what you're dealing with, and even an inch of wire can have an effect. The voltage spikes are a danger inside the MOSFETs so thats where the probe should be.

Another issue is that the voltage spikes are a result of firing into a reactive load, which is more like a motor prevented from spinning. A freewheeling motor (which I heard) will not cause inductive kickback as much as if you lock the parking brake and do it, you should try that.

A wise teacher of mine who makes giant stepper-motor controllers (and Aerco pre-amps) says that the key to protecting your fets is a combination of small and large diodes (they have different properties) and resistor-capacitor snubbers and most importantly, MOV (Metal Oxide Varistors) which are your first line of defense.

But i definitely know that the spikes are worst when the motor is stalled.
In the EV community, we use freewheeling diodes to take care of all the inductive kickback from the motor. Ususally rated at LEAST the same as the switching device. My IGBT controller(inspired by Paul's MOSFET controller) will be built for 1200 amps, with 1200 amps of freewheeling diodes, AND be run at 750 amps. Should last a while XD

It's my senior project for college. Great excuse to rip around campus with a less than legal electric car!
MPaulHolmes (author)  jerkey4 years ago
I didn't make that video. It was actually my beta tester. I've done testing with a locked rotor, and the spikes were around 25v, at least with my peak detector, which was a diode and capacitor. electrons could get in and not back out. That was the crab trap I was referring to above. A locked rotor has almost no resistance, so the current is huge, and the voltage spike is di/dt*L_stray, so a larger change in current definitely gives a larger voltage spike. The nice thing is, there may be optimal ways of doing things, but his controller has run for over a year and a half in sometimes 110 degree weather and it's still going strong, and that was not withstanding my crappy assembly process, since it was the first or 2nd one I put together.
This just goes to that what you read in a textbook doesn't necessarily apply to the real world! Nice scope. There are commercial products that aren't as well designed as yours... friggin cool!
You could also include a TVS diode to protect against the spikes if they are too large
MPaulHolmes (author)  killersquirel114 years ago
Hi Killersquirel11! Great minds think alike! haha. I'm using the P6KE20A-T transient voltage suppressor. Nothing goes over 20v from gate to source, and gate to source is rated for up to 30v, so it's kept safe.
"Any time the length of the wire between the motor controller exceeds the diameter of the wire"

I'm pretty sure every wire I've ever used was longer than it's diameter.
megapix afbcom4 years ago
Just a little correction on the math for the voltage spike. The voltage is V = L * di/dt where L is the inductance of the wire. For a couple of feet of wire this could be around 1uH (microHenry = 10e-6). So for a 1mSec switching time you would have 0.5V, and for a 1uSec switching time you would have a 500V spike. So it is worth being careful about, but not as severe as your calculation.
afbcom megapix4 years ago
thankyou for the correction. Now that I think about it, 500kvolt is a bit large sounding eh?
en2oh5 months ago

Great project. Thanks for sharing.

Anyone know of similar specs controller for 144v BLDC motor?


jolaniyan6 months ago

Hi Paul! Thanks for the great instructable. Firstly, many of the links
are dead so kindly update them. Secondly, i want to do a variant of this
controller that has 24V - 48V, and a max current of 150A (for a 2.2KW
motor). What modifications do i need to make to your controller and/or
power boards to reduce cost? (I know your set up will work but i think its an over-kill for a 2.2kW motor, what do you think?) I intend to make my first instructable out
of this and provide full credits to you. Any help will be thoroughly

pteurlings7 months ago

Would it be possible to create a controller that can handle 24V at 1000A?

Quantum11110 months ago
mihnea19703 years ago
I can not download the schematics for the control board. Please help.
kairala2 years ago
i am from india, want to build electric car as well as a bike.
for electric bike - requires a 36v controller circuit diagram with components specified.
for electric car- i was not able to download circuit diagram of 144v-500amps controller version.
so i hereby request to help me for the above project.
email id- kairala27@rediffmail.com
kairala2 years ago
hi, i am from india. want to build electric car as well as a bike.
for electric bike i require 36v controller circuit diagram with components specification.
for electric car i was not able to download the circuit diagram of 144v-500amp version.
so i request to help me for the above.
thanking you.
anriocarver2 years ago
What is the price for one 144Volt 500Amp already built. Ready to use.
My email address is anriocarver@yahoo.com
I leave in Mauritius.

Does this work for all ev conversions under 144 volts?
MPaulHolmes (author)  jimmerforpoy3 years ago
As a follow-up, Is it possible to "scale down" the design if I'm never getting near the 144V/500A power requirements? Do I just use fewer mosfets and caps?
Nav3 years ago
Okay so I am a novice in all things electric car, but I'm wondering if throwing 4 of these controllers into a car with 4 forklift motors somehow connected to the axle would result in a 400HP car? I'm sure it doesn't work like that but could someone please explain the pros/cons of this to me? Thanks and awesome instructable!
MPaulHolmes (author)  Nav3 years ago
Yes you could.
DieCastoms3 years ago
Ok, so.. I have what used to be a small-sized 3-wheeled 24-volt "Mobility Scooter". I am building a large RC vehicle out of it.

I need a motor controller for 24 volts that will run the thing either from a wired throttle or eventually a servo output from an RC receiver OR an actual servo mechanically coupled to a pot that is wired to the controller (This should give perfectly isolated power from the vehicle's 24 volt system and the RC's 6 volt system, yes?)

I WANT to have the option to run it via RC or to be able to plug in a wired controller because the vehicle will be large enough to sit on when complete.

Can someone please suggest a source for such a controller? I DO NOT have the original controller from the Mobility Scooter, or I would gladly just use it. I know I could buy another controller for the chair or a similar model, but I would like to see what else gets suggested, first.

Thank You!

abdellah3093 years ago
good job Paul, can you post the schemetic of Mosfet stage.
I'm working on electic car project in Algeria.
Many thanks,
epuneet3 years ago
Is this circuit work for lower power ratings i.e. for 20 Hp motor
bertzie3 years ago
What kind of modifications would need to be done to make it take 170v 2000amp?
IT BITz4 years ago
I have a 36v forklift motor, I was wondering if this would suffice for a electric car?
MPaulHolmes (author)  Donotmatthews4 years ago
Probably! If it weighs at least 60 pounds, and has a 1 hour rating on the name plate of at least 100 amps it should work fine. The voltage rating is almost meaningless.
How many quadrants is this thing ?

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