Introduction: 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
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. 

Step 2: Drill Your Metals and Isolation Strips

1/4" x 3/4" x 12" C110 copper bar.
Two 3/16" x 3/4" x 10" C110 copper bars.
3/4" x 1.5" x 8" aluminum bar.
3/8" x 8" x 11" aluminum plate.
3/16" x 3/4" x 8" steel bar.
Two 1/16" x 3/4" x 8" unclad FR4 used in making PCB.
1/16" x 6" x 8" unclad FR4 board.

5/16" drill bit (or 3/8" drill bit if you need slop)
1/8" drill bit.
3/16" drill bit. (Must allow a #6 screw to fit through)
Drill Press.

Do all the drilling!  It may help to take the big aluminum bar to a machine shop, since it's not easy drilling through 1.5" of aluminum accurately.   See all the pictures below for notes on hole locations and drill bit sizes.

Here's a video on how the power section pieces all get bolted together, without the electronics attached, just so you can see how it all fits:

Step 3: Order the Electronic Components

Order these components for the control board:

And order these components for the power section.  If you have already bought and drilled the metals on step 2, then don't reorder them.  They are listed here as well.

Step 4: Solder the Control Board

45 or 60 watt soldering iron.
0.032" diameter (or so) rosin core solder

This step takes about 3 or 4 hours.  It's very unforgiving.  If you have never soldered before, you should get help with this.  The ground plane doesn't have "thermals", so it takes some heat to melt the solder to it.  Check out this help file for soldering the control board.  See pages 2 through 19:,%202010.pdf

Watch for solder bridges (when big globs of solder bridge isolation gaps).  Also, you may want to socket the ATMega168.  You can program the ATMega168 in-system.  So, you can solder it in, and then program it if you want to.  Or you can get one preprogrammed.

This video walks you through soldering the control board from start to finish:

Step 5: Program the ATMega168 Microcontroller

Once the ATMega168 arrives with all the other stuff, you need to program it with the motor controller code.  Either make your own code, or use/modify the code below.  

You can make a very cheap ATMega168 programmer, or buy an AVRISP MK2:

And download the free AVR Studio development environment:

The hex file of the code is available here.  Use "coug-unified-16k.hex":

Here's the code:

The fuse bits are Extended High Low = F8 DC F7.  But if you are using Ponyprog, the fuse bits are 08 DC F7.

If you don't want to bother to program it yourself, then you can buy a preprogrammed one.

Step 6: Assemble the Power Section

There are quite a few parts to this process.  The short version is, you need to bolt together all of metal parts, and solder the 10 MOSFETs, 10 freewheel diodes, 16 large electrolytic capacitors, and 3 snubber capacitors to the power board.   Please see pictures below and the assembly help file, pages 20 through 43 for all the gory details.  You will need a 200 or 250w soldering gun:,%202010.pdf

Step 7: Mount the Control Section to the Power Section

See this video for directions on how to mount the control board to the power section.  It also shows how to solder the gate resistors and the ground wires, and how to mount an enclosure:

You can also check out pages 44-46 of the help file here:,%202010.pdf

Get Ready!!!  There's only one more step!

Step 8: Drive Away!!!

This is me driving with my car at 72v.  Notice that this one had all 3 copper bus bars coming out the same way.  That doesn't affect the functionality of the controller.

And here's a video of Joe in Phoenix using that same controller at 144v:
And here's Ben Nelson, the guy on here that made the plug-in hybrid, doing a gravel burnout with his.  He's always had a flair for the dramatic:

Now go out and build one!  Doing it yourself can save you over $1000.
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