Motor Controller- roll your own

[Powersupplyguy]

Greetings,

I bought a 4hp 48v motor for my grandson's go kart last year. I think I posted a pic of it or at least a link to it. Anyway, he is only 2 and so his power-wheel is good for now. I have a few years to get this project on the road.

I am a power conversion engineer and am very familiar with with designing AC and DC motion controllers. Thus the handle Powersupplyguy.

I am presently inviolved with designing battery chargers for lithium-Ion battery packs for starting gas turbines for jet aircraft. Lithium-Ion will probably be the future for Go-Karting.

If anyone is interested in putting together a chopper to control their motors then I would be glad to offer my design services. I can throw a schematic together, come up with a bill of material, and even and lay out a pc board no problem. Controller will have overvoltage, overcurrent, and temperature protection and will can be made to run off of anything from 12v to 60v. A 200amp controller should be doable for less than $100 bucks. A 400amp controller for more. Money is in the mosfets, and not the controller.

I would be very happy to do what I have outlined. I would like two or three others to gather parts and do the assembly, soldering and so forth. I don't want to do all the work and have the group watch. I will be pressed for time in a couple of months so I can't do it alone. Building an off-grid home this summer.

When this project is done I'm sure this controller design would be production ready. I don't really care to get involved with production, but if somebody else wants to run with it I wouldn't mind.

If any interest then email me at powersupplyguy@netzero.net or look for me on Facebook - Bob LaFrank. Not my real name, but it works.

 

[Doc Sprocket]

Hey- thanks for the offer! I'm not an electric guy, but I'm sure someone will want to take advantage of this!

 

[Powersupplyguy]

Thanks ToyStory. I can actually get it done for quite a bit less than 100 bucks. Fet prices at rock bottom these days.

These 4hp electric motors so small you could mount one on the front forks. Could do a 2wd electric bike that could compete with a rokon for short money.

 

[GrownUpKid]

The idea excites me. I am an electrician & often work on large projects. Side by side UTV's are common, but once there was an EZGO golf cart. The kind with the large utility flat bed. I loved that goofy vehicle so much that a co-worker & I actually drove it 3 miles just to go to a Wendy's drive through.

Anyway, I spent a lot of time trying to figure out how to make it go faster. I have limited electronics knowledge & eventually came to the sad conclusion that the only way to make it faster was an expensive speed controller.

I found myself wishing I could build one, but couldn't possibly design one. I would love a simple, dumbed down description of what a mosfet is. I would also love to see a schematic.

Your grandson will appreciate having a fun grandpa.

 

[Powersupplyguy]

DC motors go faster with more voltage. It's almost proportional. Can't wait to see my grandson's face after we swap out his 6v battery for a 12v unit. He is still a little small for that.

Mosfet is just an electrically controlled switch. (Like a motor contactor where a small signal is applied to control gobs of current.) Takes a little bit of charge to turn it on and off. It is a very good switch so that the resistance is very low when on and very high when off.

Motor controller is basically a buck converter type of power supply. (Google buck converter) By controlling the duty cycle of the mosfet you control the motor voltage and thus speed. Vout= Vin*D. So on a 24v battery, if the switch is on for 100microseconds and the total period is 200microseconds (5kHz) you will have effectively applied 12v to the motor Motor windings will sing at the carrier frequency - in this case 5kHz.

Since this is not a power supply where we need to filter out ripple voltage you can eliminate the capacitors. And since the motor armature is a fairly large inductor all by itself, you can eliminate the filter inductor as well. You're left with a battery, a few mosfets, and a controller. Put the fets on a heatsink and you got yourself a nice package.

Use Google to find dc motor controller schematic or Buck converter. You can look up data sheets on digikey.com.

PSG

 

[scoten7]

I don't do a lot of high power projects but I would be happy to help. I mostly work in low power and robot building.