Paul & Sabrina's cheap DIY 144v motor controller

[MPaulHolmes]

The website is being developed by my wife right now in Dreamweaver CS4 (oh ya!), so it's on my computer. I think the specifics of the controller, however, are going to be somewhere fancy and special on Ecomodder.

[GrahamMc]

Wow. Fancy AND special. You deserve it.

[SteveU]

Is there a summary page for your project? I skimmed the first 100+ posts and the last dozen or so, but a thousand posts! I dunno if I have time to read them all. I hate to say something that is already old news but based on what I've read:

This is very cool what you are doing but your electronics is not very impressive. I'm not surprised if you are burning up FETs etc. I'd like to know where you have gone from the original uC to single sided FET drive and DC motor circuit? If you are still doing that, here are my comments:
1. I’m not sure if your FETS have “body diodes” but if they don’t you should add external diodes across the FETs. This may also allow for some braking energy recovery, but ideally that would take a fully “synchronous buck regulator” type circuit. And it depends on the motor details too, ie is it a PM field or a coil. I don’t think many large motors use PM fields, yes/no? If the motor has a field coil, a separate field controller circuit would be the way to go.
2. A micro controller is an interesting way to make PWM pulses. The uC can do things a simple comparator cannot, but it will be very frequency limited and potentially hang up etc. Using a POT for a throttle is another dubious choice. I would probably just use switches like a cruise control, including the brake switch.
3. High voltage (600 to 1KV) FETs from STMicro etc are surprisingly inexpensive. I don't think IR makes anything in that range??? In any case, I think most commercial controllers use IGBTs below say 20KHz. If your PWM is above 50KHz then yes, you need FETs.
4. DC motors make the controller real simple but brushes etc are a maintenance issue. I expect most commercial EVs are actually multi phase motors similar to a 3-phase AC motor. Again, this would require a more sophisticated controller.
5. You talked a lot about pre-charge resistors but I don’t see them on the schematic? I would expect such a thing between the batteries and the capacitors, with a switch to bypass them once the system is up? You’re not talking about the FET gate network resistors, are you?

I’m already speculating and projecting too much. Please show us where you are now so I don’t look stupid making bad assumptions.

Cheers,
Steve

[MPaulHolmes]

Here's a super condensed answer to questions:

Yes, I'm a substitute teacher, so my electronics skills are not very impressive. They don't teach you about resistors in substitute teacher school, only how to kick naughty kids out of class. Everything I learned I picked up by asking questions on the EVTech list since December.

The nice thing is there are power electronics experts that are helping with the control section for free now, so it will be much more robust once it's done.

I think we are going to make a wiki on here. It will have the updated information.

The mosfet failure is pretty well understood, and the same problem can't happen now.

They have body diodes.

High voltage mosfets have a much higher RdsON then what I'm using. Find me a 1000v mosfet with an RdsON of 8 mOhms for 4 dollars, and I'll switch immediately.

DC series wound forklift motors are cheap and abundant. My goal is to make a freeway capable electric car cost $1200-1500 less than it would otherwise be by making the controller inexpensive.

It's switching at 15.5 KHz, but IGBTs are not a good idea below around 275-300 volts. They have a fixed voltage drop, which makes for greater heat loss below that range. Also, it's cheaper to use 10 $4 mosfets rather than 2 or 3 igbt modules that are several hundred dollars each new. A 1200v 600 amp IGBT module looks impressive, but it can't be run anywhere near it max ratings. They must be paralleled, which isn't the simplest thing to do in the world.

Most commercial EVs? You mean the $109,000 Tesla? The $20,000 25 mph Zenn? I'm talking about a home built $2000-4000 70 mph electric car with a 30-40 mile range. There are still basically no commercial EVs (sort of).

Good point about the u-controller being able to hang. I'm going to make use of the watchdog timer to help with that potential issue.

A PB-6 pot is the standard. You could go some sort of electronics route. I think the Zilla uses some sort of hall effect throttle, or at least has something as an option.

Don't worry, wiki coming soon.

[Intrigued]

It's okay, Paul. Come on down here to Missouri, and I'll pull that knife out of your back... :-)

Besides, we like watching paint dry around here. Does make the room smaller, though...

[brihoo2k]

For all that it worth Paul it seems to me it seems to me that you electronics knowledge is far superior to most of us diy'ers. Any and all of your efforts is much appreciated. And the fact that your making it open source gives us the freedom to change any part of it making it a controller that will evolve and get better as time goes on. I personally see it as a win win situation in the ev community.

[MPaulHolmes]

Hey Intrigued! That fork in your picture is confusing me again!

I'm FINALLY adding a watchdog timer, so that in the event of the controller hanging, the chip will just reset. You will go into high pedal lockout mode, but that just means that you would have to take your foot off the gas pedal for an instant and then drive on. I've never had the u-controller hang, so I assume it's pretty rare. I'll have to make sure the mosfet driver is disabled in the event of a u-controller reset.

[Intrigued]

Originally Posted by MPaulHolmes

Hey Intrigued! That fork in your picture is confusing me again!

I've had that picture for years: scanned it in from an old picture out of a magazine, I think... I can't decide if it is a tuning fork or an evil brainwave transmitter telling me to watch those TV shows with the really rich but kinda strange women who...

Wait a minute! I'm supposed to be working on a Final Project! Blast this second college-hood! It's so much tougher when you have 39-itis!

Bye for a day or so...

[MazdaMatt]

SteveU, your input is welcome, but you've got 900 more posts to read. There is no summary. All of the design criteria have been well thought out. They may not be like Tesla would do it... but we're talking about building a car for 105,000 dollars cheaper. That's like 9 houses in Detroit.

One of our criteria was modularity. If you don't like the drive electronics... make your own and use the logic portion of the design. If you don't like AT8's, make your own logic portion and use the power board. Don't like either, go make your own controller... we'll help

[GrahamMc]

Hey, where can I get one of those cheap and abundant forklift motors to make my car go 70 mph? I would like to eventually run at least 144 volts. I don't really know enough about DC motors to know what I could get cheaply and make work. DC, brushed, series wound, but voltages usually around 48v?