Paul & Sabrina's cheap DIY 144v motor controller

[MPaulHolmes]

That was a good idea about ramp up after thermal shutdown (or voltage). I added it to the software. Now, if things get too hot, it shuts down instantly until it cools a bit, and then gently ramps back to whatever the accelerator position is. Thanks for the sharp eyes, Darin! Too bad Curtis didn't have you beta test for them.

I don't have a voltage shutdown feature. I was thinking that because the allowed voltage would be between 12v and 156v (or so), voltage shutdown would have to be done on a case by case basis (depending on the voltage of a particular car), or it would have to be made programmable.

I'm getting close to attaching the capacitors and mosfets/diodes. The top (unattached) wire with the Anderson Connector is M-, the middle one is B-, and the bottom is B+.

The car's version will use copper bus bars instead of wire.

[MPaulHolmes]

The power board is nearing completion. I need to add the mosfets and diodes, but first I need to attach them to a heat sink, since there would be no room for screwing them in if I soldered them in first.

Then all that's left is the weenieboard, where the ATMega8 microcontroller will be. Those long red wires (which will be shortened later) will each be connected to it's own 30 ohm resistor which will be attached to the output of the gate driver (on the weenieboard).

One of the senior design engineers of brushless DC motors that writes on the EV Tech list suggested that I only need 2 of those mosfets to get 40 amps continuous out of this controller. So, I think we'll use 5! haha! A 72v 100 amp bike controller. haha! Well, the 13 gauge wire "bus bars" will probably be one of the weak links, so I'll still keep it under 50 amps, and just get practice with paralleling mosfets and making sure everything turns on at the same time.

EDIT: Safety resistors added from mosfets' gates to ground (22kOhm) just in case the mosfet driver breaks down. Without them, the mosfets' gate voltage would drop to around 5-7 volts if the driver quit working. This would mean that they would stay ON! So, power would start dumping from the battery pack until the mosfets burned themselves up. That's not good. This way, their voltage would settle at 0v after a very short time, shutting the current off from the battery pack, saving them to switch another day!

[MPaulHolmes]

We finished the low power half of the 72v motor controller. It is tested and working! The circuit was completely separated from the STK500 programmer, and is now on a breadboard (a practice circuit board that you can plug wires into). The wimpy PWM signal from the ATMega8 micro-controller was connected to the input of the big beefy IXDD414PI gate driver. That sucker can switch on and off lots of mosfets REALLY FAST! I measured the output of the gate driver, and it puts out a PWM signal where the low is 0 and the high is 12v now instead of 0 to 5v (which is what it was coming out of the micro-controller).

So, I guess you could say we now have version 2, a 12v 14amp motor controller, a pretty big jump from version 1 (the 5v 0.01amp motor controller). However, the 14amp could only be sustained for a very short period of time.

The next step is to hook up a single mosfet/diode to the power board, and maybe only run it with a single 12v battery. I'll hook it up to the bike to see if the wheel spins. Once a SINGLE mosfet/diode is included, we will officially have a 72v 20amp (continuous) motor controller!

There's a little problem with the oscilloscope. It only reads up to 20v, so we need to get a 10x voltage probe, so we could read up to 200v.

That big dang beefcake hunk of SOLID 1"x2"x8" aluminum will be the heat spreader. It's WAY overkill for the bike version of the controller, but whatever. It's all good. This is supposed to be practice for a car! The car version will use the same size aluminum heat spreader (maybe slightly longer than 8 inches though).

Going from 0 to full throttle takes a minimum of 5 seconds (even if you slammed your foot on the gas pedal), and if there was some sort of shutdown, it also takes 5 seconds to get back to full throttle (after it moves out of thermal shutdown) if you keep your foot all the way to the floor on the gas pedal.

In a couple days, I have to go back to teaching! Time is running out! Does anyone know where I can get cheap LEXAN (plexiglass) pieces? Maybe a few like 0.5"x9"x7" or something? I hear that makes a good box for the controller. Can you drill and tap plexiglass?

[bennelson]

Check your local phone listings for a place that works with plastics. You might be able to find somewhere that makes guards for machinery, or something similar.

Tell them what a fantastic project you are working on and they might just GIVE you a big pile of scrap pieces.

Plexiglass is pretty easy to work with. It's non-conductive and will show off your electronics. It is brittle, so be careful drilling holes near edges.

[Intrigued]

1/4 polycarbonate lexan sheet 11.7/8 x 48 - eBay (item 130157612514 end time Jan-18-09 16:56:58 PST)

If you can't find anything locally, I bought my 1/16 stuff for the aero on the Intrigue from this seller. Go with Lexan if you can at all, since it is less fragile than plexiglass. I cut the 1/16 with a pair of Wiss aviation yellow-handled snips, but 1/4 would have to be jigsaw/blade cut. Drilling the holes for mounting was also less messy than drilling the plexi I used for the windows in a certain car so many moons ago...

I haven't tried tapping either, but if you can't, maybe something like a sheetrock corner around the outside...that can also be used to bolt it down???

[Christ]

Easiest way I've ever found to drill/tap plexi (not lexan) is with a heating element.... put the drill bit into a soldering iron, which requires tapping the bit's backside, or using a torch to heat the bit.

Same with tapping - put a screw w/ the same threads onto a heating element, and melt it into the plexi, then back it out when it's set (not squishy). I used to build display shelves as a side job at Sears when it was slow in the shop.

Regardless, Lexan is SOOOO MUCH easier to work with, if not a little expensive. You can usually get scrap from lots of hobby places and craft shops, or look for someone tossing a display case, as many of them aren't big on doing glass cases anymore.

[MetroMPG]

Ivan got some big scraps of lexan from a dumpster at the factory where he used to work - used for machinery guards, as Ben mentioned.

[Coyote X]

The hardware store close to me that is locally owned and not a corporate one gives me their scrap lexan that is left over when they cut out windows or whatever for people. A lot of it is very small but there are a few good sized pieces sometimes. I always walk back and check the scrap barrel when I go there in case there is something good in it.

It can't hurt to go find your local mom and pop hardware store and ask. Usually they just throw it away so you can get it free or really cheap.

[MPaulHolmes]

I'll write more on the next message, since there are 3 more pictures, and I want to put them on too.

[MPaulHolmes]

The controller is mostly assembled. I decided to put 5 mosfets and 5 diodes in it, so it should now be a 84v (well, anything safely under 100v) 100amp controller if it wasn't for the crappy bus bars (ghetto 13 gauge wires). The weak link is definitely not the mosfets I think.

I was able to drill the aluminum using the trick an ecomodder told me about dropping alcohol down the holes as you drill. It's almost impossible (for me) otherwise.

The white stuff on the aluminum heat spreader was thermal grease. You are supposed to put as little on it as possible. Too much is worse than none. It fills in the microscopic holes.

I didn't have a good way to attach the stupid current sensor, and I cooked it (soldered too long!), so that's like $5 down the toilet. Fortunately, I won't need current limiting in this version, because there are plenty of mosfets and diodes to handle the current that the bike motor uses. I'll get a different type (easier to use) of current sensor for the car's version.

A better way to remove heat from the mosfets and diodes is to directly attach them to the aluminum heat spreader (with no mica backing), and then put some sort of layer of mica or something between the heat spreader and the outside heat sink. I didn't have a big piece of mica so I did it this way, which is OK in relatively low power applications like a bike controller.

I need to add a few more things to the micro-controller's program, like high-pedal lockout.

I need to figure out how to do the 2 wire throttle instead of the 3 wire version. I need to add an on/off switch, then try it on the bike, but it's really exposed to the elements, so maybe I should put it in a box first. I don't know.

I'm super tired and my fingers don't want to move to type. I shouldn't have worked in the garage with the door open for like 8 hours. I didn't notice the cold until I was done. Now I think I'll get pneumonia.

Man, soldering those mosfets and diodes onto that 5 oz. copper PCB was truly horrible. It was impossible with a normal soldering iron, so I had to use the soldering gun, which people say is bad to do. Oh no, it's too hot! It's the only way I could melt the solder though. It was so annoying soldering, that I really want to make a mean reference to a famous talk show host, but my wife won't let me.

I think the car's version will actually be easier, because the larger 200v mosfets have wider legs. Those stupid ones I am using were too close together. Oh, that makes me real angry way down deep inside.