Paul & Sabrina's cheap DIY 144v motor controller

[charlie_fd]

well ...in here: http://www.microsemi.com/micnotes/APT0402.pdf there is a nice story about using ferrite in series with a smaller gate resistor to eliminate ringing ...

The enclosures look perfect! simple and effective, the DIY way!!!

[MazdaMatt]

jyanof, i believe that your wiring solved the problem because a charger has no output inductance... we're driving a motor here, not a battery pack, so we are guaranteed to have inductance. (and by guaranteed, i mean "i think"... care to speculate?)

[MPaulHolmes]

Originally Posted by Hondo

Hey Paul,

I think I can finally help on this project. I made this up quick in my company's metal shop. It is made from 14 guage sheet metal, but I could make it out of .080 aluminum just as easily, ( except we don't have any .080 in stock right now, it's on order and will be here in a week or so). Do you think it will work? We would just need to bolt the bottom onto the flanges and make some kind of end cap. If it will work, I can make some up and send them to you for free.

Hondo

Hondo! That looks perfect! The heat sink could get bolted right to that sucker! 14 gauge is nice and thick too! Very sturdy! I think aluminum might be better for cooling purposes, but I'm not sure. Is that a lot more expensive?

I could do some lexan end caps so we wouldn't have to worry about the bus bars touching anything naughty! How should I attach the end caps? I'm actually not very good at this sort of thing (don't tell anyone though).

Hondo! How did you bend the sheet metal all perfect like that???!!!

[MazdaMatt]

Wouldn't lexan end caps defeat the EMI purpose of the metal box?

[adamj12b]

He would have to if used some form of box and pan break to bend that up like that.

The only ways I can think of to secure the end plates to that would be to either ben some flanges on the ends(which could get difficult) or screw through the sides of the metal housing into the sides of the lexan.

The aluminum box would be nice if it is also used as a heatsink, but the steel could be get a nice paint job like the Zilla.

Also, you could bend the whole box including the ends and use some form of rubber grommets for isolation of the bus bars to the box.

-Adam

[jyanof]

Originally Posted by MazdaMatt

jyanof, i believe that your wiring solved the problem because a charger has no output inductance... we're driving a motor here, not a battery pack, so we are guaranteed to have inductance. (and by guaranteed, i mean "i think"... care to speculate?)

Actually, the charger has inductors in the output loop. In fact, what I have in there is several times more inductance than these large series motors (300uH vs ~80uH, i think?). It's primary purpose is to supply the current when the mosfets are off so that the battery sees a more constant current, but I think they also serve the purpose of slowing di/dt so that the current doesn't rise too high during a single pulse.

At first I thought the output inductance were the culprit of all the ringing too! I asked the evtech list about it and they pointed out the drain-source ringing is actually caused by the inductance in the input loop (caps/flyback diode/mosfet).

That's why Paul's layout is so great - the caps/flyback diodes/mosfets are are all very close to each other and reduce the intrinsic inductance of the pcb traces by making the paths short. At first I thought it was just nifty packaging to make the whole thing smaller, but I'd say the electrical reason is far more important.

[MPaulHolmes]

Lexan would defeat the purpose of EMI, if it weren't for the "Super Shield" Conductive Nickel coating in a can that a friend of mine is sending to me, that I can spray on the lexan. I still might need a walter for the bus bars... I mean grommits. How do you spell grommit? grombit? graumbet? graumitt.

[MazdaMatt]

I'm thinking grommets in sheet metal would be perfect. You could easily mill out a sheet metal endcap, Paul. Seems that cutting lexan, then spraying it with a rattlecan nickel plate, then putting in grommets will result in an ugly mess. On the other hand, I say screw EMI!

[Hondo]

Originally Posted by MPaulHolmes

Hondo! How did you bend the sheet metal all perfect like that???!!!

I have VERY strong fingers!


Ha Ha .... I have a break press that I built a few years ago for a different project.

I can make the end caps out of metal but I can't put a flange bend on all 4 sides, only 2 opposite sides. I could put flanges on the sides but then you wouldn't be able to attach it on the top and bottom. Let me play around with this and try to figure out the ideal end caps.

The aluminum isn't much more than steel, aluminum prices are down right now. Have you tried selling cans lately? They don't want to give you much for them.

Hondo

[NiHaoMike]

I don't think shielding the circuit is of much concern since it would already be shielded quite well once installed in the car.