Paul & Sabrina's cheap DIY 144v motor controller

[Christ]

<(----- Wonders about using 30000 or so 1.2v NiMH "green" batteries... they're like 300mAH a piece LOL. That would be 3 strings of 1200V or 1 string of 3600V. Think that would work?

Check my recycling thread later tonite for a way to get freebie NiMH batteries! LOL.

Paul - What changes did you make in the rewrite? That makes it controller V2.0 right? Was it really a rewrite or just a revision?

[Intrigued]

I'll have to check into that recycling stuff! I've thought of the D Cells or the threaded ones, but couldn't afford such a thing...

I bet you won't need 1200 volts, though, unless that is what Wayland is using: (I've been surfing...) Oregon Field Guide &mdash; Electric Drag Racing · Oregon Public Broadcasting

Talk about cool! I'd LOVE to be able to build something like that on my budget!!!

[MPaulHolmes]

It was a nearly complete re-organization of the code, so I would call it a major revision. Also, the philosophy of the program changed. Now, the slow changing stuff (temperature of aluminum heat spreader and throttle position) are checked only like 100 times a second, whereas the current monitoring is happening about 2,000,000 times a second. I am determined not to allow a single current spike to sneak through!

I moved the oscilloscope to the garage, and monitored M- relative to B-. It was pretty interesting! You could see the normal PWM wave, but there was a small amount of "ringing" on the peak (small damped waves on the high times). It's hard to explain. I'll get pictures of it later. It's going to be fun. This will help me with paralleling them too.

The car's version will need 5 to run the car at 250amp max. Maybe I should do a small version like that before the full 400 or 500 amp version. It's not hard to add more mosfets later! At 144v, I don't think it would be hard to stay under 200amp anyway. I almost never get to 200amp at 72v! 160v is usually my max when I'm careful. Heck, that would only be maybe 3 or 4 mosfets! That would be way cheaper! 144v 200amp controller would cost more like $200 and something!

[bennelson]

I think this is the first time I have heard of a real number for how many amps the project was shooting for.

If the controller would do 500 amps and 144 volts, that makes 72KW! Which equals 96 HP! (and it's all torque!!!)

Whose cheap-EV are we going to hot-rod first!!?!!? (mine, mine, -- ooo, mine!)

[Christ]

Ok, so since we touched the subject of using voltage vs. current to propel the vehicle, I wonder if I have this correct -

If there is an increase in the voltage, there can be a subsequent decrease in the current to create the same power, however the RPM is increased accordingly.

So if at 120v 20A the motor spins 500RPM and creates 50lbft TQ, and I switch to 240V 10A, It will create the same 50lbft, but at 1000RPM?

So if I have that correct, that leads me into this: What happens when you've done this to the extent that you'd be making minimal torque at 6000RPM, but you gear down and use reduction to recreate that torque to the wheels?

If you have a motor that runs on 120VDC 20A and makes 50LBFT TQ @ 6kRPM,
Then you use 240V 10A, it should make 25LBFT TQ @ 6kRPM, right? So what if I gear it down 2:1, I get that 50LBFT back at the output, which is now traveling 3kRPM...

3kRPM on a 155/80R13 (71.5" Dia, 886 R/M)

3,000/866 = 3.46 Miles per minute! (208MPH, approx)

We know this isn't possible w/ the weight vs the 50lbft of TQ, so we gear it down even more, to say: 3.3:1, which gives us an output of 1818.1818 RPM, at 165lbft TQ to the wheels.

Same tire, 1818.1818 -

1818.1818/886 = 2.05 miles per minute (approx 120 MPH). With an output of 165lbft of torque, this seems quite possible!

Do I have this right? Or am I fudging my numbers somewhere? B/c honestly, that seems WAY too easy.

[MPaulHolmes]

I don't have 12 12v batteries. I only have 6. Boohoo! I think you do don't you, Ben? Can your motor handle 144v? Do the brushes need to be advanced at all? I know Darin said his was good to 120v without messing with anything (according to Jim Husted). Your motor is beefy like his.

Assuming the design continues as it is, it will be able to be run at any voltage from 12v to maybe 156v, but I don't think I'll be able to test it much above 96v without burning up my hub motor. I also could test it in the car at 72v, with it jacked up so that I could hook up the oscilloscope. What I need is a laptop and portable oscilloscope. Once I knew it worked well at 72v, maybe that would be enough information to ship it over to you to try it at higher voltages? We'd have to make sure it was as bug free as possible, because it would be tougher to fix little programming issues or whatever because of the distance. We should definitely be sure that the current limit is set to something safely under what the mosfets can handle in the testing phase.

[MazdaMatt]

Question regarding mosfets... (sorry, i'm a computer engineer, that's like electrical without any analog electronics but more programming and logic...) Their output current is relative to the input voltage, nay? Why PWM in a high voltage at a variable duty instead of provide a variable voltage? Is it something to do with the efficiency of the mosfets? Aren't there switching losses or something in PWMing a mosfet?

[dentprone]

Paul,

Have you found any lexan yet? TangoCharlie said you may need some for the enclosure. Let me know what your specs are and I'll try to dig up a sheet to send you.

-Charles

[MPaulHolmes]

Originally Posted by MazdaMatt

Question regarding mosfets... (sorry, i'm a computer engineer, that's like electrical without any analog electronics but more programming and logic...) Their output current is relative to the input voltage, nay? Why PWM in a high voltage at a variable duty instead of provide a variable voltage? Is it something to do with the efficiency of the mosfets? Aren't there switching losses or something in PWMing a mosfet?

Great question! There's 3 pins. Gate, Source, and Drain. Source is connected to ground. When gate is near 0 volts (compared to source, which is ground), the resistance from Drain to Source is around 1 million ohms or something ridiculously big, so basically no current flows from Drain to Source. Once gate gets over like 4 volts, the resistance from Drain to source suddenly plummets to like 0.004 Ohms. That's when huge current (they can handle like 100 amps or even more!) goes from drain to source.

So, there is almost no heat loss in the mosfet when the gate is 0v (no current flowing from drain to source), and almost no heat loss when the gate is over like 4 volts, but when the mosfet is transitioning from off to on, or on to off, there is a huge heat loss. So, you want the switch to happen as fast as possible, to minimize "switching losses".

Usually, to turn on the mosfet, people set the gate to at least 12v (but less than like 18v), because the gate behaves like a small capacitor. You want to fill it up as fast as possible so the voltage from gate to source gets above the turn on point as fast as possible.

So, a mosfet is an on/off switch that HATES to be in the transition state between off and on.

[MPaulHolmes]

Originally Posted by dentprone

Paul,

Have you found any lexan yet? TangoCharlie said you may need some for the enclosure. Let me know what your specs are and I'll try to dig up a sheet to send you.

-Charles

I haven't found any yet. Ebay had some, but it was pretty expensive and I haven't ordered it. That would be really really helpful!

For the car I'm estimating:

12"x8"x0.25" (bottom of controller)
12"x5"x0.25" (top. It will need room for heatsink, but I don't have that yet.)
12"x4"x0.25" (side)
12"x4"x0.25" (side)
8"x4"x0.5" (back)
8"x4"x0.5" (front)

I can cut it later once I get my mill.

I was thinking of drilling all the sides into the front and back, so I put 0.5" thick for front and back, to give more room for screws to go in. Do you think 0.25" would be OK for putting small screws in? If so, back and front could be 0.25" as well.

It's no rush, because I don't have the parts for the car's version yet. Also, I'm planning on getting a basic mill for cutting the lexan and for precision etching the heavy copper PCB. I should have the mill and controller parts by the end of Feb. I really appreciate your willingness to help! My wife says thank you, too! If the lexan is too much, even one of those pieces would make things that much cheaper. Thank you!

-Paul