Paul & Sabrina's cheap DIY 144v motor controller

[MPaulHolmes]

That's a good idea Ben. The only thing I'm trying to avoid is the "hair trigger": Getting max torque at like 5% full throttle (near 0 rpm is when this bad combination happens). But If a person wanted 100% of available torque at near 0 rpm (like climbing a steep hill) it should be available, but it should be required that you push down the throttle 100%. The program needs to be changed! Thank you Ben! I'm going to revise it.

[MPaulHolmes]

It's fixed!!! Thank you Ben! Here's the behavior now:

The torque is proportional to the real life throttle position. At full throttle, full torque is allowed, even at 0 rpm.

The goal wasn't to limit torque at 0 rpm, it was to eliminate full torque at 0 rpm at extremely low throttle positions. Now any hill can be climbed by giving it more gas, just like in a gas car! A gas car pushes down on the accelerator to get more torque. It will behave like that now. The funny thing was that I only had to change a single word in the program! hehe Those are the type of problems I like fixing!

Ben, if you were here, I would shake your hand, and pat you on the back for a job well done!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!

[MPaulHolmes]

It works perfectly now! And, no more high pitch! 16 kHz switching frequency! When in Rome, do as the romans! (the other controller makers) Well, it still has a high pitch, but I can't hear it.

[The Atomic Ass]

I find myself confused by the torque/amps - speed/voltage bit. I would have thought that pushing more WATTS would generate more torque. I've never really studied electricity seriously, though...

In essence my question is, why would you generate more torque forcing 12,000 watts through a motor at 12v than the same 12,000 watts through the same motor at 700v (assuming the motor can handle it, of course)?

Also, is this behavior the same in 3-phase AC motors?

[MPaulHolmes]

Torque is proportional to current because there are electromagnets inside the motor, and the stronger the current, the stronger the magnet. Try it with a nail with wire wrapped around it, then connect the wire to a battery. The nail becomes magnetized. The more current flowing through the coils around the nail, the stronger the magnetic field. This is because a moving electric charge causes a magnetic field. The higher the current (the more electrons that are moving) the stronger the magnetic field.

A DC motor basically plays a game of south chasing north (magnetically speaking). Once south reaches its goal of North, the north gets switched to south, and south gets repelled by south, and is attracted to the next north. It keeps switching at just the right time (because of the brushes) so south is always chasing north (and north is always chasing south) around and around in a circle!

Voltage is proportional to speed because the higher the voltage, the faster the current in the coils can switch direction. There's inductance in the coils. It's like momentum. Once the current gets flowing, it doesn't want to stop and flow the other way. You need a lot of pressure in the opposite direction (voltage) to force it to change fast. The faster the current can change, the faster the wheel can spin.

As far as AC motors go, I have no idea how they work! hehe. I would like to learn though.

[MetroMPG]

Good explanation, Paul. I can see why you're a teacher.

[MPaulHolmes]

Here are a couple pictures of a template I made for etching the power section on the (up to) 144v 600 amp controller. There is just enough space for 12 diodes and 12 mosfets.

I used Microsoft Paint. I would just like to share that Microsoft Paint is not a very good program. There, I feel better.

I made the picture in Paint and saved the size as 8" x 7" (I love that feature), which just so happens to be the perfect size so that in the real world, once it gets printed on real 8.5" x 11" paper, that it can be transferred somehow to the PCB. (I would love suggestions on how to do this better than what I did! Would ironing work? A hot air blower from sears doesn't work.) OOh, maybe using an overhead projector transparency? Print the ink onto that, and then push that onto the copper sheet?

What I did was use a box cutter to cut out enough of the paper so that I could use a permanent marker to transfer the picture to the PCB, and fill in the gaps pretty easily.

I'm just experimenting at this stage. Printing a picture of the etching and transferring that to the PCB somehow would be a nice feature for people making their own with a kit! People could use a box cutter, but that is like 1 hour of my life that I definitely want back.

This assumes using a 1 inch thick aluminum heat spreader right down the middle.

NOTE!!! The way the first thumbnail is oriented right now is flipped top to bottom. It assumes you will find a way to lay it face down the the PCB and transfer the ink to the PCB somehow. If you want to cut it out with a box cutter, you better flip top and bottom in Paint first!

[bennelson]

Have you ever run label paper through an ink jet printer when you had some labels removed already?

The ink will not stick to the part where the labels are missing, it just sits on the waxed paper.

You could actually cut a sheet of kitchen wax paper to 8.5x11 and run it through an inkjet printer, then flip it over and press it down to transfer the ink.



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[The Atomic Ass]

Originally Posted by MPaulHolmes

This is because a moving electric charge causes a magnetic field. The higher the current (the more electrons that are moving) the stronger the magnetic field.

The voltage portion of your explanation I understood, but I thought that given a fixed current, a higher voltage (entailing higher watts) would result in a greater electron flow.

[MPaulHolmes]

But increased electron flow WOULD be greater current.

Given a fixed current, the only way voltage can increase is if resistance increases (Ohms Law). So the same magnetic field results, because there are the same number of army men (electrons) moving through the jungle (wire), only now they are being pushed harder by a really mean general (higher voltage) through a nastier bog (higher resistance).

So, their speed doesn't increase because of the higher resistance.


By the way, Ben, that's a great idea! I'm going to try that.