Paul & Sabrina's cheap DIY 144v motor controller - Page 16 - Fuel Economy, Hypermiling, EcoModding News and Forum

bennelson · 01-09-2009, 11:01 AM

Ah, we are back to the idea of a big contactor kicking in direct between the motor and batteries when at full tilt!

MPaulHolmes · 01-09-2009, 02:01 PM

It depends on the current, because at full throttle, if the RPM is high, the current will be low, which will be more efficient than full throttle with low RPM, which would be high current (and more heat loss in the muppets. Kermit has a fever). I bet that a contactor is more efficient than both of those scenarios. However, I think a controller is pretty efficient at full throttle.

Loss (from mosfets) at full throttle (and full current):

0.017 Ohm * 50 Amp * 50 Amp * 10 mosfets = 425 watts.

The Total power that's being used:

500 Amp * 144 v = 72000 watts. So the loss from mosfets at full throttle is

425/72000 = 0.59%.

bennelson · 01-09-2009, 02:19 PM

Cripes!

144v x 500 amps = 72000 ÷ 750 (750ish watts = 1 hp) = 96 horsepower electric!

I have heard that as a rule of thumb, you need 5 times as many horsepower in gasoline as you do electric.

You are building a controller for the equivelant of a 500 HP engine!!!!

Great, now we need to build an Open Source Motor that can handle that!

MPaulHolmes · 01-09-2009, 03:14 PM

Isn't that amazing! It's only 10 of those mosfets! Ian is using 12 of them, and running his car at 144v 600amp. It would be just as easy to do that, but I thought that would be unnecessary. We'll just run it real conservatively. Maybe have the adjustable Max current be from 100amp to 600 amp. Then, only if you are feeling particularly evil will you drag race a corvette.

metromizer · 01-09-2009, 03:22 PM

Quote:

Originally Posted by MPaulHolmes

...Maybe have the adjustable Max current be from 100amp to 600 amp. Then, only if you are feeling particularly evil will you drag race a corvette.

Just be careful you don't peel the teeth off the pinion gear with all that torque! Been there-n-done that, more than once... LOL

MetroMPG · 01-09-2009, 07:41 PM

Thanks for the contactor vs pwm analysis, Paul.

MPaulHolmes · 01-09-2009, 11:26 PM

No problem, Darin!

So, now when you hold the wheel at 0 throttle, it only pulls gently. Just enough to get it rolling.
(not 0 current at 0 throttle! A little current at 0 throttle! Anger. That's 30 minutes of my night down the toilet! Duh! It won't move for some reason. What a mystery! Flames out of the side of my face!)

So, starts will be smooth. ya! There were a few bugs in the program. Go to garage, unhook everything, bring to room. reprogram, take to garage, plug in, test, unplug, take to room, reprogram, ... ANGER!

It works now. It's cool! must make video of it in action. It's really funny to see the PWM duty respond when I grab the wheel and say "NO! You will not turn!" It says, like a red headed step-child, "OK daddy. I'm real sorry..." Then I whoop the tar out of it.

MPaulHolmes · 01-10-2009, 01:17 AM

This video shows how the current and the PWM duty is limited by the throttle. Let's say the throttle is at 80%. Then either the current will be 80% of the max current, or the PWM duty will be 80%. If one is 80%, the other will be smaller. This makes no sense to do for the bike, but will make things very smooth on takeoff for the car.

Video!

The Atomic Ass · 01-10-2009, 02:28 AM

Quote:

Originally Posted by 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?

I'd go for D cells, if you can afford 'em. I've seen some D cells that are 12,000mah. That beats the hell out of a AA's 2,200, for roughly the same price.

Have a look see here for a D cell battery that handles a 50A peak drain. That's obscene.

bennelson · 01-10-2009, 09:50 AM

Paul, thinking about it, your "torque/speed-linked" approach is just another way of doing the "throttle ramp up" I talked about earlier.

Are there going to be unintended consequences? What if you are trying to drive up a hill, but slowly? (There actually IS a pretty steep hill in that 15 mph zone down the street from me) You need low speed, but high torque.

Would this feature be fairly simple to disable? I think it would be really interesting to road test with and without the speed/torque limiter to see how the car behaves in a variety of real world situations.