Paul & Sabrina's cheap DIY 144v motor controller

[Articus]

Originally Posted by jedsmd

Are you using a preprogramed chip from Paul? If not, have you successfully loaded the unified firmware?

Also when loading firmware for the first time the fusebits need to be set, see mora's post:

Thanks. I think that's gotten me closer. After uploading V1.1b unified to the controller, the green led turns on, then the yellow one turns on and they both hold steady. I tested full throttle lockout and led flashed yellow.

How can I verify the PWM signal? I don't think it looks right. Note, I have not attached controller board to power board yet. Can I measure on the Arduino pin 15? Signal should go up and down between 0 and 5 v?

[MPaulHolmes]

It's assuming a 0-5k pot is attached, and also the current sensor. one way to check PWM is to measure voltage from any gate resistor to ground. Well, the ground of the output of the DC-DC CINCON. (also known as the ground of the MIC4451). Measure the voltage at zero throttle, then, give it nonzero throttle, and the pwm will ramp up to 100%, so you should see the voltage climb to around 12v on the volt meter. That's because it's trying everything it can to see some current feedback to match throttle position, but the current feedback continues to be 0.

[jedsmd]

Articus
For testing you can replace the current transducer with two equal resistors wired as a voltage divider to put 2.5v on the current sense line. That way the controller thinks it is producing a nice steady current and pwm will track throttle setting.

[Articus]

Originally Posted by MPaulHolmes

It's assuming a 0-5k pot is attached, and also the current sensor. one way to check PWM is to measure voltage from any gate resistor to ground. Well, the ground of the output of the DC-DC CINCON. (also known as the ground of the MIC4451). Measure the voltage at zero throttle, then, give it nonzero throttle, and the pwm will ramp up to 100%, so you should see the voltage climb to around 12v on the volt meter. That's because it's trying everything it can to see some current feedback to match throttle position, but the current feedback continues to be 0.

Originally Posted by jedsmd

Articus
For testing you can replace the current transducer with two equal resistors wired as a voltage divider to put 2.5v on the current sense line. That way the controller thinks it is producing a nice steady current and pwm will track throttle setting.

Thanks for tips guys! With that I believe the controller board is working correctly. I was trying to figure out where to stick the ground reference on my oscilliscope and I realized there are many ways to do that incorrectly I had been probing around R17 and Pin 15 on the Atmega. With the 0-5k pot on one of these I saw a PWM duty cycle that kept growing to 100% and I figured the growth was the PI ramp up. This makes sense since my current sensor was not measuring anything that it would rail the pwm.


Now, I can't install RTD explorer for some reason.

edit!! - I go back to try to reinstall and post the error here and RTD explorer installed! So excited!

[Articus]

Would it be possible to control two electric motors with a single controller board and 2 power boards?

[thingstodo]

Originally Posted by Articus

Would it be possible to control two electric motors with a single controller board and 2 power boards?

You can connect 2 motors (or 3 or 4 or more) to the same controller terminals. But you'd have to settle for the max amps that the controller can output spread across all of the motors

One motor per wheel, with the same DC to each, is a proposed method for all wheel drive that I read about in one of the other threads.

As for multiple power boards on one control board - I don't have the insight to be able to comment

[z_power]

Well, parallel connection of motors can lead to large imbalaces in currents due to smallest differences in their resistances (or should I say impedances?). Google for CroDriver's BMW, he's had this unlucky experience. It would be more safe to connect them in series if their shafts are coupled direct or indirect trough pavement but you don't need to modify controller to do this - single "output channel" would do.

[thingstodo]

Originally Posted by z_power

Well, parallel connection of motors can lead to large imbalaces in currents due to smallest differences in their resistances (or should I say impedances?). Google for CroDriver's BMW, he's had this unlucky experience. It would be more safe to connect them in series if their shafts are coupled direct or indirect trough pavement but you don't need to modify controller to do this - single "output channel" would do.

Imbalance in current should be imbalance in power to the wheels as well? The wheel(s) that get more current should be doing more of the work?

I did a couple of simple searches - saw Crodriver's EValbum entry, a couple of videos, and a build log on DIYelectriccars ... but a search for "Crodriver", "BMW" and "imbalance" did not get any results about motors - just batteries. I'll try again later with perhaps a better set of search terms but I'd appreciate a link if you have one.

Crodriver is running a sub-10 second racer ... I think he stresses a bunch of components on each run!

I don't like the idea of putting DC motors in series. Maybe it's because I don't understand how they work together. As I understand it, they develop the same torque since they draw the same current. But if one is slipping and the other has traction, both get the same current so one will spin like mad (likely overspeed and possibly destroyed) and the other will do it's normal drive. In that case, if your controller is using twice the voltage that one motor should get (so that you can get rated voltage and rated current to each motor), the voltage drop across one motor is lower and the other is higher, so the motor doing the work will .. possibly .. have damage done to the brushes or armature due to arcing.

Motors in parallel get the same voltage instead, so as I understand it the motor without traction draws less current (it still spins like crazy because it has no traction, and so no load, and it may still damage itself with overspeed. Not sure on the overspeed stuff) but the one with traction can take more current and get you down the road.

Maybe I need to do more reading ...

[MPaulHolmes]

multiple power boards would probably be a problem. The current loop AREA from the driver OUT, through the gate resistor, into the gate leg of the mosfet, inside the mosfet to the source leg of the mosfet, and back to the gate driver ground must be as small as possible. That gets really hard to do when the distance from the driver to the mosfet gets big. Also, the gate driver would need to provide twice the gate charge if you included another power board, and it is already pushing it with 10 of IRFP4668.

[Articus]

Out of curiosity, why is the long bus bar called the "M-" bar? Why not the M+ with the M- being the vehicle chassis/ground.