1
\$\begingroup\$

I'm trying to control an electric vehicle, say scooter. Vehicle throttle meant to be controlled with potentiometer like on the picture. And it works just fine with 10K pot.

enter image description here

Now I want to control throttle electronically, thus I make some analog voltage with microcontroller and scale it appropriately to match HIREF - LOREF with op amp.

enter image description here

I check the THROTTLE voltage with oscilloscope and it is just fine, but motor controller doesn't seem to react. What can be the case? Isn't it voltage controlled? Can I emulate potentiometer with some circuit?

\$\endgroup\$
1
\$\begingroup\$

I had the exact same problem, with I think a Curtis 1234 motor controller for a hybrid vehicle project I was on as an undergrad.

It turned out, as a safety feature, the controller sent out a current through the pot and compared sourced current to sunk current to check for a broken wiper or other throttle faults, similar to a GFCI breaker.

You could enter a programming mode and change it to look for just the voltage, but the programmer was very expensive.

In the end I wound up using a digital potentiometer to interface between our computer and the motor controller.

\$\endgroup\$
  • \$\begingroup\$ Thanks for the info! I've checked on of the curtis controllers manual, they say you can control voltage of the throttle wiper if you put a 4.7K resistor between LOREF and HIREF. Unfortunately this is not curtis, but some other beast with poor manual. \$\endgroup\$ – DikobrAz Sep 24 '15 at 2:18
  • \$\begingroup\$ But still, I would try an actual potentiometer just to be sure the controller isn't broke. \$\endgroup\$ – Chuck Sep 24 '15 at 11:14
  • \$\begingroup\$ I tried, it works. \$\endgroup\$ – DikobrAz Sep 24 '15 at 16:28
  • \$\begingroup\$ @DikobrAz then I would try using a digital potentiometer. Again, some motor controllers use current in/out comparison as a safety check for throttle failure. \$\endgroup\$ – Chuck Sep 24 '15 at 17:43
1
\$\begingroup\$

I got it working. Apparently motor controller has some sort of check to ensure that potentiometer is functional, workaround is to attach a resistor of proper resistance between potentiometer LOREF and HIREF. I found this solution in manual to Curtis 1210, apparently it is applicable to other controllers as well.

enter image description here

\$\endgroup\$
0
\$\begingroup\$

That should work.

Are you sure that LOREF is the same as your microcontroller ground?

It may not be. Measure the voltage and continuity between those points before you connect the micro controller

There may be self-check circuitry to detect errors like that and disable the motor.

Have you measured the THROTTLE voltage when driven from your circuit - is it in the same range as with the real throttle?

\$\endgroup\$
  • \$\begingroup\$ LOREF and microcontroller ground are same, they are connected. The circuit works just fine, output voltage behaves as expected. \$\endgroup\$ – DikobrAz Sep 24 '15 at 1:56
  • \$\begingroup\$ What system is it? Does it do some checks at power-up to check if there is a wiring fault? \$\endgroup\$ – Kevin White Sep 24 '15 at 2:01
  • \$\begingroup\$ Unfortunately I don't have enough information about the device. It has power-up check of throttle, you shouldn't change it while powering up. But this is not the case. \$\endgroup\$ – DikobrAz Sep 24 '15 at 2:05

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.