Current way off

[tinkeringtechie]

I just installed a new Robotclaw ST 2x45 and the current readings seem very off:

While motionless: M1: 25A, M2: 4.5A
While in motion: M1: 53A, M2: 10A

Any ideas what's going on here? Both motors are identical and an external current sensor shows no current while idle, and about 15A while in motion. Seems like it needs to be calibrated or something. Is there any way to do that myself? Thanks

[Basicmicro Support]

On power up the current reading is zeroed. If this zeroing has a problem it could explain the intial offset(eg the current when not moving). Im assuming when you say the motors arent moving they are at 0 Duty, correct?

What are you using to power the board? If the power source takes too long to power up the zeroing reading for the current could be corrupted.

Also, what model/manufacture are your motors and how do you have everything wired up?

Also, send an email to support@ionmc.com. We'll send you a link to download a pre-release of the next update. I want to see if that has any effect on the readings.

The fact one side is much higher than the other may indicate a problem with the current sense circuit on that motor but the fact both sides are way off indicates something else is going on.

The more information you can provide on your setup the more likely I will catch anything that may be causing this.

[tinkeringtechie]

That's correct, it's showing significant current even at 0 duty.

The board is powered by two 35AH SLA batteries in series.

The motors are two Quantum wheelchair motors... not sure on the specific model. They're rated for 24V and 200 watts continuous. Are there any other specs that would be useful? They're wired directly to the M1/M2 terminals on the controller.

There is also a Solo 30 on the same machine that seems to zero correctly. Would powering both up at the same time cause issues?

Power is connected through a relay that has the reverse diode in parallel, but I'm not using a pre-charge resistor. Would that affect the current calibration?

I recently upgraded this machine from smaller motors and a 2x15 to the 2x45 and the previous configuration showed the current correctly. The only change was to upgrade the motors and controller.

Is it possible to just zero the current while at 0 duty, or does the regen stuff make that problematic?

[tinkeringtechie]

Also, quick follow up question: Will the Roboclaw attempt to protect itself using the incorrect current reading? It doesn't seem to be doing it at the moment, but I'm also driving it pretty gently at the moment.

[Basicmicro Support]

It sounds like there is something wrong with the current readings on the board if another board(2x15) worked correctly.

No the current cant be re-zeroed after power up but not having a pre-charge cap shouldn't make a difference. The current readings are taken on the h-brides of the controller not at the battery input so the surge of current during the initial charge wont effect that.

The controller will try to protect itself but you haven't reached the limit yet. At 25c the current limit on the 45a per channel is 60a so even your bad readings aren't high enough to cause the current limiting function to kick in.

I would like to check the pre-release firmware on the unit before you send it back or we send a replacement. Please email support@ionmc.com. We are not giving out the pre-release except in cases like this so I cant post the link here.