blowing motor controller boards

Hey guys...newbie here,

I'm in a bit of a pickle. I've bought 3 ServoCity Motor Controllers. They have all blown, though the fuses have not. The only thing I can think of is that I'm getting some form of back voltage and I'm trying to narrow it down. But does it seem logical and will a diode protect me?



Bad thing was that I thought the Motor Controller had protection for this.

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Trey

The problem is you can't use diodes across or in series with the motor if it's a 2-wire type where you invert the polarity of the wires to reverse motor direction.
But as you suggest, spike protection should be built into the controllers whether diodes in/across the "H-block" MOSFETS, or mere relay outputs.

Are the motors/actuators matched to the controller? IE 12V, 2 wire reversing, non-stepping or stepping etc?
Certainly otherwise I';d expect a 10A servo controller to handle 3A & 8A & 10A motors & actuators.


PS - are output and motor wires isolated from the 12V supply - especially the ground? Tho obvious isolation must exist for 2-wire setups, I have seen complications with 3 or 4 wire (dual coil) systems where people think output -ve (or motor GND etc) is the same as supply (12V) GND - they don't realise there maybe be MOSFETs or offsetting components.

The motors/actuators are matched. As the drawing illustrates, the 2 Linear Actuators are the same...2 wire, 12v, 2", 225lb pull, 3 Amps. The DC motor is a 2 wire, 12v, Electric Steering Assist motor, 8 amps, so I wouldn't think it would have any inductors to create a spike. The 12V motor wires are isolated.

The Motor Controllers are rated for 10amps, so you'd think that they could handle any inductive spikes from the motor.

I am at a complete loss. I don't know if ServoCity will exchange my controllers, but even if they do, I need to figure out what is blowing them.

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Trey

Well IMO it sounds like faulty controllers unless perhaps they have all been used onto the 8A motor & switch.
Not knowing about those controllers and any limitations, as I said, IMO a 10A motor controller should handle your (permanent magnet) 3A motors.

I saw a pic of one ServoCity 10A Motor Controller and it looked like it used transistors (probably MOSFETs), but the should have inductive spike protection. (Like, you can't add your own, and since they are intended for motors which tend to be inductive...)

I have a friend at NASA that indicated he had a similar problem. He believes that the fast reversing of the 8amp motor is the issue...

"During deceleration or braking of the motor, the mechanical energy of the load is converted into electrical energy that charges the power supply output capacitor to a voltage higher than the over-voltage shutdown point of the amplifier. In order to correct this situation, a large 15000 μF capacitor was wired in parallel to the power supply to absorb the energy generated during direction changes. This successfully prevented the over-voltage error from reoccurring."

I've reached out to the ServoCity techs to see if they can verify, but it sounds reasonable. Thoughts?


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Trey

Duh - what would a NASArian know? Just kidding! (Tho a NASA programmer or mech engineer may be just as good as a car audio forummer psychologist when it comes to electrics...)

But yes, an unpowered-stator rotating motor acts like a generator tho IMO - excluding transients - it would be strange to exceed its powered voltage by much unless mechanically accelerated.
Maybe the (bipolar?) cap filters transients?

Alas I lack practice and am way too rusty on motor controls, but I would have expected the controller's freewheeling diodes etc to handle reverse-polarity spikes, and MOSFETs or whatever to have suitable voltage ratings.

But you said all 3 had blown and that is why I wrote ... unless perhaps have all been used on the 8A motor....
And also what I meant by matching of motors and controller - ie, ServoCity state that f.ex the 8A motor is fine to use. Or do they exclude certain motors?