SMC03A appears to stall

I am using and SMC03A to control a 12V linear actuator with a potentiometer to give 0-5V feedback.

If I make a large change in demand (i.e. from one extreme of the actuator to the other), the red LED shows, but there is no movement at all.

If I make more gradual changes in demand (i.e. 3 or 4 steps along the travel) it appears to be fine.

I don’t believe I’m exceeding the 3A rating (actuator has been measured at 1.5-2A), and the board does not appear to be getting hot.

Is there a current limit that can “stall” the controller in these circumstances?

In case it’s relevant, I’m using an RC signal as demand input. I’ve seen the same behaviour using serial input as well.



It is definitely possible for the starting current spike of an otherwise in-spec motor to send an SMC03A’s H-bridge chip into over-current shutdown mode.

You might want to read through this thread. I used two SMC03As to control two 12V diaphragm pumps. Once they were running, the pumps drew only about 0.6A, but compressing the first stroke caused a huge current spike that would shut down the motor driver chips.

You may still be able to use the SMC03A, if you can suppress that current spike. One solution (possibly the more ‘correct’ solution) in this problem is to add a big inductor in line with your motor to suppress large current spikes, but you would probably have to mail-order those. On the other hand, you could mosey on over to your local Radio Shack and pick up a big 1ohm 10watt resistor, and try putting that in-line with your motor. This worked like a charm for me, and hey, Radio Shack is still good for something!


Hi Adam

Cheers for the response. I’ll bear in mind the high-power-low-ohm resistor trick.

As this device is controlled from a microcontroller, today I’ve added a ramp to the demand signal, which should make it a bit more of a “soft-start”.

I’ll let you know how I get on, as it might be useful for others on the forum.




That is a limitation of the SMC03A, which is getting discontinued; we recommend the jrk 21v3 for new designs. In addition to many other cool features, the new controller can deliver more current and has much more robust error and fault handling.

- Jan

Hi Jan,

So do you think a JRK21v3 would do better handling motor startup spikes?

That board I referenced in the other thread, with the two pumps run by SMC03As has been running well (and continuously!) for around eight months now, but the lab is considering upgrading to larger pumps and I’m not sure how marginal the resistor fix was in the first place with the current pumps.


Yes, the jrk 21v3 should work much better: it can handle more current, so what is too much a spike for the SMC03A might not be an issue at all; it can better detect and recover from over-current situations; and it has acceleration parameters that allow for more gradual increasing of power to limit current spikes.

- Jan