H-Bridge + Inrush Suppression

Forgive me if this has been asked/answered, the forum search doesn’t appear to be working at the moment.

I have a project requiring the driving of 2 linear actuators. From our tests, we’ve concluded that they each pull ~1.2A @ 12v while running with load. According to the spec sheet, they can pull up to 3.8A at full load (which we won’t hit). On startup, however, we’re getting inrush readings that spike to ~10A for <1 second.

So, to get straight to it: Am I safe to use an h-bridge with a rating of 5A? Do I need to suppress the 10A spike somehow?

Thanks for your help!

D.C. motors, such as are in your actuator, briefly draw the stall current when they start up, and can draw twice that if the direction of rotation is rapidly reversed. You should buy an H-bridge that can accommodate that startup current, although you could probably get away with one rated for 5 amperes steady state.

@jremington,
That was my impression as well. It was the briefest inrush, but I wasn't sure if a driver with thermal overload protection would be sufficient. Would you recommend any other passive components to smooth out that initial current, or is there nothing that can be done? The actuator won't be changing direction rapidly, so I don't anticipate a spike of more than 10A.

If your H-bridge and actuator are performing satisfactorily, there is no reason to worry about the startup current spike. That is how these motors work. A possible side effect is electrical noise in the power supply, which can cause problems with other electronic circuitry (like resetting an Arduino), unless proper precautions are taken.

Hi, if you look up the spec for the components in the H-bridge, or if you have a ready made bridge you will find that they have a surge current or impulse current rating that is much higher than the rated running current, so you should be okay.

Tom... :slight_smile:

Sounds good, guys. Thanks for the feedback. I'll try to remember to post the finished project here when it's done.

If you PWM your H-bridge you can ramp up/down the drive level and avoid stall currents