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I need to operate a small 120VAC motor for short bursts of 1 to 3 seconds using a 12VDC supply (it's for a remote antenna switch).

Operations are typically minutes to hours apart, so the duty cycle is very low. I don't know the precise power draw but it's likely in the 10-15 watt range, so not very great.

A typical inverter seems like overkill where the average power requirement is so small. In my mind I picture some caps storing energy for the output pulses, but I can't picture a nice implementation.

Any suggestions for a simple and physically compact circuit that could handle this?

Thanks!

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  • \$\begingroup\$ Before you start specing anything out you should scope the actual current draw of the motor as it starts up. Inrush currents can be pretty serious. \$\endgroup\$
    – τεκ
    Commented Nov 22, 2019 at 22:03
  • \$\begingroup\$ possibly a step down transformer with centre tap on LV side used in reverse with Q,Q! to driver transistors on each leg. \$\endgroup\$ Commented Nov 22, 2019 at 22:04
  • \$\begingroup\$ The inrush current thing is a good point. I'll try to check that tomorrow. I suppose putting a scope in single-sweep peak-hold mode across a small resistor in series with the power lead to catch the voltage drop would be a good way to characterize that. \$\endgroup\$ Commented Nov 22, 2019 at 22:06

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If your motor can tolerate a square wave, it is fairly easy to create a push-pull driver connected to a center-tapped transformer. You can use a transformer normally used for step-down reversed as a step-up.

I successfully drove my telescope synchronous motor with a DIY circuit as I described. Sorry, I don't know where the schematic is.

Edit: Here is a circuit that will create a modified square wave (less harmonics, better than what I built). This is untested, you shouldn't attempt this unless you have some experience.

schematic

simulate this circuit – Schematic created using CircuitLab

The output should look like this:

enter image description here

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