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Can I use an AC solid state relay to control a DC current as long as the DC voltage doesn't exceed the rated AC voltages?

I want to control a solenoid but I'm concerned about the inductance problem of the device. Will a solid state relay survive the back EMF of the solenoid when turned off by itself?

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  • \$\begingroup\$ You could use a Power-MOSFET to control the solenoid and a switching diode to short the EMF. Same circuit as you would use the control a normal relay (one with a coil). Sorry for not answering the question directly, but you can generally use a switching diode to short the EMF, when controlling a solenoid (with a DC current). \$\endgroup\$ – JakobJ Apr 27 '11 at 11:13
  • \$\begingroup\$ Put it in am answer, add a circuit our two and you've answered the question based on what I needed as opposed what I thought I wanted. I'd accept that ad am answer. \$\endgroup\$ – Faken Apr 27 '11 at 18:44
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It depends on the relay. Many solid state relays use a thyristor as their main switching component, and a thyristor can't be turned off simply by removing the trigger voltage. They rely on the reverse-bias portion of the AC cycle to switch off. Other solid state relays use FETs as their switching component and those relays may work with DC. It all depends on what the specific relay is rated for, and the only way to know is to carefully read the relay's data sheet.

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The answer is no! There is a diode in reverse on most MOS devices a which will allow the current to run backwards into your circuit. A thyristor will block the reverse current, but cannot be turned off while the current is positive. Thyristor regulators turn on part of the cycle and turn off when the voltage goes to zero (or reverse).

If the solid state relay is for AC it has two thyristors in parallel, one for each half pulse. If the relay is DC, it probably has a diode across it which would be a short when the inlut(?) goes negative.

I'm trying to make a battery charger without a final diode in series (save power loss), but the semiconductor internal diodes always foil it. When the charge voltage goes off, the current wants to run back from the battery into the generator (not alternator which has diodes).

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  • \$\begingroup\$ @Faken said "use an AC solid-state relay to control a DC current", so any backward currents is not an issue, since the relay was designed for AC in the first place, so it can handle the DC fine (the other way around is when you would run into problems). \$\endgroup\$ – gbmhunter Dec 5 '13 at 2:50

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