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Im looking to drive a 16 vac solenoid from a battery pack. Specifically I want an electric door catch to function when mains are down. I want to do this with out with out using a commercial UPS. Im not worried about doing the switch over from mains to battery; just how to get the correct form of power to that latch. Im assuming I will only need about 650-800mA of current for maybe 5 seconds per unlock event.

Ive seen 4047 multivibe based inverter designs with a center tapped transformer but I have also seen that there are some issues with most of those designs (lack of any kind of regulation.) Im also wondering If I need simulated AC or if I can just send pwm dc at the door catch and get the desired result. I've heard there is a way to do it called "peak and hold" basically do one high low switch then like 50% duty pwm on high to drive ac selonoides from DC but i have only seen this mentioned once. any advice would be appreciated.

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  • \$\begingroup\$ Try running the solenoid on 16V DC while measuring the current to make sure it is within reason (e.g. close to 800 mA or whatever it is rated fpr). There's a good chance DC will work fine. \$\endgroup\$
    – Vince Patron
    Commented May 4, 2016 at 6:25
  • \$\begingroup\$ i was seriously green when i wrote this lol. for the record you were correct, dc will work. Ill be going with what ever existing supply voltage (and presumably existing door strike) rectified for the initial pullin and then pwming it so it doesnt burn out. just about back to this project, got distracted on DLC bank fet switched spot welder(which taught me a lot) thanks for the info \$\endgroup\$
    – John Wuethrich
    Commented May 11, 2018 at 15:35

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You probably don't need AC at all. Normal solenoids work on both AC and DC. The only difference is that on DC they don't need as much voltage because the coil inductance doesn't reduce current like it does on AC.

If your battery voltage is too high then you can apply PWM to reduce it at the solenoid. Even if you don't use PWM, you should put a flyback diode across the coil to soak up back-emf (which would otherwise damage your driver circuit when the solenoid is turned off).

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  • \$\begingroup\$ yeah, this got back shelved while i taught myself uv litho then designed a fet based dlc powered spot welder for bat packs. also a project putting a HID Proxi reader in a backpack which also involved using converters so other things were on diferential busses. learned to use my DI2C lol ill probably go all dc and p fet. with rectified voltage from existing tf (which presumably matches coil design +1.4%) just let it rip for a fraction of a second to pull solenoid in then pulse low duty to hold. played with sig gen door strike, fet and bench psu, seemed to work. Ty for the advice! \$\endgroup\$
    – John Wuethrich
    Commented May 11, 2018 at 15:42

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