Solenoids burn power when turned on and get hot, what is a way I can reduce the power while keeping the coil actuated?
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1Years ago, I saw here a special circuit I think based on a Roman Black design. Hmm.. Ah: Russell McMahon answer. Also, why not just use an RC and tie the solenoid at the junction. When you low-side switch the relay, the capacitor is at full voltage. But soon, you are relying upon the added resistor there to limit the relay voltage to 70%. – jonk May 11 '18 at 18:26
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Thats a cool circuit. In my application I couldn't afford any energy loss because I was replacing a circuit on a previous design and even the losses from a BJT would have not sufficiently driven the solenoid. – Voltage Spike May 11 '18 at 19:20
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This is a 'hit and hold' strategy for use in induction coils. The hit is to apply all of the current to the solenoid with a higher voltage, the hold is to apply a lower amount of power with a lower voltage. The way I have switch solenoids in the past is this:
So the idea is you hit the solenoid with a higher voltage momentarily and then back off the current with a lower voltage (or resistance in series). However
Q1 is switched on first, then switched off momentarily (this can be timed) and then the other gate switched on. There is a schottky diode to prevent backflow in case a software switches both fets on at the same time.
If your using a micro controller to drive the lines you can use a pull down GPIO port and tie the pins to the rails ( and you might want to put in a protection diode)
I have used DC to DC converters to drive the rails, for example I'll use a 12V rail for the high voltage and a 6V rail for the low voltage, which will give you roughly half the current for the holding current. You'll need to look at the solenoid and its holding current to choose the voltage for the high and low voltage.
Neil_UK
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Voltage Spike
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