Interlocks and High Voltage

Author: sgeorge, Posted on: 26 October 2015 20:24

One of the things things a pinball machine has that I have been thinking about for a long time is that it couples its high voltage to the coin door interlock. When you open the coin door, the high voltage to all the coils gets disabled (this is often the first thing bypassed for competition machines).

Since I have a dedicated high voltage supply for all the coils, it takes time for the PSU to ramp back up, so turning it 'off' off, is not a good idea.

Enter the relay.

To be specific, the DC solid state relay.

Using this I can leave the PSU on, and have it sit on the live output rail and use it to switch the voltage on or off with just 5 volts.

Ideally I'd just use a MOSFET to switch it on and off, but a postive voltage requires a P-Channel requires you to pull the voltager higher than the gate, so if your powering your solenoids with 50V, you need more than 50V to turn them on.

Inside is basically an IGBT and a couple of resistors and it uses the base to push heat through.

The one picture is an ebay score, cost less than $10. Genuine DC SSR's cost 20$ and more, this one is light, but its specced at 250VDC at 25A. I know its a knock off, but I'm hoping that since I'm only going to push 50VDC at maybe 4A I'll be well under its failure envelope.

I tested this running 8A at 16V through it for an hour, the heat sink its screwed ont got just above room temperature. Nothing too bad.

tags: SSR, voltage


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