Relay substitute

Ian Gilchrist

Joined Sep 11, 2016
15
I have a circuit which needs to be normally closed(NC) bit I want to momentarily interrupt that circuit for about 500mS. it's a 12volt circuit with typically about 20amps running thought it.

Planning to use a SPDT relay and just wire my circuit into the Normally closed path of that relay.. then when I need to interrupt power I'll energize the coil which will pull the relay Cct open and then upon remove power from the coil the relay will go back to closed. Perfect. I'm looking for a way to do this without a big heavy duty relay..is there some kind of FET or something which has a normally closed circuit path (short circuit)..?

Joined Jul 18, 2013
24,248
Suitable Mosfet and heatsink.
What is the nature of the load?

Ian Gilchrist

Joined Sep 11, 2016
15
Simple load. Think old style 12v driving/spot light...10-20amps.

I've not done much with MOSFETs....a little..but not much. Which device would you recommend and what is the normally short circuit path?

Ian Gilchrist

Joined Sep 11, 2016
15
Is there a power off zero ohms path through the MOSFET You're thinking of? .. that would be required

sghioto

Joined Dec 31, 2017
2,746
Wired this way the power to the load is normally ON.
Press button to interrupt the circuit.

Ian Gilchrist

Joined Sep 11, 2016
15

Joined Jul 18, 2013
24,248
You may find it easier to use a through-hole device, and strip board etc.
You can also do it the conventional way using a NC switch.
Digikey are a good source.

Ian Gilchrist

Joined Sep 11, 2016
15
You may find it easier to use a through-hole device, and strip board etc.
You can also do it the conventional way using a NC switch.
Digikey are a good source.
Thanks Max...the MOSFET is the go for this application me thinking

Joined Jul 18, 2013
24,248
For the through hole, Digikey have the IRFP048N for < $1.00 sghioto Joined Dec 31, 2017 2,746 For the through hole, Digikey have the IRFP048N for <$1.00
That's a N channel mosfet.

Joined Jul 18, 2013
24,248

Tron Jockey

Joined May 3, 2020
19
I have a circuit which needs to be normally closed(NC) bit I want to momentarily interrupt that circuit for about 500mS. it's a 12volt circuit with typically about 20amps running thought it.

Planning to use a SPDT relay and just wire my circuit into the Normally closed path of that relay.. then when I need to interrupt power I'll energize the coil which will pull the relay Cct open and then upon remove power from the coil the relay will go back to closed. Perfect. I'm looking for a way to do this without a big heavy duty relay..is there some kind of FET or something which has a normally closed circuit path (short circuit)..?
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You can go the simple route and use a Solid State Relay (SSR). Wire it so it's always on (NC) and turn it off when you need. Easily controlled with a low voltage DC pulse. Depending upon duty cycle you may not need much of a heat sync. Make sure the "On Resistance" is acceptable for your circuit.
https://www.amazon.com/SSR-100DD-Solid-State-Relay-Module/dp/B07PFDJQLV/