Questions on using a relay - Electrical gurus please

[Nobody]

The standard installation of a relay is to put the high current switch between the ground and the accessory (Pin 30->Grnd, Pin 87->Accessroy->12v) so that when the power is applied to the low current side, the high current side provides a ground.

I would like to know if a relay can be used to simply open a circuit. I am installing an MSD window switch and I want to interrupt the TPS signal of a ZEX kit. Here's the diagram:

 

[HISSIN50]

if you use an SPDT relay (with a terminal 87A) you can use this to open the circuit (not unlike how the WOT relay opens the A/C clutch circuit).

I dont understand what you are doing (something is being lost in terms we use), but what you want to do sounds simple. you need a ground and 12 volts on the control side of the relay, and you can have the common (and NC) terminal provide power or ground.

good luck.

 

[Nobody]

Hey thanks Hissin50. I guess I wasn't exactly clear on what I wanted to do.

The Window switch has a "Normally open" line which provides a Ground only at the specified "On RPM" and then removes the ground at the "Off RPM". Since I want to control the TPS signal going to the Nitrous Management Unit (NMU) I want to use a relay so that the Window switch turns the relay off and on based on RPM, this in turn will open or close the TPS voltage circuit to the box.

Thanks!

 

[Michael Yount]

Almost all of the relays I install I don't use to provide ground when the coil is energized - I use them to close the hot side of the circuit. They'll work just fine either way -- current is current after all.

 

[HISSIN50]

ok, I think I am getting this (I am decent with wiring, but have not done a nitrous install, so that part is new to me).

In your schematic above, when the window switch supplies ground, 87 and 30 connect. otherwise, they are separate (open). so when the window switch is not providing ground, 87 and 30 are not connected.

I am not sure how I can help though (I think i reiterated what you said, but now I get what you are doing a little better, I think).

NOTE: Since I am not familiar with what you are doing, Please dont act on anything I say here without confirmation from someone else. I would hate to not understand what you are doing and give bad info for your application.

Here is something else to consider: you can wire the circuit through the relay actively or passively. the way you have it is active - the relay must energize for your TPS and NMU to connect. should the relay fail, will that cause a meltdown?

you could wire it so the relay energizes to kill the connection (so by default or in case the relay stops energizing, the TPS and NMU stay connected). Is that better?

I have no idea which is better (the last method would be a little more involved wiring wise).

Bump for others with Nitrous and knowhow to comment on.

good luck.