How much Current through Distributor Sensor Leads?

[TomoHawk]

the two leads that go from the distributor to an HEI ignition module or the factory ignition box would be a good place to cut into and add a  kill switch of some kind,  such as a mechanical switch or a remotely-controlled relay.  I have a remote relay, and it has a 10A current rating. 

I think the relay would work well as theft-prevention, because it doesn't require heavy wiring, like the fuel pump does, and you can easily hide the thin wires in the wire bundle.  I also think that there probably isn't much current in those two sensor wires, since they only control the ignition module instead of  the current going to or from the module or coil.

I just wanted to confirm the idea, before taking a chance at ruining a useful relay module.

thxZ

 

[Zed Head]

I don't think that the ignition module actually "flows" much current.  It senses voltage but the current flow is probably more like what a capacitor might see, I'd guess.   

[zKars]

Just use the same gauge or larger wire that is used in the stock harness and you can't go wrong.

The voltage signal wave forms are very low. Make sure all you new connections are high quality and properly insulated. 

[TomoHawk]

I though that I could put a small bulb in-line  to the sensor wire to see if it burns brightly or burns up.  I could even try an LED, which only need a few mA to work. the LED would make the engine run badly tho.

[TomoHawk]

On 6/23/2017 at 8:50 PM, zKars said:

Just use the same gauge or larger wire that is used in the stock harness and you can't go wrong.

I'm not worried about the wiring.  I just don't want to burn up the relay that is making the circuit.  Too bad those remote relays only use a cheap SPST relay.  A DPST relay would like more like a normal part of the ignition system, and fool a thief.

 

BGW-  the Kiwis just won the America's Cup.  They will be taking it back down under again. 

[Zed Head]

The wiring will melt before the relay.  The VR sensors can generate high voltage at high RPM, so sparking to a ground point might be a concern.  But heat from current is probably not since there's essentially no current flow.  Look at the connection terminal for the distributor wires, on the fenderwell, and you'll see that the wires are small gauge but the terminals are well separated and kept dry.  Might be focused on the wrong thing.

[Captain Obvious]

I haven't measured it, but I suspect the current drawn by the ignition module is in the milliamp range. I suspect they used the gauge wire they did (for the red and green) simply because that's the smallest they used anywhere in any harness.

I would be happy to defer to someone who has actually taken measurements, but my instincts tell me that you can use any relay you want without worry.

I also believe an SPST relay to disable the circuit would be fine as well. Since those two wires don't go anywhere else other than the ignition module, you don't have to break both legs.  In other words... It's a loop. And a loop with one break is just as broken as a loop with two breaks.

[TomoHawk]

I agree with what you say, but I'd put a DPST relay just so you can set it up to look like part of the ignition stuff;  only ground wires travel by themselves.

I suppose you could put your digital multimeter inline with the distributor sensor wire to measure current, but since the signal is so brief (2000+ per second, at idle), a digital meter won't register.  You'd need some kind of averaging module, or maybe an analog meter.

Edited June 27, 2017 by TomoHawk

[TomoHawk]

I think of it this way:  How much current could you get from a metal star-wheel whizzing by an inductive coil? 

Edited July 1, 2017 by TomoHawk

[Captain Obvious]

Q - How much current could you get from a metal star-wheel whizzing by an inductive coil?

A - Infinite if the resistance in the loop is zero. Zero if the resistance in the loop is infinite.

It's the Law. 

[jwtaylor]

Well stated Captain Obvious!