Wire with Power only when the Engine is running/starting?

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Wire with Power only when the Engine is running/starting?

Postby tom_kauf » Fri Jun 16, 2017 12:32 pm

So I've burnt out my Bosch Wideband O2 Sensor in less than 9months and 10,000km, probably because of shock cooling. This seems to be very common unfortunately. See below for a very interesting article on why sensors last 100,000km+ in stock applications, but fail much quicker in aftermarket installs.

The Question: Is there a circuit or wire that only has Power when the Engine is running??

Or one at the ignition barrel that gets power when the Key is on Start?

I could use a relay to pull on, and hold until the ignition is fully turned off.

I tried to find a wire like that last year when I installed the Wideband, but had no luck. But I only checked for circuits at the Fuse Boxes (LH engine bay, and RH front interior). After checking every Fuse, they all got power when the Ignition was turned on (engine still off) :?.

*Why Bosch Wide-band air/fuel ratio sensors fail so often in aftermarket applications*
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Re: Wire with Power only when the Engine is running/starting

Postby tom_kauf » Fri Jun 16, 2017 9:58 pm

I've had no luck finding a Circuit that only has power with the engine running (there might be something at the ECU, but not directly at the fuse boxes), so I'll do the following:

I will find the contact at the Ignition Barrel that switches when the key is turned to start.
But because that's only momentary (it switches off as soon as the Key is released), I'll use a Latching Relay Circuit (below).

I already have the relay to switch the power to the Wideband, which is a direct connection to the Battery. And in my case the Diode is internal.

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Re: Wire with Power only when the Engine is running/starting

Postby BillyCorgi » Fri Jun 16, 2017 10:20 pm

What about the main relay that powers the oxygen sensors and the fuel injectors, etc?
The main relay is turned on by the ECU?
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Re: Wire with Power only when the Engine is running/starting

Postby tom_kauf » Fri Jun 16, 2017 10:40 pm

BillyCorgi wrote:What about the main relay that powers the oxygen sensors and the fuel injectors, etc?
The main relay is turned on by the ECU?

Yeah that's a good idea. I didn't know how to easily check the output of Relays while they're still inplace, but I will find a way. A thin wire attached to the multimeter probe should work.

Do you know if that Relay in the main fuse box in the engine bay?
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Re: Wire with Power only when the Engine is running/starting

Postby bigBADbenny » Sat Jun 17, 2017 7:51 am

Iirc you can use a fuse tap to one of the cabin box fuses.
There's a specific fuse to use, and one to not use as it momentarily loses power as the car is started.
I'll dig up the info ;)

Quote: from https://forums.nasioc.com/forums/showth ... ?t=1685461

Now, find the switched ignition power source that you want to tap into. I used a heavy gauge wire on the back of the fuse block. Verify voltage to the wire you decide to use by checking it for 12 volts with the key in and turned to the “ON” (Ignition On) position and no voltage when the key is in and turned to the “Acc” (accessory) position with a 12V circuit light or voltmeter/multimeter. To isolate the LC-1 from cranking voltage fluctuations be sure you dont use a power source that is 12V+ hot on the Accessory bus. Fellow NASIOC member 'Williaty' pointed out an important detail that I overlooked. That is to be sure to verify that the power source you choose maintains 12v or very close to 12v when cranking. this can be tested for by attaching your voltmeter to the desired power source with one lead and a ground with the other... then crank over your engine and observe your voltmeter reading. if it bounces between 12v and anything lower than 12v, i would suggest you keep looking for another power source. Or, if i shuts off when cranking, as some circuits do, to protect them from these voltage changes, keep looking. said voltage spikes and valleys will probably be hard on your LC-1 controller circuitry. If you use my method, a small pocket screwdriver can be used to pry the locking tab away from the spade connector on the chosen wire by sticking it through the front of the fuse block harness plug just below the spade that you want to tap into, and this will allow the spade connector to be pulled out of the fuse block connector through the back. You can then solder your fuse block wire lead (or other circuit protection device, 5 amp minimum) to the spade connector, being careful not to solder into the connecting surface for the fuse that plugs into that location. Be sure to shring wrap this, and all other solder joints, its common sense and good practice. I included pics with part #'s for the fuse block and fuses, in case anyone needs them.
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Re: Wire with Power only when the Engine is running/starting

Postby bigBADbenny » Sat Jun 17, 2017 8:14 am

IGN2 is the one: constant power during cranking :)

https://www.google.com.au/search?biw=56 ... G93J2v0DDc
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Re: Wire with Power only when the Engine is running/starting

Postby RX25SE » Sat Jun 17, 2017 10:29 am

tom_kauf wrote:But because that's only momentary (it switches off as soon as the Key is released), I'll use a Latching Relay Circuit (below).


How will the relay turn off once activated by the crank circuit? Latching relays are power to 'latch on' and power to power to 'latch off' via two separate control coil circuits.
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Re: Wire with Power only when the Engine is running/starting

Postby tom_kauf » Sat Jun 17, 2017 10:37 am

Thanks for the Info Ben :D . I will do some work on it later today. I thought I had tried to find the IGN2 circuit last time, but I will check again.

EDIT: And yes, I have a Fuse Tap at the moment, but it's connected to Acc power.
Last edited by tom_kauf on Sat Jun 17, 2017 10:51 am, edited 1 time in total.
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Re: Wire with Power only when the Engine is running/starting

Postby tom_kauf » Sat Jun 17, 2017 10:48 am

RX25SE wrote:
tom_kauf wrote:But because that's only momentary (it switches off as soon as the Key is released), I'll use a Latching Relay Circuit (below).


How will the relay turn off once activated by the crank circuit? Latching relays are power to 'latch on' and power to power to 'latch off' via two separate control coil circuits.

That's right. The diagram did have a 2nd switch to Latch Off, but I removed it because it isn't needed in this case. As soon as the Ignition is turned off, the Relay is de-energised automatically. Although the diagram isn't 100% correct (it's just one I found online), it doesn't show exactly how it'd be done in this case. The Coil would be connected to a separate 12V source that switches off when the Ignition is turned off (any Acc source).

I quickly set up the Relay with a bench power supply yesterday, and it worked. The only 12V line that connects to constant power (battery) is the 'Common'.
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Re: Wire with Power only when the Engine is running/starting

Postby RX25SE » Sat Jun 17, 2017 3:22 pm

I may have missed something, but I thought you wanted a circuit that powered up only when the engine is actually running, not when the ignition is on?

Typically a latching relay remains in its last state until voltage is supplied momentarily to the opposite coil. They retain the state they are in (open or closed) even when removed from the vehicle.

If the relay you are describing turns off when the single coil de-energises, then that is a standard relay.
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Re: Wire with Power only when the Engine is running/starting

Postby tom_kauf » Sat Jun 17, 2017 3:41 pm

RX25SE wrote:I may have missed something, but I thought you wanted a circuit that powered up only when the engine is actually running, not when the ignition is on?

Typically a latching relay remains in its last state until voltage is supplied momentarily to the opposite coil. They retain the state they are in (open or closed) even when removed from the vehicle.

If the relay you are describing turns off when the single coil de-energises, then that is a standard relay.


Yeah, that's right but maybe I'm not explaining it correctly. I'll draw a diagram once I'm home this afternoon. I just used this one as an example for a latching relay circuit, and it worked on the test bench.

You're correct, it is a standard relay used in a latching circuit. It'd be impractical to have to press a button every time the car is turned off, to stop the Wideband Heater.
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Re: Wire with Power only when the Engine is running/starting

Postby bigBADbenny » Sun Jun 18, 2017 9:06 am

IGN2 is right there in the cabin fuse box, lowest row iirc:)
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Re: Wire with Power only when the Engine is running/starting

Postby RX25SE » Sun Jun 18, 2017 10:46 am

tom_kauf wrote:
Yeah, that's right but maybe I'm not explaining it correctly. I'll draw a diagram once I'm home this afternoon. I just used this one as an example for a latching relay circuit, and it worked on the test bench.

You're correct, it is a standard relay used in a latching circuit. It'd be impractical to have to press a button every time the car is turned off, to stop the Wideband Heater.


Yep I see, you are keeping the standard relay self energised so it opens at key off.

You could see if the alternator has an output that goes live when it rotates? (can be modded to provide this) This would eliminate having to set the relay each time the car is started.
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Re: Wire with Power only when the Engine is running/starting

Postby tom_kauf » Mon Jun 19, 2017 11:20 am

RX25SE wrote:
tom_kauf wrote:
Yeah, that's right but maybe I'm not explaining it correctly. I'll draw a diagram once I'm home this afternoon. I just used this one as an example for a latching relay circuit, and it worked on the test bench.

You're correct, it is a standard relay used in a latching circuit. It'd be impractical to have to press a button every time the car is turned off, to stop the Wideband Heater.


Yep I see, you are keeping the standard relay self energised so it opens at key off.

You could see if the alternator has an output that goes live when it rotates? (can be modded to provide this) This would eliminate having to set the relay each time the car is started.


Thanks for the idea about the alternator output. I'll look into it.
After a crazy busy weekend, I finally updated the diagram. I'm not sure if I'll use this in the end, but it does work.

You were correct in saying it can't be hard-wired to the battery without a latch-off switch (which I won't have). So the source of the circuit's 12V has to turn off to de-energise the relay. Any source that turns off with the Ignition will do, as long as it can supply the couple of Amps the Sensor needs.

- When the Ignition is turned on, the 'Common' terminal of the Relay gets 12V, but the Coil isn't energised yet.
- When the Key is turned to START, the Coil is energised and turns the relay on.
- START is dis-engaged after the Key is released, but the Latching Circuit (with a standard relay) keeps it energised.
- When the Ignition is turned fully off, the Relay de-energises.

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Re: Wire with Power only when the Engine is running/starting

Postby bigBADbenny » Mon Jun 19, 2017 12:19 pm

Awesome but why not use ign2?
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