Engine Running Sense Wire???

I've picked up a DC-DC charger that uses a sense wire to tell it when the motor is running, so it will kick in and start charging.

I'm hoping someone can tell me where I could connect this sense wire? I don't want to hook it up to any accessory wires as I don't want the charger to start up when I'm parked and listening to the radio for example, so it needs to be only when the engine is running.

The charger and the battery it charges are both inside the vehicle, so if there's somewhere inside that'd be great.

Thanks.

Hmmmm, @nissannewby i reckon this one is yours bud.. With the 24v system in my GQ i added an excite circuit using a halogen globe at teh dash. The globe lights when the ignition is on and when the engine starts excites the 24v alternator and the globe goes out.

Was thinking.

In case this is easier, I've run a chunky 12v cable from the crank battery inside to the DC-DC charger.

I could use a relay to activate that chunky cable, this way I could hook up a sense wire under the bonnet to the relay.

But again, where from?

Most DC/DC chargers have their own inbuilt VSR (voltage sensitive relay) and only start charging around 13.3 then stop when feed drops to around 12.7.

What is this sense wire? Which DCDC unit is it?
Most use ignition and/or voltage threshold of some kind , as John said to activate them selves...
Ignition is easy to find depending on where you mount the unit.

It's a Renogy DC-DC charger. The doco says it won't turn on until is gets a signal on its' sense wire, they just skimped on the circuitry other brands use I guess.

I've been over the schematics and have found that I can get the signal from the wiper fuse as they have power when the ign key is in the 'On' spot. It's a hassle having to do this, but I guess that's why the charger was cheaper than alot of others.

I just read a review on the Renogy that says it has an inbuilt VSR for vehicles that don’t have a smart alternator.

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Originally Posted by 10G

It's a Renogy DC-DC charger. The doco says it won't turn on until is gets a signal on its' sense wire, they just skimped on the circuitry other brands use I guess.

I've been over the schematics and have found that I can get the signal from the wiper fuse as they have power when the ign key is in the 'On' spot. It's a hassle having to do this, but I guess that's why the charger was cheaper than alot of others.

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If it really needs a signal on that sense wire, you can simply connect it to the cable on the charger that comes from your main battery. That will be the same as sensing 12v from ignition.

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Originally Posted by jff45

If it really needs a signal on that sense wire, you can simply connect it to the cable on the charger that comes from your main battery. That will be the same as sensing 12v from ignition.

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It will charge full time/even if the engine is stopped if you do that. My ctek has the same wire, apparently the smart alternators don't always reach the "on voltage" required to activate the charger so you need to connect that wire to a 12v ignition source. You can try it without it, my (Gu) alternator looks close to standard(non smart) voltages. I've never seen mine drop below 12.7 when running and usually hits 14.1 when first started.

Thanks everyone for the help.

You're correct 0-TJ-0, that would charge all the time. I'm going to choose a place from within the fuse panel, the fuses are even marked (IGN) just to make a little easier.

Thanks everyone for the help.

If you do want to connect it you can run a wire direct from the ignition or find a suitable fuse and run a fuse tap from down by your right knee. I'm not an auto elec but for the minimal current draw something like this might be your easiest solution;

https://www.ebay.com.au/itm/2-x-Add-....m46890.l49286

Just hook up to the ignition. Simple. Renogy a simply using the term "sense" wire. Quick flick through the manual it actually does cut off at a certain volt threshold.

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Originally Posted by 0-TJ-0

It will charge full time/even if the engine is stopped if you do that. My ctek has the same wire, apparently the smart alternators don't always reach the "on voltage" required to activate the charger so you need to connect that wire to a 12v ignition source. You can try it without it, my (Gu) alternator looks close to standard(non smart) voltages. I've never seen mine drop below 12.7 when running and usually hits 14.1 when first started.

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I did say “if it really needs that wire connected” to turn on. The VSR should handle it from there. I don’t believe it will continue to charge until the main battery runs flat.
My Projecta IDC25 continues to charge when I switch off until the main battery gets down to 12.7v

Just had a look at the Renogy wiring and it apparently needs that wire to switch it on. Strange if it has a VSR already..

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Originally Posted by jff45

I did say “if it really needs that wire connected” to turn on. The VSR should handle it from there. I don’t believe it will continue to charge until the main battery runs flat.
My Projecta IDC25 continues to charge when I switch off until the main battery gets down to 12.7v

Just had a look at the Renogy wiring and it apparently needs that wire to switch it on. Strange if it has a VSR already..

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I wasn't trying to be short with ya mate. I never ran the main battery down far enough through the ctek to see what voltage it would stop at. I assume you're right and wouldn't run it flat. Nice to shut it down with 2 batteries at full charge though.

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Originally Posted by jff45

I did say “if it really needs that wire connected” to turn on. The VSR should handle it from there. I don’t believe it will continue to charge until the main battery runs flat.
My Projecta IDC25 continues to charge when I switch off until the main battery gets down to 12.7v

Just had a look at the Renogy wiring and it apparently needs that wire to switch it on. Strange if it has a VSR already..

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My Intervolt is the same, if its on the "Ignition" option it will ONLY run if IGN is on and will only cut off if minimum volt threshold is reached.
But there is a voltage sense option too.

I wonder why they have that option. It obviously can’t be switched on when it’s getting solar input so why have it with vehicle charge.
12.7 is normal standing voltage for a battery so it’s not like the DC/DC is hurting the main battery when the vehicle is switched off.

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Originally Posted by jff45

I wonder why they have that option. It obviously can’t be switched on when it’s getting solar input so why have it with vehicle charge.
12.7 is normal standing voltage for a battery so it’s not like the DC/DC is hurting the main battery when the vehicle is switched off.

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Intervolt will kick the unit into action if it detects Solar volts. But in IGN mode, it will entirely isolate its self from main battery if IGN is off, no matter what.

I haven't had anything to do with the Renology stuff but every other Dc/Dc I have installed/played with the "sense wire" is only req'd if the vehicle is a smart alternator config.

Old school vehicles you leave that wire disconnected and the VSR does all the work.

The sense wire is there if/when the Alt drops below the VSR cutout due to the "smart" Alternator function of the ECU dropping to, say 12.8.
The sense wire input then overrides the VSR low volt cut and the DC/DC keeps working.

If you do need the sense wire connected on a "dumb" Alternator vehicle to get the Renolgy to work at all then any of the "Ign On" circuits will be your best bet

Ah, I think you guys are looking at the combined DC-DC & MPPT models. I've got just the DC-DC model & a seperate MPPT charge controller. See below ...

Attachment 83700

I went this way as the seperate MPPT can take up to 100v solar input, where as the combined unit can take up to 25v solar input, it's a more efficient way to use the solar panels I have.

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Originally Posted by 0-TJ-0

If you do want to connect it you can run a wire direct from the ignition or find a suitable fuse and run a fuse tap from down by your right knee. I'm not an auto elec but for the minimal current draw something like this might be your easiest solution;

https://www.ebay.com.au/itm/2-x-Add-....m46890.l49286

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Thanks 0-TJ-0, that's what I'm looking for. Do they call those adaptors 'add a circuit' or something??? Anyway, bloody useful.

I haven't really ever thought of using them but a couple things I've ordered recently came with them pre-installed. I don't use them because I have some easy access ign/acc points already setup. Perfect for simple little things like you want though.

I soldered a wire to the back of a cigarette lighter socket to use as a sense wire for relays and things.

Alternatively you could go with a voltage sensing relay which only connects when the alternator is making upwards of 13.3v