Cigarette outlet "leaking" power when off

[Manic]

I tried searching, but couldn't find anything about this.

I'm ditching my cigarette lighter outlet and using it as a keyed power for some gauges. I checked the voltage when then engine was off, but the key was on. Hit 12volts. Bingo, then I turned the power off to just double check that a PO didn't modify it so that it was constantly on. Instead of being at 0.0 volts, it popped up as being 0.43 volts.

I'm not a sparky, but I have a general idea of how electricity works, but this is throwing me for a loop.

Can someone else check their outlet to see if my is just an anomaly? If it's just me, how does just a little bit of power "leak" by?

Thanks ahead!

 

[DLM_2002]

I have seen that in 277/480v commercial but not in a 12v system. Basically its voltage being induced from another circuit that is running next to the other circuit. Only thing i can think of

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[Manic]

Good possibility, that's what I was hoping it wasn't just me.

 

[TheDurk]

I see those stray voltages from time to time. They don't bother me. The GAUGE circuit goes a lot of different places through various PCBs (Printed Circuit Boards) that also have full-time power. A little voltage leakage from a full-time circuit can happen just through dirt and gook that accumulates. But it won't affect anything.

Try this. Take that meter and set it to amperage. Start with the highest range and then keep going as low as you can to try to get a reading. I bet you get less than 1mA which is margin of error. It might show voltage, but it won't supply any meaningful current, and that is what wastes battery.

Induced current is a neat idea, but I don't think it can happen in a DC circuit unless there is motion involved (rotating motor or generator). Not sure though, and I'm too lazy to research it.

 

[IBallEngineer]

I see those stray voltages from time to time. They don't bother me. The GAUGE circuit goes a lot of different places through various PCBs (Printed Circuit Boards) that also have full-time power. A little voltage leakage from a full-time circuit can happen just through dirt and gook that accumulates. But it won't affect anything.

Try this. Take that meter and set it to amperage. Start with the highest range and then keep going as low as you can to try to get a reading. I bet you get less than 1mA which is margin of error. It might show voltage, but it won't supply any meaningful current, and that is what wastes battery.

Induced current is a neat idea, but I don't think it can happen in a DC circuit unless there is motion involved (rotating motor or generator). Not sure though, and I'm too lazy to research it.

I've never studied it, but I think induced voltage can happen. If you coil wire around a screwdriver then touch the stripped ends to positive and negative you create a field which magnetizes the screwdriver. So maybe something like that "can" happen?

 

[TheDurk]

I've never studied it, but I think induced voltage can happen. If you coil wire around a screwdriver then touch the stripped ends to positive and negative you create a field which magnetizes the screwdriver. So maybe something like that "can" happen?

But that is exactly half of a transformer. If you then wrap a second wire around the same screwdriver, you get nothing out of that wire. You need AC to do that. Or would you like to buy a nice DC transformer?

https://van.physics.illinois.edu/qa/listing.php?id=2354

For a transformer to work, the current in one coil has to somehow make current flow in the other coil and the circuit it's connected to. A DC current in one coil will make a magnetic field on the other coil, but a magnetic field by itself won't drive any electrons around. A CHANGING magnetic field, however, does create an electric force which will accelerate those electrons in the other coil into carrying a current. This process is described by Faraday's law of induction. You get a changing field from an AC current, since the current which makes the field is changing.

I like what [MENTION=67856]4R#3[/MENTION] is saying above. That stray voltage may well disappear with a quick short. Might be residual charge in a capacitor somewhere in the system. The stock radio key-on power comes off that circuit, and those are full of capacitors.

 

[Manic]

Great conversation. I design yards for 345-26kv, I still don't understand all the magic of electrical systems.
[MENTION=67856]4R#3[/MENTION] I'll drain the system and take another look, I had the door open when I checked. All of my electrical mods I have done have been completely different systems and I'll disable them to make sure there is no feedback or backflow. Unless, the electrical conditioner I installed is back feeding through the amps, back to the head unit and out to the lighter?

The PO added a aftermarket security system, I need to take it out as it just quit working, possible culprit.

 

[Manic]

Thanks for the mention [MENTION=10169]TheDurk[/MENTION].! I like what you're saying too especially about negligible current draw through 0.43 V being the real issue or non-issue and 15-20 years of dirt, condensation, pet dander and hair, smoking, cheetohs, etc. can create some bizarre high impedance paths (read: stray voltages) where there only an open circuit is expected.

I love a puzzle so took a closer look. See (large) image below with comments.

Would you direct me towards where suspect #1 is located?

 

[Manic]

I won't be able to get to this until Thursday, I have one more thing to do under dash before I can button all that up. I'll just start going through the stock harness, unplug everything, clean, toss in some dielectric grease. I'll see what I can do about removing the old security system. They tossed the stock one, so hopefully everything will still work with nothing being there.

dangit, I just can't rip it out. Time to dig up the FSM diagrams and see what the one lines show.

 

[TheDurk]

Would you direct me towards where suspect #1 is located?

I'll take it. The gray box is the Center Junction Box, which sits almost underneath the steering wheel tube under the dash. Plugs 3B, 3C and 3F (which are the ones in the cigar lighter circuit) are the ones on top right (3B), the second one down--big one (3C) and the big one on the bottom (3F). It definitely wouldn't hurt to pull those and clean out with some compressed air, then hit the contacts with contact cleaner. But I'd do the short test first. If the voltage doesn't persist after a short, I'd forget about it completely.

 

[GangsterOfLove]

Is the voltage still there after you disconnect the battery?

Can you see it with an analog meter?

 

[phattyduck]

0.43V is just about where standard silicon diodes and bipolar transistor bases start drawing microamps of current. Any tiny leakage (microamps) would be clamped at that voltage. It isn't anything to worry about.

The amount of current to get that kind of voltage on that wire is less than the self-discharge of the battery internally.

-Charlie

 

[Manic]

It's just weird because the other keyed power wires I've ran into before didn't have any power when turned off.

I'm just probably being overly cautious, but I don't want to wake up one more and have a dead battery.

It's been a sickly week, cold meds are fun, I'll check the amperage this weekend.

Thanks everyone for the help and talking me off the ledge!