What should be a basic electrical question

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4.2 V8 40v biturbo - 480 bhp (plus)
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IchBautAuto
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What should be a basic electrical question

Post by IchBautAuto » Fri Feb 14, 2020 6:14 am

I'm not a sparky but have a working knowledge. What I would like to do is to monitor the total electrical consumption from the battery while the car is shut down. The gauge would be isolated before start so only looking at hotel load consumption, no start and no charge. A maintenance tool as you would have it.

I purchased a 12v 10A led dual gauge from Jaycar, along with mount hardware etc for the boot. I have a bucket of high quality switches and all the usual heat shrink, cable etc etc needed. Somehow I'm missing something basic in the wiring required. The gauge is a three terminal unit with a shunt included, + & - to the battery terminals, complete the circuit with a lead from the neg side of the load on the + circuit back to terminal 3.

This is where I come to a halt. Where is the neg side of the total load in the Rs6 circuitry ???

I can check individual fuses for parasitic load but to get a total reading has me stumped. To the many who well exceed my level, any suggestions or wise words. Everything appreciated.
C5 RS6, Milltek and Wagners: B5 RS4 450 + HP: A4 1.8 GP TQS original: 1963 UNIMOG 404:

HPsauce
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Re: What should be a basic electrical question

Post by HPsauce » Fri Feb 14, 2020 9:44 am

Loads of circuits in any car are just earthed back to the chassis at multiple earth points, which goes back eventually to the battery.
Surely the only place that the total negative side of the load is combined is the battery negative terminal?

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Shoppinit
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Re: What should be a basic electrical question

Post by Shoppinit » Fri Feb 14, 2020 11:13 am

^Yup, that.

Put a multimeter in series with each fuse to see how much current is being pulled by each circuit group.
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Re: What should be a basic electrical question

Post by Classik » Fri Feb 14, 2020 1:27 pm

This is not a straight reply to your your Q but FWIW my battery health and longevity has dramatically increased since I've changed the alternator. Nevertheless I'm following the thread with great interest..
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IchBautAuto
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Re: What should be a basic electrical question

Post by IchBautAuto » Sat Feb 15, 2020 2:00 am

Classik wrote:
Fri Feb 14, 2020 1:27 pm
This is not a straight reply to your your Q but FWIW my battery health and longevity has dramatically increased since I've changed the alternator. Nevertheless I'm following the thread with great interest..
Brand new Varta DIN110 battery, I'd love that to be the answer but after a multi day charge with a 10A CTEK, 12.8v once settled, it still drops gradually to 12.4 or less within a week of just sitting. Something is taking it's share when the car is idle.
C5 RS6, Milltek and Wagners: B5 RS4 450 + HP: A4 1.8 GP TQS original: 1963 UNIMOG 404:

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IchBautAuto
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Re: What should be a basic electrical question

Post by IchBautAuto » Sat Feb 15, 2020 2:22 am

HPsauce wrote:
Fri Feb 14, 2020 9:44 am
Loads of circuits in any car are just earthed back to the chassis at multiple earth points, which goes back eventually to the battery.
Surely the only place that the total negative side of the load is combined is the battery negative terminal?
We're on the same page and what I expected but it is contradicted by what I'm reading. So far it seems there are two ammeter designs (in circuit). One with an external shunt and one with a built in shunt (usually the low amp gauges). The external shunt is sited in the pos cable (in series) and the gauge is in parallel with the shunt. Not so useful for automotive use in my application.

What should be the simple solution is the internal shunt gauge. A simple circuit with my Volt / Amp gauge would have terminal 1 to 12v +, terminal 3 to 12v- for the volt meter, then the amp meter component also uses terminal 1 as a common terminal on the pos cable and terminal 2 is connected to the + cable after the load. If you made up a simple circuit with a light bulb, it would be + terminal, light bulb, ammeter terminal 3 connection then - terminal.

All I've read says if you put it across the battery (+ to - terminal ) it will blow, as it creates a short circuit, and I'm having difficulty in seeing the difference in outcome between that and putting it to an earth point on the body. Got it that I need a load in the circuit and there must be one there anyway consuming the stored power, I'm just trying to get my head around what will happen if I do just connect terminal 2 to earth. Maybe I should just join the flat earth society.
C5 RS6, Milltek and Wagners: B5 RS4 450 + HP: A4 1.8 GP TQS original: 1963 UNIMOG 404:

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IchBautAuto
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Re: What should be a basic electrical question

Post by IchBautAuto » Sat Feb 15, 2020 2:29 am

Shoppinit wrote:
Fri Feb 14, 2020 11:13 am
^Yup, that.

Put a multimeter in series with each fuse to see how much current is being pulled by each circuit group.
Can do that no problems. What I had in mind was a simple maintenance tool that would be long term in addition to the specific issue I have at the moment. I'm expecting this to be one of the living with RS6 things that will crop up from time to time. Concept is to flip up the boot, make the switch that makes / breaks terminal 2 for the ammeter and just check what the total idle amp consumption is. All being well, turn the switch off and shut boot lid. At this rate it may be quicker to do the individual fuse thing.

I have briefly considered a DC clamp meter. Haven't done any research yet but I can get one for a good price, just not sure of their accuracy at the low end of the scale. It could do the same thing in the long run.
C5 RS6, Milltek and Wagners: B5 RS4 450 + HP: A4 1.8 GP TQS original: 1963 UNIMOG 404:

Classik
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Re: What should be a basic electrical question

Post by Classik » Sat Feb 15, 2020 7:04 am

IchBautAuto wrote:
Sat Feb 15, 2020 2:00 am
Classik wrote:
Fri Feb 14, 2020 1:27 pm
This is not a straight reply to your your Q but FWIW my battery health and longevity has dramatically increased since I've changed the alternator. Nevertheless I'm following the thread with great interest..
Brand new Varta DIN110 battery, I'd love that to be the answer but after a multi day charge with a 10A CTEK, 12.8v once settled, it still drops gradually to 12.4 or less within a week of just sitting. Something is taking it's share when the car is idle.
I know exactly what you're talking about, but what I meant is that I suspect the alternator itself (or more likely its regulator circuitry) to play a role in the current leak. This will be confirmed over time but FWIW I haven't had a dead battery since I've changed the alternator. Meanwhile I'm following the suggestions to identify the source of those current leaks.
RS6 C5 Avant 2003 Daytona Grey
Milltek cat-back - 200 cells cats - Wagner IC - Multimap e85/98RON - MTM Wheels - Bilstein B16 - Hybrid Loba 650 turbos - Soon to come: upgraded fuel pumps

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Re: What should be a basic electrical question

Post by bilko1 » Sat Feb 15, 2020 11:47 am

I recently had the pleasure of a current drain, turned out to be the drivers door lock. Only found it by accident as one night I was walking past the car and noticed the dash display lit up just as I does when you open the door. My nominal drain through the earth terminal on the battery is now 23 milliamps after 5 minutes.
Avus Avant, RNS-E with sds and Bluetooth, Milltek, Hotchkis, Bilstein, Forge, ITG, A.C.E, Wagner, FBMFSW, MTM.

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IchBautAuto
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Re: What should be a basic electrical question

Post by IchBautAuto » Sun Feb 16, 2020 2:35 am

Thanks, very handy figure to have for comparison. Also the dash light issue. I might just have to do a once over for dodgy lights inside glove boxes and boots.
C5 RS6, Milltek and Wagners: B5 RS4 450 + HP: A4 1.8 GP TQS original: 1963 UNIMOG 404:

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