Another drama, 6 hour wait for the AA, massive power drain?

[datsundrew]

So, My other half flew to France on Monday morning, returned to Heathrow at 8pm last night to find the battery completely dead.
I replaced the battery 3 weeks ago as a precaution for winter as it occasionally seemed a bit slow to start, but hasn’t been a problem, it’s a top quality varta F18.
After a 6 hour wait for the AA to arrive, a parking security guy drove by and had a jump pack and it started immediately and he drove home with no issues and didn’t stop, getting in at 5.30 am this morning!! How rubbish is that?!
so this morning I go to investigate, put the old (charged )battery on and get quite a spark as I connect the negative terminal…..more than expecte.
I connected my multimeter up to see what the car was pulling, and it promptly blew my 10 amp max meter!! So this quite a drain!
I’ve just ordered another multi meter and deemed the car out of action until further notice
where do I go from here? Start pulling fuses for central locking?
As you can imagine, A2 popularity has gone down a tad after a night without sleep

 

[audifan]

First item I would check / replace is the ALTERNATOR. They have been known for the regulator to partially fail, not put the charge light on but discharge the battery.

 

[Clackers]

So, My other half flew to France on Monday morning, returned to Heathrow at 8pm last night to find the battery completely dead.
I replaced the battery 3 weeks ago as a precaution for winter as it occasionally seemed a bit slow to start, but hasn’t been a problem, it’s a top quality varta F18.
After a 6 hour wait for the AA to arrive, a parking security guy drove by and had a jump pack and it started immediately and he drove home with no issues and didn’t stop, getting in at 5.30 am this morning!! How rubbish is that?!
so this morning I go to investigate, put the old (charged )battery on and get quite a spark as I connect the negative terminal…..more than expecte.
I connected my multimeter up to see what the car was pulling, and it promptly blew my 10 amp max meter!! So this quite a drain!
I’ve just ordered another multi meter and deemed the car out of action until further notice
where do I go from here? Start pulling fuses for central locking?
As you can imagine, A2 popularity has gone down a tad after a night without sleep

Other halves don't like it when our cars play up, especially when they are either driving them or passenger in them!!! I've found that out too...we came home from Mexico to a flat tyre, and no compressor in the boot....nobody willing to even check their boot for a tyre inflator, £135 later, the AA turned up some 5hrs later and pumped it up, then swiftly drove off...I now have compressor in every car!

 

[PlasticMac]

First item I would check / replace is the ALTERNATOR. They have been known for the regulator to partially fail, not put the charge light on but discharge the battery.

You could disconnect the positive wire, that goes to the alternator from the battery, at the alternator. Big black cable. The rest of the car will still be connected to the battery. That would rule the alternator in or out, I think ...
Mac.

 

[audifan]

Big RED wire on the alternator. Make sure you insulate the bare terminal to prevent further shorts.

 

[PlasticMac]

Edited my post.
Mac.

@audifan and @datsundrew
I think you should check again.
I had looked at the circuit diagram, before I posted, but assumed I'd made a mistake, but I just looked again.
Here's the circuit, and the + battery to alternator is, black, (SW).

If the battery is charged, disconnect it, disconnect the black wire from the alternator, insulate it, so it cannot touch anything, re-connect the battery.
If the alternator is the problem, the car will start and run.
Mac.

 

[datsundrew]

First item I would check / replace is the ALTERNATOR. They have been known for the regulator to partially fail, not put the charge light on but discharge the battery.

Will do, it was brand new and £300 last year, but yes it’s possible. I’m amazed it kept charging enough to do the 100 miles in the dark with lights, heater and wipers

 

[datsundrew]

Other halves don't like it when our cars play up, especially when they are either driving them or passenger in them!!! I've found that out too...we came home from Mexico to a flat tyre, and no compressor in the boot....nobody willing to even check their boot for a tyre inflator, £135 later, the AA turned up some 5hrs later and pumped it up, then swiftly drove off...I now have compressor in every car!

Yup, and we are now buying a jump pack for rack car too!

 

[JavaGreen]

@audifan and @datsundrew
I think you should check again.
I had looked at the circuit diagram, before I posted, but assumed I'd made a mistake, but I just looked again.
Here's the circuit, and the + battery to alternator is, black, (SW).

If the battery is charged, disconnect it, disconnect the black wire from the alternator, insulate it, so it cannot touch anything, re-connect the battery.
If the alternator is the problem, the car will start and run.
Mac.

View attachment 114741
View attachment 114742

Wow
Electrics has always been my weak point when things go south.. fantastic advice and elimination. Great stuff

 

[audifan]

While running the alternator may just be putting enough out to keep the warning lamp off but when the engine has stopped the regulator could be shorting out and draining the battery quite quickly. Note this could potentially be a fire risk if things get overheated.

 

[datsundrew]

While running the alternator may just be putting enough out to keep the warning lamp off but when the engine has stopped the regulator could be shorting out and draining the battery quite quickly. Note this could potentially be a fire risk if things get overheated.

that was my thought as soon as I saw there was such a big drain on the battery. It’s disconnected now until I have time to investigate it.

 

[Providence]

I had exactly the same problem and it was the alternator sucking the life out of the battery. My colour DIS showed that the alternator was not delivering the 13+ volts while the car was running, which was the give away. It was enough to keep everything going but leave the car switched off and the battery drained very low. So low that central locking failed.

If you have no colour DIS, getting one of those cheap cigar lighter voltmeters can monitor your alternator well.

After I got the alternator replaced the (new) battery failed and the garage boys reckoned it must have been destroyed by the duff alternator. The DIS revealed that it would not hold more than 9 volts.

 

[PlasticMac]

Wow
Electrics has always been my weak point when things go south.. fantastic advice and elimination. Great stuff

Instead of thinking electrics, think water, header tank in the loft.
The height of the tank is pressure, (= voltage).
The size of the pipe is the flow rate, (= current).
The size of the tank is capacity, (= battery Amp hours, Ah)
So our tank is in a bungalow, so the pressure, (= voltage) is quite low at 12 volts.
The apparent high current drain, (large pipe/big leak), means the header tank, (battery), is emptying quickly.
So, you're looking for a big leak, because all the taps are off, but the tank is still emptying, and wherever it's flowing will get very wet if it was water, (or hot with electricity).
As an example, both headlights on will draw about 10 amps.
Finding the problem will be a process of elimination. The alternator is an obvious suspect, as it contains components that should only allow high current, (to charge the battery), to flow out of it, but a failed one can allow current, (our leak), to flow in too.
Mac.

 

[PlasticMac]

While running the alternator may just be putting enough out to keep the warning lamp off but when the engine has stopped the regulator could be shorting out and draining the battery quite quickly. Note this could potentially be a fire risk if things get overheated.

When the engine is running, the alternator output voltage is greater than the battery voltage, so current only flows out of the alternator into the battery. Once the engine stops, alternator output is zero. If the alternator is good, the regulator circuitry prevents current flowing out of the battery into the alternator. If that circuit fails, then the battery will discharge into the alternator, as you describe. Typically, it's a diode in the diode pack that fails short circuit. Diode packs can usually be replaced.
Mac.

 

[MickAli]

Yup, and we are now buying a jump pack for rack car too!

Hope you get it sorted soon. I always keep a jump pack in the boot and it's proved invaluable and especially when returning to a car park after a long holiday like you.
I have one of those NOCO Boost ones from Halfords for aroung £80, small but brilliant.

 

[datsundrew]

Right, so now I’m even more baffled. I’ve spent a few hours this evening on it with a new meter. Initially the draw was 9.98 amps, which then settled to 5 amps, plus or minus a bit.
I disconnected the main alternator feed cable, no change. I left it disconnected and then pulled each fuse out , 1 out, replace, next one out an so on, still 5 amps. I took up the cover on the passenger floor and pulled the fuses in there…..big ones and one 10amp, still 5 amps?? is it possible I would have to pull multiple fuses to cut the power to say the central locking?
The next possible clue was when I connected the battery (big spark!!!). started the engine and the door locks cycle once- I think it’s been doing this a while possibly. With this clue I hooked up the VCDS, but there is no communication at all. I tried engine, abs etc and that all communicates, but nothing on central locking ??
I noticed the CCCU was a Q code, date 2001 so I believe this is the iffy one ? so in my excitement that I’d cracked it I swapped it for a known working one (AF) ….and it’s still pulling 5 amps!!! What’s even more odd is there is still no communication with the AF unit?
I read somewhere about a door control module going duff in a door, causing a battery drain, but is it possible that this could be the case, and if so would it interfere with the VCDS communication?? And why would pulling fuses not cut the power to that module?
Oh…..and where is the door module located?
Being into classic cars I feel a bit out of my depth here

 

[datsundrew]

Another eureka moment that soon died was the fact I fitted a dash cam, then realised of course that I’d pulled the fuse-doh!

 

[audifan]

Hmmmmm

One thing to note the car can not power down all systems unless the car is locked. It is possible the current draw is down to systems that have not yet gone to sleep. So place the meter in the boot so you can see it through a window and close all doors and lock the car. monitor the meter and it should drop indicating all systems now are asleep. Note it will not drop to zero as some items are still live like the clock and alarm so less than 0.5A.

Repeat the test with the alternator connected then again with the other CCCU.

Standard Audi audio equipment or aftermarket?

The lack of communications does hint at further issues.

 

[datsundrew]

Hmmmmm

One thing to note the car can not power down all systems unless the car is locked. It is possible the current draw is down to systems that have not yet gone to sleep. So place the meter in the boot so you can see it through a window and close all doors and lock the car. monitor the meter and it should drop indicating all systems now are asleep. Note it will not drop to zero as some items are still live like the clock and alarm so less than 0.5A.

Repeat the test with the alternator connected then again with the other CCCU.

Standard Audi audio equipment or aftermarket?

The lack of communications does hint at further issues.

I tried that, but it seems there’s not enough power with the loop through the tester to allow the central locking to lock? I suppose if there’s already a 5 amp draw that the extra required to lock it too much for it to deal with?
I suppose I could get in the boot, connect the battery, lock myself in then disconnect the battery and connect the meter again? Hope the neighbours aren’t watching! Lol.

 

[audifan]

Not sure if this will work but...

Sit in the car with the meter connected and visible, lock the car using the switch on the drivers door ( hopefully will work ) open the drivers door only and get out, now lock the drivers door using the key and watch the meter.