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Discuss Car battery drain in the DIY Electrical Forum area at ElectriciansForums.net

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Serious power drain on battery on Audi 80 1992.30 mins after turning engine off no battery power won't start.ALL main components seem fine.After turning engine off a humming noise comes from back of engine ?this stops if I disconnect negative terminal on battery.Could this be causing power drain.?.if I disconnect negative terminal after turning off it starts fine when reconnected.Any help would be appreciated.thanks.
 
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telectrix

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after switching off get a d.c clamp meter on one of the battery leads. this will tell you what current is being drawn. then investigate, starting with whatever is humming.
 

rapparee

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You obviously have a parasitic drain.

Is there a light in the glove box or boot staying on?
 

telectrix

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think it's more than a courtesy light if draining battery in half an hour.
 
Clamp meter then whilst showing it's draining start taking out fuses until it stop then will know where to start looking and the noise from rear may be fuel pump
 

Lucien Nunes

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I think you have two problems, one of which is that the battery is not holding anything like a normal charge. For a normal battery to discharge in 30 minutes to the point where it will not start the engine, the load would need to be 50-100+ amps, which is more than any individual item in the car and will hardly go unnoticed as it will kick out a lot of heat, whatever it is. I suspect that you have a modest parasitic load and a battery of very limited capacity (or that is nor being properly charged).
 
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Could some fault with fuel pump cause such a quick battery drain.?if so which part ?thanks.
 

telectrix

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first issue would be a battery check. get it discharge tested. and a test of the charging system. then if battery is OK, look for the drain. as Lucian says, have to be a serious fault to drain a good battery in 30 mins.
 

plugsandsparks

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Find it, order exactly the same part from bosch or whoever and replace. fuel pump should not be running when you switch off so if it is, the relay is stuck or have wiring fault
 
Often make specific forums are a good place to find answers to this sort of problem, if it's a common problem it will have cropped up on an Audi Forum.
 

ruston

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Advent Win
If the noise is coming from the back of the engine the relay could well be in the nearside windscreen motor well.
In some Audi models some electrics are housed there.
A common problem was that access required damaging the water seal of the trim of the wiper grill and allowed water ingress into the fuel pump relay , this caused erratic fuel pump problems and eventually failure of the relay, causing the car not to start or erratic running.
This may not apply to your model , but may be a similar issue.
As has been said a visit to an Audi site may be prudent, and this problem alone would not drain your battery in 30 minutes.
Some Audi fuel pumps had a switched negative on cranking.
 
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static zap

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30 mins is fast for a fully charged battery.
(For rattling clicking noises as it flattens ,could still be a red herring ,due to dropping voltage.)
Fresh charged battery , attached to a cold car ,see if anything warms in 10 mins -- (not very professional ) but saves £80 on DC ammeter-probe. (no experience of your model ,but thinking a cooling fan / chunky resilliant wiper motor ,or alternator --Any long forgotten in boot audio gear/alarms)..may feel warm / smell toasty .
 

James

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Your local car spares shop will have a battery tester.
It is basically a large resistor and a volt meter combined.

When they put it on the battery terminals it shows the condition of the battery when it is under load.
Maybe asking them to check the battery would be a good first step.

Alternatively if you have a volt meter, you could with a fully charged battery, disconnect it from the car, put a known load I.e. a light bulb on the battery as a load and check the voltage every 5 min.
I suspect that before half hour is up the voltage will be well below 12v signifying a battery that is well past its sell by date.
 
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