Battery failing?

RUM4MO

Active Member
Jun 4, 2008
6,489
522
South Scotland
I mentioned that increased current draw with ignition on as I've seen the current draw on some of our VW Group cars (within VCDS) with only the ignition on, ie cabin fan OFF, I've forgotten what values I saw, but I was surprised - though I was only basing my own guessed value from previous much older cars, in my case, I felt that it justified me having just bought a "computer support" lead that connects in via the OBD2 port and so with the ignition key out of the car.

Edit:- I think that I had read about what could happen coils wise before I did in deed prove that correct, in the past.
 

Crossthreaded

Active Member
Apr 16, 2019
309
70
Hello RUM. Was the car you saw this current drain on a diesel? If so the most likely explanation would be heater plugs? - just a guess.

As you may know, but for the edification of others, with the old points type ignitions the coil was a "short rated" electrical component. It was basically an electrical transformer with a very hard job to do, transforming the 12 volts (probably nearer 13.5 volts if your dynamo was working properly) into around 10,000 volts to fire the plugs. When the points were closed the battery voltage could flow through the primary windings of the coil and when the points were open the current flow ceased. So current would only be flowing for approximately 50% of the time the engine was running. However if you turned the ignition switch to the "run" position and the engine had come to rest with the points closed you were allowing current to flow without interruption. The result of this was that the multiple windings in the coil just got hotter and hotter until they burned out. If it was an oil filled coil, as was common on many cars, you might experience a nice little bonfire or at best a car which subsequently wouldn't start.
 

RUM4MO

Active Member
Jun 4, 2008
6,489
522
South Scotland
I think that it would have been my 2011 Audi S4 that I was checking through the many battery associated channels and found the one that revealed the present current draw, though I'd expect any smaller engine would still end up with similar current being drawn with the ignition on and the HVAC fan switched off.
 

Crossthreaded

Active Member
Apr 16, 2019
309
70
I think that it would have been my 2011 Audi S4 that I was checking through the many battery associated channels and found the one that revealed the present current draw, though I'd expect any smaller engine would still end up with similar current being drawn with the ignition on and the HVAC fan switched off.
Thanks RUM. Did it give you actual current draw in amps or some other recognizable unit? I'm just wondering, and interested, to know what magnitude of current we're looking at here.
 

RUM4MO

Active Member
Jun 4, 2008
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522
South Scotland
I'll check it again sometime maybe this time on my wife's Polo as the OBD2 port on my S4 has a physical lock on it to protect that car, and removing and refitting that is a pain in the bottom, and add my findings to this thread.
 
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Crossthreaded

Active Member
Apr 16, 2019
309
70
I'll check it again sometime maybe this time on my wife's Polo as the OBD2 port on my S4 has a physical lock on it to protect that car, and removing and refitting that is a pain in the bottom, and add my findings to this thread.
Thank you - no hurry though, just a passing interest.
 

collywobble

Active Member
Jun 20, 2019
72
16
North Devon
All sorted now - the son of friends of ours (who runs a BDA escort in historic rallying and who has just completely restored an Hillman Imp) recommended a local mobile electrician. Half and hour later the car was starting again. He used a power source from which he connected the earth to the lifting eye on top of the engine and the positive to the fuse box on top of the battery. The old battery had a failed cell. All I have had to reset was the clock...
 

RUM4MO

Active Member
Jun 4, 2008
6,489
522
South Scotland
@collywobble, good result, I would have hoped to not have to correct the clock if your old battery was not already badly discharged as well as one cell down.

@Crossthreaded, I blundered across a VCDS screen taken from an Audi A4 with the ignition and nothing else on, and the logged current draw was 12.6Amps - that I think was similar to what I saw, I will try to check the same thing with my wife's 2015 Polo although different details are offered from these newer cars, remember design wise and so electronics wise, an Audi A4 B8 dates from 2009 where as these Polos/Ibizas date from late 2014.
 
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Crossthreaded

Active Member
Apr 16, 2019
309
70
@collywobble, good result, I would have hoped to not have to correct the clock if your old battery was not already badly discharged as well as one cell down.

@Crossthreaded, I blundered across a VCDS screen taken from an Audi A4 with the ignition and nothing else on, and the logged current draw was 12.6Amps - that I think was similar to what I saw, I will try to check the same thing with my wife's 2015 Polo although different details are offered from these newer cars, remember design wise and so electronics wise, an Audi A4 B8 dates from 2009 where as these Polos/Ibizas date from late 2014.
Thanks Rum. 12+ amps just with ign on but not running and no auxiliaries like h/lamps or screen heater? That's something to think on!
 
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