Technical Excessive Battery Drain / Voltage Drop

Jacquess

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Joined
Sep 27, 2013
Messages
1
Hi Guys

I know this topic has been covered a few times and I've followed the suggested remedies but to no avail.

First off, the car is a GP 1.4 16V 2006, with regular service and no major issues until now (apart from a centre brake light that was on the blink for awhile).

Anyway, a few weeks ago the car died on the road and subsequently had its battery replaced (the original Fiat battery - 7 years old) and the mechanic also sent the alternator in for repair (which they struggled with, apparently). The car came back after about 2 weeks and still has issues. Being holidays they are closed until January so I am self diagnosing while its parked in the driveway.

The battery drains down from 12.85V to 10V in less than 5 hours.

Yesterday I removed each and every fuse in the engine compartment, dashboard and boot systematically, but this does not stop the drain. At one point it appeared as if the removal of the main 60A fuse did the trick, but it now seems that that was a once-off only.

I've checked the earthing as it's been suggested that it could be a bad earth causing a battery drain. Its seems ok, but the reading varies. I have another punto (2012 model) and use it to compare voltages, amps and resistance. Sometimes the reading on the troubled car is the same as the 2012 model and sometimes the resistance is 3 times as high. I check this by connecting the negative DMM terminal to the negative battery post and connecting the positive DMM terminal to the engine or chassis. As yet I can't see a pattern. Could a bad earthing cable be causing battery drain this severe? Then again, considering the following, maybe it's not the problem:

I have been able to stop the draw by disconnecting the negative terminal from the battery post directly after switching off the car, then reconnecting the terminal to the respective post a few seconds later. The car then draws about 280mA for about 20 seconds, dropping to 80mA for a while, then eventually going too low for the multimeter to read. This stops the voltage from dropping any further and I can start the car whenever. The drain starts again when the car is switched on and off again and means I have to disconnect the negative post to prevent the battery being killed.

I have read somewhere that the alternator could be the cause and draw power when the car is off, causing the severe voltage drop, but I don't understand what the battery disconnection does to cause it to stop. Am I unknowningly cutting power to a diode or relay that I am not aware of - perhaps somwhere outside the fuse boxes or inside the alternator?

Tomorrow I will check the current through the alternator when the car is off (if any) and hopefully this will hint at something. I'm assuming the DMM should read almost 0 amps at the alternator when the car is at rest - is this correct?

I used to hear a faint click in the cabin from somwhere in the dashboard after I switch off the ignition, usually within 10 seconds, but I have not heard it recently. Are there relays in the dash that I'm not aware of causing a continuous current draw?

Any comments or suggestions would really help!
 
Last edited:

WesM

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Joined
Jan 1, 2018
Messages
8
Hi.... So the 'click' 10 seconds after swith off could be the relay so that the electric windows still function (incase you forget to close them beforehand)... My 03 plate has this function... Wonder if the lack of the click is a sticky/stuck relay? And causing a draw until fully disconnected from the battery?.. Only a guess but worth checking before you start to take it back to a garage
 

Bernievarian

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Joined
Jan 15, 2017
Messages
2,994
A self-maintained relay would have this exact behavior: you shut all power and the relay relaxes, untill you power it again ...

I'd troubleshoot like this:

- disconnect battery - terminal
- reconnect it thru a switch (like circuit breaker used in rally cars)
- connect the DMM across the switch (in //) in 10A mode
- turn switch ON
- cycle the engine on and off as usual, at that moment the battery should drain itself
- turn the switch OFF, the DMM will show what current is drawn
- turn the switch ON again and disconnect the DMM
- turn the switch back OFF and LISTEN TO A RELAY THAT WOULD RELEASE at that exact time
- once found you probably got the culprit or at least and good indication where the problem resides ...

BRs, Bernie

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