Electrical charging problem

Welshboy

Member
Yesterday afternoon as I got home the power steering stopped so I reversed the car into the drive. From the forum I found out that the power steering pump is electrically driven. Multimeter shows 12v battery. I plugged in the intelligent battery charger into the cigarette socket and it said fully charged. Multimeter on the battery said 12.3 volts so barely charging. Put on a normal trickle charger using again the cig lighter socket it showed the fully charged light in the charger. Started the car and the multimeter said 12.54 volts at 2500rpm- I expected 14v. Read the forum again and cleaned the earth under the passenger headlight. Repeated the start car 2500 rpm multimeter 12.5 volts. Went back to reading the forum. This morning I put the normal trickle charger directly connected to the battery and it has now been charging for 3 hours with the fully charged light dead. Any Ideas anyone ? TIA
 
Assuming the alternator is turning (!) then the voltage regulator module in it may have died. You have to remove the alternator to change the module which is a drag, but it's not too difficult and the voltage regulator is a LOT cheaper than an alternator.
 
Assuming the alternator is turning (!) then the voltage regulator module in it may have died. You have to remove the alternator to change the module which is a drag, but it's not too difficult and the voltage regulator is a LOT cheaper than an alternator.
Thank you. Yes the alternator is turning. Just checked again the multimeter reads 13.2 volts now and the charger is still charging. Weird how the Cig lighter connection method says fully charged but the direct battery connection says different . Now nearly 4 hours with 6 amp charger.
 
Check the date code on the battery, if it's the original, then replace it, if it's more than 5 years, it may also need replacement.
The charger probably monitors the current, amps, thats being fed to the battery. A worn out battery will not charge, hence no current, so will not get to the 13.8 volts that a good battery would.
The cells of the battery degrade, gradually, and irreversibly, over time.
It might be the alternator/regulator, but as it does charge on the charger seems to me to be battery.
Mac.
 
Thank you. Yes the alternator is turning. Just checked again the multimeter reads 13.2 volts now and the charger is still charging. Weird how the Cig lighter connection method says fully charged but the direct battery connection says different . Now nearly 4 hours with 6 amp charger.
There may be a poor connection between your charger, and the cig socket, not all plugs give a good connection to the socket, as sizes can vary more than you'd think.
Mac.
 
Just an update. Turns out the alternator was no good and the battery was ok. A new alternator fixed the problem.
It seems to me that the cig lighter socket charger was getting the state of charge from the ecu which must have a parameter of how many volts being last delivered and cos the alt was duff only just over 12v the ecu thinks the battery was fully charged. cig lighter charging with the intelligent charger works now. Thanks all for your input.
 
Just an update. Turns out the alternator was no good and the battery was ok. A new alternator fixed the problem.
It seems to me that the cig lighter socket charger was getting the state of charge from the ecu which must have a parameter of how many volts being last delivered and cos the alt was duff only just over 12v the ecu thinks the battery was fully charged. cig lighter charging with the intelligent charger works now. Thanks all for your input.
The ciggy socket is connected to the battery via a fuse, so no ecu involvement. The ciggy socket should measure the same voltage as the battery, but if there is a poor connection, ground or positive side, then the difference in voltage between the two is the voltage dropped across that poor connection.
Battery charge state may be based on current drawn by the battery, not just voltage, so low current draw, due to poor connections, can give false indication. The only 100% reliable way is multimeter direct across the battery posts.
Check connections at ciggy socket, and the earth point near the ciggy socket. Also check the condition of the socket itself, as a ciggy igniter, it gets very hot, so surfaces, particularly the outer shell, can get badly tarnished.
I understand reservations about charging via the socket, but my experience, on both the A2 and the Mk1 TT are all positive (pun intended).
Mac.
 
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