Mk iv Golf battery running down AFTER driving!

BigCon

I bought a 2002 MK iv Golf recently but I'm having a charging issue with it.
After driving it sometimes won't start due to a flat battery.

If it's left to sit for a while it seems that the voltage comes back up in the battery and it starts.
I checked the battery voltage when it was idling and it was reading 14.35V, so I ruled out the charging system.

The battery looked like the original one so I (wrongly) thought that it was f***ed.
Bought a new battery and the same thing is happening.

I drove 20 miles 2 nights ago and after stopping the car would not start, however the next morning it started fine.

I went out just now and checked the voltage at idle - 14.35V.
I revved to 2000rpm and it stayed the same.
Same for 3000rpm and 4000rpm (I thought maybe the charging system wasn't working above idle or at higher RPMs, but I think this is now ruled out).
I repeated the test turning on lights, wipers, demister etc, but it was charging fine at all RPMs.

I'm at a loss now to figure out what's happening.
Also when I bought the car there was an aftermarket radio in it, which I removed after the first instance of the flat battery (thought maybe it was drawing too much current).

So boardies - any suggestions?

swhyte027

Sounds to me like you have a lose power connecting or bad battery connecting check the wires on the starter and the altenator.failing that ul have to do a drain test.but sounds to me like a bad connection

George Dalton

How do you know it won't start due to the battery being flat? It could be a dodgy starter motor or a bad earth strap or a number of other things.

Presumably you have a multimeter since you have been taking voltage measurements. Google how to perform voltage drop testing of the starting system and it should point you in the right direction towards pinpointing the fault.

Mar4ix

are you checking voltage on alternator or battery ? If that voltage on battery, than id say could be bad wire contact.Check wire connections on starter motor, alternator and battery . in last two months, i had two cars with similar problems.

BigCon

Mar4ix wrote: »

are you checking voltage on alternator or battery ? If that voltage on battery, than id say could be bad wire contact.Check wire connections on starter motor, alternator and battery . in last two months, i had two cars with similar problems.

George Dalton wrote: »

How do you know it won't start due to the battery being flat? It could be a dodgy starter motor or a bad earth strap or a number of other things.

Presumably you have a multimeter since you have been taking voltage measurements. Google how to perform voltage drop testing of the starting system and it should point you in
the right direction towards pinpointing the fault.

I should have mentioned that I removed the starter and took it to a shop that reconditions them, they checked it and said it was fine (is there any point in performing a voltage drop test?
I'll check the connections on the starter and alternator while I'm at it.
Thanks for the info...

George Dalton

Of course there is. You do want to know where the problem is don't you?

BigCon

Ok, I performed the starter voltage drop test as per this link:

Based on the results below I think I have an issue with the starter or the starter connections. Next step to remove and reinstall the starter while checking the connections? Any other ideas?
(the page says that the voltage drop should be less than 0.2V in all cases).

Mar4ix

there is another circuit, starter + alternator. alternator is connected to starter, and charge battery via starter connection. usually there loose connection on wire connected from alternator to starter.
Perform different check. start car, and check what voltage you have on alternator, and check what is on battery. if on battery voltage between 13 and 14.4, than alternator charge battery.
Could be alternator working intermittent, reckon, need connect 2 wires on battery, wire up to inside car(through window), and properly connect to tester, drive for some miles, ask somebody drive with you, to keep on eye tester, is any changes there while driving.

could be also something else, like relay is on all times, or some wire shorting somewhere.

Also good could be to check is any load on battery while ignition off, if you know how to check, if not, suggest visit car electrician , and find fault.

for this while you are driving, before night, might just take off plus terminal off battery for night, and in morning, put it back, and start your car with no problems

BigCon

Mar4ix wrote: »

there is another circuit, starter + alternator. alternator is connected to starter, and charge battery via starter connection. usually there loose connection on wire connected from alternator to starter.

Ok, sounds good, I'll check this as well.

Mar4ix wrote: »

Perform different check. start car, and check what voltage you have on alternator, and check what is on battery. if on battery voltage between 13 and 14.4, than alternator charge battery.

I checked this already and it was fine (see op).

Mar4ix wrote: »

Could be alternator working intermittent, reckon, need connect 2 wires on battery, wire up to inside car(through window), and properly connect to tester, drive for some miles, ask somebody drive with you, to keep on eye tester, is any changes there while driving.

Sounds good in theory, but there's no way I'm going to do that!

Mar4ix wrote: »

could be also something else, like relay is on all times, or some wire shorting somewhere.

Could be something like this alright!

Mar4ix wrote: »

Also good could be to check is any load on battery while ignition off, if you know how to check, if not, suggest visit car electrician , and find fault.

Checked this already and it's not drawing current with ignition off.

Mar4ix wrote: »

for this while you are driving, before night, might just take off plus terminal off battery for night, and in morning, put it back, and start your car with no problems

No need to do this as the battery only drains when driving...