Battery "discharge" problem

[nikkj]

My V reg Polo has an electrical problem that needs to be sorted out.

If the car is left unused for three days (two when it's cold outside) it refuses to start :zx11:. The symptoms are like a pancake flat battery and the clock and radio unset themselves.

Once the car is jump started and left runing for 5 minutes or so then it's OK until the next three day rest. The battery is new and the alternator seems to be charging OK according to my multimeter.

Can anyone give me pointers on how to find the problem, please?

Thanks

[Daz Seaton]

check there isnt anything draining the battery such as the boot light etc. i'm sure you can get someone to check if the battery is being discharged.

[nikkj]

Hi Daz
I've already tried leaving the boot light, courtesy light and the central locking disconnected without stopping the problem.

The battery shows a good voltage on a meter - not under load - soon after being jump started.

[Daz Seaton]

have you checked your battery to starter motor and battery to earth connections. if these are poor then you can get the symptoms of a flat battery. a good wire bruch and contact paste sorts them out.

[nikkj]

Thanks for the tip. I'll clean up the contacts this weekend and report back when I know if it's worked.

[vwjoe]

I agree with Daz, when connections are too worn or dirty they give the symptoms of a discharged battery. if cleaning the main connections don't work then there's probably a short circuit somewhere in the electrical system.

[nikkj]

I finally left the car unused for 48 hours and had the same problem :mad:



Daz you said: have you checked your battery to starter motor and battery to earth connections. if these are poor then you can get the symptoms of a flat battery. a good wire bruch and contact paste sorts them out.


So far:

I've cleaned the terminals and made sure everything is tight. Checked the earth points and they show as being good (I couldn't get to the starter motor terminal though). I came across a nice little gadget that has spade connectors and lets me check for current going through each fuse terminal - nothing is showing a drain. It seems to be a drain because the car tries to start, turns over VERY slowly and the electrical stuff resets itself - clock to zero, radio memory lost etc.

The battery is heavy duty and is one year old - it was replaced under guarantee because the previous new one gave up the ghost.

Can someone talk me through how to check the alternator is charging, please? The voltage at the battery goes up to 14 when the engine is being reved but I don't know if that's the best way to check for correct charging.

I've had it checked out by a garage last year and no-one can seem to find a power drain. It's a particularly bad problemin the cold weather.

[Daz Seaton]

sounds like a faulty new battery then. worn batterys fail totallly in cold weather and the first signs a weaking battery is loss over of power over a short period. if it was a half decent battery it should have a 2, 3 or 4 year guarantee. worth checking.

[crauch6]

Hi, if battery is OK and it's cold starting problem have you checked coolant temp. sensor. My polo had cold starting problem and after changing temp. sensor problem was fixed.


sounds like a faulty new battery then. worn batterys fail totallly in cold weather and the first signs a weaking battery is loss over of power over a short period. if it was a half decent battery it should have a 2, 3 or 4 year guarantee. worth checking.

[Crasher]

Does your multimeter have a 10amp current range and do you know how to use it to measure current flow? Is the battery a Bosch Silver?

[nikkj]

Thanks for the replies guys.

Daz,
The battery is top of the range Halfords heavy duty one with a good guarantee. I put one in when the problem first showed itself a few years ago and Halfords have replaced it twice already - for free with a new guarantee. That's four batteries in total that have failed to stop the problem.

crauch6,
Can I check/defeat the probe to see if it's the problem? Remember the problem is still there in the summer, just worse in the cold weather. That's not too surprising though.

Crasher,
Yes. My meter does have a 10amp range. I've never used it but I guess it's a matter of putting the meter in series on the circuit being tested?
The battery is a Halfords own brand not a Bosch.


FYI
At one stage I thought the alarm system was activating the central locking system (CLS) randomly but when I disconnected the CLS pump for a wek, it didn't help matters.

[Crasher]

Yes, just take off the thick red wire on the positive terminal and attach that to the common on the multimeter and attach the lead to the amp connection of the meter to the red wire. The very thick black wire from the battery goes to the starter but also to the alternator so there is a chance that the alternator could be the problem if you don’t find a significant draw on the other wire. This nearly caught me out a few weeks ago on an Audi A3 1.8T with a similar problem. I tested the draw into the car and found nothing and then tested the draw into the alternator and found 1.3 amp being consumed by the alternator with the engine not running, the first time I had even seen that.

[nikkj]

I've finally managed to look at the current at the battery. The car failed to start yesterday and needed a jump start from another car - my portable jump start battery was not good enough. After one start it was fine for the rest of the day and started first time this morning even though it was cold overnight.

The earth terminal to earth lead shows 0.2A for a second or so and then drops to a steady 0.02/0.03A

The red wire to positive terminal shows an initial 0.3A (the alarm siren sounds) and drops to 0.13A for about 10 seconds and then setles at 0.02/0.03 A.

The black wire to positive shows 0.0A .

So I suppose that's good news in a way - no short circuits. What's an acceptable discharge rate?

[Crasher]

Those drains are fine, you need a new battery or alternator but probably the battery.

[nikkj]

I think I'm getting to the bottom of the problem.

A bit of history first:
I had a Sigma alarm fitted as soon as I got the car and discovered that the car had central locking but that the pump needed to be replaced. I also had the optional extra of automatic window closing when the alarm is activated. I was never sure if the discharge problem came with the car or the alarm. To be fair, the alarm people put meters on the car several time in the early days and couldn't pinpoint the problem.

Until recently I thought the alarms self locking system was periodically activating and that this caused the power drain over a day or so. I'd disconnected the CL pump for a week without solving the problem and had given up on that idea.

While I was playing around with fuses to find a power drain, I disconnected the automatic window module(AWM). After three days of non-driiving over the holidays I tried the car this morning and it started first time :D .

It seems that the self locking is being activated but it's the windows that were taking the power.

Someone told me that the windows have a thermal cutout and so can draw a lot of power before swithing off. Can anyone tell me exactly how the window electrics work with an automatic closing module? More importantly, how do I tell if the AWM is faulty and can be replaced or whether things are best left lone? Normally I'd just put a replacement unit in but from what I remember this option cost me quite a bit on the alarm and I don't want to throw money away on something taht may be of no use to me.

[Crasher]

Those window closers are useless on that system; the facelift Polo 6N2 used a different system that doesn’t require a separate window closer unit. The Golf 2 used the same switches and wiring as the 6N1 and I never got one to work properly due to the switch design. Those windows have a thermal trip fuse on the fuse box which is a little metal can in a fuse holder.

[nikkj]

Looks like it's not worth replacing then.
Well, hopefully the problem is solved.
:beerchug:Thanks for the help. Have a Happy New Year. :beerchug: