More electricity woes!

T

thecremeegg

Active member
 North Hampshire
So I replaced the starter motor a few weeks ago, all fine!
Yesterday I come home from a friends and lots of yellow lights pop up on the dash and the steering goes stiff.
Pull over and think this screams of no alternator so checked the battery with the multimeter I had handily left in the boot!

The battery had 10v running across it.....I wiggled the battery cables a bit and kicked the tyres etc and got back in the car. The lights then went off and it drove fine all the way home (9 miles or so).
Fast forward to this morning...car starts fine, I set off...get half a mile and again all lights come on and I lose everything electrical.
Get out, check the battery with a multimeter and it's again putting across about 10v.
I then opened the bonnet, hit the alternator with a spanner a few times and wiggled the connector. The reading then read 12v and everything was functioning fine so I drove to work.

Sooooo, any ideas on the problem? Does it scream dodgy alternator or anything else?

Thanks!
 
Possible your battery is dying? My car had a hiccup in July when my intravee started playing up but everything esle seemed fine. A week later I went to start the car and nothing happened - the battery read 10 Volts. Replaced the battery and all has been fine since.
 
You need to measure the voltage with the engine running, preferably around 1500rpm. Voltage across the battery should be around 13.8-14.0v in which case the alternator is working. If the battery then drops to 10v or so when engine off, you probably have a dead cell and the battery is scrap.

Mike
 
That voltage is with the engine running, sorry should have been clear!
Battery is new when I put the starter motor in 2 weeks back - I'll see what it reads with the engine off later.
 
Battery is certainly goosed now anyway so will need replacing once you've fixed the fault. Sounds like the alternator is dead, though worth checking the output directly from the alternator when running to rule out a wiring fault.
 
That's annoying, it's new!
Gah! How easy is an alternator to change as I can't see any guides online?
Also, where do I read the voltage on the alternator itself?

Finally, how come when the battery is reading 10-11v does it start the car with no issues - I thought they were toast under 12v?

Thanks
 
If it's been completely discharged then it will never hold the same charge again. I suspect you've got a slightly more complicated issue, to test the alternator when running just put positive probe on alt output and earth the neg, should be around 14 V
 
Battery will be fine once you replace the alternator, being only a few weeks old it should recover ok once the charging issue is sorted if the battery was older then you would be replacing that too.

Stuart
 
You may find if you check the alternator may be outputting a ripple of AC which will goose all the electrics including the battery and this is normally due to a diode pack fault in the alternator. Check with you multimeter on the AC range.
 
Well it wouldn't start on teh way out of work so that's that.
New alternator coming my way tomorrow, just need to see if I can fit it!
 
Three bolts and I do believe it's quite accessible from the passenger side.

Just don't forget to reconnect the main battery feed like I did when I did mine, thought it had all been in vain.

:rofl:
 
Am I right in thinking they are ali bolts? You HAVE to replace these once release if they are. Usually torque + angle too.
 
Nelly Welly said:
Three bolts and I do believe it's quite accessible from the passenger side.

Just don't forget to reconnect the main battery feed like I did when I did mine, thought it had all been in vain.

:rofl:
Click to expand...

We've all been there I'm sure!

I'm a bit confused as to how to release the tension in the belt - which part is the tensioner?
 
Stuartt said:
Battery will be fine once you replace the alternator, being only a few weeks old it should recover ok once the charging issue is sorted if the battery was older then you would be replacing that too.

Stuart
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^^^this

I know the Z4 is particularly prone to gremlins caused by a bad battery but to suggest battery wil be knackered after being low on or discharged is incorrect . Especially after its only a few weeks old .,and if it wasn't holding a charge I'd be back at the retailer asking for a replacement under warranty .

Check the output from the alternator as suggested above and that the battery holds a charge overnight them eliminate them as possible causes to your problem . You can then move on to other causes like connections etc .
 
Once a battery has fully discharged it will never hold the same charge again. With our cars being so sensitive to gremlins even at 50-60% charge it's a small price to pay to not gave to worry about it again.
 
Scooba_Steve said:
Once a battery has fully discharged it will never hold the same charge again. With our cars being so sensitive to gremlins even at 50-60% charge it's a small price to pay to not gave to worry about it again.
Click to expand...

He's right, over discharge permanently damages the cells.

Mike
 
Scooba_Steve said:
Once a battery has fully discharged it will never hold the same charge again. With our cars being so sensitive to gremlins even at 50-60% charge it's a small price to pay to not gave to worry about it again.
Click to expand...

I'm sorry I disagree , on what basis do you base your assumptions here ? Unless the battery is old and the cells plates have suffer damage from being old or abused and deep sulpheration ( depositing a coating on the cells that won't turn back to electrolyte when charging ) has occurred ,the battery will be ok and return to a fully charged state. Deep cell batteries such as milk float batteries or boating/ caravan batteries are more suseptable to plate damage if they go completely flat . These really need trickle charging when they aren't in use to extend their life. Most modern car batteries have two functions, one is for cold cranking an engine to start it and secondly to help run electrical circuits within the car such as ECU's warning lights sensors etc like a deep cell cycle battery. High power output is needed for starting which deep cell batteries aren't good for so ......There has to be a compromise with this on a car, ideally the secondary function would work better with a deep cell cycle battery but the car also needs cold cranking power ( amps) to turn the starter motor ( which turns the flywheel and hopefully starts the cars firing cycle ) . The more demanding applications on a newer car the more stress on the batteries secondary function increases, but we still need to start the car in the first place . Assuming the alternator is working correctly, the power we take out at starting is replaced with power supplied by the alternator . All this happens with a chemical reaction within the battery with electrolyte turning to sulpheration and back to electrolyte as we start and then recharge the battery. So unless the battery has been abused, or is old then a two week old battery will be fine, if it's not , it's been abused or faulty . As I remember the OP bought the correct Battery , so it's not like it's under powered and trying to work too hard .
 
Ducklakeview said:
Scooba_Steve said:
Once a battery has fully discharged it will never hold the same charge again. With our cars being so sensitive to gremlins even at 50-60% charge it's a small price to pay to not gave to worry about it again.
Click to expand...

He's right, over discharge permanently damages the cells.

Mike
Click to expand...

That is how a battery works, the life span is directly proportionate to 1. the amount of discharge and recharge that takes place , and 2. , it's a chemical reaction that can only take place a number of times before the battery comes to the end of its life , otherwise batteries would go on forever, but with a two week old battery, the chemical reaction still has thousands of times to cycle , and assuming it's is regularly charged it will go on for ages . It's like savings, if you take more out than you put back in, eventually you will run out, but also its time and cycle dependant, like age, over the years we can't do what we could when we were younger .
 
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