6 replies to this topic

[Philly1983]

I bought my mini earlier this week and in the pack was a receipt for a new 45 AH battery, the first few days has been fine however i have noticed the voltmeter going down and down when starting.
Came out this morning and when i went to start the car there was a little life in the battery but not enough to turn it over fully to start the car.
So after bump starting the car i drove to work which is about 17 mile, now as a self confessed novice i would expect the voltmeter to go up surely as i drive since the car should be charging the battery ? Not mine, the faster i go the lower the needle, as low as 9 volts however when im sitting still with the car just ticking over it sits at 13 volts/
Now i know ive definatly not left the lights on or anything silly the only thing ive been doing is arming the alarm, and i wouldnt have thought that this should drain the battery ?
The battery light is illuminating on start up but going off as normal/

Any advice would be greatly appreciated

Philip

[DaveRob]

worth checking is the alternator belt for tightness.... if the belt is loose then the car will discharge at higher revs and the light will go out on the dash..... but the car will not charge properly

If its not the belt then could be a few things but id suspect the alternator first..... To check this take multimeter and place over battery terminals on the DC voltage range

For an accurate assessment of battery state the following are general voltage ranges for six-cell lead-acid batteries ie what we use.

Note the difference in measurement states ie open circuit and loaded. once your battery gets much below the full discharge voltage read at open circuit the battery is usualy considered dead. It my well take a charge but in all probability will never regain its rated capacity again. so In answer to the question . Measure your battery voltages and find out the readings in all states, in your case at different revs ie idle and say 3000rpm. If its lower than 11.8 volts open circuit or 10.5 with a load on, (maybe lights on BUT ENGINE NOT RUNNING). then when you charge it dont expect the full capacity to return. If after charging THEN LEAVING for 30 mins its 12.8 volts plus open circuit it will be ok but you might not have full rated capacity to play with and it might be worth changing cause sure as eggs are eggs that cold frost in Feb will leave you stranded.

Open-circuit at full charge: 12.6 V to 12.8 V
Open-circuit at full discharge: 11.8 V to 12.0 V
Loaded at full discharge: 10.5 V.
Continuous-preservation (float) charging: 13.4 V for flooded cell construction
All voltages are at 20 °C, and must be adjusted for temperature changes.
Float voltage recommendations vary.
Precise (±0.05 V) float voltage is critical to longevity; too low (sulfation) is almost as bad as too high (corrosion and electrolyte loss)
Typical (daily) charging: 14.2 V to 14.5 V
Equalization charging (for flooded lead acids): 15 V to 16 V
Gassing threshold: 14.4 V
After full charge the terminal voltage will drop quickly to 13.2 V and then slowly to 12.6 V

Technically you should also check the charge current.... but to do that you will need a current clamp meter around the earth lead.... you cant use the ammeter in the multimeter....

Worth checking your battery earth in the boot and also ..... but check that belt for tighness first

Rob

[Philly1983]

Right, my reading are as follow:

Engine off, open circuit :12.00v
Engine off, on load :11.73v

Idle Engine :13.25v

Couldn't check at 3000 rev's because i couldn't reach the throttle from the boot
However at this point id already gathered that from what you were saying Rob it seems the battery has bit the dust, the only explaination i can think is because it might have been standing in the garage where i bout it from because the receipt is from March ?
I checked the belt for the alternator and it was going round at idle, 3000 revs and above so that seems OK, although it still puzzles me why the voltmeter goes down when im driving the car and goes back up to 13v even if Im just sitting at some traffic lights ?
Also checked the connections to the battery and the earth strap and all are good, so it does seem like it may just be a buggered battery ?

[DaveRob]

the readings you have suggest that the alternator is generating a charge at idle...... consequently the battery will be charging at idle..... the problem is at revs.... if the belt is slipping as you rev up the the charge isnt what its supposed to be. I had this prob when I bought my Mini.... idle was ok... but put your foot down and the belt slipped a bit..... not enough to stop the charge light comminig on.... but enought to stop a full charge getting to the battery..... check or change the belt .... onely a few quid... or tension the belt that you have a bit tighter......... if the volt meter is dropping at revs then its prob the belt tension...

Rob

[Philly1983]

the readings you have suggest that the alternator is generating a charge at idle...... consequently the battery will be charging at idle..... the problem is at revs.... if the belt is slipping as you rev up the the charge isnt what its supposed to be. I had this prob when I bought my Mini.... idle was ok... but put your foot down and the belt slipped a bit..... not enough to stop the charge light comminig on.... but enought to stop a full charge getting to the battery..... check or change the belt .... onely a few quid... or tension the belt that you have a bit tighter......... if the volt meter is dropping at revs then its prob the belt tension...

Rob

As always thanks again Rob, Its going into Green and whites on Monday so ill ask them to have a look and change if necessary.

Much Appreciated, suppose its lucky i live at the top of a hill )

Philip

[clydecat]

Check the earth strap on the top of the engine to the firewall. I had very similar symptoms on mine, found the top earth strap is bolted to the engine at the top engine steady, and the bushings had worn, allowing the strap to be loose. Retightened and all was good. Afterwords I did add an additional earth strap from the bottom of the engine. Oh and for a simple test, I wrapped a small wire around an easily accessible bolt on the engine, to a bolt on the body and Viola! charging was normal. Fixed the strap and good for almost three years now.

Good luck!

[Philly1983]

Check the earth strap on the top of the engine to the firewall. I had very similar symptoms on mine, found the top earth strap is bolted to the engine at the top engine steady, and the bushings had worn, allowing the strap to be loose. Retightened and all was good. Afterwords I did add an additional earth strap from the bottom of the engine. Oh and for a simple test, I wrapped a small wire around an easily accessible bolt on the engine, to a bolt on the body and Viola! charging was normal. Fixed the strap and good for almost three years now.

Good luck!

Hi thanks for the advice, i checked the earth strap and everything seemed fine but as a check i tried what you suggested and no change.
Took it to a Mini specialist near me and he said he thinks the alternator is on its way out as the voltage keeps fluxtuating and that when running it should put out about 14.1 v but mine is only giving 12v.

Time to use up that warranty )

Edited by Philly1983, 15 June 2009 - 02:16 PM.