10 replies to this topic

[Amy_Green11]

Cooper
1992
1275cc

Hi there. I recently bought the above car and when I got it home I found it wouldn't start the next day. My boyfriend has been knocking around with her for a while and reckons that the alternator brushes have to be changed. I have had to buy a new battery for the car because the one I got with it was wrecked. So it was starting fine for a couple of days after fitting the new battery and then boom she's not starting again. So it's losing charge now and the fan belt started squeeling so we had a look at it and it turns out that the retaining bolt which goes underneath the alternator wasn't even there! So we got a nut+bolt and tightened up the fan belt to a deflection of about 13mm (the fan belt is fine by the way) and we're getting a charge from the alternator now. We did a few tests, the following readings were taken from the battery:

Ignition off, car idle: 12.35 V
Car started and ticking over: 13.4 V
Headlights on: 13.14 V
Headlights and radio on: 13.1 V
Headlights, radio, and wipers on: 13.01 V
Headlights, radio, wipers and heating on: 12.9 V

0.5 V difference

So there is a charge there but it is being diminished everytime there is a load placed on it. Of coures you want a charge of at least 1V. So taking all of that into account my boyfriend thinks the alternator brushes need to be changed. I'm just wondering whether the community agrees? If so can you tell me where I could buy a set of them because I wouldn't know where to start looking as I am a new Mini owner I'm fairly sure everything fitted is currently standard by the way. It's a bit of a baptism of fire for me with this Mini hehe

Thanks in advance for your help,

Amy.

[Stevee]

what one looks like in an exploded diagram or technical drawing

to be fair don't sound like its playing up it seems to be charging the system if its making funny noises its the bearings on there way out.

[xBR4DLEY]

Yeah , does sound fine , all the voltages are fine. If the old one was on the way out , I personally would just buy a new one.

[cooperrodeo]

Voltages don't look fine to me. You should have more like 14+volts off load and about 14v on load. If the brushes are dodgy then I would have expected an intermittent output or none at all. The brushes last for absolutely ages unless the slip rings are clapped.

[Amy_Green11]

Thanks for the replies guys Does it not seem though that everytime a load is added that those loads are taking power from the battery itself and the alternator is not making up for the charge that is being taken? Hence pointing to the alternator brushes not creating enough charge to replenish the battery and take responsibility for the loads that are added.

Edit: I agree with what cooperrodeo has said about the voltages. if you wouldn't have thought the symptoms would point to the the brushes where do you reckon the problem could lie?

Edited by Amy_Green11, 08 March 2011 - 07:48 PM.

[Bob_R]

Thanks for the replies guys Does it not seem though that everytime a load is added that those loads are taking power from the battery itself and the alternator is not making up for the charge that is being taken? Hence pointing to the alternator brushes not creating enough charge to replenish the battery and take responsibility for the loads that are added.

Edit: I agree with what cooperrodeo has said about the voltages. if you wouldn't have thought the symptoms would point to the the brushes where do you reckon the problem could lie?

It is possible that the brushes are worn, and the noise is arcing. A good motor factors should be able to help you out. Also check the voltages at the back of the alternator and solenoid, sometimes a little bit of dirty on the battery terminals creates a resistance. Plus check your earth bonding cables for tightness and corrosion, at the sub frame and boot connection. Dead battery sympton could also be a loose earth.

[Amy_Green11]

Thanks for the replies everyone, they've been very helfpful!

[Amy_Green11]

Hello again guys. Was just down to try and start her and she didn't start. It is cold this morning but she should still start. I took a reading off the battery and it's gone down overnight to about 12.01-12.1. Maybe the alternator is just screwed and is discharging the battery overnight? Would you recommend I just replace the alternator? That's the line I'm thinking along at the moment.

Thanks.

[redhotminilewis]

Have you checked to see if anything is draining the battery when the car is off?

[Dan]

Reconditioned alternators are so cheap and plentiful now that it's not really worth wondering what's actually wrong with it, let the reconditioner deal with that. Once you have found the running voltage is not sufficient, and you've eliminated possible causes like bad earth staps, poor connections or a slipping or worn out fan belt or dirty pulleys just change it.

Of course if you have added a lot of electircal accessories the alternator might simply not be up to the job. 0.3v loss overnight is a little high, even if you have a radio memory and alarm being powered. Is there a lot of stuff in the car that constantly uses power? Or a lot of accessories?

Incidentally to those posting above who thought and advised that the voltage was acceptable, anything less than 14v at the battery with the engine at fast idle and the headlamps on is a fail. As is anything over 14.7v. Maybe not due to the alternator itself, but a fail of the test. Please remember the warning given at the top of technical pages.

[Amy_Green11]

@ redhotminilewis: Nothing should be draining the battery overnight. The only additional electrical accessory in the car is a new radio, But I even disconnected the constant live so it wouldn't drain the battery.

@Dan: The earth in the boot is looking dodgy so I'm going to get a new cable and things for that. I also plan to mount an earth strap to the engine for the sake of it. As I've said the fan belt is fine and there's no dirt on the pullies. Can you recommend a place to get reconditioned alternators? Also, as I'm new to Mini could you recommend a good strong alternator as I do intend to eventually install a satnav alongside the radio and I need to get my fogs working. Will probably fit an alarm system too.

Thanks for the help so far