Major MINI problem

[Capsaisin]

Sure, but the alternator is impedance matched to the battery, not the standard car circuitry. We are obviously going to disagree on this, but I was brought up to understand that if you wanted to diconnect the battery, you had to switch on the headlights and maybe also the heater blower.

If you wanted to isolate the battery, for example on a circuit car, you couldn't just fit an on-off switch, the switch had to have a built in ballast resistor which cut across the alternator to prevent it frying.

[MINI-Morgan]

News to me too.... my personal opinion would be that the power steering pump, ignition system and endless list of ECUs will provide enough load A charged battery will only load the alternator max of half an amp! And before I get loads of responses I did say Charged! so a battery after 30mins running.

Here's the but! But the alternator cant account for surges in power where the battery normally acts as a big capacitor so how would it cope alternatively..... hmmmm

If someone ever tries it let us know! Just dont touch the positive against the chassis with the engine running

[DaFlake]

, I have done it. I did it when my car battery died about a year ago as I wanted to make sure my alternator wasn't bad. No problems so for.

As mentioned by MINI-Morgan, the battery isn't putting that much of a load on the car. It is your car system that is providing the load.

Anyway, we are talking about trouble shooting a system that is already having problems. The other method is to simply breakout the multi meter and test it. Both are easy to do....

[MINI-Morgan]

Like above a simple voltage check should tell you if its working ok. Or put the alternator in series through the multimeter if it supports amps too see how much its providing. All very simple stuff any half decent mechanic should be able to do..... well hopefully.

[oldmots]

I agree, without the battery, all kinds of stray currents develop which can wreak havoc with chips. It is not smart to remove the battery and run the motor, sometimes you will be lucky, other times, you will fry stuff. I have seen alternators melt down and smoke in shops where characters did this.

[DaFlake]

Quote: Originally Posted by oldmots (original)

I agree, without the battery, all kinds of stray currents develop which can wreak havoc with chips. It is not smart to remove the battery and run the motor, sometimes you will be lucky, other times, you will fry stuff. I have seen alternators melt down and smoke in shops where characters did this.

Hmmm... In my efforts to support my quote above I have found that I am in the minority and although I have done this and not had any problems, I am considered lucky.

So, let me go on the record and retract my previous statement.

The best and only method that should be used to test and alternator is by multimeter. It is still a very simple thing to do.

[boobels]

Quote: Originally Posted by DaFlake (original)

It is a fairly common part to fail on any car. 40K does seem a little shy, but I have replaced them at as low as 15 on some cars. 300 pounds seems very high for the cost, who is doing the work? You didn't take it back to the dealer that didn't know something was wrong with it did you?

If you are out of warranty, I highly suggest that you find a good local garage.

Nah it is in the local indie garage, not going back to a stealership, especially after they couldn't find the problem given 4 days of looking!!

Thanks everyone for your help and advice, hopefully tomorrow I can go back to enjoying my car

[THEWORKSMINI]

Which dealer did you take it to? Name and Shame time I think! Testing the alternator is a very easy job in a BMW dealership, the GT1 has a complete test schedule too! What many people forget is that a good voltage output from an alternator doesn't necessarly mean it's ok. The charge current under load should be checked too!