Technical Alternator troubleshooting?

[Tex Gore]

Hi All,

I'm new to this and Fiats if I'm honest. I'm not much of a mechanic either, so all is going really well.

The problem is an S-Reg Punto 1.2s. Won't start without jumpleads, won't run immediately after starting with the jump if I take the leads off, and measuring the voltage across the battery without the leads (after the car has run for a good 10 minutes with the jump leads on) the voltage plummets - starts at 14ish and drops until it hits 5v and the car stalls. This takes about 30 seconds.

When running, no warning signs are illuminated in the car. When I switch on the ignition (after a full battery charge) all lights are illuminated as you would expect (battery, oil etc.) then go out when the car is started. The car starts fine with a jump.

There are no belt squeaking noises and I'd have thought that if it was that loose the battery light would be on in the car when it ran. Also I cannot move the belt on the pulleys.

Any thoughts or suggestions please?

Ah - the previous owner has just informed me that he tried the jump the car and managed to put the jumpleads on backwards - i.e. red to black, black to red with the other car. "There was a lot of smoke from the alternator'. Perhaps this has something to do with it?!

Thanks!

Tex

 

[MikeSalt]

It sounds like the previous owner has fried the voltage regulators on the alternator circuit. Now I think these are part of the alternator itself, so a new alternator should cure this. It's curious that the battery light doesn't come on, unless the detection circuit was damaged in the process.

 

[fingers99]

How old is the battery?

My guess is that if the alternator is putting out in excess of 14v, then thre issue may be with the battery itself. (Can you borrow a decent battery for a day to check this out?)

That previous owner has had to jump it may give the lie to this............

 

[Tex Gore]

Thanks for this. The battery is brand new. The alternator doesn't seem to be putting out 14v. When I run the car and meter it across the battery, the voltage drops down to 5 (when the car stalls) within a few seconds. In other words, I start metering as soon as I take the jump leads off, and it drops from 14 down to 5.

 

[fingers99]

In that case, looks like the alternator. Your choices are -- get one from a scrappy, get a recon one, get a new one, take yours to a starter motor/alternator specialist and get it tested/rebuilt.

I'd go for the first or last, but then, I've a scrappy and an alternator specialist within walking distance.