New Alternator Seemingly Not Charging Properly.

[davemar 16]

I've just replaced my alternator as I suspected it wasn't charging the battery. I wasn't getting any battery warning light on the dash, but when I measured the voltage with the engine running it was around 12.2v at low rpm and dropping to 11.6v at higher rpm (the battery was quite drained at this stage). This explained why I kept having trouble starting after a longish drive.

 

So I decided the replace the alternator, and now the charging voltage is 12.7v and not increasing with rpm. The battery is freshly charged using a charger, hence the higher voltage. This time the battery warning light is coming on, but intermitantly. So I'm thinking something else is at fault. What does the exciter connection actually do or require? I did put a fresh connector on there, so the contact should be good. If this connection is a fault can this prevent charging? I don't want to go to all the hassle of replacing the alternator again!

[Mikey S 29 1 Cars]

I've just replaced my alternator as I suspected it wasn't charging the battery. I wasn't getting any battery warning light on the dash, but when I measured the voltage with the engine running it was around 12.2v at low rpm and dropping to 11.6v at higher rpm (the battery was quite drained at this stage). This explained why I kept having trouble starting after a longish drive.

 

So I decided the replace the alternator, and now the charging voltage is 12.7v and not increasing with rpm. The battery is freshly charged using a charger, hence the higher voltage. This time the battery warning light is coming on, but intermitantly. So I'm thinking something else is at fault. What does the exciter connection actually do or require? I did put a fresh connector on there, so the contact should be good. If this connection is a fault can this prevent charging? I don't want to go to all the hassle of replacing the alternator again!

 

the excitor wire does exactly what it says, excites the alternator into charging. if it wasnt there the alternator wouldnt start charging until about 2500 rpm. have you measured voltage at the alternator to eliminate the main wiring harness?

 

mike

[Alan_M 66 1 Cars]

I've just replaced my alternator as I suspected it wasn't charging the battery. I wasn't getting any battery warning light on the dash, but when I measured the voltage with the engine running it was around 12.2v at low rpm and dropping to 11.6v at higher rpm (the battery was quite drained at this stage). This explained why I kept having trouble starting after a longish drive.

 

So I decided the replace the alternator, and now the charging voltage is 12.7v and not increasing with rpm. The battery is freshly charged using a charger, hence the higher voltage. This time the battery warning light is coming on, but intermitantly. So I'm thinking something else is at fault. What does the exciter connection actually do or require? I did put a fresh connector on there, so the contact should be good. If this connection is a fault can this prevent charging? I don't want to go to all the hassle of replacing the alternator again!

 

Where'd you get the alternator from?

 

I got one from GSF last year (refurbed item) and whacked it on only to find it refused to charge above 5krpm. Useless on an Mi16!

 

Took it back and had to wait a month whilst it was verified on a testbench. Got the money back though.

[davemar 16]

Where'd you get the alternator from?

 

I got one from GSF last year (refurbed item) and whacked it on only to find it refused to charge above 5krpm. Useless on an Mi16!

 

Took it back and had to wait a month whilst it was verified on a testbench. Got the money back though.

 

Got it from Euro Car Parts. Supposedly a new item, not refurbed (they don't ask for my old one back).

 

I was measuring the voltage at the battery rather than the alternator, but I can always try and measure it there instead. Bit awkward to get to though!

[Mikey S 29 1 Cars]

Got it from Euro Car Parts. Supposedly a new item, not refurbed (they don't ask for my old one back).

 

I was measuring the voltage at the battery rather than the alternator, but I can always try and measure it there instead. Bit awkward to get to though!

 

Its not easy but its something i would to rule it out. But,

As Alan said, Ive had LOTS of problems with supposedly reconditioned alternators in the past myself, so much so that i have a chap local to me who takes my unit, rebuilds it and returns it to me usually in a couple of hours. i would reccomend this route if you have a decent auto electrics place by yourself.

[GLPoomobile 958]

Measure the voltage at the alternator first. If like mine, your +VE cable piggy backs the starter motor, you could have a loose connection there (like I did).

[davemar 16]

Measure the voltage at the alternator first. If like mine, your +VE cable piggy backs the starter motor, you could have a loose connection there (like I did).

I remade that cable a few days ago when I replaced the starter, so it should be in good nick. Still no harm in measuring it though.

 

Just took the car out for a short drive and the warning light was lit the whole time, even when revving above 4k. I might take a wire direct from the excited connector on the alternator direct to the battery (via an ammeter) to measure the current. What sort of current should I expect, and do I need some resistance in line?

[Alan_M 66 1 Cars]

Have you got juice on the excitor wire? As if it's an 8v, I'm sure the excitor goes through that brown multiplug on the gearbox, tha cause of many a wiring issue!

 

I think you can check the wiring by grounding it to the chassis.

[davemar 16]

Have you got juice on the excitor wire? As if it's an 8v, I'm sure the excitor goes through that brown multiplug on the gearbox, tha cause of many a wiring issue!

 

I think you can check the wiring by grounding it to the chassis.

 

There's about 200mA flowing through the excitor wire when it's connected, and the engine running. So the excitor wiring seems fine.

 

I measured the alternator's voltage at it's +ve terminal (in case the +ve supply cable was dodgy) and it still sits at around 12.2v (the batteries uncharging voltage).

 

Maybe this new alternator is faulty, but in a slightly different way to the old one (which also didn't charge, but got on warning light), and I'm just unlucky.

[davemar 16]

Yep, duff new alternator. Went back and got a replacement, and the new one charges like a good 'un. Finally might be able to get the thing MOTed before it runs out.