Turn an alternator by hand?

Feek · 29-12-2008, 22:14

Simple question, should I be able to turn an alternator by hand?

Long reason for asking - I've got a problem with the Feekmobile which KwikFit told me is down to the alternator, they put their tool thingie on the car and it appears that it's overcharging. The result is that the battery light is on all the time and I notice the lights getting brighter and dimmer. I can even tell this from the interior light or the battery light on the dash.

A couple of years ago I had electrical problems with turned out not to be the alternator but it was replaced anyway. I had the old one which was taken off the car tested and it was good.

So today I grabbed the old one out of the outhouse, doesn't get damp or too cold) and tried to turn it by hand, but I can't. Does this mean it's seized or should I not expect to manually crank it around?

Jonny69 · 29-12-2008, 22:27

Alternator should spin quite freely with no resistance. Light on permanently means it's dead. The circuitry has burned out most likely and it'll need replacing

Feek · 29-12-2008, 22:31

Damnit, so the one in the car is knackered and the one which came out of the car two years ago and was tested A-OK straight after now doesn't turn. Arse.

Justsomebloke · 30-12-2008, 10:39

They are not that complex if you want to have a go at fixing it mate.
Back in the day I would quite often rip an Alternator apart to replace the Brushes, With a bit of Lube as well they came back brand new, Laugh of it is the new brushes were only £1.87p (How I remember that I don't know) You don't see the brushes up for sale these days but that wouldn't stop me popping one apart to unsieze it.

Lopez · 30-12-2008, 14:00

Get a second hand one from the scrappy. They're not expensive and I bet there will be loads of Focus ones around. They usually test them on the spot for you before you take them away.

phykell · 30-12-2008, 16:25

I agree with JSB - the brushes can stick to the rotor contacts if the unit is left outside in the damp as they're typically spring loaded. The existing brushes can often be re-dressed with emery paper and it wouldn't hurt to re-dress the rotor contacts as well of course.

Replacement brushes, which often cost only pennies, can also revitalise otherwise broken drills, electric garden shears, etc. Brushes can usually be sourced from a machine tools shop.

Before you write off your in-situ alternator make sure the wiring is all in perfect condition. The alternator relies on measuring the battery voltage as you can imagine and there's typically a sense wire for this. Verify it with a wire between the sense and the positive terminal on the battery to duplicate the sense wire function.

mejinks · 30-12-2008, 23:03

My old golf did that, but all it turned out to be was a diode pack on the back of the alternator. It took seconds to fit.

29-12-2008, 22:14	#1
Feek ex SAS Join Date: Jun 2006 Location: JO01ou Posts: 10,062	Turn an alternator by hand? Simple question, should I be able to turn an alternator by hand? Long reason for asking - I've got a problem with the Feekmobile which KwikFit told me is down to the alternator, they put their tool thingie on the car and it appears that it's overcharging. The result is that the battery light is on all the time and I notice the lights getting brighter and dimmer. I can even tell this from the interior light or the battery light on the dash. A couple of years ago I had electrical problems with turned out not to be the alternator but it was replaced anyway. I had the old one which was taken off the car tested and it was good. So today I grabbed the old one out of the outhouse, doesn't get damp or too cold) and tried to turn it by hand, but I can't. Does this mean it's seized or should I not expect to manually crank it around? __________________

29-12-2008, 22:27	#2
Jonny69 Noob Join Date: Oct 2006 Location: Socialist Republik of Kent Posts: 5,032	Alternator should spin quite freely with no resistance. Light on permanently means it's dead. The circuitry has burned out most likely and it'll need replacing __________________

29-12-2008, 22:31	#3
Feek ex SAS Join Date: Jun 2006 Location: JO01ou Posts: 10,062	Damnit, so the one in the car is knackered and the one which came out of the car two years ago and was tested A-OK straight after now doesn't turn. Arse. __________________

30-12-2008, 10:39	#4
Justsomebloke The Night Worker Join Date: Jul 2006 Posts: 5,228	They are not that complex if you want to have a go at fixing it mate. Back in the day I would quite often rip an Alternator apart to replace the Brushes, With a bit of Lube as well they came back brand new, Laugh of it is the new brushes were only £1.87p (How I remember that I don't know) You don't see the brushes up for sale these days but that wouldn't stop me popping one apart to unsieze it. __________________

30-12-2008, 14:00	#5
Lopez Bad Cat Join Date: Jul 2006 Location: Leicestershire Posts: 808	Get a second hand one from the scrappy. They're not expensive and I bet there will be loads of Focus ones around. They usually test them on the spot for you before you take them away. __________________ NO

30-12-2008, 16:25	#6
phykell Vodka Martini Join Date: Sep 2007 Posts: 833	I agree with JSB - the brushes can stick to the rotor contacts if the unit is left outside in the damp as they're typically spring loaded. The existing brushes can often be re-dressed with emery paper and it wouldn't hurt to re-dress the rotor contacts as well of course. Replacement brushes, which often cost only pennies, can also revitalise otherwise broken drills, electric garden shears, etc. Brushes can usually be sourced from a machine tools shop. Before you write off your in-situ alternator make sure the wiring is all in perfect condition. The alternator relies on measuring the battery voltage as you can imagine and there's typically a sense wire for this. Verify it with a wire between the sense and the positive terminal on the battery to duplicate the sense wire function. __________________