Alternators bless 'em

[Oldromola]

I have read of some Stag owners who allege their alternators have nevermissed a beat since the day - 10 or more years ago naturally - they bought the car. And this despite the fact they never evenbother to send the poor thing birthday or Christmas cards.

Well, not so in North Yorkshire where some of us have been chosen, by whom I don't know, to iron out all the potential problems with which alternators can be blessed. At the moment one of mine is working as I believe it should but the other is being slightly bolshie. On start up the voltmeter will show a charge of only 12 volts (less at night if the lights are on) and there it will remain for up to 10 miles before gently swinging up to about 14 volts. There is no sign of the ignition light showing, even dimly, so I'm not unduly worried. I am assuming the problem could be generated (no pun intended) from one or other of the following causes;

• a loose or worn fan belt
• a faulty voltmeter - maybe it's sticking
• a fault in the alternator
• a wiring fault

I have fitted a new fan belt and there has been no change. I don't think the voltmeter is faulty because, at night, when I have the lights on they get brighter when the full chargeis eventually reached. That leaves the possiblilty of a fault in the alternator for the first 10 miles or so or, less likely I should imagine, a fault in the wiring.

Before I change the alternator yet again, I wonder if anybody with electrical knowledge might explain to me what part of itcould be faulty and causing the problem. I am told by an experienced auto electrician that there are refurbished alternators and there are refurbished alternators. It looks as though I have one of the former type here! Fortunately I have on the garage shelf not one but two alternators that he has taken apart and refurbished thoroughly.

[DJT]

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Robert,

I am no auto-electrician so I could be talking out of my fusebox. The voltmeter is, as it says, an indication of battery voltage, not charging amps.Could itbe an indication your battery is on its way out? Or perhaps battery connections getting dirty or loose?

Dave

[seaside bill]

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When your voltmeter shows a no or low charge condition, check if the charging current is reaching the battery. With the engine running at high idle (1500 rpm), measure the voltage at the battery terminals - on high idle, the voltage at the terminals should be between 13.6 and 14.4 volts. Outside that range indicates bad or dirty connections or defective alternator. Other than bearings and carbon brushes there's not much mechanically that can wrong with alternators, so if yours is defective suspect the diodes or regulator. Diodes have the function of keeping the current flowing in one direction - like all semi conductors they're very durable, but one or more of them can fail completely or intermittently. The regulator maintains alternator output to avoid overcharging the battery. Early Stags had external regulators, but most you'll find fitted now have internal solid state regulators - also very durable. Although DIY possible, testing semi conductors is a specialist job, so unless you're an electrical wizz (another) replacement alternator is the way to go

[GDPR]

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OK - please bear in mind that the voltmeter is a very primitive "hot wire" device and cannot be trusted to be any more than a rough guide....

I used to have to do an awful lot of electrical work when in the game and this sounds like it could be one of 2 things - the battery is "cattled" and is presenting an incorrect internal resistance or you have a massive volt drop somewhere......

Using a voltmeter (a proper one) place the probes between the alternator metal casing and the battery negative post and run the engine at about 1500 rpm with the lights on - you should see no more than 0.2 volt - if you have more than that then you have an earth lead or similar in trouble.

If that's OK do the same, but flick the back cover off the wiring terminal block on the back of the alternator and stick one probe on the thick brown wire and the other to the battery positive post - again less than 0.2 volts and you are OK, more than that and you need to check the alternator/starter/battery wiring for corroded connections.

If you have a battery sensed alternator check the thin brown wire is OK at the alternator- this would cause the alternator to give the wrong output voltage as it needs this wire to detect the actual battery voltage.

Also worth just putting the voltmeter across the battery with the engine at 1500 with the lights on - anything over 13.6 volts and the battery should charge fine......

Apologies Bill for echoing many of your points but we were typing at the same time....

[Oldromola]

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Hmmm........the battery is over 4 years old so I am thinking it might well be less efficient that it used to be. Might try to investigate that first before changing the alternator. Thanks for all the suggestions so far - I am most grateful.

[Oldromola]

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Have had the battery tested at my local friendly Halfords, and although they were quite keen to sell me an exact replacement (HB071) at £89.99 they tested my old one and declared it ito be on top form.

Looks like I shall have to try replacing the alternator. Fortunately the one that apperas to be faulty is still under guarantee, and I bought it not 6 miles for home! At last, a result.

[jbuckl]

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I had bad luck with re-con alternators(3) from a'tier one speciallist' based not too far from hertford.... gave up with them ....didnt really seem tocare like they used to.

got a brand new one from a local supplier for less than the rob-dogs!

Goodwins Auto - more info »
301 Highfield Rd, Hall Green, Birmingham, West Midlands, B28 0BX
0121 778 6828

good to deal with these people for a stag alternator new or rebuild
Incidentally the battery on my car was a fourteen year old Bosch Silver (longest battery life ever for any of my cars!)

[Stagdad]

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Robert 2 Stags wrote:

Have had the battery tested at my local friendly Halfords, and although they were quite keen to sell me an exact replacement (HB071) at £89.99 they tested my old one and declared it ito be on top form.

Looks like I shall have to try replacing the alternator. Fortunately the one that apperas to be faulty is still under guarantee, and I bought it not 6 miles for home! At last, a result.

Can't you try the one off your other stag before you pay out?

Doh!!! just read it through,you don't need to pay.