Alternator woes...

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tom bola

tom bola

New Member
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121
Location
East Lothian
Help needed before I take ma Landy to Dunbar harbour and drive it off the pier.

Charge light would not go out, all connectors clean, so ordered new alt. Britpart one came, which was fitted, but the light still would not go out after 80 mile essential trip. Local garage suspected duff alt from Britpart and gave me a Lucas one to fit. On fitting the lucas one, the light went off - wayhay I thought. Switch off, clear up tools etc and then decide to go for a run to check all is well. On starting up the second time, the light would not go out. Rev engine, still wont go out. Drive off and within 100 yds, the light went out. Good I though.

Today, same thing, light wont go out when revving, but will after 100 yds or so. After 15 miles, the light goes into disco mode and the ammeter needle is swinging back and forth. About turn and drive home. Stumped.

I have made a temp earth off the alt casing, but this makes no difference. There is 12.7v in the battery and the same volts coming out of both large spade connectors on the plug, so the alt is getting power to begin with.

Any ideas before I head to the harbour? Surely the light will go out after the landy is driven off the pier??????

Cheers.
 
Sorry should have added that get 12.7v across batter with engine running. Ammeter on dash shows zero current or neg current with something switched on. Either I have had 2 duff alts in a row (is that normal???) or there is something else after the alternator? Am stumped.
 
tis not normal to have ammeter with an alt. by pass the fooker and go striaght to yer battery. 12.7 is not a good voltage for a running engine with an alt.
by passing the fooker will have the addded advantage of elimiating it from causeing the problem
how many wires are going into the alt??
have you check the main earth to the battery?
is the battery in good condition?
 
Slob - the battery is grand. 12.7v. The ammeter is in the dash. I thought that running a temp earth from the alt casing to the neg on the battery would rule out a bad earth elsewhere - it didnay make any difference....
 
Standard 3 pin lucas plug on the alt. 2 large spades and one wee one. The 2 big ones show 12.7v an nowt on the wee one. Am I right in thinking one bog one is the pos to energise the alt and the other is the return with the wee one being the warning light?
 
remove the bulb. That'll stop it bugging you and save polluting dunbar harbour. Then if your battery goes flat, it's the alternator. If it keeps its charge, your light wire is frayed somewhere... it's what I'd do, but I'm useless with car wiring - you could borrow my Haynes auto-wiring book, I suppose.
 
Erm, I used a jump lead from the alt casing to the neg on the battery. Had a multi meter across the battery, did not move from 12.7v so no leccy getting made/getting thru.
 
Sounds a bit advanced/dangerous for a lowly peasant like me im afraid. U really think the ammeter could be the route of all evil? Never considered it, but as I said, am a peasant at this sort o stuff, amongst other things.
 
fook sake if youve got a new alt, nah two new alts. you've eliminated the earth side of it and the battery , that only leaves the wire from alt to batt and the ammeter that is wired in series.
soBYPASS THE FOOKING AMMETER and if all yer connections are well then bob should be yer mam's brother
 
On da wiring diagram, only 2 outs on the ammeter are used. One to the batt and the other the warning light. Does ma third one go to the ammeter??? They are all ****ty brown coloured and look the same age. The ammeter has only been fitted for aboot 9 months.
 
oooooo! yer alternator will usually only have two outs..(the two big ones being common). big fooker goes tae battery, sometimes via the solenoid. the small in is the warning light.
when injun int turning and ign is on, the batt volts go through the warning light and earths through the alt. so yer light lights up. when yer alt is kickin out more than the batt then the alt volts go through warning light and cancels out the batt volts. light goes out
yer two big fookers on the back of yer alt are yer charging output. on some alts one is used to excite the alt to get it charging. but i think that has all bin done away wiff theses days. so what then do is join them both up on the rectifier or as some folk call it the diode pack. so you can take one of these and run it up to the battery. then start yer injun and see if the voltage is any higher than it wur before.
 
Cheers slob but this is getting way beyond me! I understand the theory of the above, but I have put oot a call tae a mate who has a mate who's an auto spark.

I will let ee ken how ah get on so ye cun say Ah telt ee so! Impressive knowledge frae a nurse tho.....
 
http://www.c-realevents.demon.co.uk/altgen/hrcircdiag.GIF

The alternator is probably fine.

The BIG tag and cable should always be connected direct to battery + positive, even when the IGN is turned off. There is NO reason why not to connect this cable through your ammeter. It is a good idea, but it will only tell you alternator output, not current draw. Alternator output should instantly match or exceed current draw automatically, so you will always see what is being consumed, because that is exactly what the alternator will make when the battery is up to par, 13.8 volts or so.

The SMALL tag should be connected also to battery + BUT through the IGN switch and the red warning lamp bulb. The bulb is part of the circuit in many systems.

Inside the alternator is a REGULATOR that is desperate to make the battery voltage up to 13.8 volts (nominal).

When the IGN is ON, and the engine running normally, the wee wire tells the regulator what the battery voltage is. If it is less than the nominal 13.8 volts, the regulator takes current from battery up the wee wire, through the alternator brushes, and into the rotor windings. This increases the magnetic field of the rotor, and makes more electricity in the stator windings. This makes three-phase AC electricity which is no good to us, so the alternator uses a pack of diodes to rectify the AC to direct current, which heads off down the big wire to the battery.

It is ESSENTIAL that
1. the wee wire is NOT LIVE when the IGN key is turned off.
2. the wee wire IS LIVE when the IGN key is turned ON, at FULL BATTERY VOLTAGE.
3. the alternator body is well earthed.
4. all the cables are terminated with good connections.

It sounds to me like you are not getting (any or enough) FIELD current to the alternator, which is likely to mean the wee wire is not live when IGN is ON, or is wrongly connected, possibly with a resistance of some sort in series with it, or a really lousy connection somewhere.

Let me know how you resolve it.

CharlesY
 
slob said:
ah think he even put himself to sleep with that one
Click to expand...

No Slob, my friend, wide awake.
The whole answer reached me, so if it didn't reach you it isn't my fault.

Alternator wiring is dead simple. NO mystery there.

It just needs a little logical thought to sort out problems.

CharlesY
 
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