Reconditioned alternator problems

[bazyr]

Hi all

My alternator recently gave up the ghost, so I bought another one off eBay - fitted it and the voltmeter on the dash started reading 18V at anything over about 1500RPM!

Took the old alternator to be reconditioned, mentioned to the guys that it probably had an internal voltage regulator, and have just picked it up and refitted it. No charge comin out of it at all!

Oddly enough, with the overcharging alternator installed I get the dash christmas tree effect (all lights on), but not with the reconditioned alternator - although the electrics still work, presumably just from battery power.

Called the place I took it in to and they reckon it's a "fuse in the dash" that's blown. They think the alternator with integrated voltage regulator uses this, but the eBay alternator that overcharges/has no regulator doesn't. I'm stumped. The fuses in the engine bay are all fine. Anyone any ideas? Know what the guy's talking about?

Cheers

[greecysurf]

Hi, you will probaly find the overcharging one has not got a regulater or it has been bypassed, and the original one the regulater failed and not the alternater, a good vehicle electrician should be able to sort it very quickly and cheaply, most reconditioners will recon the alternater but not the regulater. Hope this helps.

[darkdezigns]

when yr recon one is attached,get a multimeter,,start engine,u sud get 13.5v to 14.5v start there first

[SoundsDigital]

Does the light on the dash come on when the ignition is on, but the engine is not running? This light turns the alternator on. The over charging alternator may well have been tampered with and this bypassed. First thing to check is that the light works. If this is the case, then check the voltage at the alternator with the engine running. If this is low then the alternator is defective. It is not unknown for a reconditioned alternator to be faulty. Out of interent, was the recoditioned alternator reconditioned locally, or was it done by one of the big reconditioning companies. There used to be a number of small companies reconditioning alternators around, most have ceased to do this as they can buy in reconditioned alternators and starter motors for less than they can buy the parts in.

An autoelectrician will have a test rig so can show you the alternator charging. If you got it from an autoelectrician then I would ask them to show you it on a test rig as I suspect you have a faulty alternator.

[bazyr]

Thanks for the replies guys!

The alternator is definitely not charging - voltmeter across it with engine running reads 11.5V, ie just the batteries, and no response to revving.

I'm working this weekend so haven't been able to do anything, but will take the alt back tomorrow to the auto electrician's and test it, hopefully in and out of the truck. What I wanted to know was does anyone know how the electrics work for alternators with vs. without integrated regulators? What is this about the dash light turning on the alternator?

Incidentally the place is independent yeah, Khan's auto electricians off Hangar Lane roundabout/North Circular in London. £120 to recondition, but it looks brand new and he had it ready in a day. Will keep you all posted tomorrow...

[SoundsDigital]

Basically, power from the ignition passes through the lamp on the dash to power up the rotor coils in the alternator via the brushes. This starts the alternator charging. Ones it starts charging, the alternator puts power onto the rotor coils through a diode. This puts power to both sides of the light and turns it off. Unless the lamp comes on, there will be no power to the rotor and it cannot charge. The regulator usually comes in a unit complete with brushes.

[bazyr]

Thanks for the help! Got it sussed now...

Basically the pins in the reconditioned alternator plug were wired up differently, one of the parallel pins was the warning lamp pin but when I swapped it to be the "top" pin it worked fine!

From what I gather there are 3 connections; one to battery (voltage sensing), one to ignition (to turn the alternator on?) and one to dash warning lamp... On the wiring loom the always-12v pin must have been the battery, the pin that was 12v with ignition on was the ignition pin, and the third one was dead with ignition on or off, so presumably warning lamp.