Alternator or regulator?

[robin]

S1 or S2 (assuming it's a Rover K-series engine, not a Toyota?)?

IMPORTANT: always disconnect the battery before working on the alternator; the battery should be disconnected -ve terminal first; reconnected -ve terminal last - if you work on the +ve battery terminal while the -ve terminal is still hooked up you risk damage, fire and injury. Always disarm your alarm just before removing the -ve terminal (you have <60s from disarming alarm to disconnecting terminal; otherwise alarm goes ape).

For the S1 I would lay money on the little wire (and possibly the big wire too) having broken off right at the back of the alternator. You'll need to remove the undertray and reach up and pull on the wires to see if any of them come loose. A little mirror on a telescopic stick (like the sort of thing a dentist uses) might help too. If you ignored my advice, you will just have discovered why you needed to disconnect the battery

For the S2 the failure is more likely to be inside the plastic cover on the back of the alternator itself, though still just a fractured wire that could be repaired by removing the alternator, removing the back cover, spotting broken wire and the rewiring it.

In all cases, finding something durable to rewire it with is the hard part. The crimp terminals are prone to vibration fracture and the wires are exposed to a lot of radiated heat from the exhaust manifold - you need to make sure all your heatshields are in order. Where the heatshields are broken (or for early S1s) not fitted, replace or fit them - otherwise you'll have repeat failures.

If the crimp terminals/associated wiring fails more than once every couple of years you have a heatshielding or vibration issue, IMHO.

In either case you could still have a broken regulator pack; this can be replaced without replacing the alternator if the coils and brushes are still in good working order - but I don't have a source for the regulator pack, so a recon unit might be best bet. The packs sometimes break when the control or load wires go make/break/make/break repeatedly while the alternator is under load - the broken wire is the root cause of the problem, but the reg pack takes it in the shorts at the same time unfortunately.

Cheers,
Robin

[whaleys]

Cheers Robin, time to get me hands dirty I think. Will get that wire seen to then check out the regulator pack. (I have a K-series S2)

When the wiring is all good, if the regulator pack has shorted, will the light on the dash come on? or will it still act like the wire has snapped?

Ta

[robin]

IF the regulator just fuses itself because it hates you rather than broken wire syndrome then it's still possible the light on the dash won't come on.

If the wires are good on the back of the alternator then you need to check the wires inside that plastic cover (on S2 - on S1 the wires on the back is all there is). I should add I've never actually done that - just what I read on a thread in SELOC technical.

Good luck - let us know what you find ...

Cheers,
Robin

[whaleys]

Got the alternator out of the car through the wheel arch (needed that extra elbow) and tested the wiring by earthing the positive side of the dash light sender and wiggling it around. The dash light came on and stayed on, so looks like the wiring is all good. Will be taking the alternator apart tonight...

[whaleys]

Ok guys I need to draw on some more experience...

I have taken the alternator to a very nice chap who tested it for me and it is most definately dead. He cant say whether its the alternator or the regulator, he would have to strip it down and that would incur labour costs. I can get a replacement regulator for it for £37+VAT, but if i fit it to test and it doesnt work I cant take that back and I have to buy a new/refurbished alternator with a regulator on it, but wasting £45inc VAT. Or I could get the alternator, when it was only the regulator gone and spend £120 more than I needed.

So obviously the cheaper is the better option but I just want to check with the experts on this, is the problem with alternators usually 99% of the time the regulator, or is it really a more 50/50? If you were in my shoes what would you do? The current alternator has only done 25,000 miles.

Cheers,
Graeme

[robin]

Have you taken the plastic cover off the back of the alternator yet?

Usually you can see/smell damaged regulator pack because when the electronics go, they go in style leaving craters in components.

There are four parts to the electronics:

rotor coil - this is the spinning coil and is hooked up via two slip rings on the shaft to two brushes that connect back to the rectifier. This is the coil that produces the magnetic field.

stator coils - there are three of these in most alternators; these are the coils that "experience" the moving magnetic field produced by the spinning rotor and output an AC current (each coil produces an AC current, they are 120 degrees out of phase to each other - the results of this are summed together to produce an output that is more "flat").

rectifier - there are two or three diodes per stator coil - two diodes will be big un's that rectify the main current; the little diode, if fitted, is there to feed the current back to the rotor coil - so called "excitation diodes".

regulator - the regulator is a bit of electronics that monitors the output voltage of the alternator and then controls the excitation current - if the output voltage is above the target 14-ish volts, it reduces the excitation current and thus the strength of the magnetic field produced by the rotor and thus less voltage is produced in the stators; conversely if the output is too low, it increases excitation current and the output voltage goes up.

rotor coil should be a very low resistance when measured between the two slip rings - I would aim for 1 to 10 ohms.

stator coils should be very low resistance when measured at the common points of their diode pair - basically I doubt you'll distinguish the stator coil resistance from what you see when you short the multimeter probes together (remember, it generates 40A or so; power dissipation in a resistor is I*I*R, so that would be 40*40*R - if R = 1 that would be 1.6kW!!; so I reckon R needs to be <1 ohm for sure).

diodes should all check out OK with a diode tester (typical modern multimeter gives you a diode test that shows either 0L or a voltage - when showing 0L you have no conduction path; when showing a voltage, that's the "forward voltage" of the diode; for all the big diodes in your rectifier you're looking for 0L in one direction and <1v in the other direction).

The regulator is hard to test without an oscilloscope and some detailed knowledge of the regulation circuit - I could probably test it here, but it's a bit much to explain in text ...

The regulator and rectifier probably come as a single printed circuit board assembly, so you would swap together whichever part is broken.

In summary:

Check for molten/exploded diodes first -> if you find some, the regulator is dead for sure.

Check 1xrotor coil resistance -> if <1 ohm or >10 ohms, new alternator.

Check 3xstator coils resistance -> if >10 ohms deffo broken - if > 1 ohm I would be suspicious; if <1 ohm, probably OK.

Check forward voltage of each of the six big diodes -> should be OL one way, < 1v the other way.

If all is well, err on side of replacing regulator first unless you really don't want to risk buying the regulator and then a new alternator, in which case you can either pony express the whole thing down to me and I'll check it out for you, or you'll have to buy a recon alternator.

BTW, if you want to strip it down as far as removing the plastic cover and exposing the electronics, then post a good picture of it, I can annotate the picture with some lines showing you what to test where.

Cheers,
Robin

[whaleys]

I had the regulator off, it's a whole sealed unit that looks like this...

http://www.woodauto.com/Component.aspx?Ref=VRG46446

The only thing noticeable was that the regulator cover (the left half of the regulator in the pic) was loose and could easily have let moisture in. Other than that there werent any scorch marks or smells. The brushes are also part of the unit.

I'll try testing it tonight with the instructions you've given. I decided to order the regulator anyway, but should any of the tests show a problem I can just take it back without fitting/testing.

[whaleys]

OK got too interested and just tested...

Rotor coil resistence is 2.5ohms
The 3 stator coils resistence are all at 0.4 ohms
All diodes give readings as expected

I dont have an oscilloscope or the knowledge to test the regulator, but hopefully all the readings untill now point to the regulator

[robin]

Forgot to mention that you should also measure resistance to the chassis on each coil - should be open circuit .... if any coil is shorted to ground, the alternator won't work.

However, given that the wires back to the dash are OK and not fractured, it is rather looking like the regulator itself is fried. Once you fit new one and assuming it corrects the fault, you could pop the old one in the post to me for some forensics - would be interested to know what's failed ...

Cheers,
Robin

[robin]

Oh and another thing - see that 2-pin socket, I'm assuming that is the socket that the car loom plugs into, or is there a wee loomlet that goes from outside alternator to this socket? Only it would be well worth inspecting the insides of all the connectors for signs of corrosion ... if there's any white or green powder in or around any of the connectors then there's been water ingress and the problem may be entirely limited to the terminals in the plugs no longer making contact with their counter parts in the sockets if you see what I mean.

Cheers,
Robin

[robin]

Oh and another another thing - there is an 80A (I think - big, anyway) inline fuse in the heavy duty cable that goes from the back of the alternator to the starter motor stud - it's worth using your multimeter to measure the resistance from the currently disconnected end dangling behind the engine back to the stud on the back of the starter motor - you should see very low resistance - if it's open circuit then the alternator won't work (though this doesn't really fit your symptoms, it's worth a check before refitting the repaired alternator).

Cheers,
Robin

[whaleys]

Hi Robin,

Happy to pop it in the post to you, could you PM me the address to send it to?

The two pin socket is what the car loom plugs into, I checked it over for corrosion and it looked ok. Thats what I used to ground the circuit and test the dash indicator, so think thats ok. Having looked more closely at the regulator, the "loose" bit I mentioned I dont think should be loose, I think there has been something cause it (maybe something going pop like you said).

I'll test the resistence between the alternator and starter motor stud.

Thanks loads,
Graeme

[whaleys]

Ok, for those interested, I received the new regulator which gave me a bit more confidence in pulling the fixed cover off the possibley broken regulator. I took the photos using a phone, was all i had at work.

The first is the regulator, the cover is circled...



The second is the cover removed, I've put 3 yellow circles around 3 tiny wires that appear to have snapped from the main core. The two left have slight scorch marks. The red is around another wire that has a strong scorch mark where it connects to the main core.



As you can see a lot of crap has got in under the loose cover. It looks like its in a hard poxy resin but its more like a soft gel. One thing I noted though was that the two wires on the right were sitting proud of the gel.

Possible problem now is I'm not 100% sure if this was the problem or the result of a different problem...

Will be sending the part off to Robin for further forensics

Graeme

[Shug]

Graeme - reduce the size of the images and read this post on how to get them up properly.

http://www.scottishelises.com/phpbb/vie ... f=9&t=1350

[whaleys]

Sorry bout that Shug, tis all fixed now