Friday 23 March 2018

Lets talk alternators ....

We need them more than they need us. They go about their business charging our batteries until one day, usually at a quite inconvenient time they just stop - or worse, become inconsistent, sometimes charging and sometime not.

To my great shame I have not even got a spare belt on Percy, I know  - I had problems with belts and alternators when we were out on Waterlily in June 2012. I think the breakdown we had that day put the seed of doubt in my mind about engines under deckboards with the result we had Percy (with an engine room) a year or less later.  The problem then was a shorting wire under the alternator that was under or below the engine. Phil at Oxley Marine did a sterling job that day to find and repair the fault.

Anyhow the reason for the self reminder on belts and alternators it we got the charging light pop up on the dash on the car on Sunday just as we were about to set off on our weekly (for the last several months) trip back down south. Breakdown guy turned up - no meter, and said alternator is dead. 13 hours later including 4 hours at Leicester Forest East waiting for the second relay truck to relay us back south we were back in West Ashling. That was on top of 5 hours Friday afternoon/evening getting up... a pivotal weekend of crap journeys.

I live in a wonderful age of the internet where there is endless knowledge and some fine forums. The Rover  75 and MG owners forum is one such, masses of not just info but enthusiastic advice to get things repaired, not just thrown away.

So with all my virtual friends helping I went at the alternator in situ and took off the regulator and brush set. Now the real reason is this job is a pig on the car, a breeze on the boat (when ever I will do it) A bike ride to Screwfix for some deep small sockets and a tiny 1/4 inch drive ratchet, got the query defective stuff off. I think the brushes have just worn out after 130,000 miles ( its the original alternator) I could try a £1 fix, I had the new brushes in my hand at a little workshop that sells such stuff, but bottled it and decided to order the regulator and brush assembly. Fitting hopefully later to see if the diagnosis is correct....

So much easier on a boat that a car  - in the main. A pic of the exposed slip rings waiting for their new brushes. They are worn but the consensus it they have many more miles in them.






12 comments:

Dave Ward said...

You'll need to be careful fitting the replacement assembly - the new brushes will be longer than the old ones. With that black plastic enclosure I can't (easily) see how you'll be able to push the brushes back into the holder and get them round the slip rings. Any sideways force will break them off! Is the "spring end" accessible so you can release the pressure? If that cover is removable and can be refitted in situ you should be able to press the brushes in with a small screwdriver as you offer them up. Another possibility is to feed a piece of thin card in between and carefully pull it out once they are in place.

The worn slip rings will certainly be good for some time yet - I replaced one set of brushes on my car's alternator when the slip rings were worse than yours, and got several years more life. The next time I completely stripped the unit down (on the bench) replacing the slip rings, brushes and bearings...

Nev Wells said...

Dave,

Moved on a bit .... I could not get a replacement regulator with new brushes but the local alternator repair man put new brushes in the old unit and left the cover off so i could slot it on after putting back on the alternator. Sadly the new brushes did not sort the problem (Q - do new brushes need running in to get the best contact) I still had the charging light on the dash so am now thinking it is the regulator .... Thanks for the reply, the info on the slip rings gives me confidence once up and running I should be good for quite a few more miles.

I relation to canal alternators I am more aware now that they can be fixed and not swapped for refurbed or new ones fitted. There is a reason there are refurbed alternators out there = new brushes and /or regulators.

Nev

Dave Ward said...

Usually if the "charge warning" light comes on it means the brushes and regulator are passing current. Can you pull back (or temporarily) insulate one of the brushes, and see if the light then fails to come on? That would verify continuity. If the light comes on but doesn't go out once the engine is running can be due to several things.

I once had an old Lucas alternator fail, and it turned out to be the rotor coil having gone short circuit. This foxed me at first as I hadn't accurately tested the resistance, merely that there was continuity. The result was insufficient magnetic flux being created to induce any useful output in the main stator windings. Other possibilities are failure(s) of one or more diodes in the rectifier pack. If the field diodes have failed you won't get sufficient (or any) excitation - like in my example above. If one or more main diodes (or the stator windings) have failed there might be some output, but not enough to extinguish the light.

Do you have a multimeter handy? If so I could suggest a few basic tests you can carry out.

Dave Ward said...

After a bit of research it looks as if your regulator/brush holder is one of these:
https://www.woodauto.com/bom/50723/VALEO-A13VI234
Am I right?

Nev Wells said...

HI Dave,

You know your stuff !

Spent a happy 2 hours today at the local scrap yard taking a regulator off an alternator to try. It looked in good condition, lots of life left in the brushes and little slip ring wear so I think it might have been a recent replacement. However still no joy.

I am thinking I have knackered the alternator when I did a service. I was very careful not to spill any oil on to the alternator as it sits (bad design) below the oil filter that is a pull out cartridge type on the 75's, I am starting to think I was not careful enough.

I do have a meter so any advice would be welcome.

Problem is the swap out of the alternator is not a small job and one I'd rather not chance as atm at least I can drive it to a garage locally on a fully charged battery. One of the aside benefits is I have brought myself a new charger so at least the boat will benefit when this is all done.

Thanks Nev

Nev Wells said...

Dave,

its this one,

https://www.dmgrs.co.uk/products/rover-75-mg-zt-cdti-alternator-regulator-and-brush-kit-fits-yle000260-and-yle102500

The one you ID'd is also a fitment but on an earlier alternator

Nev

Dave Ward said...

I have been searching (unsuccessfully) for a wiring diagram to identify what the terminals do. So the best I can offer is to suggest you test the resistance across the slip rings (regulator removed) with a digital multimeter. Select the lowest ohms range (the horseshoe shaped symbol). Firstly hold the leads together to see what you get (most meters will show a few tenths of an ohm due to the inherent resistance of the leads), then compare with what you get across the slip rings. The difference is the important value - I would expect something between 3-5 ohms. If it's either very high or similar to the leads themselves the rotor is faulty. If you are able to access the slip ring leads in situ (with the regulator in place) see what voltage is showing across them with the ignition on but before starting the engine. Do this on the 0-20volt DC scale. If there is any possibility of slipping something insulating (a bit of paper or card) under one brush, it would be interesting to see what you now get - in other words - with no load on the regulator. If a diode or main winding has failed you can't really do any testing without removing the whole unit.

Nev Wells said...

Thanks again Dave, I'll get the meter out tomorrow and see what readings I get. The two terminals off the regulator are described in this link

https://www.woodauto.com/product/ALT14214

middle is control lamp and outer is ignition.

Dave Ward said...

That's helpful - at least you don't appear to have a "smart" alternator controlled by the engine ECU! Obviously the control lamp terminal must be working, but make sure the "ignition" terminal has +12v when the key is turned, as this unit may rely on it to energize the field circuit, rather than be internally excited.

Nev Wells said...

Cheers Dave, there is a 5 amp fuse that I guess is there to give it the 12v - I have checked that. Put the meter on the slip rings this am ...00.5 when the probes are connected and nothing when the probes are on the two respective rings both with the key out and again when the key is turned the car on (not running of course).

I am fairly sure the alternator is knackered - all back together now and hoping to get a local garage to put me a new one on - just the 3 hours plus parts I expect it to be that is a bit annoying but I have taken it as far as I can - really thankful for your support, are you a boater? I owe you a drink.



Dave Ward said...

"00.5 when the probes are connected and nothing when the probes are on the two respective rings"

Well there's your problem - the rotor has gone open circuit. No continuity means no current flowing, and hence no magnetic field to induce a voltage in the stator coils. It could be repaired - IF you had the time and equipment to remove and strip it down. A second hand rotor is an unknown quantity, and might be fine if you don't mind the hassle and risk. Alternatively a new rotor would probably cost nearly as much as complete factory rebuilt unit, and that will have a years warranty!

No, I'm not a boater - I was considering it a year ago, but decided I didn't fancy the extra hassle of trying to work through numerous locks on my own. If you ever find your way in to the Fens (or even as far as Brandon Lock), get in touch - you should already have my email.

Nev Wells said...

Cheers Dave, I'll get a new one fitted - I'd like to keep the car as it is like a little limo and based on its age it is cheap motoring (when its working of course) Single hading is not too hard and you get a lot of help and meet a lot of nice people. If I get over to the fens I'll certainly let you know . If you are Fradley way, likewise there is a pint at the swan for you ! Take care