Alternator Issue

[artyfharty]

Excuse the idiot question, but:

My boat has a single alternator running of a Lister SR2

There is an indication light on the control panel that indicates when the alt is charging. When lit green its not charging, increase the revs, it goes out.

I've had the boat six months, when I first got it, it would only charge at high revs and then I'd ease the revs and it would still charge, but stop charging at idle. AT cruising speed my ancient ampmeter would show about 10 amps.
Then it stopped charging at any rev speed. I tightened the belt, it started charging again as it was. I thought the belt tension was a bit much, ie only perhaps 5 mm on the longest length.

It's now stopped charging at any rev speed, the belt is already as tight as it can get, the belt is not slipping and the alternator is turning with no noise.

What I haven't done:
Taken a volt reading off the alternator itself.

Found out what the alternator type is.

 

Does this sound like the alternator is knackered?

 

Is it worth taking it to a car electrical place or simply get a replacement?

 

Incidentally I have very low electrical requirements, ie no fridge, TV, etc. and an 8o w solar panel that keeps the batteries at about 12.9v (so far)

 

Thanks in advance for any help
AF

 

 

 

[Alastair]

Your alternator could have lost the residual field.

 

There is an article about this here:

 

http://www.dieselduck.net/machine/03%20electricity/flashing_generator.htm

[Chalky]

There is an indication light on the control panel that indicates when the alt is charging.

 

being pedantic the light shows that the alternator is producing enough power to self excite i.e. it's producing enough power to power the field coils (which provide the magnetism) rather than taking power out of the battery to power the field coils. It doesn't mean that it's actually charging. Subtle difference, but an important one.

 

Having to increase the speed to start the alternator isn't unusual. Cutting out as the speed slows suggests there may be a belt problem, but you've ruled this out. Have you checked the brushes? Also check the light - this is part of the regulator control circuit and can affect operation.

[Tony Brooks]

First of all get it revving and take a small lead from battery + to the small (W) terminal on the alternator for a few seconds. If Alastair is correct it should start to charge and then revert to its "working state.

 

I think the SRs may have the alternator pulley on the camshaft so it will only be turning at half the engine speed, that will not help it energise or produce full output unless you have a much larger than "usual" pulley ratio.

 

10 amps at cruising speed, which I assume was the maximum, suggests to me that the alternator may have been faulty for a long time and now it has finally given up. It would be worth taking it to your local car electrical specialist, even if only to have the smallest pulley they can get fitted, especially if I am correct about the camshaft.

 

Check the bulb in the warning lamp. In some cases cheap "push" in warning lamps use a grain of wheat bulb that is not enough to energise the alternator and I have come across LEDs where the same thing applies. You need a minimum of 1.5 watts and 2.2 is better. Both of those are proper bayonet or screw in bulbs.

[artyfharty]

Thanks All
Tony
There are two leads from the alternator, what is meant by "W"?
Cheers

AF

[Alastair]

The terminals are often marked - you'll need to look closely.

 

If it isn't marked, then look up the model of alternator. There will be a diagram showing the ID of each terminal.

[Tony Brooks]

The thin one normally but even if you touched the thick one it would not hurt - UNLESS both wires are thick, but if so I would want to see a photo of the alternator before saying much else.

 

To be sure disconnect a thin wire and insulate it, turn on the ignition and if the light will not go on you have found the W wire.

Edited September 24, 2013 by Tony Brooks

[frangar]

Tony....are you sure about the W terminal?

 

That's usally the rev counter one

 

I would have thought you meant the one marked D+ or sometimes Ign

 

I stand to be corrected tho.....I am quite often wrong!

 

Cheers

 

Gareth

[Sir Nibble]

Tony....are you sure about the W terminal?

 

That's usally the rev counter one

 

I would have thought you meant the one marked D+ or sometimes Ign

 

I stand to be corrected tho.....I am quite often wrong!

 

Cheers

 

Gareth

Or IND on old lucas ACRs, which is what I suspect it is. Artyfharty, (good grief) Is this a little thing about 4.5" across and 8" long with a plastic cover on the end?

I've met this sort of problem on harbour launches and the failure to remain "cut in" at tickover is a function of too slow an alternator speed. I suspect from your symptoms that your alternator has gone to where good alternators go. If it is an ACR, there are many causes of failure on these but the built in life limiter is that the positive brush bears on the centre of the axial slip ring. So it wears the copper like a very slow drill. Eventually it pierces the slip ring and drops onto the rotor shaft end to complete the warning light circuit whilst shutting the alternator down. Sounds like that might be the case here. For those who follow the CWDF floating alternator seminar, I think this is a good case for a 70A A127 with snibble's patent low speed modification.

[Tony Brooks]

Sorry about that, it should be D+ abut its still the thin wire if only two and my "test" is still correct. No idea why I wrote W, certainly not too much red, probably old age.

 

Cheers

[bizzard]

The SR's alternator will almost certainly be driven from the camshaft, so if you you haven't already got one, a large diameter camshaft drive pulley is almost absolutely necessary to get enough speed on the alternator. With the small say 4'' dia pulley you would have to rev the cobblers off the engine to even excite the alt. My old boats SR had the large 10'' pulley and my present boats ST also has a 10'' pulley, and even so I need to rev the engine to about 1200 rpm to start the charge. Large pulley kits for these engines camshafts are still available I think from places like Marine engine services Uxbridge.

[artyfharty]

The SR's alternator will almost certainly be driven from the camshaft, so if you you haven't already got one, a large diameter camshaft drive pulley is almost absolutely necessary to get enough speed on the alternator. With the small say 4'' dia pulley you would have to rev the cobblers off the engine to even excite the alt. My old boats SR had the large 10'' pulley and my present boats ST also has a 10'' pulley, and even so I need to rev the engine to about 1200 rpm to start the charge. Large pulley kits for these engines camshafts are still available I think from places like Marine engine services Uxbridge.

Ok, thanks all, I do have a large cam shaft pulley, I'm going to do all the tests at the weekend, and then if it looks knackered, take it off and get a replacement/rebuild with a smaller pulley on the alternator.

Many thanks for all the help

AF

[artyfharty]

OK, have done some tests this evening.

All tests done in neutral.

Low revs the alternator puts out 12.5 volts.

Increase the revs to perhaps 1000 rpm and the ampmeter shows approx 15 amps output and the volts read 13.5 v and the green light goes out.

 

The starter battery measured 12.6 volts at tickover and 13.45 at approx 1000 rpm.

 

So, basically if you kick the revs up in neutral the alternator will charge the batteries, you have to take the revs right up before charging starts but then taking them down to perhaps 600 rpm results in a charge.

 

In drive it doesn't appear to do so, perhaps I never took the revs up higher but this was an unscientific test on the weekend and I didnt want to upset the boats we were going past.

 

My conclusion is that the alternator needs a smaller pulley, the one on it is approx 2 inches across. It'll then run at lower revs and I wont have to thrash hell out of the engine to get a charge?

 

Does the team agree?

[bizzard]

OK, have done some tests this evening.

All tests done in neutral.

Low revs the alternator puts out 12.5 volts.

Increase the revs to perhaps 1000 rpm and the ampmeter shows approx 15 amps output and the volts read 13.5 v and the green light goes out.

 

The starter battery measured 12.6 volts at tickover and 13.45 at approx 1000 rpm.

 

So, basically if you kick the revs up in neutral the alternator will charge the batteries, you have to take the revs right up before charging starts but then taking them down to perhaps 600 rpm results in a charge.

 

In drive it doesn't appear to do so, perhaps I never took the revs up higher but this was an unscientific test on the weekend and I didnt want to upset the boats we were going past.

 

My conclusion is that the alternator needs a smaller pulley, the one on it is approx 2 inches across. It'll then run at lower revs and I wont have to thrash hell out of the engine to get a charge?

 

Does the team agree?

Personally I wouldn't go smaller than the 2'' one you have for wrap around grip and belt stress reasons. If anything a larger still camshaft pulley would be better. But its doesn't sound too bad to me, I'd just rev it up in neutral to start the charge before setting off. A more modern alternator would probably excite and begin charging at lower revs.

[MtB]

Ok, thanks all, I do have a large cam shaft pulley, I'm going to do all the tests at the weekend, and then if it looks knackered, take it off and get a replacement/rebuild with a smaller pulley on the alternator.

Many thanks for all the help

AF

 

 

It's driven by a CAMSHAFT pulley??!!

 

As the cam rotates at half engine speed, this is prolly the problem unless your camshaft pulley is about 24" in diameter, which seems unlikely!

 

MtB

[Timleech]

 

 

It's driven by a CAMSHAFT pulley??!!

 

As the cam rotates at half engine speed, this is prolly the problem unless your camshaft pulley is about 24" in diameter, which seems unlikely!

 

MtB

 

Yes, Lister SR etc usually only have the camshaft extended at the front, & not the crankshaft.

Early alternator versions had the 11AC alternator, which has two external boxes to potentially go wrong although they were actually generally fairly reliable in my experience.

 

Tim

[bizzard]

 

 

It's driven by a CAMSHAFT pulley??!!

 

As the cam rotates at half engine speed, this is prolly the problem unless your camshaft pulley is about 24" in diameter, which seems unlikely!

 

MtB

On the SR engine there is no crankshaft stub sticking out at the front, only the big long gear driven camshaft stub which ancillaries like an alternator are driven from. The usual size camshaft pulley for these camshaft driven alternators is around 10'' dia I believe larger still are available.