Alternator working or not?

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aquaplane
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Alternator working or not?

Postby aquaplane » Tue Apr 07, 2009 10:31 am

Last W/E I noticed that the alternator light was on when we were motoring, it was dusk and it showed up well. I haven't noticed it on before but have to confess that I haven't looked too hard. The temp warning light is much brighter when lit, and that goes off when the engine runs.

My two nice new batteries started life @ 12.65 volts, I check them every morning before starting the engine. They have dropped at what I thought was a managable rate to 12.5 and then 12.4 volts over a couple of weekends. This is despite about half a minute cranking the engine to get it to cough into life first thing when it's cold. It's a Volvo MD11C BTW.

On Sunday the 12.4 reading dropped to 12.3 V immediatly after starting the engine, I was looking for 14+V if the alternator was working, and the alternator light was on too.

I have had "a man" look at it and on a test bench the alternator seems to be working as it should.

Is there anything between the alternator and the batteries that can break?

There are 3 wires to the alternator, a fairly beefy one and two others, I'll clean the terminals up to make sure they aren't the problem when I put it back but I would be suprised it the fault was there they were securely bolted on.

Am I optimistic expecting 14 V at the battery when it's supposed to be charging? I got that when I tried my new multimeter out on the car and it seemed to be about right to me, never having played with such things before.

Any sugestions what to look for or what voltages to expect?

All replies before Thursday evening are more than welcome.

I wait with baited breath, thanks in advance.
Seminole.
Cheers Bob.

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Re: Alternator working or not?

Postby ash » Tue Apr 07, 2009 11:36 am

Hi Bob

The voltages measured would indicate that the batteries are not being charged.

The wiring diagram is on page 37 of Workshop Manual. It's not very easy to follow the wiring. It would be best to draw a simplified diagram of the bit you're interested in.

Do you remember or notice if the warning light comes on when you switch on ignition - before the engine is started.

If the alternator has checked out OK then it's likely to be dodgy wiring.

How an Alternator works

I'll have another think about it and post again.

Ash

Edit - Bob - What make is your alternator? The 6A was Paris Rhone but that had an external regulator - don't yours has .
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Re: Alternator working or not?

Postby DaveS » Tue Apr 07, 2009 11:39 am

From the voltages you are measuring it's certain that no charging is taking place.

I would start by measuring the voltage between the alternator main output terminal and the alternator attachment bolt (I assume since there's only one heavy wire that it's an automotive type with frame return). You might want to use leads with croc clips to keep fingers away from moving bits. If you see 14.x volts at the alternator then it's working and you have a wiring problem: probe methodically with the voltmeter to find the fault. If you see 12.x volts then the alternator isn't working. (Given that the "no charge" warning light's on, I would expect this to be the case, but it's worth checking the output to be sure.)

There are a number of possibilities: worn brushes, blown diodes, failed regulator. The brushes and regulator are often combined as a single unit which comes out by undoing two screws: a short or sticking brush will be fairly obvious, and a replacement unit should only be about £15 or so from a supplier or auto electrician. Trying to solder on replacement brushes is fiddly and not worth the hassle. If nothing is obvious, then the best solution might be to take the alternator to a supplier for diagnosis. I would have suggested LSUK, but they've gone bust. Must be others.

As a side issue, and for looking at once you get your charging problem fixed, you say you have two batteries. Would I be correct in thinking that these are permanently connected together in parallel and supply both engine starting and everything else? If so, you might want to think about modifying the setup to give a dedicated starting battery, which has a number of advantages.
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Re: Alternator working or not?

Postby ash » Tue Apr 07, 2009 12:00 pm

Hi Dave

I had hoped that you would be here.

Reading Bob's post - he's removed the alternator and had it bench tested - so the fault is within the install.

Bob had a previous post - he has two batteries and an Off/1/Both/2 switch. He has just fitted new batteries - as part of the flush of new ownership.

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Re: Alternator working or not?

Postby Nick » Tue Apr 07, 2009 3:50 pm

I've had this on our old MD6A

The charge light was always on dully like this, but the battery charged - usually at about 13.5 volts. On teh way North on oooour Orkney trip in 2005 it stopped charging altogether. I had a spare alternator with me.

Here's the quote from our 2005 blog:

Got up at eight and by nine was off on the resumed quest for alternator guidance. The man in the shed up the road turned out to have gone to Barra for the week, so I tried the second recommendation, the lifeboat coxswain. He turned up in the middle of breakfast and removed the alternator, replacing it with the 'new' one - which didn't work either. He assured me that the alternator was the problem, and that the other one must be knackered as well. A nice guy, and he wouldn't take any money. I was not convinced that he was right however, and found yet another dodgy connection behind the switch panel. It was a big red lead plus an earth onto something that might have been an external diode pack, or it could have been a dilithium crystal for all I know. Anyway, after emery paper and spannering we are mysteriously charging again.

And that was it . . . a dodgy connection. We had no more problems until we scrapped the engine the folowing year. My advice is to get the emery paper out and check everything before deciding to spend any more time or money on the problem.
- Nick 8)

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Re: Alternator working or not?

Postby ash » Tue Apr 07, 2009 6:24 pm

This image shows the wiring 'jumps' more clearly.

Image

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Re: Alternator working or not?

Postby sahona » Tue Apr 07, 2009 6:31 pm

Is this one of these 'brushless' french alternators? They need more revs/amp than some of the more modern ones.
Does the light ever go out - I mean: is it on before the engine is started. does it go out and then on again (high field voltage) does it change in brilliance (go a bit dimmer when running) Have you given it full revs? (sometimes thay like that to get started...)
If there's any doubt, you could do a lot worse than spend £14 at the local scrappy and get a 70amp job in there.
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Re: Alternator working or not?

Postby ash » Tue Apr 07, 2009 7:01 pm

Bob talks of 3 connections - it would be good to know the markings. It's difficult to know if some of the wires shown in the diagram are internal in the alternator or external.

Anyway - plunging blindly onwards.... :wink:

Connection B+ should be the heavy duty one. This is the alternator output - cable goes to starter solenoid - to O/1/B/2 switch common - to battery positive when switch closed.

Connection D - This is the negative connection and may not exist as an external connection - I would expect the negative connection to be made through the mounting lugs.

Connection 61 - This connection goes to the ignition warning light - black cable - 1.5mm2

Connection DF - I would have thought that this was the connection to the field windings - not sure if it exists externally.

Now it gets messy

Cable B' and cable C" would appear to connect Connection D- to Connection 61 which doesn't make sense to me.

Cable B' and cable J' would appear to connect Connection D- to Connection 61 which again doesn't make sense to me.

The (internal) voltage regulator is in there somewhere between Connection 61 and Connection DF

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Re: Alternator working or not?

Postby DaveS » Tue Apr 07, 2009 8:19 pm

Ah, on re-reading the OP more carefully I now see the comment about a successful alternator bench test. I would still measure its output voltage with it running on the boat, regardless. If it's working, then finding the fault in the wiring should be fairly straightforward. I would start by measuring voltages between battery -ve and alternator frame, then alternator output and battery +ve. Find the voltage that's too high and narrow it down from there.

I share your confusion over the wiring diagram. I cannot make sense of the various internal(?) connections either. I assumed that the three wires originally reported were output, field and tacho, but the diagram doesn't show a tacho wire leaving the alternator, so what can this mysterious third wire be?
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Re: Alternator working or not?

Postby aquaplane » Tue Apr 07, 2009 8:27 pm

TFT Nick, I suspect that it's going to be a dodgy connection, or I do now I have been told the alternator seems to be OK, or it's an intermittent fault. I'm certainly going to have a good go with emery paper before going back to Woodautos and spending £240. They did say that they would knock off the £15 + VAT test fee though.

Bill, It's a Marchal, so I think you may have something, that and the made in France I just found. The light was on but dim, but it was dim when the engine was off! I didn't notice if it was brighter or not when the revs went up, but it's something I can look for now I know to look. It would be nice to think I could source a suitable replacement in a scrapyard, I'll keep that as an alternative last resort, well, before buying another new one resort.

Ash is going to be putting weight on!

Image

The bigger connection bottom right is marked B+ and takes the big wire.

The other connection at the bottom left is labelled D-

Connection 61 takes the other wire, it's only a spade connection.

The finned jobbie has 3 wires, red to 61, green labelled DF and the black one is connected to the case. Would that be the regulator?

I don't know about "plunging blindly on", you knew more about it than I did and it's sat here infront of me where I can see it.

I have much more idea what to look for and what to try to do a fault tree now.

Edit, Dave, is the "alternator frame" the metal body of it? Where the black wire goes to? I think I undestand the rest of what you suggest to test, it seems logical at any rate.
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Cheers Bob.

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Re: Alternator working or not?

Postby Clyde_Wanderer » Tue Apr 07, 2009 10:07 pm

AP did you check the belt for tightness and condition before you removed the alt?
Its just that I dident see any mention of the belt anywhere above.

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Re: Alternator working or not?

Postby aquaplane » Tue Apr 07, 2009 10:25 pm

C_W, I have to admit that the belt didn't look as tight as it could have, but in my defence, there isn't a lot of black rubber crap about in the front of the engine bay to indicate excessive wear on the drive belt.

The Tiger I looked at looked grim in that department. And another Centaur with a BMC 4 cylinder engine too.

I watched the alternator and belt for a while with the engine running and decided that things looked to be keeping up with each other. With the lack of black crap, slippage dropped down the list of probable explanations.

Good point though, I should have mentioned it before.
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Re: Alternator working or not?

Postby ash » Tue Apr 07, 2009 10:33 pm

A picture is worth a thousand words!!!

If the starter is spinning over happily and fast then we can assume that the 12 volt positive from battery through O/1/B/2 switch to solenoid is in good condition. Can also assume that 12 volt negative from battery to engine block is in good condition.

Need to check alternator B+ to solenoid visually and for DaveS's volt drop test.

Need to check alternator D- to engine block visually and for DavS's volt drop test. I think that this alternator will have the chassis isolated.

I think that the problem is with the wiring to connection 61. This supply will excite the alternator to get it producing volts. An alternator might self excite but not reliable.

With ignition in the run position, but engine stopped, remove wire from 61 and connect to battery negative - light should be bright. If not then use multimeter to check the 12V + from battery through ignition switch and light connections.

Disconnect wire from battery negative and connect to alternator 61 - light should still be bright.

Start engine and give a rev then run at fast idle - the light should have gone out.

My money would be on dodgy connections in the warning light module - either the wire connections or the bulb connections.

Ash

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Edit : Yes, the finned jobby will be the regulator.
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Re: Alternator working or not?

Postby DaveS » Tue Apr 07, 2009 10:35 pm

The picture makes things a bit clearer. The diagram shows the negative output brought out on terminal D- which in turn is connected to the engine frame by a blue 4 mm2 cable. This would suggest that the -ve is perhaps not connected internally to the frame as I initially guessed. Before re-fitting the alternator I would check with an ohmmeter to resolve whether or not D- is internally connected to the case. This could matter (see below). You said you had two small wire connections: the diagram shows a black 1.5 mm2 going from terminal 61 to the warning lamp and a second blue 4 mm2 wire from terminal D- to the engine control panel. How does this compare with your actual set up?

All the "internal" wires shown on the diagram appear to be there. The three wires from the regulator (the finned thing) would appear to be those labelled J', C'' and B' on the diagram, going to the field winding (DF), terminal 61 and -ve respectively. The last one is interesting, because the diagram shows it going to D- but the picture shows it connected to the case, which as discussed above may or may not be internally connected. Now, with an independent -ve output terminal the case would only be connected to -ve if D- is connected to engine metalwork and all connections are sound. If the case is not connected to -ve then the B' wire will not be doing anything and the regulator won't work, so a continuity check between the B' wire's terminal and terminal D- would be worthwhile.
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Re: Alternator working or not?

Postby ash » Tue Apr 07, 2009 10:55 pm

Once you realise that the 'nodule' which I've circled isn't 3 wires connected together but 3 wires comming out of the regulator - all with different functions - then the diagram makes sense.

DaveS's call about the regulator "earth" is a good one.

Where does your wire from D- go to?

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