2GM alternator

[kgi]

Not being very clever with elektrickery i thought i would solicit the help of people who know far more than i,... nearly new yanmar 2gm.. the problem is it appears to be charging to 11.7 and thats it, i've put the multimeter on it and even at2000 rpm its still11.7the charging light goes out when it starts, thats as far as i've been with it, any ideas greatly appreciated..............cheers .....keith

 

[Guest]

I have 2GM 20.Is there black dust around the forward end of the engine bay?This would indicate belt slip.You could try taking the alternator off (remember to mark the connections with indelible marker) and take it to a Lucas outlet for testing.Hope this is of some use.

 

[steve_cronin]

When you say "it's charging to 11.7volts", is this from a voltmeter installed in the boat or are you putting a meter across the battery?

With loads on like fridge & lights it might well be only 11.7 but for the 55Amp machine fitted to new 2gm20s it would need a hell of a load. Belt slippage COULD be an answer but if the engine is new I would get in touch with your dealer as those engines get two years warranty for private use and one year for commercial.

Steve Cronin

 

[kgi]

I've put the meter across the battery terminals, and across theterminals on the back of the alternator, the engine battery is used purely for starting the engine, and is not connected to the house bank........cheers.......keith

 

[paulrossall]

I seem to get black dust from my GM20 alternator belt and I have changed it 3 times now and do keep it at the correct tension. I do think the alternator adjustment does move with vibration but I dare not tighten it any more. I am going to go down the scrap yard and get the alternator adjuster from a Volvo 240 or 740 as they have a big bolt-like adjustment that does not allow any movement. It sits parallel to the two finger adjuster bar.

 

[pete]

I have just had same thing on my car,I took the alternator in for testing they said there was nothing wrong with it but pointed out signs of pitting where tension adjuster bolts to alternator they said it was a common fault and to check for a good earth to the engine I cleaned all bolts and surfaces between altenator and engine and fitted a earth strap which solved the problem.good luck

Pete

 

[charles_reed]

The question is:
1. Is it the alternator or
2. The earth return or
3. The regulator or
4. Belt slippage.

1. Alternators tend to be fairly robust and I'd suggest this is the least likely.
2. An inadequate earth-return could probably produce these symptoms, easily checked by going over the connections and cleaning them - look out for any stainless washers, they have a much higher impedance than mild steel or best copper.
3. The most likely one is the regulator - my old 55 amp Hitachi used to put out 13.7 volts quite easily, but until I fitted the Adverc I never got a really decent voltage (14.4 -14.5).
4. The standard Yanmar belt is a spineless thing, I quite soon replaced it with a heavy-duty belt (Goodyear is best, but Quinton Hazell produce an adequate substitute).

I now use a Magnetti-Marelli/Lucas marine alternator with a 90 amp output which is far better than the 55 amp alternator fitted as standard for 300 AH of battery I have on the boat.
I'd seriously consider replacing the regulator with a "smart" one such as the Adverc, Sterling, TWC etc. With a standard regulator, designed for automobile use you'll never get more than 80% charge into your batteries.

 

[colinroybarrett]

I suspect a diode, or:-

Assuming you are using a reasonably accurate digital V/Meter, 11.7 volts is not much at all. Does it rise from some lower voltage when the engine starts, or not move, with or without the engine running?

A short-circuit diode will cause the volts to ‘drop’ when the alternator starts up, (the battery is draining into the alternator) but doesn’t always cause the ign light to stop working normally. Remove the main battery lead from the alternator, (with the engine at rest and ignition OFF) stick a normal car side-light between the wire and the alternator terminal, if it lights up, you have a faulty alternator, try this with and without the ‘ignition’ switched on.

Do you have automatic cold-start heaters on this engine, the so-called ‘glow-plug’? The relay that controls these can fail, and they take a heck of a lot of power, albeit only (normally) for a short period.

Black rubber dust can also be a sign of pulley misalignment, try placing a long straightedge on the alternator pulley and ‘point it at the crankshaft one; they may also be one ahead of the other, causing the belt to dogleg. Diesels are much tougher on fan belts than a petrol engine, because of the high-torque pulses at low idle speeds, this wrecks havoc with belts and cheap those ‘tin-plate’ pulleys, so loved by the automotive suppliers.

Cheers,
Colin & Urszula Barrett
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