Yanmar 1GM10 alternator.

Topcat47

Well-known member
Joined
2 Jun 2005
Messages
5,032
Location
Solent, UK
Probably one for Viv. I got a replacement alternator for my wee 1GM10. It's a Bosch, not a Hitachi and it has an extra wire, leading from terminal "P" and a slightly smaller plastic pulley. Can I safely ignore the extra wire and should I swap the pulleys over or assume Bosch knows what it's doing?

Apparently the "P" terminal is to connect a tachograph, not required on "voyage." Only the pulley question left to answer.....
 
Last edited:

JumbleDuck

Well-known member
Joined
8 Aug 2013
Messages
24,169
Location
SW Scotland
Probably one for Viv. I got a replacement alternator for my wee 1GM10. It's a Bosch, not a Hitachi and it has an extra wire, leading from terminal "P" and a slightly smaller plastic pulley. Can I safely ignore the extra wire and should I swap the pulleys over or assume Bosch knows what it's doing?

Apparently the "P" terminal is to connect a tachograph, not required on "voyage." Only the pulley question left to answer.....

I'd leave the pulley. Alternators are pretty insensitive to shaft speed (the faster they turn the higher the frequency so the higher the reactance and so they self-limit) and in any case a boat engine won't go anywhere near fast enough to worry it ... these things are designed for car engines which regularly reach six times idle speed while a boat engine is unlike ever to hit three times idle.
 

RichardS

N/A
Joined
5 Nov 2009
Messages
29,240
Location
Home UK Midlands / Boat Croatia
Probably one for Viv. I got a replacement alternator for my wee 1GM10. It's a Bosch, not a Hitachi and it has an extra wire, leading from terminal "P" and a slightly smaller plastic pulley. Can I safely ignore the extra wire and should I swap the pulleys over or assume Bosch knows what it's doing?

Apparently the "P" terminal is to connect a tachograph, not required on "voyage." Only the pulley question left to answer.....

Probably a tachometer rather than a tachograph unless you have restricted sailing hours and mandatory rest periods on your vessel. :)

As JD says, a smaller plastic pulley sounds like a higher-revving, non-rusting improvement on the original.

Richard
 

Tranona

Well-known member
Joined
10 Nov 2007
Messages
40,554
May not, however be enough adjustment to use the standard belt
 

Topcat47

Well-known member
Joined
2 Jun 2005
Messages
5,032
Location
Solent, UK
The standard belt is too long to tension even at max extension. I've sourced one that's about 30mm shorter between the pulleys and I'm trying that one, thanks for the advice. For anyone faced with a similar problem, it's Dayco Sectorflex 10A0700C. I suspect the 0700 refers to it's overall length in mm.
 

Appledore

Member
Joined
13 Nov 2011
Messages
809
Location
Bodmin Moor, Cornwall
The standard belt is too long to tension even at max extension. I've sourced one that's about 30mm shorter between the pulleys and I'm trying that one, thanks for the advice. For anyone faced with a similar problem, it's Dayco Sectorflex 10A0700C. I suspect the 0700 refers to it's overall length in mm.

Slight tangent here, but when you need a new belt for your 1GM 10 do check out the prices. The Yanmar (??) belt on Ebay from a marine supplier cost me £10.50, whereas the exact same one (Gates Dayco) from an Ebay Auto shop cost me only £5.62. As I say, they are exactly the same belts. I bought the cheaper one 7 months later as my spare!
 

RichardS

N/A
Joined
5 Nov 2009
Messages
29,240
Location
Home UK Midlands / Boat Croatia
The standard belt is too long to tension even at max extension. I've sourced one that's about 30mm shorter between the pulleys and I'm trying that one, thanks for the advice. For anyone faced with a similar problem, it's Dayco Sectorflex 10A0700C. I suspect the 0700 refers to it's overall length in mm.

It's also important to ensure that the belt rides so that it outer side is level with the top of the pulleys. Belts which are too narrow and sink down into the pulley groove wear more quickly.

Richard
 

Topcat47

Well-known member
Joined
2 Jun 2005
Messages
5,032
Location
Solent, UK
The 10A0700C was too short. They fill the grooves when new, but I need the next size up. My auto factor charges £4.00 for the Dayco belt as opposed to the mitsubishi belt Yanmar provide. I couldn't get the Dayco belt this afternoon, so had to get the mitsubishi from Marine Power. The 1250 belt fits nicely and I'll get a Dayco equivalent as a spare.
 

black mercury

Active member
Joined
4 Jun 2013
Messages
418
Location
scotland
Just a quick thought, the 1gm series were fitted with smaller crankshaft pulleys than the bigger gm engines so as to prevent the alternator 'kicking in' early before the engine fired. Once the engine was up and running and at idle the alternator would charge as normal, its just a precaution that yanmar took for the small hp 1gm. And yes i know that 9hp is more than enough to run the alternator, but the last thing you need is the alternator starting to charge when the small engine is trying to get to its idle speed. If your alternator has a smaller pulley it will start to charge earlier. I would fit it and see what happens, but do take this into account if you are having problems.
 

Topcat47

Well-known member
Joined
2 Jun 2005
Messages
5,032
Location
Solent, UK
Hmm, that's possible. The "new" replacement had a smaller diameter pulley. It's rated as 35w on the website, however, after fitting it I discovered a problem. The cold engine doesn't produce enough "puff" to drive the oil pump and the alternator at the same time. Marine Power sent an engineer in response to an SOS from me this morning (excellent service by the way). The engine started but ran slowly, eventually stopping altogether at full throttle. Unplug and disconnect the alternator and the problem disappeared.

Apparently there's a Mod which cuts out the alternator until the oil is up to temperature. This needs a new sump and harness as well as an "oil temperature " thermostatic switch. Free with your "new engine, of course. (The original Hitachi alternator from Marine Power is over £600.00 and there's no guarantee that this would cure the problem). The charging lamp certaily goes out quicker than before.
 

Billjratt

Active member
Joined
9 Sep 2004
Messages
2,963
Location
Firth of Clyde
I'm not happy with what's been said here.
a 35 amp alternator is less than 500 watts at 14 volts.
1 HP = 745.7 watts. If the alternator is stalling the engine, it would appear the engine is incapable of producing the first horse, never mind the other nine.
Or do I not understand the situation?
I assume there isn't a short on the alternator output? If the battery can swing the engine, it can't be flat enough to 'kill' the alt.

Just saying, before you go all round the houses.
 

Topcat47

Well-known member
Joined
2 Jun 2005
Messages
5,032
Location
Solent, UK
I can understand this. I'm not going to argue against a Yanmar specialist. We ran the engine with the alternator connected, the engine died. Disconnected the alternator, the engine runs fine.

The lower end of the power curve is ~3kW at 1800rpm for a new engine; mine is nearly 20 years old so is probably a little down on power anyway. The charging warning lamp went off with the engine running at around 800rpm. The engine has to drive the oil and water pumps and cope with the losses associated with driving the belt itself (not inconsiderable) and the drive side of the gearbox slopping about in cold lubricant. If you extrapolate the power and torque curves below this part of the graph they pretty soon vanish once you're around the 1000 rpm mark.

The alternator "spikes" initially trying to top up power loss in the battery due to starting the engine. If you've ever tried to start one by hand you'll appreciate this is not inconsiderable. If the engine hasn't reached the "bottom" of the power curve, it's also woefully lacking in torque. ( It doesn't help if people try to start it without easing things with the decompressor).

It sort of makes sense to me
 

Eygthene

Member
Joined
11 Aug 2007
Messages
417
Location
Falmouth
I think, if you were to fit a switch between the charge lamp and the alternator, it would be able to stop the alternator charging until you closed the switch. You could open this switch when starting the engine and close it once the revs picked up.
 

Topcat47

Well-known member
Joined
2 Jun 2005
Messages
5,032
Location
Solent, UK
The lamp actually goes out once the alternator starts charging so this wouldn't work. Of course I don't know where the lamp wiring is within the harness as the boat is not at home, where I am and I can't trace it back and compare it to the wiring diagram. I suspect putting a switch in the power output line might do the trick, but I'm inclined to try the pulley swap first, if it's a goer.
 

Sniper

Member
Joined
9 Jul 2001
Messages
857
Location
East Coast
This is very interesting. I hadn't realised that the alternator could give so much resistance at low revs to hinder starting . If an electrical solution is complicated, how about some sort of overthrow lever in the belt tensioning system (like those which used to be available for running back stays) to take the alternator drive out until the engine is running? Probably lots of practical issues, buts an alternative to consider.
 

Topcat47

Well-known member
Joined
2 Jun 2005
Messages
5,032
Location
Solent, UK
I rather think an electrical switch might be easier to incorporate than a highfield lever. the engine compartment is already cramped and was too small to fit a FW cooled engine when I placed the old MD1b.
 

surekandoo

Member
Joined
23 Feb 2002
Messages
494
Location
Home:Nottinghamshire Boat: Blackwater Marina, Esse
Just a quick thought, the 1gm series were fitted with smaller crankshaft pulleys than the bigger gm engines so as to prevent the alternator 'kicking in' early before the engine fired. Once the engine was up and running and at idle the alternator would charge as normal, its just a precaution that yanmar took for the small hp 1gm. And yes i know that 9hp is more than enough to run the alternator, but the last thing you need is the alternator starting to charge when the small engine is trying to get to its idle speed. If your alternator has a smaller pulley it will start to charge earlier. I would fit it and see what happens, but do take this into account if you are having problems.


I ordered a brand new 1gm10 to be installed in june 2014 to replace a Vire 12hp.

The supplying dealer was horrified to find that the engine had been supplied with a 55a alternator rather than the std 35a unit after the engine had been fitted in the boat. All E P Barrus & Yanmar Europe stock was the same! As reported in this thread the engine wouldn't "get off it's knees" if the battery was asking for charge. Initially they looked changing the alternator but the wiring loom was incomptible, then at retrofitting the oil temperature switch (std on the saildrive units apparently) but the wiring loom was again incompatible. I suggested that a soft start alternator controller could be fitted but the agent refused as he said it would invalidate the Yanmar warranty.

A new engine with the correct spec had to be obtained from Japan. I finally got back sailing in Sept 2014.

I still think a soft start controller is the way to go and maybe the OP could consider this option if his budget will stand it.
 

Eygthene

Member
Joined
11 Aug 2007
Messages
417
Location
Falmouth
Re: Yanmar 1GM10 alternator.

"The lamp actually goes out once the alternator starts charging so this wouldn't work. Of course I don't know where the lamp wiring is within the harness as the boat is not at home, where I am and I can't trace it back and compare it to the wiring diagram. I suspect putting a switch in the power output line might do the trick, but I'm inclined to try the pulley swap first, if it's a goer. "

I think you will find that initially, current flows through the lamp into the field coils to "liven" the rotor i.e. to produce a magnetic field in the rotor. When the generator's output exceeds the voltage supplied via the lamp, no more current flows into the field coils from the lamp, as sufficient current is available from within the generator itself. The insertion of a switch should prevent this initial current from flowing in from the lamp, so reducing the initial output from the generator. When the engine's revs have picked up, you could close the switch and allow the generator to start up.

Don't consider putting a switch in the power output line as we are always advised that disconnecting the battery from the generator is likely to damage the regulator.
 

Billjratt

Active member
Joined
9 Sep 2004
Messages
2,963
Location
Firth of Clyde
If you want to delay the alternator startup, then a switch in series with the ign light is the correct way.
The ign lamp allows/supplies the initial current to energise the alternator field. If it ain't in circuit the alt will not start and the engine can be brought up to a comfortable temperature/speed before the switch is thrown. Another way is to fit a manual regulator to limit the initial draw, but manual stuff gets abused/forgotten about and usually causes more trouble.
You can test the process by just taking out the ign bulb and starting the engine, then (with the engine still running) either replacing it or momentarily shorting the wires to it when you feel the engine can stand the strain.
If you're happy with the outcome, simply fit a switch beside the lamp ( I assume it's in a handy place when you're starting. )
I have to say I'm astounded that engines are marketed to propel boats, but can't swing the alternator - and the manufacturer hasn't provided a normally open oil pressure switch in the alt cct.
My 4108 has one and it's 40 -odd horse!
An enhancement to this system would be another lamp to remind you that you hadn't switched on the alternator yet...
 
Last edited:
Top