Yanmar 2GM20 - Sea Water Cooled

[372RTM]

Hi all...can you help ?
I have a YANMAR 2GM20 - sea water cooled. The alternator has packed up.
It is perhaps the original alternator. Happy with the performance, but what the hell is it other than a Hitachi ? I see 55amp and 35amp in various links I look at. My manual says 35 Amps.

Can anyone identify what size the alternator is from the photo's ? No markings on it other than an adhesive mark where I guess there used to be a sticker.

Wondering what to replace it with ? Suggestions ?
The boat has a BEP controller and a split diode controller, two batteries, one start, one house (deep cycle).

Thanks.
RTM.

[Wotname]

Welcome aboard CF, 372RTM.

You could of course, get your existing alternator repaired. It could be as simple as replacing the internal regulator.

As for a replacement, any internally regulated Hitachi alternator up to say 80 amps should fit. Check it has the same terminal arrangement as your existing one.

[Compass790]

I would replace with something else myself. Look up mainesails tutorial on Hitachi alternators or maybe its under battery charging on his site.
Agree with Wottie likely it can be repaired but if you want more effective charging I'd use something else as the Hitachi cuts down the power output when it gets hot. saves the alternator but very slow charging.
Still if you are happy with the performance just try for repair.


FWIW We had the 35 amp Hitachi on our Yanmar YSM8 but the boat came with a 55 amp Bosch that works much better once I got it going. The Bosch only puts out 35amps max when hot but it does it continuously whereas the Hitachi will throttle back to 15 once hot.
Dont know if it will fit yr mounts though.

[372RTM]

Originally Posted by Wotname

Welcome aboard CF, 372RTM.

You could of course, get your existing alternator repaired. It could be as simple as replacing the internal regulator.

As for a replacement, any internally regulated Hitachi alternator up to say 80 amps should fit. Check it has the same terminal arrangement as your existing one.

Long time lurker. Yes, that is an option.
Hard to get work done at this time of year.
The alternator is certainly old, >3500hrs ?...we've had boat for ¬20 years. How long before something else on it fails ? Doesn't owe us anything.
I feel replacement might be easiest & most reliable option.
But I'd like to know what I'm replacing....35 or 55 or ??, As the same will be fine.

Thanks for your comment.

[372RTM]

Originally Posted by Compass790

I would replace with something else myself. Look up mainesails tutorial on Hitachi alternators or maybe its under battery charging on his site.
Agree with Wottie likely it can be repaired but if you want more effective charging I'd use something else as the Hitachi cuts down the power output when it gets hot. saves the alternator but very slow charging.

We had the 35 amp Hitachi on our Yanmar YSM8 but the boat came with a 55 amp Bosch that works much better once I got it going. The Bosch only puts out 35amps max when hot but it does it continuously whereas the Hitachi will throttle back to 15 once hot.
Dont know if it will fit yr mounts though.

Maybe that is why it has lasted so long ?
Thanks...I'll chase down the tutorial.

[john2445]

Where are you located? I have the same Hitachi in Tampa, FL cheap. It came with the boat as a spare but the boat has a different mount.

[George_SD]

Interested in this subject as I'm also running 2GM20 with original alternator. I plan on adding 2 more batteries, so this is relevant.

[brucebach]

It's 35 AMP. The 55 AMP was considered an upgrade for the 2GM20F (which I have). Believe the Hitachi model # is LR-135.

[372RTM]

Originally Posted by john2445

Where are you located? I have the same Hitachi in Tampa, FL cheap. It came with the boat as a spare but the boat has a different mount.

Hi John, Kerikeri New Zealand so a wee bit far away. Its summer here so unfortunately I need a quick solution. On the alternator you have can you see what size it is ? I can only see an adhesive mark where a sticker which presumably held that information has fallen off. THanks, RTM.

[SRQsailor]

Any alternator shop can rewind and repair your original Yanmar alternator which may be better quality in general then most replacements. I had mine done in Sarasota Florida very reasonably. Note: If a repair shop rewinds the alternator you'll a choice as to what output amperage you want. I went from 40 to 70 amps, thinking more output would be a good thing. The added load on the engine caused a significant decrease in PRM when the battery charge was low, and also caused excessive belt wear. I was replacing belts every 2-3 hours of run time. I had it rewound back to 40 amps and all is fine again.

[372RTM]

Originally Posted by brucebach

It's 35 AMP. The 55 AMP was considered an upgrade for the 2GM20F (which I have). Believe the Hitachi model # is LR-135.

Thank you Bruce. You have confirmed what I though, I think I can get a 40 amp one that is similar, I'll go with that unless someone local comes up with a better suggestion.

[372RTM]

Originally Posted by SRQsailor

Any alternator shop can rewind and repair your original Yanmar alternator which may be better quality in general then most replacements. I had mine done in Sarasota Florida very reasonably. Note: If a repair shop rewinds the alternator you'll a choice as to what output amperage you want. I went from 40 to 70 amps, thinking more output would be a good thing. The added load on the engine caused a significant decrease in PRM when the battery charge was low, and also caused excessive belt wear. I was replacing belts every 2-3 hours of run time. I had it rewound back to 40 amps and all is fine again.

Thanks, great information. Yes, I wondered about taking power away from the main purpose of the engine - propulsion - as well. So I'll stick with the lower amperage alternator for now. Hard to get that work done now...everyone on holiday and it would probably have to be couriered to a bigger town / city. I need it NOW.

Appreciate everyone who took the time to respond. Very helpful.
Thank you.

[Martkimwat]

I have a 2GM20 raw water cooled. It came with a 35 Amp alternator although as others have said, a 55 Amp alternator is an option on the later models. I replaced mine with a 65 Amp alternator from a car breaker because I needed more power to match my much larger battery capacity. kept the alternator below 70 Amps which is the maximum you can run on a single "V" belt pulley. I did that 4 years back and have never had a problem with it after 400+ hours of running. Mind you I do have 140 Watts of solar as well so rarely need much Amps except with consecutive really gloomy/cloudy days.

[NorthCoastJoe]

I replaced an alternator on the same engine a few months ago. I found a standard replacement at an auto parts store ( Auto Zone, in California ) If I do some digging I might be able to find the model number.

[chris mac]

I have 3gm30f, 55 amp alternator. I just replaced both of mine and ordered them off amazon. 80 bucks a piece.
I would think they would have the 35 as well??? Or good time to upgrade.