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Alternator upgrade for Yanmar 3GM30


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We currently have a noisy bearing in the Alternator, fortunately we have a spare to borrow for the Xmas cruise to get us through.

As we run 12V fridge and freezer I thought this would be a good excuse to go with a bigger alternator.

Currently we have the standard 55amp alt with approx 250ah of house battery (will have to double check this next time I'm at the boat). At an initial search for a straight bolt on upgrade it jumps to 120amp.

Is that to big for my application? Should I be trying to find something around 80amp?

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3 hours ago, Kick Ass said:

We currently have a noisy bearing in the Alternator, fortunately we have a spare to borrow for the Xmas cruise to get us through.

As we run 12V fridge and freezer I thought this would be a good excuse to go with a bigger alternator.

Currently we have the standard 55amp alt with approx 250ah of house battery (will have to double check this next time I'm at the boat). At an initial search for a straight bolt on upgrade it jumps to 120amp.

Is that to big for my application? Should I be trying to find something around 80amp?

Do you currently have an external regulator?  (That seems like a lot of battery to be charging without one...)

The size will only matter if you need to use it and your pulley's are too small.  250A of battery could get close to 120a of draw at 50%DOD. Which would be too much for a single v-belt. 

I would be doing one of:

1/ Buy the biggest alternator with an external regulator and lock it down to 75a

2/ Buy the biggest alternator and upgrade the pulley's to Serpentine and let the battery dictate the current 

Both the above give you some upgrade options in the future assuming that one day you will be upgrading the LAs to Lithium when the time comes to replace them... 

For me, buying a smaller alternator to get round any belt limitation is throwing away good money. You'd possibly be better to replace the bearings yourself...

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53 minutes ago, aardvarkash10 said:

Go for as large as you can easily fit.  It will regulate anyway to match what the batteries need, and having spare capacity is never a bad thing.

 

That's is good to know, have been told in the past can boil the batteries if trying out to many amps in.

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4 minutes ago, CarpeDiem said:

Do you currently have an external regulator?  (That seems like a lot of battery to be charging without one...)

The size will only matter if you need to use it and your pulley's are too small.  250A of battery could get close to 120a of draw at 50%DOD. Which would be too much for a single v-belt. 

I would be doing one of:

1/ Buy the biggest alternator with an external regulator and lock it down to 75a

2/ Buy the biggest alternator and upgrade the pulley's to Serpentine and let the battery dictate the current 

Both the above give you some upgrade options in the future assuming that one day you will be upgrading the LAs to Lithium when the time comes to replace them... 

For me, buying a smaller alternator to get round any belt limitation is throwing away good money. You'd possibly be better to replace the bearings yourself...

Am running a mastervolt external reg.

The direct replacement 120amp alt has a single belt, will give it ago. Not opposed to upgrading pulleys but won't do it if I don't have to.

Biggest worry was going from 55amps to 120amps if there was any consequences.

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58 minutes ago, Kick Ass said:

Biggest worry was going from 55amps to 120amps if there was any consequences.

My understanding is that a single v-belt tops out at 100a in a 12v system.  And I believe belts should be kept at 75% of the max rating.   

I have to admit that I can't find anything to back this up so not sure how valid that snippet of knowledge is anymore. 

With the external regulator you'll be able to limit this if belt dust becomes a problem...

1 hour ago, Kick Ass said:

That's is good to know, have been told in the past can boil the batteries if trying out to many amps in.

You might want to check the current limit on your batteries and set your regulator accordingly if necessary. It's perfectly possible to 'boil' them if the conditions are right and all the swiss cheese holes align.

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I have run Bosch 115A  altternator on a 3GM30F as a direct swap for the hitachi 55A for last five years.

At  60%  discharged battery  it will put out 100+ A's  slowly dropping to 60A over ~30mins as battery

voltage/emf comes up.

Single V belt gates green stripe. yep belts have to be perfectly aligned, with polished pullys

or it will eat belts. 

As it has integrated air cowl I force feed cool air from

saloon thru it. It never derates via zener. 

Best thing about them is the external brushset/regulator can be replace with proprietry

brush set and terminals for external plug in regulator.  Big saving over a hot rated small frame/

 large frame high output. Cheap as chips if you know where to look.

I saw one  on TM for $50.  Graham bought it!

I'm going to run it on Li's soon, derated to 80%. ( Or maybe 60 to start with)

 

 

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1 hour ago, Kick Ass said:

Am running a mastervolt external reg.

The direct replacement 120amp alt has a single belt, will give it ago. Not opposed to upgrading pulleys but won't do it if I don't have to.

Biggest worry was going from 55amps to 120amps if there was any consequences.

You will need to get the new alternator modified to work with your external regulator.

All the recent Yanmar marine engines appear to be shipped with 120A Valeo alternators, even the 3ym20 I replaced my 2gm20 with. It was set up with a serpentine belt and I utilised the belt load manager in my Balmar mc-614 reg to drop the max charging current to 90A.

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If you are concerned about belt slip, try a larger diameter alternator pulley before going serpentine.  More diameter = more surface area = more grip = more power handling.

Don't go mental on this - you can quickly reach a point where the alternator is not spinning fast enough to reach output at idle.

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12 hours ago, Guest said:

I have run Bosch 115A  altternator on a 3GM30F as a direct swap for the hitachi 55A for last five years.

 

Do you know a model/part number? I assume these with fit the 3YM30 as well as they both have the 3.15in dual foot mounting?

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CD is right for over 100A go for a serpentine belt and you will be happy, for the later YM Yanmars with the Valeo alternator Balmar do a kit which fits easily and requires no change to the standard set up. And no new alternator.

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4 hours ago, Adrianp said:

Do you know a model/part number? I assume these with fit the 3YM30 as well as they both have the 3.15in dual foot mounting?

New For gm 928603011FX- Bosch AL-129x 

Old see label on pic.

Dont know about YM.

For 3gm30:
Graham should have a reconditioned one. You will need to grind 3mm off inside of back leg. The rounded boss section and shim front leg same for V belt align. Also you will need a bolt on ext brush set with terminals for quick connect to ext regulator. Graham used to have them. https://www.smartregulator.co.nz/page/

This is the cheap way out if you score an alternator off a Porsche 944 make sure you get the later one 115A as opposed 90A. And get the cowl for external air. Big difference.

CD has the more comprehensive  methodology. Ignore 14V, that is Vset for auto internal regulator.

1AA991BA-A6C9-4A80-AFB2-ADE4A390AF43.jpeg

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Another option is to keep the existing alternator for the start battery and add the 120 amp alternator for the houser batterries. This gives redundency if one fails. Ive been running this system for 20 years absolutely trouble free. I have 2 belts on the 120 amp alternator (bosch off the shelf automotive)  with a BEP smart charger.  I think I may have renewed  the belts once a long time ago. Also a Yanmar 3J series.

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1 hour ago, Kick Ass said:

I will contact Graham before making any moves to make sure I get this right.

Im not after 120amp, would be more than happy with an 80amp if there was a direct bolt on replacement.

I would limit it to 80a with the existing regulator.  (actually I would limit it to ~75A).

Then:

  • You won't chew the belt. 
  • You're unlikely to boil your battery's (but check the specs)
  • You are prolonging the life of the alt 
  • You have a future proofed solution for the day that LAs need replacing and you hum & arr your LiFePO4 options :)
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In my engineering days, I was taught that any Alternator above 85A should be doubled belted. In a Vee belt situation that is. Graham sold me a 140A Alt and said no they were fine up to 140. I was sceptical at the time and now after having run it for some time, yes it chews through belts and you have to tension belts far too tightly to not be a major issue to side loading. So I stick to my view that anything 85 and higher should be double belted.

Also, unless they have a new regulator that has changed the type of Alternator required, when I bought mine, we had to go for a modified Car Alt. That had several issues of course. Like the Case being connected to Ground. Marine ALT's have the Case lifted from Ground. The Alt earth should always go to the common Engine Earth, whuch is normally found at the Starter motor. I ran a copper cable from ALT to common engine ground to reduce as much as possible, any stray currents running through the engine block.

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