high output alternator on 3YM30 Yanmar?

[c.spots]

My engines are Yanmar 3YM30, 29 hp, with SD 20 saildrives. They have 80 aH alternators. I would like to have high output 115 aH alternators, but was informed that Yanmar does not recommend the high output alternator for this engine (but does for the smaller 19 hp engine,and indeed is a standard item for the boat with the smaller engine).

There seems to be plenty of space in the engine compartments. The battery bank is 3 X 180 aH AGM batteries.

Can somebody help me make sense out of why you shouldn't put a high output alternator on the larger engine (or any, for that matter)?

[MidLandOne]

I am not familiar with the engine but to start the ball rolling I suggest that a likely explanation is that the rating of the bearing on the pulley end of the crankshaft means it cannot reliably carry the bigger alternator's belt loads. This could be just because the bearing is "small" or the configuration of the engine means that there would be a big overhang away from the bearing to the added belt pulley.

[svquest2]

I have a Yanmar 3HM 35F which came with a 50 amp alternator and the same caution. The problem was the the bearing on the idler pulley which is the fresh water pump. The higher rated alternators require much higher torque to turn them so the drive belt has to be so tight that it overloads the fresh water pump pulley bearing

I put on a small frame 124 amp "Ample Power" alternator over their objections, and sure enough, I could not get the belt tight enough, and the belt spalled all over the engine compartment. I had a machine shop make up double pulleys and that has worked just fine for 13 or 14 years. I have not hurt the bearings or the water pump, or over tensioned the belts.

Good Luck

Joe S

[David M]

Cummins uses a toothed belt that looks similar to a timing belt. Ask if that type of belt is an option for your engine. For obvious reasons, it can pull harder with less belt tension.

Also there are shops that can take an alternator and rebuild it with more output. I did that with my engines years ago. I went from a 105 amp alternator to a 160 amp alternator. The downside is I had to rev the engine up a bit to excite the field enough to get the amps I needed.

I would check Balmar's website or call them to see if they have any solutions.

David

[c.spots]

I can understand why a high output alternator could cause problems with an engine, but what really puzzles me is why it is ok for the smaller 19 hp, but not for the larger 29 hp 3YM30 engine. Could it even be true? Yanmar hasn't gotten back to me yet.

[Strygaldwir]

Robert:

Are you going to put new alternators on both engines? How do you balance the runtimes between the engines if you're only going to put them on one?

Are you sure you have 80 amps currently? I think mine are only 55 amps and they are the stock alternators that came with the engines.

[svquest2]

Robert, difference could simply be the orientation of the alternator belts. The smaller engine may have a dedicated alternator belt where it has approximately 270% contact on each of two different pulleys (drive and alt), Your engine may be like mine, where the one belt goes over three pulleys, with only about 120% of contact on the alternator pulley. Thats why I couldn't tighten my belt tight enough; and it worked fine when I doubled the contact area by adding a second pulley.

Make sense?

Joe S

[c.spots]

My amp meters were showing 70 to 75 amps max. The boat was supposed to already have an upgrade to high output 115 aH per the brochure specifications. When I checked the alternators, they were 80 aH. When I mentioned the discrepancy, I was informed that the 115 aH high output alternators were only for the basic 19 hp engines, not for the 29 hp upgrade engines, since it was not recommended by the manufacturer for the larger 3YM30 engine!
It doesn't make sense to me.
I think Yanmar has their own upgrade from 60 to 80 aH alternators.

[Alan Wheeler]

80A is at the top end of a single belt installation. Over 80A, you should be going to a double belt. Certainly a 115A Alt needs to have double belts. Either that, or a tooth or ribbed belt system, but that requires specialised pulleys on all areas.
Is there a chance that the small engine has a double belt system fitted?

[Pelagic]

I thought I would drive a large case 24v alternator off of my Northern Light 12Kw Generator. (Which is oversized for our live aboard use). My plan was to install a 240A @ 24V

I know Dick Gee from Northern Lights, (He is the VP and Engineering adviser for them) and I asked if they could make a custom PTO for this and mount it the way it should be.

He pretty much shot down that idea by saying:
“The problem is the tremendous side load imposed onto the nose of the engine crankshaft by the "V" belts when driving the alternator. We know from experience this can cause catastrophic failure. Based on this experience our 24v alternator limit is 40 Amps.

Also Nick, belt driven batter charging alternators are famously inefficient. On average they are 50% efficient. Have you considered a very large battery charger that could use the AC power from the generator OR shore power?"

So I think it probably can be done but the issue is that if not done right, you have major problems in the lower end, so the manufacturers are understandably conservative

[white rabbitt]

What were the cost of Yanmar 3YM30-SD marine saildrive engine 29 hp ?

[Cheechako]

It sounds like the smaller engine doesnt use an idler and the bigger one does...?

[SvLetitgo]

Just did that install on this specific engine model. If you have any question don't hesitate

You can find the first post of the installation here

Electromaax install. · SV Letitgo

You will find more after

Good luck

[Ram]

i have a Balmar 125 amp single pully on my 3ym30 since 2006 works perfect with over 1300 hours on it- the smart external regulator went bad twice- likly due to my own fault