3GM30F Alternator Query

Ralph Johnstone · Saturday at 3:55 PM

nhodgson said:
.the guy who can service/repair the 60 is offering me an Hitachi 80 amp off the shelf.....

I don't believe your batteries will receive one additional amp from a 20A increase in alternator size. AS LONG YOUR ALTERNATOR IS ALREADY BIG ENOUGH TO SUPPLY YOUR BATTERIES IN A REASONABLE AMOUNT OF TIME.

First question, what does your current 60A alternator supply to your batteries ? If you don't have some form of battery monitor, you don't know what a 60A alt. supplies.

By comparison, my alt. on my Hitachi - model #LR155-20B - 55A alternator on a Yanmar 2GM20F used to put out 14A cold to a battery at 12.2V and drop to 10.5A when hot. Not too impressive.

Back in 2011, I decided to install a Balmar ARS-5 external alternator regulator after reading their literature to see how many additional amps I could squeeze out of the new regulator. What everybody's problem is that their Hitachi alternator is regulated to supply a bulk voltage of 14.2V. It's the difference between the bulk voltage supplied by the alternator and the battery voltage which forces the amperage into the battery. Simple enough. Raise the regulated bulk voltage and Ohm's law happens :

.................. except the higher voltage will now overcharge the batteries and cook them if run for an extended period of time. What you really need is someone (or something) to reduce that higher voltage once the batteries are charged. With current labour rates, food, lodging, clothing etc. it's much cheaper to install a Balmar controller (a something) and be done with it.

With the smart Balmar regulator now doing the work, it now controls the bulk voltage up to 14.7V which drives the amperage up to :

............. a big increase over the previous cold 14A at 14.2V. As the battery charge increases, the smart regulator reduces the voltage which causes the amperage to reduce and no damage to the batteries.

In fact, I have to question most of the discussions on increasing alternator size on this site because most people have no idea where they are starting from nor any idea what the improvement is with with the new alternator.

No installed digital ammeter = no idea of what the amperages are.

If you think about it, how can a new, bigger alternator with an internal regulator set to the same old 14.2V (same as your smaller one) possibly supply one additional amp. The voltage supply has to be increased to supply any additional amperage and for this, you go to an external voltage regulator.

Ralph Johnstone · Saturday at 4:52 PM

As far as brackets and belts go, that would depend entirely on the shape of the new Hitachi 80A alt.

marcham · Saturday at 11:18 PM

I work on a 3GM30F that has an 80A Delco. If it fits is more a function of the enclosure than the brackets. Do you have a dual v belt pulley? As you go up in Amps, you'll get more belt dust. Around 100A is when a serpentine belt is beneficial.

I see way too many v-belts that are overtightened.... that's a great way of destroying bearings!

Davidasailor26 · 2024-12-22T03:43:11-0800

I know the 3YM30 can be equipped from the factory with the 60A Hitachi or the 80A as an option. Ours came with the 80A (with a normal V belt). I presume the fact that it can come with either means the two are fairly interchangeable, at least in every dimension that matters to the YM.

When discharged below 60% SOC my 300AH of AGM absorb about 50A from the 80A Hitachi, tapering down as SOC increases.

shemandr · 2024-12-22T06:11:02-0800

Da, da, da. The plot thickens!

dlochner · 2024-12-22T06:20:19-0800

The internal regulators on Hitachi alternators are set up to protect the alternator not charge the battery. The output voltage on the 80a Hitachi is reduced for every 1°C above 20°C of alternator temperature. As a result the alternator's output and charging ability declines pretty quickly, leaving batteries undercharged. I wouldn't spend a lot of money on a spare Hitachi alternator. See the article below.

As for the fit, the two alternators are small case alternators, the physical size should be the same. I think most Yanmars have a dual foot, just make sure they are the same dimension. And don't lose the small compression tube that goes between the feet when you reinstall the alternator.

Automotive Alternators vs. Deep Cycle Batteries - Marine How To

A Deep Cycle Battery Assassin The alternator pictured here helped to destroy a very expensive bank of TPPL AGM batteries in under two years. These batteries need an absorption voltage of 14.7V. The highest voltage I recorded on this vessel was 13.58V at the battery terminals. At this

marinehowto.com

marcham · 2024-12-22T06:48:16-0800

nhodgson said:
Marcham, that's what I think I have done. I'll release the tension and see if I can save the situation.....although if I take the belt off and spin it freely and there's gating/grinding/rumbling/roughness, at least there's a local guy that can repair it for me.

I have the single belt installation, and don't see the need for 100A and above as I have 550W of solar atop my davits too.

You may start wearing out belts very quickly.... I'd strongly suggest a dual v belt at a minimum for an 80A alternator.

Ralph Johnstone · 2024-12-22T09:37:56-0800

Davidasailor26 said:
When discharged below 60% SOC my 300AH of AGM absorb about 50A

@Davidasailor26 , do you have an external alternator regulator controlling your 80A alternator ?

Davidasailor26 · 2024-12-22T09:44:15-0800

Ralph Johnstone said:
@Davidasailor26 , do you have an external alternator regulator controlling your 80A alternator ?

No, just a dumb internally regulated Hitachi. It hasn't melted from the strain of the three G31 AGM's yet. It self-regulates to about 14.3 when cool and with high SOC of batteries. At lower SOC (around 50-60%) once warmed up it can only get to about 13.2V, but that's still enough for the batteries to absorb close to 50A. From about 70% to 90% SOC it runs in mid-high 13's and around 40A.

Davidasailor26 · 2024-12-22T09:46:38-0800

marcham said:
You may start wearing out belts very quickly.... I'd strongly suggest a dual v belt at a minimum for an 80A alternator.

I've never seen any belt dust from our 80A internally regulated Hitachi with single V belt. If using an externally regulated "real" 80A alternator that actually outputs close to 80A instead of sustaining 40-50 the belts might matter more.

dlochner · 2024-12-22T09:52:47-0800

Davidasailor26 said:
I've never seen any belt dust from our 80A internally regulated Hitachi with single V belt. If using an externally regulated "real" 80A alternator that actually outputs close to 80A instead of sustaining 40-50 the belts might matter more.

I never got belt dust with the 80a Hitachi and when I added a Compass Marine 90a externally regulated alternator, I didn't get any either with a ½" belt charging 4 135a GC batteries.

Ralph Johnstone · 2024-12-22T09:56:28-0800

Davidasailor26 said:
It hasn't melted from the strain of the three G31 AGM's yet.

Time to consider an exhaust fan for the engine enclosure.

Over heating was my biggest worry when I installed a Balmar ARS-5 external regulator and put the 55A alternator to work for the first time in its life. I had to dial the belt % (on the regulator) way back to avoid the ARS-5 cutting back on the alternator output. The exhaust fan seems to keep everybody "relatively" happy for the last 15 years even though sitting on a razor's edge.

Maine Sail · 2024-12-22T12:08:46-0800

nhodgson said:
Hello Brain Trust!! ....Don't shame me if this is an old joke but......

I may or may not have overmentioned the belts on the Hitachi 60 Amp alternator as I'm hearing a 'fluttering' synonymous with failing bearings. I'm going to the boat tomorrow to investigate the alternator, raw water and cooling water pumps.

So my question is have any of you replaced the Hitachi 60 with an 80, and is it a drop in replacement? I am considering having mine rebuilt and also carrying a spare as I'm heading to the Islands in March and am not averse to carrying a spare...the guy who can service/repair the 60 is offering me an Hitachi 80 amp off the shelf.....

Neil

Hitachi no longer produces those alts. Rebuilding what you have is far better than getting a cheap Chinese clone... Even if you can find a new old stock genuine Hitachi you will never get 80A out of it so, belt wise, you're fine........