Is a 100 amp Alternator Too Large ?

[wilsodf]

I would call the Yanmar Distributor (Mack Boring) in New Jersey. I have a 3YM30 and the 80 amp is the biggest you can put on a single belt. They have a great tech line.

[hellosailor]

The differences between an 80 and 100 A nominal installation could easily be swamped by the quality and tension of the belt (come on, who actually owns and uses a belt tension guage? Show your hands) as well as your regulator and the hunger of your batteries. Hungry AGMs and a good regulator, and sure they may really suck 100A and slow down the engine. Same battery capacity, wet acid, only 40% discharged, and they may never demand it.

But I've also seen a lesser system where quite literally switching to both batteries, when they were hungry, caused the alternator belt to hump up like an inchworm and ride right off the pulley, as the engine slowed down under the increased load. (Yeah, that got fixed too.)

100A, single belt, single engine..."it depends".

[Highlander40]

I am running a 100A alternator with one V-belt but the external regulator is set to 80A. That way the alternator has a little more head room.

I had hoped to run at 100 with the poly-V belt but it didn't work out.

[senormechanico]

Wouldn't it be great if engines were designed to have a GEAR DRIVEN alternator?

[phantomracer]

Been running a balmar alternator with a balmar regulator without any problem on our 3GM30F. The hardest problem the previous owner (installer) had was finding a vbelt that fit. Other than that, no problems. Performs great. Charges the large battery bank without issue, and quickly.

No belt dust, slipping, nothing.

[Highlander40]

Just to be clear, belt dust indicates low belt tension.

A better quality belt helps too.
There are 3 or 4 power levels in belt style for belts that are the same size and shape. Belts with notches are better.
Belts that look like they are wraped in fabric are low power, old school.

Anything with a "raw edge" grooved or not is better.

[SoonerSailor]

Balmar says a single 3/8 inch v belt will be ok up to a 100 amp alternator.

I use a Krikit belt tension gauge. You would be surprised at how hard it is to get adequate tension on the belts - typically 100 lbs for a single v-belt and 50 lbs each for a double belt setup.

[richardhula]

Any battery bank size of 300 a/h or more can be safely be charged from a 100 amp alternator with smart regulator.

I have seen 140 amp alternators driven by single A groove large section belt but the norm for 100 amp or over is twin belt or single polygroove (6 teeth).

Regarding drain on engine power - this will only be at maximum when alternator is producing max amps. Unless your 100 amp alternator is too small for task the period of time when its maxed out will be relatively small.

I have two alternators both with smart regulators collectively producing 210 amps & feeding three battery banks totaling 800 a/h.

[John A]

Originally Posted by Highlander40

Just to be clear, belt dust indicates low belt tension.

A better quality belt helps too.
There are 3 or 4 power levels in belt style for belts that are the same size and shape. Belts with notches are better.
Belts that look like they are wraped in fabric are low power, old school.

Anything with a "raw edge" grooved or not is better.

Low belt tension causes the belt to slip resulting in a shinny surface on the inside of the belt.
Belt dust is caused by an improper alignment of the pullys and wear on the side of the belt. Or an improper sized belt.
At least this was the case on grain combines and all sorts of our farm machinery and I doubt that the belts on my boat were any different.

[hellosailor]

Gear driven alternator? Surely, there must be a British Sports Car using one of those. A gen-you-whine Lucas, no doubt? <VBG>

I found out nearly ten years ago, V-belts are an endangered species. Cars don't use 'em any more, so the auto shops don't carry many of them. If you don't want to pay marine prices and wait for the wrong parts to be shipped...shop around now for spares, talc them and seal them up airtight and save them. Because you can't just hop down to the local auto parts store and expect to find them in stock anymore, even with no brand name.

[Highlander40]

John A, the glaze you report is seen on wraped style belts that are now so out of date that they can't be found.
The raw edge style that has taken over has better grip but can shed some material when under tensioned.
Bad pulley alignment is, well just bad. Bad design. Bad manufacture. Bad quality controll.
Industrial uses are still common for V-belts and will continue for many decades to come.

A by product of my foray into poly-V belts is an excellent screw tension adjuster. No more hammer handles wedging alternators to some unknown belt tension.

[delmarrey]

Before we start insulting ourselves on belt quality and function this is a must read. High-modulous v-belts, micro-v belts and polyflex JB | Gates Corporation

[Highlander40]

Yup, that also falls into the way too much information cat.
But you can see how many choices there are.
Metric standards only add to the confusion.

30 years ago you could choose A,B etc. section or 2L,3L section.
That was it.

Then the V and VX came to the market with three times the HP capability.

The Predator has the advantage of aramid tensile cords. This stuff doesn't improve the HP rating so much as it allows the belt to absorb huge shock loads. Which lets you run closer to edge. This is similar to the invention of the folding bicycle tire. Flexible, strong and fatigue resistant. Don't know if it's really best for engine use.

So the real answer is-- with good pulleys and a good belt with proper installation and care, you can run 100A with one V-belt.

The long term answer is that any new modern engine will have a flat poly-V belt like the Micro-V.

[John A]

Originally Posted by Highlander40

The long term answer is that any new modern engine will have a flat poly-V belt like the Micro-V.

So the short term answer is that with an older engine, improperly matched pullys, or pullys that are not aligned correctly, and older fanbelts in use, your experience with this topic may vary.

If you do an add-on of a 100 amp to a Perkins 4-108 manufactured in 1977, different considerations must be taken, than with a new engine..

So everyone's right depending on their situation.

[hellosailor]

flat poly-v?

Is that what most of us called a "ribbed" belt? Inch ormore wide, flat on top (outside) multiple V's on the bottom (inside) ? Standard for automobile serpentine belts for the last 15-20 years or so?

Simple V-belts are dead, they're just not commonly stocked in the auto supply stores, and the Grainger and McMaster type industrial suppliers are WAY fewer and far between. You know, 'round the corner from the buggy whip outlet store? <G>