Yanmar 3hmf alternator upgrade

[CapnBrown]

I have an 80's era 3hmf whose alternator stopped working. It has a lot of corrosion and I'd like to just replace it now that I'm drying out my engine compartment and want regular dependability. The replacement part is a 35amp Alternator of which a number of aftermarket companies readily sell. I would like to have something that will charge at a higher rate as I don't run the engine for very long. I try to keep the engine running for 20 minutes minimum but that is already longer than necessary to get sailing.

Anyway, I heard the 80 amp alternator requires so much tension on the belt for the 3hmf that it will damage the water pump unless a second belt is added. I'd rather not go through so much trouble and think maybe the 55 amp alternator the 3GM's come with would be a good balance to keep a single belt with a little more amperage. Does anyone know if putting the 55amp alternator designed to fit the 3GM models will mount up without a problem and if this is a reasonable thing to do?

Or am I asking for trouble and just go with the 35amp stock alternator?

TIA

[Stu Jackson]

Second time I've posted this this week: just be aware of the features of these alternators, no reason why you can't buy a "regular" one.

Thanks to MS

The problem with all Yanmar/Hitachi alternators, except some very old models, is that they can lead to chronic under charging and extremely slow bulk & absorption charging. Why? These alternators have a built in thermal protection system that works by lowing the target voltage point as the alt heats up.

Most of the Yanmar/Hitachi alts begin temp compensation at 20C / 68F and drop the voltage by 0.01V for every degree above 68F. When you consider that most of these alts will run at 210-220F+ in bulk that means:

220F - 68F = 152 degree difference

152 X -.01 = -1.52V drop in the alternators max voltage output at 220F.

The specs will also say things like 14.4V (+/-0.3V) for the regulated voltage. Let's assume your reg was producing the spec of 14.4V and your alt is now running at 200F.

That is a 132 degree rise above 68F so 132 X -.01V = -1.32V

14.4V - 1.32V = 13.08V at the batteries

This is NOT INCLUDING ANY VOLTAGE DROP IN THE WIRING

Lowering the voltage point reduces accepted current by the battery bank and allows the alt to cool... It is a safety feature for the alternator but a death feature to your batteries...

Any upgrade beyond a factory Yanmar/Hitachi alt is a good one.... ShareThis
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-Maine Sail / CS-36T

[CapnBrown]

So do you (or any other guys knowledgeable with this motor) know if the Hitachi 55amp (LR155) is a drop in replacement for the Hitachi 35amp (LR135) for the 3hmf? And, is there an alternative +-50amp replacement for the 35amp that is reasonable in cost that does a better job of handling heat?

[hlev00]

Originally Posted by CapnBrown

I have an 80's era 3hmf whose alternator stopped working. It has a lot of corrosion and I'd like to just replace it now that I'm drying out my engine compartment and want regular dependability. The replacement part is a 35amp Alternator of which a number of aftermarket companies readily sell. I would like to have something that will charge at a higher rate as I don't run the engine for very long. I try to keep the engine running for 20 minutes minimum but that is already longer than necessary to get sailing.

Anyway, I heard the 80 amp alternator requires so much tension on the belt for the 3hmf that it will damage the water pump unless a second belt is added. I'd rather not go through so much trouble and think maybe the 55 amp alternator the 3GM's come with would be a good balance to keep a single belt with a little more amperage. Does anyone know if putting the 55amp alternator designed to fit the 3GM models will mount up without a problem and if this is a reasonable thing to do?

Or am I asking for trouble and just go with the 35amp stock alternator?

TIA

Balmar engineers can help you evaluate what higher capacity alternator options you have. However, you need to start with what kind of batteries and what size they are to determine how much a larger alternator will benefit you. batteryuniversity.com is a good website for learning more about what goes into batteries and how to get the most out of them. If you batteries are lead-acid and relatively small, and you don't use a lot of power normally, the 35 amp might be sufficient. Lead-acid batteries don't have a very high charge acceptance rate when they are 85%-90% charged. The can take up to 10 hours to fully charge which is a waste of diesel fuel and not so good for the engine anyway. Other battery technologies do charge better.

You might find that an external regulator will help you charging even with a smaller alternator as it will keep the voltage at the maximum voltage for the conditions. Even that won't overcome the low acceptance rate of lead-acid. I suggest getting a digital multimeter with a clamp on ammeter. That will help you get a feel for when charging is occurring and at what level. For example, after we have been using our electrics for a day of cruising, when we first start the engine to charge, idling is too low and the alternator isn't putting out its maximum amps. When the batteries are low, they can handle that rate. After a while though the batteries can't handle the extra current so idle speed is plenty.

We have lead-acid and get by with the stock alternator, but supplement with a 60 watt solar panel to top off the batteries while we are off the boat. Our boat is on a mooring and unfortunately we are only there weekends, but it is sunny in the summer and the panel does a fair job of topping off the batteries by the time we come back down the following weekend.

[a64pilot]

I think your faced with two options

1. stay stock and spend little money, but accept that the alt does little to charge batteries.
2. spend considerable coin upgrading to a better alt w external regulator and possibly a serpentine belt.

I think it depends on how much motoring and how often your on shore power. If you motor rarely and then only for short times, maybe you'd be better off putting the money into solar?

Or if you often plugged in to shore power, maybe that alone is enough. Me, I'm the shore power guy now, but I plan on going more towards solar when I leave as I'm expecting to cruise in warm water and maybe I'm foolish, but I think I'd rather run a small generator if I need to rather than run the main to recharge batteries, but plan on having Solar do the job.

[gordwedman]

Originally Posted by CapnBrown

So do you (or any other guys knowledgeable with this motor) know if the Hitachi 55amp (LR155) is a drop in replacement for the Hitachi 35amp (LR135) for the 3hmf? And, is there an alternative +-50amp replacement for the 35amp that is reasonable in cost that does a better job of handling heat?

I think all the old Yanmars used a dual foot Hitachi alternator. If the 55 amp unit is dual foot it will very likely fit. You could measure the spacing between the feet to confirm. If you don't run your batteries down I Don' t think you will see much benefit really.

[Cheechako]

I had a 75 amp Ample Power on the 3qm30. That was about as high as you could go on that engine with a single belt. How do I know? I also had a 100 amp alternator I tried. I spent more time changing belts than using the boat. Every time I started the engine the belt would squeal like hell. I tried every highly touted belt out there. (BTW: the notched back Dayco did better than the Greenstripe I usually used) I must have aligned the thing 3 times to no avail. You just have to have more belt contact/wrap around the pulley.
Unfortunately I don't know the answer to your Hitachi question. If you don't need a lot more charging from your alternator then I would stay 50 amps or below.

[Stu Jackson]

OK, you want to switch to a higher output alternator. That should be a given, your boat, your choice, right?

The issue is as I've written from MS, Hitachi alternators are built with the built in temp compensation that you can't bypass without potentially damaging the alternator, 'cuz that's how they're made.

So, find a dual foot alternator that will match your mounting, decide on internal vs. external regulation, and just do it.

Good luck.

Here's a source for alternators: Leece Neville*110-603 - 12V 90 amp ALTERNATOR

While this links to an alternator that fits my engine, not yours, look around the site. Call them, Bob is very helpful.

[evm1024]

Originally Posted by CapnBrown

So do you (or any other guys knowledgeable with this motor) know if the Hitachi 55amp (LR155) is a drop in replacement for the Hitachi 35amp (LR135) for the 3hmf? And, is there an alternative +-50amp replacement for the 35amp that is reasonable in cost that does a better job of handling heat?

Yes it is. I ran a Hitachi 55 amp alt on my 3hmf for about 10 years till I sold the boat. THe alternator dropped right in and did not cause any belt problems.

I did have the coolant water pump shaft break but that was due to corrosion at the seal on a 20+ year old pump.

My energy usage was minimal but it had no trouble charging up 4 golf cart batteries in the house bank after a week on them (at 50% discharge). Charging run time was typical of a small alternator (35 to 45 amps was a typical charge current).

By the way, the 3HMF is a great engine. It has almost twice the oil capacity as the 3GM and is a bit more robust (of course at a greater weight).

Regards!

PS my 3HMF was in an Ericson 39.

[CapnBrown]

...

Originally Posted by hlev00

We have lead-acid and get by with the stock alternator, but supplement with a 60 watt solar panel to top off the batteries while we are off the boat. Our boat is on a mooring and unfortunately we are only there weekends, but it is sunny in the summer and the panel does a fair job of topping off the batteries by the time we come back down the following weekend.

I will be adding a solar panel shortly and this really does seem to match how the boat is going to be used. IE Sitting for periods waiting to be used on weekends. If it's a power hungry weekend I'll just have to run the motor for a while at some point.

I have 4 6v batteries (2 parallel/2 series) for a house bank that I run everything on with a separate start batter.

I think I'm going to go with inexpensive 35amp for now and let the solar panel do its work as soon as I have it set up.

I want to thank everyone for chiming in. Never forget what a great resource this site is; I know I won't.

Thanks again...
Fair winds and cool rum drinks...

[Tx J]

Originally Posted by CapnBrown

I have an 80's era 3hmf whose alternator stopped working. It has a lot of corrosion and I'd like to just replace it now that I'm drying out my engine compartment and want regular dependability. The replacement part is a 35amp Alternator of which a number of aftermarket companies readily sell. I would like to have something that will charge at a higher rate as I don't run the engine for very long. I try to keep the engine running for 20 minutes minimum but that is already longer than necessary to get sailing.

Anyway, I heard the 80 amp alternator requires so much tension on the belt for the 3hmf that it will damage the water pump unless a second belt is added. I'd rather not go through so much trouble and think maybe the 55 amp alternator the 3GM's come with would be a good balance to keep a single belt with a little more amperage. Does anyone know if putting the 55amp alternator designed to fit the 3GM models will mount up without a problem and if this is a reasonable thing to do?

Or am I asking for trouble and just go with the 35amp stock alternator?

TIA

I have the same Hitachi 35A alternator on a smaller engine. I haven't done it yet, but all my digging leads me to using a "Sterling Power ProAlt C Alternator to Battery Charger", a smart multistage charger wired between a stock alternator and the battery bank(s).
It comes in 120A or 210A (max) versions. So even if you fit a 55A or greater alternator the smaller one will work. I'll put a link to a Defender page, but it's widely available elsewhere: (I guess I won't as it's too long, just go to defender.com or wherever and search for "Sterling" or "sterling power").

Here is the link to the install and operation manual: http://www.defender.com/pdf/STER_AB130.pdf .
It covers everything, read it over and see if this will work for you.
I don't see much here on CF about these units, maybe I miss it, but they seem to be an ideal, simple, relatively inexpensive ($280-350 all up, optional remote is $80-100) solution for a common 'problem' for older boats; compared to fitting a fancy name alternator/regulator/etc.

It seems simple enough to install and set up, will work with two banks (engine and house), or other variations, and has both battery and alternator temp sensing (supplied options I think), a remote head is also available for full data displays.
It's 'programmable' (via switch setting) for different battery types too.

"It transforms the output of your alternator into a sophisticated multi-stage battery charger resulting in faster and more complete charging of your battery bank(s)."

It works as a 'buffer' between the stock alternator and the battery(s). It takes the power output of the alternator as an input, whatever the voltage and amps available, and 'adjusts' that power on its output side to suit the needs of the battery bank(s).
IE: the normal four stage charge routines, initially a higher voltage and max acceptance current, then through the other stages. So your alternator might be limited (stock) to, say, 13.8-14.2V/30A, the ProAltC will output 14.4/6V (see the manual for different charge profiles), slightly less than 30A to start, then scales through the charge profile.

You're still limited to your alternators max power output of course, but that output is 'smartly' shaped to fit a given battery bank.
This may be all you need to do. A 55A alternator upgrade (or not), the ProAlt C, and for about 300-400 clams, you're set.
No fussing with engine mounts, pulley mods, belt changes, wiring mods, etc., just wire it between the alternator and the battery(s) and go.