I have a 1998 Hunter 376 with the original Yanmar 3JH2E (non-turbo) engine, with only 1,300 hours. It currently has the original 55A alternator, which is working fine. I want to purchase a spare alternator for cruising, and I'm thinking about getting the 105A that's a straight replacement, then keeping the original 55A as the spare. The engine is only 27hp, is the 105A too much for it? Any thoughts or concerns? Batteries are AGI and brand new. Thanks in advance.
Pro/con of high capacity alternator for Yanmar 3JH2E
- Thread starter bmohr
- Start date
Just buying a high capacity internally regulated alternator doesn't make much sense. To get the benefit of the high output, the regulator needs to be externally regulated and the batteries must be able to absorb the current. Internally regulated alternators are usually programmed to quickly charge the start battery and then the output decreases. The article below from Rod Collins does a much better job than I can explaining this see the link below.
If you are looking to upgrade the charging, then buy an externally regulated alternator and program it to properly charge the batteries. A Group 31 AGM battery has about 100 amphour capacity and can be charged at 20% of that (usually noted as .2C) some can be charged at higher current as much as .4C. Assuming you have 2 Group 31 batteries, an alternator that can produce 40-50 amps for an extended period would be an improvement in charging time and battery health.
In addition to the article linked below, Rod has several other articles on alternators and charging well worth the read. You will learn that batteries and charging technology has become much more sophisticated than when we were kids.
If you are looking to upgrade the charging, then buy an externally regulated alternator and program it to properly charge the batteries. A Group 31 AGM battery has about 100 amphour capacity and can be charged at 20% of that (usually noted as .2C) some can be charged at higher current as much as .4C. Assuming you have 2 Group 31 batteries, an alternator that can produce 40-50 amps for an extended period would be an improvement in charging time and battery health.
In addition to the article linked below, Rod has several other articles on alternators and charging well worth the read. You will learn that batteries and charging technology has become much more sophisticated than when we were kids.
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
Hard to recommend course of action without knowing what you intend to charge, capacity and type. But in general, stepping up in alternators you may also need to beef up the belt to a serpentine. The higher drag can chew up v-belts. You could always wait and see on that one. High output also means high heat. Depending on what you are doing, a temp sensor may be a good addition (between the alternator and the external regulator). And an external regulator like a Wakespeed or Balmar unit have so many advantages over an internal regulator I wouldn't even consider an internal regulator as an option anymore.
So what are you charging? Any solar?
So what are you charging? Any solar?
Before even brushing your teeth this morning, consider an external alternator regulator. I most likely have exactly the same alternator as you do, the Hitachi LR155-20B. It faithfully limped along and offered up 10A at 14.2V feeding a 50% SOC battery bank when under full load. Remember, it doesn't have a smart regulator so no bulk charge. I installed a Balmar ARS-5 three stage regulator about 10 years ago and went from 10A to :
at 14.7V feeding the same 50% SOC bank. This may be a bit over the recommended 0.2C charging rate for my battery bank but certainly no problems with the last batteries which lasted about eight years.
Don't remember the cost of the regulator but I'm guessing it is significantly cheaper than the Balmar 110A alternator. Also, I believe the new Balmar will require a dual belt pulley which makes for a fun swap out back to the old Yanmar (should the new Balmar fail) while away from home.
Last edited:
In addition to the link in Dave's #2 reply, there's this about Hitachi alternators:
Hitachi/Yanmar Alternators: (by Maine Sail)
Some alternators though, such as those made by Hitachi and found on Yanmar diesels, are dumber than a pound of beetle poop. Actually, to the alternator, they are pretty smart but to your batteries and the speed of charging they are flat out stupid. Why?
Hitachi alts with dumb regulators, and some others, limit voltage but also reduce voltage based on alternator temperature. This is a self protective feature installed in the internal dumb regulator to prevent the alternator from cooking itself. Remember voltage is the pressure that allows more current to flow. So, if we reduce the absorption voltage, then we also reduce the current the alternator is supplying.. Any battery at any state of charge simply will not accept the same current at 13.4V that it did at 14.4V and as a result the alternator will run cooler. What do you suppose this does to your batteries over time.......?
The problem is that when cold you will get 14.3V to 14.4V out of the Hitachi but as the alternator heats up the dumb regulator begins to reduce the CV/voltage limit based on the alternators internal temperature. It is not uncommon to find a Hitachi alternator at 13.4V when hot. This is REALLY, REALLY DUMB....
If you have a dumb regulator, and notice the voltage dropping, it is likely a temp compensated dumb regulator. Get rid of it or plan to buy new batteries more often.
If you have a temp compensated alternator or a Hitachi alternator on a Yanmar you really are in dire need of external regulation if deep cycling a larger battery bank.
This is from:
http://forums.sbo.sailboatowners.com/showthread.php?t=125392
and these, too:
Hitachi Alternator and Smart Regulator Instal Question - Cruisers & Sailing Forums
Most practical way to upgrade Yanmar alternator? - Cruisers & Sailing Forums
