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?
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.