Hello All -
Has anyone installed a high-output alternator on a W27a ? I’m finding that because I use the motor so little that charging is a challenge when I’m not connected to shore power. I can get 24 hrs on my new 375 ah AGM batteries running the fridge and the basics. I motored for about 45 min and didn’t make much of a dent in the SOC. I think my alternator is the original.
Thanks -
Bob Gehrman
NS30U #396 “Quickbeam”
Baltimore, Maryland hon
I’m curious about this too. I’ve done a little research and it appears to not be as easy as just hanging a higher output alternator on the engine as it also looks to need the drive belt and pulleys upgraded along with a different charge regulator. Nigel Calder’s Electrical and Mechanical book had a section on this topic.
Bill Mortensen
NS30U #335
Noank, CT
I have a 75 amp Balmar on my 27A with a smart regulator using the original sized belts. I believe this is about as high as you would want to go. If you do a little research on alternators with “Dumb” controls you will be convinced of the need for a smart regulator for marine applications.
With my set up, I have “de tuned” the alternator a bit so that it does not overload the belt too much at start up. Even then, I get some squeal if I rev the engine too soon after starting.
Don Ringsmuth
Selkie 30U 425
East Hampton, NY
I’m curious about this too. I’ve done a little research and it appears to not be as easy as just hanging a higher output alternator on the engine as it also looks to need the drive belt and pulleys upgraded along with a different charge regulator. Nigel Calder’s Electrical and Mechanical book had a section on this topic.
Bill Mortensen
NS30U #335
Noank, CT
Are you using the factory battery isolator? They were diode isolators and turned a horrendous amount of charging current into heat. Replacing it with a FET isolator will make a huge difference to engine charging your batteries. Victron makes them for two and three bank installations.
Paul M
NS30U #211, Sandpiper
Cowichan Bay, B.C.
I have done what Don has, a 120 amp alternator de tuned to 80 amps to accommodate the standard belt. Truth of the matter my wet cells can only take 80 amps for a very short period.
But AGM’s can take almost anything you can throw at them, so a larger alternator and serpentine belt may be a good move. But up sizing the output wires from the alternator is a must. Often two smaller wires vs one large one is the best solution.
I have a have an alternator from these folks. They only make heavy service units.
https://hdpsi.com/collections/23hd-series-models
Belt kits
https://www.boundlessoutfitters.com/product/altmount-serpentine-pulley-kit-westerbeke-13a-21-27/
Isn’t the factory alternator rated at least 50A on a Westerbeke w27? Have you ever seen it charge 50A on your battery monitor?
WHAT??? - You don’t have a battery monitor?? This is the first thing I would recommend: get a Victron BMV7xx. Gotta know what’s going on, before engineering something that works like it should.
If your standard alternator does charge, but only so-so (10 amps), I would suggest altering the behavior of your current alternator. It is perfectly capably of charging what it’s rated for but it’s (internal) regulator sucks. It’s basically designed for automotive use, not marine. The alternator itself does not make a great deal of difference, the regulator is where the magic happens!
I would suggest using a product like:
Sterling alternator booster - this product is excellent but requires technical skills to install
https://sterling-power.com/collections/alternator-regulators
Balmar alternator booster - probably the same as Sterling but more orientated on USA market.
https://balmar.net/balmar-technology/multi-stage-regulation/
My experiences with alternator boosters (Sterling): I’ve lived aboard for 4 years nonstop cruising Europe, Bahama’s and USA using noting but a few poorly functioning solar panels (lots of shade on deck) and a Sterling booster hooked to stock alternator. Man, that thing works amazing, even with an idling diesel engine - full output from the alternator 45A +
Mark H, N36#25, Europe, NL
Thanks All - It occurs to me now that I should test the alternator and the Xantrex combiner that is installed. It’s possibly not charging the house batteries when running on the engine.
I’ll check Calder’s book on this subject to do some testing.
I do have a Balmar battery monitor, too.
Hi Bob, we upgraded to a small body 120 amp alternator and smart regulator when we added refrigeration. Wiring was also upgraded to handle the additional load. The stock adjusting arm was not robust enough to handle the new alternator so a new one, with threaded adjustment, was installed. The pulleys are stock but the single belt was swapped out for a stronger variety. The regulator ramps up slowly and I have not heard the squeal usually associated with a slipping belt. I made these changes about 15 years ago and have made one belt change. BTW the house bank is 4 X 6 volt golf cart batteries for 440 amp-hours in total.
Regards…Ron
Ron & Diane Schryver
“Alpha Waves” '87 NS30U #393
Georgian Bay Midland ON