What's a sensible sized alternator

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NPMR

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I am thinking of adding more battery capacity on the boat.

The idea is to have 340 A/h plus the 75 A/h engine start battery, with a splitter to manage the various 'needs'. And an Adverc or similar to help.

The suggestion is to have a higher output alternator as well, on a Yanmar 3YM20.

What would be a sensible output from the alternator?
 
Do you mean an additional loss of 2hp or a total of 2hp if the additional load is applied? And at what output rate were you suggesting this would happen? Is this an average, just normal - is there somewhere I can look up options?
 
NPMR said:
The suggestion is to have a higher output alternator as well, on a Yanmar 3YM20.

What would be a sensible output from the alternator?
Click to expand...

You can't sensibly drive much more than a 90A-100A alternator on a single belt. I'd suggest you look for a 90A Prestolite alternator - these have good output at low revs and are very ruggedly built. If you're thinking of an Adverc controller, note that Adverc will sell you a package including a ready-modified Prestolite alternator, making installation very easy. You'd need a twin-lug alternator, the Prestolite A128e would fit the bill. Even with 340Ah of batteries, you won't often see much more than 60-70A charge, and this won't excessively overload your engine.
 
I have almost exactly the same battery power + Sterling, on a 3GM30F. My alternator is the standard 55 Amp one and it copes perfectly well. After running the fridge overnight the alternator will charge at its maximum for no more than a few minutes, gradually declining to float current, around 7 Amps, after an hour. I do have 125 watts of solar panel, which helps, but I feel pretty sure the alternator is plenty big enough.
 
Yanmar upgrade alternator for my 3YM30 is a Hitachi LR180.03C 80a - straight swap. As has been said, this is reaching the upper limit for single belt operation, and may also affect tickover on full electrical load.
 
FullCircle said:
Yanmar upgrade alternator for my 3YM30 is a Hitachi LR180.03C 80a - straight swap. As has been said, this is reaching the upper limit for single belt operation, and may also affect tickover on full electrical load.
Click to expand...

The Prestolite has considerably better low-speed output, though.
 
pvb said:
You can't sensibly drive much more than a 90A-100A alternator on a single belt. I'd suggest you look for a 90A Prestolite alternator - these have good output at low revs and are very ruggedly built. If you're thinking of an Adverc controller, note that Adverc will sell you a package including a ready-modified Prestolite alternator, making installation very easy. You'd need a twin-lug alternator, the Prestolite A128e would fit the bill. Even with 340Ah of batteries, you won't often see much more than 60-70A charge, and this won't excessively overload your engine.
Click to expand...

This is exactly the set up I put in this year as a result of recommends on this forum, 90A prestolite and an Adverc, Yanmar 2GM20 so smaller engine, 220Ah Domestic ( but hope to add another 110Ah over the winter ) with 100w Solar panel to keep up with F/Fzr. Had no issues with losss of hp but aternator has n't put in anymore than 20A at any time, quickly reducing to a 5amp charge which the alternator will put in on tickover.

Very pleased with results, and the rewire which has twin battery issolators and a combiner should one set go down, both sets charged by a Merlin Bi- directional VSR
 
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On a small engine, it can pay to look for a boost controller that keeps the charge rate down initially.
I had a Bosch alternator out of a Mondeo, with about 260Ah of battery, any boost above 14V resulted in a lot of belt wear on start up. Once the boat was underway with some revs on, the belt would take full boost, plus of course the initial demand of the battery has had the edge taken off it by then.

Typically, I might run the engine for a couple of minutes on the mooring before letting go.

I am not up to date with how the controllers rate on this?

Belts are cheap and easy to change though!
 
vyv_cox said:
I have almost exactly the same battery power + Sterling, on a 3GM30F. My alternator is the standard 55 Amp one and it copes perfectly well. After running the fridge overnight the alternator will charge at its maximum for no more than a few minutes, gradually declining to float current, around 7 Amps, after an hour. I do have 125 watts of solar panel, which helps, but I feel pretty sure the alternator is plenty big enough.
Click to expand...

I ran 310ah of battery with an Adverc controller for 3 years from a 35 amp Hitachi. This did get very hot and finally melted - my next was a 90 amp Lucas which did good service for 5 years and then a 110 Magnetti Marelli which did ok for 11 years. If you do put on a larger alternator you'll need to put on a heavier, serrated belt than the standard Yanmar (that wore out with only a 35 amp alternator) and replace the feed from the alternator with about x2 the cross-section to the standard Yanmar harness.
IMHO there's little point in changing the alternator because the controller and battery bank will determine the charge rate - the bigger alternator will just not get quite as hot. I'm completely in agreement with Vyv.
 
charles_reed said:
I ran 310ah of battery with an Adverc controller for 3 years from a 35 amp Hitachi. This did get very hot and finally melted - my next was a 90 amp Lucas which did good service for 5 years and then a 110 Magnetti Marelli which did ok for 11 years. If you do put on a larger alternator you'll need to put on a heavier, serrated belt than the standard Yanmar (that wore out with only a 35 amp alternator) and replace the feed from the alternator with about x2 the cross-section to the standard Yanmar harness.
IMHO there's little point in changing the alternator because the controller and battery bank will determine the charge rate - the bigger alternator will just not get quite as hot. I'm completely in agreement with Vyv.
Click to expand...

Haven't had any problems with belt wear on new alternator as I use Gates tooth belts anyway, but agree Yanmar belts wear very quickly.
 
vyv_cox said:
I have almost exactly the same battery power + Sterling, on a 3GM30F. My alternator is the standard 55 Amp one and it copes perfectly well. After running the fridge overnight the alternator will charge at its maximum for no more than a few minutes, gradually declining to float current, around 7 Amps, after an hour. I do have 125 watts of solar panel, which helps, but I feel pretty sure the alternator is plenty big enough.
Click to expand...

Where that may fall down is when you want to charge the batteries at the same time as getting the fridge cold from nowhere. If you start adding in a lot more demand, as some people seem to do, the flavour of it can change.
My original alternator may have been older, but it needed a few revs on it to deliver its rated current.
But part of my reason for changing was that I wanted to leave the original alternator unmolested and modify one I got for £20 from a scrapyard.
I eventually sold the original for rather more than £20....
 
lw395 said:
But how slow? Adjustable?
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Budget units like the Adverc and Sterling aren't adjustable. The Sterling has, I think, a 2 minute delay before it starts boosting; the Adverc waits until the voltage at the batteries has risen to around 14v. Premium-priced units like Balmar are fully adjustable.
 
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