Alternator upgrade .. advice please

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Albert Ross

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My Yanmar 3YM30 engine has a Yanmar / Hitachi 60 Amp alternator supplying a total of 400 Amp/hours of sealed wet acid batteries (4 x 80 domestic 1 x80 engine)
Charging is very slow so I thought a bigger alternator plus a Sterling advanced alternator regulator might be the answer.

My questions:
How many amps and what make of alternator should I go for?
Will it fit in place of the original unit without any special metalwork?

Thanks.
 
Your start battery will require very little charge, so you're really looking at charging 320Ah of "sealed" batteries. You can only charge at a current which the batteries will accept - just having a bigger alternator won't increase the charge current. I'd be surprised if your 320Ah bank would routinely accept much more than 50-60A, so you wouldn't necessarily benefit from a bigger alternator.

An add-on regulator (Sterling, Adverc, etc) may boost the charge current by increasing the charging voltage. You need to measure what the charging voltage at your batteries is at the moment. If it's around 14.2-14.3 or less, an add-on regulator would improve things. If it's 14.4 or more, an add-on regulator wouldn't help much.

If you tend to charge your batteries with the engine running at low revs, the alternator's output current may be low. Alternator output capability increases with speed. Having a higher output alternator can be an advantage in some circumstances, as it will usually have a better output at low revs.
 
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Thanks.
When batteries are need a charge and I run the engine I get about 14.3 Volts and they accept about 20 amps for the first few minutes rapidly reducing to about 10 amps. The batteries are nearly new and have been well cared for.
 
flat1 said:
Thanks.
When batteries are need a charge and I run the engine I get about 14.3 Volts and they accept about 20 amps for the first few minutes rapidly reducing to about 10 amps. The batteries are nearly new and have been well cared for.
Click to expand...

You might see an improvement with an add-on regulator, certainly I'd try that before looking at a bigger alternator.

Another possibility, which is easier to fit as it needs no modification to the alternator, is the Sterling Alternator-to-Battery charger. This has an added benefit in that the isolated output for the start battery is unboosted, so isn't likely to overcharge it.
 
Hi, I am doing away with my 2 alternators and replacing them with a 100 ah Balmar plus a 4 stage regulator, to keep the 2 6volt Trojans and 2 12 volt batteries charged, the Balmar unit will charge at lower revs than 'car type alternators
 
halb said:
Hi, I am doing away with my 2 alternators and replacing them with a 100 ah Balmar plus a 4 stage regulator, to keep the 2 6volt Trojans and 2 12 volt batteries charged, the Balmar unit will charge at lower revs than 'car type alternators
Click to expand...

Relatively cheap Prestolite alternators have very good output at lower revs, and can be fitted with external regulators. Prestolite make the alternators for Balmar.
 
pvb said:
You might see an improvement with an add-on regulator, certainly I'd try that before looking at a bigger alternator.

Another possibility, which is easier to fit as it needs no modification to the alternator, is the Sterling Alternator-to-Battery charger. This has an added benefit in that the isolated output for the start battery is unboosted, so isn't likely to overcharge it.
Click to expand...

This is what I have..... thoroughly recommended. I have the remote readout unit too, although I fitted a NASA BM-2 battery monitor, which is good for a rough guide.
 
A lot of car alternators these days have remarkably high current output at tickover.

What alternator you need is dictated by what you expect from it.
If you generally motor for several hours when you go out and have shore power on your berth, it's not that demanding.
But if you want to charge your batteries in the shortest possible time, while also running a fridge, or you use a windlass heavily perhaps, you will need more amps.

FWIW, I found a bosch altenator from a mondeo, with a boost regulator setting, worked for me.
IIRC it was rated at about 120A at 6000 engine RPM and about 80A at 1200 engine rpm.
£20 from a scrappy, plus about £4 for a pulley.
The boost to the regulator was manually switched, a DIY circuit so cost nothing.
Only issue was, boost charging could be hard on belts.
And I had to saw a little bit off the Yanmar bracket to make the belts line up.
Personally, if I was going to spend proper money, I'd consider spending it on solar first, priority being running a fridge with minimum engine use, and float charging in winter.

Be aware that not all alternators will physically fit, not even all modeo ones, the brackets vary.
I went to a scrappy and measured several.

HTH?
 
I was thinking about a Prestolite 90 amp alternator in place of my Yanmar / Hitachi 60 amp (which I would keep as a spare) plus a sterling smart regulator (the variety that has to be wired into the works of the alternator) because they are much less expensive than the Sterling alternator-to-battery gizmo. I have solar already but as we sail a lot and rarely go into marinas I need to be able to charge more quickly.
My main concern is to buy an alternator that will exactly fit where the existing Hitachi comes off .. the boat is in Scotland and I'm in Sussex so measuring it is not a great option .. is there a way of telling whether the mountings are the same or not ?
 
flat1 said:
I was thinking about a Prestolite 90 amp alternator in place of my Yanmar / Hitachi 60 amp (which I would keep as a spare) plus a sterling smart regulator (the variety that has to be wired into the works of the alternator) because they are much less expensive than the Sterling alternator-to-battery gizmo. I have solar already but as we sail a lot and rarely go into marinas I need to be able to charge more quickly.
My main concern is to buy an alternator that will exactly fit where the existing Hitachi comes off .. the boat is in Scotland and I'm in Sussex so measuring it is not a great option .. is there a way of telling whether the mountings are the same or not ?
Click to expand...

Both my 3YM30s have the factory-fit Hitachi 80 amp alternator which was a Yanmar option.

Richard
 
Endorse everything PVB says and you are already onto the Prestolite alternator route - which is good. Adverc certainly used to supply them though you don't need to go through them if you can get the field wire modification done yourself.

My preference is for the Adverc system as I believe it to be more robust than the Sterling.

You will need to think about belts. A single V belt will not IMHO be adequate to deal with a 90A alternator at full chat; either double up or, better, get a poly V belt system if you can bolt it on.
 
flat1 said:
I was thinking about a Prestolite 90 amp alternator in place of my Yanmar / Hitachi 60 amp (which I would keep as a spare) plus a sterling smart regulator (the variety that has to be wired into the works of the alternator) because they are much less expensive than the Sterling alternator-to-battery gizmo. I have solar already but as we sail a lot and rarely go into marinas I need to be able to charge more quickly.
My main concern is to buy an alternator that will exactly fit where the existing Hitachi comes off .. the boat is in Scotland and I'm in Sussex so measuring it is not a great option .. is there a way of telling whether the mountings are the same or not ?
Click to expand...

The Sterling A-to-B charger is about the same price as a new alternator plus a Sterling regulator, is easier to fit, has inbuilt diode splitter to give isolated outputs, and won't overstress your start battery. But if you don't want that, with only 320Ah of domestic batteries, you're never going to push in much more than 50A charge, so why not just go for an ordinary Sterling regulator first, and see what the results are? If you regularly see 50-60A charge current, then perhaps consider changing the alternator (the Sterling regulator will still control it).
 
pvb said:
The Sterling A-to-B charger is about the same price as a new alternator plus a Sterling regulator, is easier to fit, has inbuilt diode splitter to give isolated outputs, and won't overstress your start battery. But if you don't want that, with only 320Ah of domestic batteries, you're never going to push in much more than 50A charge, so why not just go for an ordinary Sterling regulator first, and see what the results are? If you regularly see 50-60A charge current, then perhaps consider changing the alternator (the Sterling regulator will still control it).
Click to expand...

Thank you. That's good advice.
 
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