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Old 04-09-2012
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Alternator advice, dealer recommendation

I have been upgrading my DC electrical system in the past month. So far I have installed a new 240 amp golf cart batteries for my house bank and an IOTA 30 AMP Charger which are working very well, but when I do some extended cruising this summer I will need a larger alternator to charge my batteries more quickly. What I have now is a Lucas ACR 15 alternator. It has an internal regulator and outputs 28 amps. My engine is a Petter AC1W, one cylinder diesel rated at 6.5 HP at 3600 RPM. I am thinking that the largest alternator I can expect to drive with my little engine is a 50 or 60 amp alternator, which would be about 25% of my battery bank. Is that a reasonable expectation? About how much horsepower would the alternator take away from the engine when charging. This concerns me because I have been in situations where I could not make headway in 30 knots of wind.

Can anyone suggest how to proceed and a reputable on-line vendor?

Please let me know what you recommend and what the price might be.

Thanks for your help.

Larry
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Old 04-09-2012
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Re: Alternator advice, dealer recommendation

A Lucas 17 ACR or 18 ACR will be a bolt on replacement. Just watch which hand yours is. Ebay has them for $85

You need to add a disconnect to switch off the alternator and allow those 6.5 hp to work for you. Just add a switch in the line between the regulator and the brush gear.

At full field they give 45 amps or so requiring about 1 hp to drive the alternator.

Last edited by TQA; 04-09-2012 at 09:46 PM.
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Old 04-10-2012
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Re: Alternator advice, dealer recommendation

An alternator is commonly thought to require 1 hp for every 25 amps output. Balmar also posts this on their site.

I am in the same position - Yanmar YSE-8 one cylinder 8 hp. My solution is solar as for a reasonable bank size it would require many hours of engine running with any alt my engine could handle. And even with a large alt you are only charging to about 80-85% state of charge. The last 15% takes many hours no matter how large the alternator. I don't want to listen to the engine anyway.
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Re: Alternator advice, dealer recommendation

I have 2 solar panels mounted on movable mounts off the stern pulpit, but they only output 5 ah a day. i am thinking of upgrading them to a newer and larger size, but i don't think give me all the power necessary to bring up the bank to 80%, so a bigger alternator is needed as well.
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Re: Alternator advice, dealer recommendation

My shaft turns clockwise. Is that "right hand"?
Its been a while since I messed with the alternator.How do I tell which is the line between the regulator and the brush gear? Is that the line that causes "excitation"? Would the switch be something like a toggle that I would mount up in the cockpit to disconnect the alternator?
Thanks for the advice, sourcing an Lucas 18 will save me tons of investigation!!!
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Re: Alternator advice, dealer recommendation

I checked ebay and discovered that the Lucas 18 outputs only 43 Amps. Do you know of another "bolt on" replacement that would output closer to 60 amps?

My engine turns slowly and so the alternator does not charge a low speeds or at low RPMs. A few years ago, I tried to find a smaller pulley to put on the shaft to make the alternator go faster at lower RPM, but was unsuccessful. Probably because I looked in the wrong places. Can someone give me a lead on where to find alternator pulleys?
Any comments on the pros and cons of this?
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Re: Alternator advice, dealer recommendation

The Lucas ACR 20 is rated at 66 amps they were fitted to lots of British built cars like the Jag XJ 6. You might find one in a scrapyard.

I don't know of any alternator alternative pulleys but I have turned up a larger crankshaft pulley for a similar project many years ago when I had access to full machine shop. Two hours work. This is thought to be the better solution as it improves belt life. WARNING if yo do this you need to do your sums and ensure that at maximum engine rpm you do not exceed maximum alternator rpm. The results of this are not pretty.

If you really want to maximise your alternator output and minimse the time you run the engine then you should replace the internal 'dumb' regulator with a multi-stage "smart" voltage regulator which will be mounted externally. Costs about $250.

Yes the switch can be anywhere. I mounted mine down below so I did not have to worry about waterproofing it. Just have a warning light somewhere to show either charging or not charging. You just interupt the wire to the slip ring brush from the regulator.

Last edited by TQA; 04-10-2012 at 04:19 PM.
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Re: Alternator advice, dealer recommendation

An elegant, though not inexpensive solution, would be to fit a 70A or 90A alternator and a Balmar MC-612 or MC-614 external regulator.

These regulators have 2 ways of limiting charge current (and, thus, load on the engine):

1. you can "de-rate" any alternator to whatever percentage you like; and
2. a simple on-off toggle switch can cut the charge current in half.

When you're underway, you might want to limit the charge somewhat. When you're at anchor, though, you might want the full or near-full output of the alternator for fast battery charging.

Those 240AH batteries will only take a maximum of about 60A when they're well discharged, and much less when the SOC begins to rise significantly. But, you might later want to change to a larger battery bank or to AGMs (which can take a MUCH larger charging current), so the extra capacity would be there if/when you need it.

FWIW,

Bill
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Old 04-11-2012
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Re: Alternator advice, dealer recommendation

Thanks for all the suggestions. I'll start working on them today!
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Re: Alternator advice, dealer recommendation

Larry-
If that is 240AH combined, total capacity, as opposed to two 240AH batteries?
then in theory you only want to draw down 120AH maximum (50% cycle) and preferably more like 75AH (30% cycle). Split the difference, say you want to recharge about 100AH when you run the alternator. Conventional wet cells are usually supposed to be cahrged at some 20% of their capacity, which would be 48A (let's call it 50A) charge rate, so a 50A alternator or anything higher would do the recharge, in two hours.
More power could could them faster, but might also boil off more electrolyte and exceed charge rate recommendations, although there's lots of debate on that.
A bigger alternator, rated higher than 50A, would have more reserve power and run cooler, so that's a good idea, but once you exceeded 75A I'd call it simply excessive and unneeded.
So...a 60A or 70A alternator probably would work very nicely for you, right in line with your expectations.
746 watts is equal to one horsepower, so a 60A 14.4V alternator putting out about 850 watts actually puts out a little over one hp. With inefficiencies and friction, that might consume 2-3hp from your engine when it was running at full power.
Proper belt tension will help reduce some of the losses, but you'll also find folks have installed manual switches to lower alternator power consumption, i.e. to cut it back to "low" power, when or if you think you'll need the engine for propulsion.
And again--if your batteries are charged up, the alternator will simply not consume that much power, it will only be "sipping" regardless of how powerful it is.

If I may suggest, before you replace the alternator, look at properly matching alternator speed to engine speed. This is done by selecting the right pulley size for the alternator, which may mean having one custom made for $100. (A simple lathe job in a machine shop, but nothing simple is cheap anymore.) Ideally you want an alternator that puts out good power during engine idle speeds, but isn't over-revving at full cruising speeds in a storm. Alternator makers have spec sheets. It might say "60A alternator, puts out 20A @500rpm, 30A @1000 rpm, 40A @ 1200rpm, 60A @1500-3000 rpm, not for continuous duty above 3500 rpm."

So if the pulley ratios have your alternator running 1:1 with your engine speed, you'll get damned little power at 500rpm, and you'll need 1500rpm to get the rated 60A. With a 3:1 ratio you'd get full charging power at idle--but burn out the alternator at high engine speeds. You need to make sure whatever pulley you use puts you somewhere in the middle ground, so you get good power at "normal" speeds. Different alternators come with different stock pulley sizes available and different output curves, and picking the right one can literally double your alternator life--and cut your charging time in half.
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