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Old 07-05-2014, 00:49   #1
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Replacing Engine driven fridge compressor with alternator.

Hey folks,

Happened upon a post made a year or two ago about replacing a fridge compressor run of a pulley on the engine crankshaft with a large frame alternator.

Would like some opinions as to the feasibility and options available if you'd be so kind.

I'm out in Singapore, so the usual stuff like Balmar tend to be pretty pricey.

I've got a substantial mounting at the front of the engine to house a large frame alternator, so no worries there. May need to upgrade to a serpentine belt for the bigger alternator though? Not sure here.

I currently charge mainly with Solar, as my usage is usually only at weekends. I have a 450ah FLA (6v trojan) house bank.

My 30hp engine has a weedy 20amp alternator on it.

What I'd like to do is have a switch that would allow me to (electro clutch) engage a big alternator to charge the batteries with the engine at anchor, or while under sail in neutral.

What do you reckon is the biggest feasible size of alternator I could use (given I'd not be using it at the same time as asking the engine for propulsion, if indeed this is possible)...?

The idea behind the big auxillary alternator would be to recharge the house bank quickly, if my indented dc loads (from new fridge, and perhaps aircon in future) deplete the bank faster than the solar can keep up.

Thanks,

James
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Old 07-05-2014, 01:52   #2
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Re: Replacing Engine driven fridge compressor with alternator.

No need to worry about a clutch all you need to do is have an external regulator that you can turn off and on as you wish. While the three stage or smart regs are nice you can do the same thing with several external regulators. Transpo markets an agjustable "ford"style regulator. I used to have three on a small kubota I bulit for battery charging. One was set about 13.5 because the small engine was not capable of drivng the alternator at full output. Another was set at 14.2 I would turn on after a few minutes when the engine could handle the load. The third was set to equalize and only used occasionally. Using an automotive alternater of 125 amps rating and the transpo regs.my investment was only about 100 usd. There really is nothing special about "marine" alternators. When I was in business in St Maarten I was a distributor for lestek alternators. While I ordered their stock numbers occasionally I would get a "balmar"alternator from them as they also supplied to balmar. I might add that I was able to sell these alternators at 1/2 the price of a Balmar and still make money
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Old 08-05-2014, 16:21   #3
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Re: Replacing Engine driven fridge compressor with alternator.

Thanks for that. Plenty to chew on.
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Old 08-05-2014, 17:03   #4
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Re: Replacing Engine driven fridge compressor with alternator.

A 30 hp engine should easily be able to drive a 100A to 130A alternator with a good quality Gates or equivalent belt. We have a 21 hp engine and run a 100A alternator with our 3/8" belt. We have a 390 ah house bank, wet cell, and find that at a 50% SOC the most we see is around 50-75A output from the alternator. Note this is for your wet cells, NOT AGMs which have a much higher acceptance and can burn out alternators.

We have a Balmar MC-612 external regulator, and we use the Small Engine Mode to toggle the output to 50% when necessary (startup cruising speed after a night or two on the hook). Once the charging amperage drops down to 25A, I kick it back up to 100%.

But internal regulators will work just fine, since its battery acceptance that determines alternator output.

How Alternators & Regulators Work PLUS External vs. Internal Regulators (by Maine Sail): Musings Regarding External Regulation - SailboatOwners.com
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Old 08-05-2014, 18:24   #5
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Re: Replacing Engine driven fridge compressor with alternator.

Fantastic... just the kind of info I need.

Much obliged.
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