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Old 08-01-2014, 13:23   #1
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A/C running from main engine/inverter

Hello all: here we go...

This is related to my other recent post

Inverter/Generator permanant installation

One of the boats I am looking at has a relatively new Heart Interface inverter/charger, rated 2500W, peak 4500W. I am wondering what the pros and cons might be for using this to power a 16,500btu A/C (120V 13A rated/23A starting), as well as other standard purposes )battery charging, etc.), using the main auxiliary diesel as the power source (which is a 46hp Westerbeke, 130A alternator). Especially since a lot of people are now suggesting that DC generators and inverters are the way to go anyway, it seems to make sense. Obviously more hours on the engine, but the same hours would go on a DC or AC generator...

Thanks for your input. Pete
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Old 08-01-2014, 13:59   #2
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Re: A/C running from main engine/inverter

And before we get too far, I am guessing that one problem would be the 130A alternator, so I would amend the question to include possible alternatives to that. As I recall, there are some issues with larger alternators, but again I am hardly an expert in this field beyond volts x amps = watts (approximately...).
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Old 08-01-2014, 14:09   #3
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Re: A/C running from main engine/inverter

Downsides to the idea

1. Lots of hours on the main engine which will wear out sooner and cost a lot more to replace than a generator.

2. Also, not good to run your diesel at low rpm with a light load for long periods.

3. Most boats, running the main engine is pretty noisy as well.

4. The alternator would not be able to supply the power needed so would slowly deplete your batteries.

5. To get an alternator big enough to supply the load would cost a lot of money, especially if you get one rated continuous duty to put out a couple hundred amps. And it would take a serious mounting bracket AND unless you did something to counteract (serpentine belt, opposing idler pulley, etc) you will be putting a large side load on the crankshaft that could cause early death to the front seals and maybe even bearings.

As a very occasional way to run an AC at anchor it could be an option but wouldn't do it on a regular basis.
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Old 08-01-2014, 14:11   #4
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Re: A/C running from main engine/inverter

Quote:
Originally Posted by skipmac View Post
Downsides to the idea

1. Lots of hours on the main engine which will wear out sooner and cost a lot more to replace than a generator.

2. Also, not good to run your diesel at low rpm with a light load for long periods.

3. Most boats, running the main engine is pretty noisy as well.

4. The alternator would not be able to supply the power needed so would slowly deplete your batteries.

5. To get an alternator big enough to supply the load would cost a lot of money, especially if you get one rated continuous duty to put out a couple hundred amps. And it would take a serious mounting bracket AND unless you did something to counteract (serpentine belt, opposing idler pulley, etc) you will be putting a large side load on the crankshaft that could cause early death to the front seals and maybe even bearings.

As a very occasional way to run an AC at anchor it could be an option but wouldn't do it on a regular basis.
Kind of what I figured, but I thought it was worth a swing...hope it's warming up up there! pete
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Old 08-01-2014, 14:16   #5
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Re: A/C running from main engine/inverter

Yup - P=IE - it's not even approximate for DC, it's the law.

No way will 130A (which it will not likely output, and definitely not output continuously) run your A/C.

You need lots more DC, lots more heat will be generated, and you may find that inverter won't start your A/C so you'll need to tweak with some hard start kits.

A/C is the one load that is simpler to go with an AC generator.
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Old 08-01-2014, 16:25   #6
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Re: A/C running from main engine/inverter

Quote:
Originally Posted by pete33458 View Post
Kind of what I figured, but I thought it was worth a swing...hope it's warming up up there! pete
It's still really cold in N Florida. I've had to wear a long sleeve shirt for two days in a row.
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