AC / Aircon without a generator (running off alternators) It works!!!!

[Rugger]

Hi all,

I want to throw this topic out there. Some may be interested.

So I took over my buddy’s cruising hobby in December. He gave me his boat and everything involved with it. Yeah…big score.

You can see the story here: http://www.cruisersforum.com/forums/...re-166196.html

With some help from knowledgable friends, I got her back together and cleaned up.

its now in the Tampa area…and summer is here. Lots of projects were completed but a couple months ago I stopped everything and focused 100% on the AC. He had bought all the parts years ago and they were sitting on the boat in their boxes. They just needed to be installed. Major pain but I got it done.

I have a 2000 watt Heart Interface (Xantrex) Inverter from around 2001 and 4 6v golf cart batteries (Trojan and Interstate) making 450 ish Ah.

Its a 5200 BTU Mermaid: https://www.mmair.com/marine-divisio...00-btu-system/

It spikes up to about 40 amps to get going but runs on 5 amps on 110 off the inverter. Runs great.

He came to town 2-3 weeks ago. This was the first time he’s seen the system installed. He put a LOT of thought into designing this system and very carefully picked the components.

We went sailing.

On our way back to the dock, we were motoring. We gave the tiller to a buddy, went into the cabin, and he says “watch this”. He flipped the breaker and the AC started. I was dumbfounded.

This is a 29ft blue water cruiser with a Yanmar 2GM20…with 2 high output alternators with fancy regulators. We have the regulators set to let out 30 amps each, going 20 amps over the required 40. The LED lights dim briefly on startup, but the AC runs cool and maintains the cabin while motoring underway.

The alternators and regulators were purchased and installed by him in the early 2000’s. The links below are from the same company but obviously updated to today’s technology.

HDPSI POWERLINE Alternators

HDPSI Aqualine Plus Regulators


He kept telling me how big of a deal this was and was stocked to see it work while underway. He tells me its a $20k option on other boats by the time you add the genset and everything else.

Needless to say, I agree.and am very thankful.

Is this a big deal?

I’d love to hear your thoughts and / or concerns.

-Rugger

[skipmac]

Well, bottom line, you give it enough power and an air conditioner will run. Doesn't matter if the power comes from a generator or inverter. However, running from an inverter you need 1000 lbs of batteries (more or less) or you have to run the engine and drive an alternator big enough to supply the power.

All that being said, if I read your post correctly, your math doesn't work out. The point, in very round numbers, it takes about 10 times more amps at 12V DC to run the inverter output at 110V AC. So your statement that it takes about 40 amps to start the air con and the alternators make 60 amps or 20 amps more than needed for startup doesn't add up. The 40 amp startup current (at 110V AC) for the air con will take over 400 amps from the batteries and/or alternator (at 12V DC). In your case the 2000 Watt inverter can probably make the higher output very short term to start the air con compressor.

Of course, unless plugged into shore power you would have to run the engine to have cool, not a great proposition.

[Pizzazz]

This is known and many people have this setup. The AC is about 500W or 40 amps at 12.5V. You can even add a hard start capacitor to make it easier to start. However, it is not really practical. The engine will radiate more heat in the cabin than the AC can remove. This is why most people either run the AC at the dock or off a small generator that is located outside the cabin. It is more efficient this way. You can try to isolate the engine compartment, feed and extract air, etc. but it is not worth it. I have a 5,000 BTU unit in my 31' boat and it struggles on a hot summer day in California + you have to keep the hatches closed which is inconvenient during the day.

In my opinion, during the day it is best to just ventilate the boat and take advantage of the afternoon breeze. During the night, if you are in Florida, you need either a generator or 8 hrs x 40 amps x 1.25 (for high current draw) / 50% discharge = 1,000 AHrs minimum. Not practical.

[StuM]

Originally Posted by Pizzazz

This is known and many people have this setup. The AC is about 500W or 40 amps at 12.5V. You can even add a hard start capacitor to make it easier to start. However, it is not really practical. The engine will radiate more heat in the cabin than the AC can remove. This is why most people either run the AC at the dock or off a small generator that is located outside the cabin. It is more efficient this way. You can try to isolate the engine compartment, feed and extract air, etc. but it is not worth it. I have a 5,000 BTU unit in my 31' boat and it struggles on a hot summer day in California + you have to keep the hatches closed which is inconvenient during the day.

In my opinion, during the day it is best to just ventilate the boat and take advantage of the afternoon breeze. During the night, if you are in Florida, you need either a generator or 8 hrs x 40 amps x 1.25 (for high current draw) / 50% discharge = 1,000 AHrs minimum. Not practical.

I tend to agree with you. I doubt that 5000 BTU will be sufficient to cool the interior efficiently when it has to counter the amount of heat generated inside the boat by the diesel engine running at sufficient revs to generate the required power.

[Rugger]

I should have been more clear. I'm at the bottom of the food chain electrically. That start up surge is 40 to 50 amps DC.

[Rugger]

Originally Posted by StuM

I tend to agree with you. I doubt that 5000 BTU will be sufficient to cool the interior efficiently when it has to counter the amount of heat generated inside the boat by the diesel engine running at sufficient revs to generate the required power.

Interesting. Time to spend a night on the hook and monitor consumption (of diesel)

I'll post the results.

[skipmac]

Originally Posted by Rugger

I should have been more clear. I'm at the bottom of the food chain electrically. That start up surge is 40 to 50 amps DC.

Sorry, the math still doesn't work. Ignoring efficiency and conversion losses 50 amps at 12V DC only gives you a little over 4 amps at 110V AC. That is in the ballpark of what it would take to keep a 5000 BTU air con running which matches your original post where you said it runs on "5 amps on 110 off the inverter."

Startup on a air con compressor is typically several times the steady state. For your unit I would guess at the very least 15-20 amps at 110V AC from the inverter (around 2000 Watts) which will be 150-200 amps from your 12V system. Since the startup is a very short term draw your batteries should be able to supply that if the cables are good and the batteries charged.

For a very rough approximation, multiply amps at 110V AC by 10 to get amps at 12V DC.

[stnick]

I have a ac system and generator the ac is 16kw good for a 38 at anchor in summer wife insists on cool so i run the gen. Noise is about 63 DB with the I phone DB meter app. I could build a box for it and would be quieter. Than access would be a hassle when changing oil etc.

[Rugger]

This video will do the talking. Have a look.

https://youtu.be/Ti-OTdPJHc0

[Brewgyver]

Originally Posted by stnick

I have a ac system and generator the ac is 16kw good for a 38 at anchor in summer wife insists on cool so i run the gen. Noise is about 63 DB with the I phone DB meter app. I could build a box for it and would be quieter. Than access would be a hassle when changing oil etc.

I think you mean your A/C is 16k BTUH, one and a third ton capacity. "16kw" would be over 50,000 BTUH, or more than four tons, enough for a 1600 sf house.

[Rugger]

Originally Posted by skipmac

Sorry, the math still doesn't work. Ignoring efficiency and conversion losses 50 amps at 12V DC only gives you a little over 4 amps at 110V AC. That is in the ballpark of what it would take to keep a 5000 BTU air con running which matches your original post where you said it runs on "5 amps on 110 off the inverter."

Startup on a air con compressor is typically several times the steady state. For your unit I would guess at the very least 15-20 amps at 110V AC from the inverter (around 2000 Watts) which will be 150-200 amps from your 12V system. Since the startup is a very short term draw your batteries should be able to supply that if the cables are good and the batteries charged.

For a very rough approximation, multiply amps at 110V AC by 10 to get amps at 12V DC.

This video will do the talking. Have a look.

https://youtu.be/Ti-OTdPJHc0

[Hoosiersailor]

Not sure I understand the question. Is it a big deal? Not really. After start up if you run it constantly it will pull approximately 55 DC amps per hour at 100% duty cycle. If you wanted to run it off the batteries/inverter for a couple of hours in the evening to cool the cabin area down, it should pull approximately 110 amp-hours from your battery bank. Less if the compressor isn't running constantly.

5 amps x 120 volts = 600 watts
600 watts x .9 = 666 watts (efficiency for inverter)
666/12 DC volts = 55.5 DC amps

The start up is probably going to be 3-4 times the running current (1800-2400 watts). The inverter might handle it.

[hellosailor]

The thing is, the dog talks. (Punchline of an old joke.) That's miracle enough. But I would be concerned about the longevity of the setup. I think the impulse draw of the AC starting, from the inverter, well exceeds the inverter's startup surge limit. It may keep working, but surges like that can radically shorten the life of the components. So my first thought would be to put an ammeter in that circuit and try to confirm just how big a starting surge the AC was taking. And possibly to add the soft-inrush type starting capacitor as well, to minimize that in any case.

Second issue would be the alternator BELTS. After doing a gut rebuild on an electrical system, including a new alternator with custom pulley to get the optimum power from it, we were confounded to see the engine V-belt literally hunch up like an inchworm and neatly remove itself from the main pulley every time a heavy load kicked in.

Well, it turned out the old alternator was so feeble that wasn't an issue, but with the new one capable of feeding the new batteries all they wanted...the draw on the alternator made it "kick" the belt, which fortunately walked off instead of bursting. (The solution was a tighter belt and "don't run the batteries down that far", a working kludge.)

So I'm thinking that even if the two alternators can power the AC, the AC may be putting a strain on the belt and creating more problems. Check it, eyeball it when the AC is being turned on/off, and make sure you've got spare belts. If it is a V-belt, they've gotten damned hard to find, so get two spares.

And oh, PS? If the boat has the usual old analog battery voltmeter on board? Get a good digital battery meter (or something better) and make sure it is reading correctly, The old analog ones were often very inaccurate, and running that AC could do a number on your batteries if it is allowed to pull them down too low, too often.

[skipmac]

Originally Posted by Rugger

This video will do the talking. Have a look.

https://youtu.be/Ti-OTdPJHc0

OK, I watched but exactly what is it I'm supposed to be looking for?

One thing, I'm guessing that little jump you saw on the AC ammeter was the compressor on the air con kicking in. That was the startup surge for the compressor.

The meter showed about 20 amps at 110V AC which would require about 250 amps at 12V DC to make. Of course that isn't coming from the alternators, that is coming from the batteries which can supply that much current for a short time. Even at 250 amps draw from the battery since it's only a few seconds you're probably only pulling 0.5 amp hour from the batteries.

[Ironman162]

10/10 for giving it a go and getting it working!

I wouldn't worry too much what people have to say as every boat is different. Sit back and enjoy your achievement and revel in the boating experience.

I too am high on the creature comforts scale but there are hardcore sailors that prefer to do it tough.

So, from me, every bit of comfort you can muster, I say, 'good on you' from Australia.