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Old 09-07-2012, 19:16   #1
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air conditioning / ac on batteries, generator to maintain charge

Hello,
I was wondering if it is at all advisable to run a 16kbtu air conditioner from a large inverter while using a generator to keep the charge on the batteries (would only be one 130ampH battery) topped off. I have a 2kwatt generator that is unable to handle the surge of the generator, but also have an inverter that can handle the load, so this seemed like a reasonable approach. I'm concerned about killing the deep cycles, but perhaps this is not too much of an issue.

Anyone have any experience / suggestions about this?
Thanks!
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Old 09-07-2012, 19:22   #2
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Re: air conditioning / ac on batteries, generator to maintain charge

Have you looked into something like this?

http://marine-ac.com/marketplace/mar...st-by-dometic/
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Old 09-07-2012, 19:26   #3
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Re: air conditioning / ac on batteries, generator to maintain charge

That's a great point. I've been looking at these but they run just shy of $400 right now. Perhaps I should look into whether or not they will refund it if it doesn't work for my particular setup, otherwise, its a hefty gamble.

Thanks!
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Old 09-07-2012, 20:06   #4
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Re: air conditioning / ac on batteries, generator to maintain charge

Also have to look at the capacity of the battery charger you would run from your 2 KW generator.

As a very rough guess I think you would need a battery charger able to put out well over 100 A continuous output to keep up with the AC draw on your inverter.
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Old 09-07-2012, 21:26   #5
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Re: air conditioning / ac on batteries, generator to maintain charge

Are you sure the inverter will handle the starting surge?

My 16k btu units run on 12-13a each but take 57a surge at start. You might get by with somewhat less than 57a, but I would guess you'll need at least 35a to get the compressor started.

Ideally, an inverter with assist for the generator is what you need.
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Old 10-07-2012, 06:02   #6
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Re: air conditioning / ac on batteries, generator to maintain charge

SUPCO offer numerous Compressor Hard Start Kits, most priced under $50.

Ie ➥ Hard Start Kit, AC Compressor - Cooling Equipment Relays - HVAC Controls - 4E241 : Grainger Industrial Supply

& ➥ Hard Start Kit, AC Compressor - Cooling Equipment Relays - HVAC Controls - 4E240 : Grainger Industrial Supply

etc
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Old 10-07-2012, 06:56   #7
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Re: air conditioning / ac on batteries, generator to maintain charge

I saw a boat with that set-up.... well sort of... it was all electric; main drive propulsion included. It had a DC genset and a lot of switchgear.... about 1/2 ton of batteries.

Last I saw it, it was back in the yard to re-fit back to conventional propulsion/generation... it didn't work out long term!
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Old 11-07-2012, 02:48   #8
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Re: air conditioning / ac on batteries, generator to maintain charge

You seem to be asking a 130 amp battery to help kick start an air con system. I don't think that will work!

We have a 12,000 BTU air con that we run off our battery bank for an hour - via a 2.5Kva Victron MultiPlus inverter. It takes 1 Kw from our 12 volt 1050 Ah capacity house bank.

We also have a DC genset - charges at 12 volts at 250 amps - which we run when we need air con for more than an hour.

The problem is that you must run the generator long enough to charge the battery first so that all the genset power can then go to running the air con. Your genset may have a 2Kw maximum rating, but what is its continuous rating?

There is also the power factor of about 0.8 to take into account - that means the genset will deliver 20% less to an inductive load like a compressor or motor.

So what power does your aircon take? Work back wards from there and see what your 130 Ah battery will have to provide, either continuously or just at start up.
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Old 16-07-2012, 12:41   #9
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Re: air conditioning / ac on batteries, generator to maintain charge

I think it will run for a while longer than without the gen running, but the battery charger wont be able to keep up with the battery drain.

16kbtu air conditioner draws maybe 15 amps with seawater pump.
maybe 1800 watts of power at 120 volts ac, which is perhaps 150 amps of DC power needed.

If gen and invertor could be synced up, then they could share the load.
That is unlikely to be accomplished.

So you really need a big DC gen or a bigger AC gen or maybe one of the soft start devices.

If that Dometic soft start would work, then your using up almost all your gen capacity on your AC.

Here is another, have no idea on cost and works on single phase asynchronous AC motors. just reading more specs on this and dont think it will help. A lot of these are for 3 phase motors.
http://static.schneider-electric.us/...8637BR0401.pdf
http://products.schneider-electric.u...-01-softstart/

here is another possibility
http://www.hypereng.com/single_phase.html

a video of sure start includes a single phase system.
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Old 16-07-2012, 13:10   #10
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Re: air conditioning / ac on batteries, generator to maintain charge

Well, I emailed them and it came back fairly quick and much cheaper than I thought.
The Dometic soft start is more like $500.

Quote:
Sent: Monday, July 16, 2012 3:05 PM
To: sales@hypereng.com
Subject: SS6S0.5-1.75-USL-115V price?

How much does this cost?
Do you sell to retail?
A friend with a 16k heat pump is looking to start using a 2000 watt AC generator his ac unit.
This typically draws 14 to 15 amps running and startup surge maybe 50 amps.

thanks
Quote:
Scott,
The Sure-Start soft-starter is $165.12 + S/H. You would have to our it direct by credit card.

Regards, Michael


Michael Kerrigan
Global Sales Manager
Hyper Engineering
1739 Canton Lane.
Marietta, GA 30062 USA
P (877) 304-0724
F (877) 799-3947
Hyper Engineering | Home
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Old 16-07-2012, 15:59   #11
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Re: air conditioning / ac on batteries, generator to maintain charge

Quote:
Originally Posted by sailinglegend View Post
You seem to be asking a 130 amp battery to help kick start an air con system. I don't think that will work!

We have a 12,000 BTU air con that we run off our battery bank for an hour - via a 2.5Kva Victron MultiPlus inverter. It takes 1 Kw from our 12 volt 1050 Ah capacity house bank.

We also have a DC genset - charges at 12 volts at 250 amps - which we run when we need air con for more than an hour.

The problem is that you must run the generator long enough to charge the battery first so that all the genset power can then go to running the air con. Your genset may have a 2Kw maximum rating, but what is its continuous rating?

There is also the power factor of about 0.8 to take into account - that means the genset will deliver 20% less to an inductive load like a compressor or motor.

So what power does your aircon take? Work back wards from there and see what your 130 Ah battery will have to provide, either continuously or just at start up.

What Make/model is your DC generator? 250 Amps is impressive. Is that the continuous current rating? As to the power factor, I'm not sure. It would be the inverter that would need to deal with the inductive load. The DC gen only needs to supply the inverter, which is a DC load.
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Old 16-07-2012, 20:57   #12
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Re: air conditioning / ac on batteries, generator to maintain charge

On my charter boat I run a 16K BTU AC unit off a 5KW 12 volt inverter. The inverter is tied to a 8D battery that starts the main engine. The inverter draws around 130 amps with the AC on. A 150 amp delco alternator wouldn't handle the load. A 240 amp Leece Newville does a very nice job. The 8D battery acts as a surge reserve to start the AC compressor. I run the AC about 300 hours a year this way. The first inverter died after 7 years and the AC unit which runs almost continuously 3 months a year lasts about 7 years also. A lot of double ought cable went into the wiring of this system to avoid voltage drops.

Ted
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Old 16-07-2012, 22:47   #13
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Re: air conditioning / ac on batteries, generator to maintain charge

I have a 5K BTU air conditioner on my boat. It needs about 600 watts to run including the sea water pump. It needs about 3000 watts to start. I put one of the Supco Hard Start Kits (see Gord Mays post) on the air conditioner and I can start it and run it with a 1000 watt Honda. This may solve your problem for less than thirty bucks.
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Old 17-07-2012, 00:07   #14
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Re: air conditioning / ac on batteries, generator to maintain charge

Quote:
Originally Posted by Saltyhog View Post
What Make/model is your DC generator? 250 Amps is impressive. Is that the continuous current rating?
Fischer Panda AGT-DC 4000 PMS - 280 amps maximum. Only ever seen one other boat in the Med with one.

More efficient and quieter than an AC genny, not a fixed speed but runs at the speed it needs to supply the load.
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Old 17-07-2012, 00:22   #15
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Re: air conditioning / ac on batteries, generator to maintain charge

Quote:
Originally Posted by Saltyhog View Post
What Make/model is your DC generator? 250 Amps is impressive. Is that the continuous current rating? As to the power factor, I'm not sure. It would be the inverter that would need to deal with the inductive load. The DC gen only needs to supply the inverter, which is a DC load.

Home built, 2 cylinder perky\cat/volvo diesel, 320 amp cold rated Leece Neville=250 amps continious, Balmar MC614 Regulator, Variable speed govner. Magnum 3k SW inverter.

About 1.25 liters every other day, which includes all the domestic hot water I /We need.

Lloyd
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