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Roof AC running off inverter...
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andy1canada
Posted 2019-07-07 10:28 AM (#6581)
Subject: Roof AC running off inverter...


Elite Veteran

500100100
Location: Victoria, BC. Canada
Since Lenny shared his cool inverter set up plan to run his roof AC, I've also been pining to get rid of my auto AC system, too.

Scored a good deal on a Dometic (DuoTherm) unit and am going to designate it as the primary (read: only) AC unit on board #846.

Stumbled on a Go Power 3000 watt inverter and wondered if it would suffice to get the roof AC going while mobile. My plan is to add a second high-amp alternator to run the roof AC while underway. Specs on the 13,500 btu AC units claim they draw about 2800-3000 watts on start up. So, since I already learned that it's not good to max out your inverter I guess this pretty much rules out this 3000-watt unit.

Or does it?

https://www.microair.net/collections/easystart-soft-starters/product...

Then there's this guy for about 1/3 of the money:
https://www.ebay.com/itm/RV-A-C-Starter-Easy-start-your-Camper-Rooft...

Any one out there use one of these?
Feedback appreciated.

Thanks,
Terry
#846
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LCAC_Man
Posted 2019-07-08 7:47 AM (#6582 - in reply to #6581)
Subject: Re: Roof AC running off inverter...


Elite Veteran

5001001001002525
Location: Oceanside, CA
you would be running it full continuous capacity all the time
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andy1canada
Posted 2019-07-08 7:58 AM (#6583 - in reply to #6581)
Subject: Re: Roof AC running off inverter...


Elite Veteran

500100100
Location: Victoria, BC. Canada
Are you referring to the inverter, or, the lone AC unit?

Terry
#846
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LCAC_Man
Posted 2019-07-08 9:56 PM (#6584 - in reply to #6583)
Subject: Re: Roof AC running off inverter...


Elite Veteran

5001001001002525
Location: Oceanside, CA
If it's the cheapy modified squarewave version then it will not handle the inductive style motor load, you will burn up both the inverter and the ac compressor motor(even with the soft start capacitor kit). If it's the better pure sine wave version, that one will actually provide an honest 3000w continuous and it will probably be fine(its 3 times the price). You will need an alternator that can handle 140amps conrtinuous at idle, you will have some considerable efficiency losses, I have a smaller 9200btu unit and it draws 110amps (dc from house alternator) when the compressor is running.
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andy1canada
Posted 2019-07-08 11:26 PM (#6585 - in reply to #6581)
Subject: Re: Roof AC running off inverter...


Elite Veteran

500100100
Location: Victoria, BC. Canada
This is the one, it came up for sale locally but sold quick: https://www.amazon.com/Go-Power-GP-SW3000-12-3000-Watt-Inverter/dp/B...

How does a 9200 btu AC unit draw over 100 amps - even at startup?

The 13,500 btu Dometic unit I just picked up draws 12 - 13 amps on startup. What 'DC electrical theory' am I missing here?

Was looking at these: https://victoria.craigslist.org/pts/d/vancouver-reduced-sprinter-rbl...

But can't find any output graphs on them. Pricey suckers, too!

Picking up my trans rebuild kit tomorrow - speaking of pricey! I'll be walkin' funny for a bit...

Terry
#846

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LCAC_Man
Posted 2019-07-09 7:09 AM (#6586 - in reply to #6581)
Subject: Re: Roof AC running off inverter...


Elite Veteran

5001001001002525
Location: Oceanside, CA
That is a good inverter.
Reread what I wrote about the 100amps dc
The standard 13.5 dometic will pull much more than 12-13amps ac at start up (my 9200 pulls more than that), and you have to have surge capacity to handle something close to the 50-ish LRA requirement, the capacitor kit softens the blow but it's not the "silver bullet" that everyone wants it to be...there are dozens of post about folks who want to use their Honda eu2000 generators to power a 13.5(even with the cap kit) that just give up, Honda saw that market and the new eu2200 has just enough ass to do (most of the time) and they build the best inverter generators on the market, they under rate them to keep their consumer base on the hook.
There are some very new roof models out there (coleman mach 3) that report very low power consumption and surge requirements,I've never seen an actual testimonial, just coleman marketing.
The real difficulty comes in when it's hot out and the pressures in the refrigerant system are much higher and the compressor/fans are running almost all the time. Everyone want's to focus on the numbers in the brochure(usually a 72dg day)...that's not reality,reality is an 88dg day and a heat soaked unit.
If your power supply (dc to ac inverter, inverter generator, whatever it is) spends most of it's time running 75%-85% capacity it's going to get hot, heat reduces efficiency and output and that requires more input power...it's a self-licking ice cream cone...
The moral of the story with these devices is to buy 50% bigger than you think your load might be and you'll get good service and long life out of them.
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andy1canada
Posted 2019-07-09 8:47 AM (#6587 - in reply to #6581)
Subject: Re: Roof AC running off inverter...


Elite Veteran

500100100
Location: Victoria, BC. Canada
Thanks Len. Still, 140 amp alternator idle output requirement seems steep. I guess if you factor in ancillary loads (microwave, turbo-juicer, 72" flat-screen with 700 watt Yamaha surround sound, auto canoe-loader, six-way leveling jacks, 18 cfm compressor in case you decide to repaint coach on the road) then better to 'go-big' I suppose.

Again, thanks!
Terry
#
846
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andy1canada
Posted 2019-07-09 8:53 AM (#6588 - in reply to #6581)
Subject: Re: Roof AC running off inverter...


Elite Veteran

500100100
Location: Victoria, BC. Canada
Oh, forgot the 18,000-lb winch! Them babies can suck a few amps while yer' tryin' to winch yerself outta' some canyon during the zombie-apocalypse!

Terry
#846
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LCAC_Man
Posted 2019-07-09 9:18 AM (#6589 - in reply to #6581)
Subject: Re: Roof AC running off inverter...


Elite Veteran

5001001001002525
Location: Oceanside, CA
with 100% efficiency it takes 12v 100amps dc to make 120v 10amps ac, you should plan for 80%, that will take in account all your new connections/line loss and component rated efficiency.
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BigRabbitMan
Posted 2019-07-09 9:22 AM (#6590 - in reply to #6581)
Subject: Re: Roof AC running off inverter...



Expert

100010010025
Location: Cottage Grove, OR
Terry, get your engine in and running before start thinking about other projects. Until you are going down the road, you don’t need any AC of any kind!
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andy1canada
Posted 2019-07-09 9:28 AM (#6591 - in reply to #6581)
Subject: Re: Roof AC running off inverter...


Elite Veteran

500100100
Location: Victoria, BC. Canada
Getting my trans-rebuild kit today; start building tomorrow.

Terry
#846
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byegorge
Posted 2019-07-10 1:15 AM (#6596 - in reply to #6581)
Subject: Re: Roof AC running off inverter...


Veteran

1002525
Location: Olympia, Washington
I don't know Stephen I think I would like to step into air conditioned comfort occasionally while working on the coach. When the coach doesn't run the house AC should. A nice cool place to de-stress and dream about when the coach does run.
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andy1canada
Posted 2019-07-10 7:17 AM (#6597 - in reply to #6581)
Subject: Re: Roof AC running off inverter...


Elite Veteran

500100100
Location: Victoria, BC. Canada
Stephen has a point. It's cooler up here generally and I tend to camp in the shoulder seasons, spring & fall, when campgrounds are more available and there's no campfire-ban on, so AC is not as big as an issue; however, I do plan to run south more often in the future and will certainly need it then.

Don't want to cook my dog.

Terry
#846
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woodlandfarms
Posted 2019-07-11 11:37 AM (#6604 - in reply to #6581)
Subject: Re: Roof AC running off inverter...


Regular

252525
So I have zero luck in searching this forum. Len, could you share your link on your proposed (or active) ac system? We found out just recently that both our house system and engine powered system do not work. They blow, but nothing cool comes out. Oh, actually our dash does not blow any air, not sure if it is the fan motor or what.

Still have to fix the brakes but that is for another day I ugess.
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BigRabbitMan
Posted 2019-07-11 1:07 PM (#6606 - in reply to #6581)
Subject: Re: Roof AC running off inverter...



Expert

100010010025
Location: Cottage Grove, OR
You did let the house air run for five or more minutes as there is a time delay built into the system between being turned on and when the compressor starts up. One compressor will take longer than the other.
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woodlandfarms
Posted 2019-07-11 1:26 PM (#6607 - in reply to #6581)
Subject: Re: Roof AC running off inverter...


Regular

252525
Hmm. Don't remember. Due to this will give it another try.
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dkarnath
Posted 2019-07-11 5:09 PM (#6611 - in reply to #6607)
Subject: Re: Roof AC running off inverter...


Elite Veteran

5001002525
Location: Medford, OR
My time delay relay works in #1 AC, usually take 5-8 minutes before the compressor kicks on. My #2 AC doesn't have a time delay relay, or it doesn't work because the AC compressor immediately kicks on when I put power to it from my manual thermostat.
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andy1canada
Posted 2019-07-11 8:44 PM (#6612 - in reply to #6581)
Subject: Re: Roof AC running off inverter...


Elite Veteran

500100100
Location: Victoria, BC. Canada
Maybe your system needs coolant/refrigerant recharge? Did that to mine a few yrs back and it still blows cold.

Terry
#846
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LCAC_Man
Posted 2019-07-12 7:50 AM (#6613 - in reply to #6612)
Subject: Re: Roof AC running off inverter...


Elite Veteran

5001001001002525
Location: Oceanside, CA
I gutted all remnants of the engine/house units and converted to roof air conditioners only. I put some detail in my build thread and there are pictures in my album.
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andy1canada
Posted 2019-07-12 7:55 AM (#6614 - in reply to #6581)
Subject: Re: Roof AC running off inverter...


Elite Veteran

500100100
Location: Victoria, BC. Canada
Mighty fine job you did, too! You did.

That Go-Power '3000' inverter is back on the market and I'm after it. Pure-sine; 3000 watts continuous; 6000 watt surge. 'Top-10' rated apparently. Looks like they're made here in Victoria. Maybe just the company is based here. Not sure yet.

Terry
#846
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andy1canada
Posted 2019-07-12 9:19 AM (#6615 - in reply to #6581)
Subject: Re: Roof AC running off inverter...


Elite Veteran

500100100
Location: Victoria, BC. Canada
Well there goes another Canadian outfit absorbed by Uncle Sam...

Go Power: "Now a subsidiary of California-based Valterra Products..."

Terry
#846
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LCAC_Man
Posted 2019-07-13 8:23 AM (#6616 - in reply to #6615)
Subject: Re: Roof AC running off inverter...


Elite Veteran

5001001001002525
Location: Oceanside, CA
This is one size down from what I have in my FMC- https://invertersrus.com/product/aims-picoglf30w12v120vr/
I also run their 1250w unit in my camper van project. Nothing but good things to say, similar quality to the high end inverters at about half the cost.
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andy1canada
Posted 2019-07-13 9:14 AM (#6617 - in reply to #6581)
Subject: Re: Roof AC running off inverter...


Elite Veteran

500100100
Location: Victoria, BC. Canada
They 'Aims' to please!

Looks like huge punch for the buck. Charger as well as a triple-surge rate looks hard to beat. Only possible concern I can see is idle amp draw seems high to me but I guess it's as simple as turning the inverter off if you don't need it.

I already have the battery charging end of things taken care of: https://www.progressivedyn.com/rv/power-converters/pd9100-series-rv-...

I got the optional Charge Wizard with this unit and it has performed flawlessly.

Pretty cool though, to have the inverter/charger all in one unit.

Terry
#846
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