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Old 04-12-2006, 10:06 PM   #197
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Watts or Jules

Quote:
Originally Posted by ankornuta
.......
Okay, jumping back to the batteries... I know the inverter is going to lose some energy, but if the A/C takes 14.1 approximate full-load amps for cooling, and the batteries can maintain 25 amps for about 14 hours... does that mean that this would be enough power to run the A/C on battery power for a several hours? I think I'm missing something.
Andrew,

An a/c uses huge amounts of power. No battery or solar panel that could fit in an Airstream will run one. Think generator or tapping into the grid. 12v times 14.1 amps does not equal 110v times 14.1 amps. Someone please help out here as I am not current on these jules.

R
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Old 04-12-2006, 10:35 PM   #198
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Hello ,

How can the batteries maintain 25 amps for 14 hours? You will need continous power to run that a/c ,shore power or say an eu3000 or 2 2000s or equivilent type generators of your choice. The batteries just wont maintain that load without a source to keep them at a constant voltage . the unit will not tolerate unstable voltage for very long Im afraid.Dont know the jules either but know it cant work unfortunatly , I would think you would be worried about your battery life on a hot day boondocking if that a/c was on and if youll have enough juice for the weekend.


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Old 04-13-2006, 03:36 AM   #199
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The typical 13,500 btu AC uses about 15A at 120V while running, or 1800W. You'd defintely want at least a quality 3000W inverter to try to handle the start-up surge. Because it's only about 90% effiecient, the inverter would draw about 2000W or 175 amps from the batteries. An inverter typically draws at least 11 times in current at 12VDC from the batteries as it's supplying at 120VAC. Another rule of thumb is that it will draw (120V output wattage)/10 in amps from the batteries.

Let's say we install 7 Group 27 batteries (500 pounds) dedicated to the air-conditioner to spread the load to 25A each. Group 27 batteries have a Reserve Capacity (full charge to full discharge at 25A) of about 180 minutes or 3 hours. To have a decent life, we won't discharge them to less than 50% charge, so on our first night of use, we can run the air-conditioner for about 1-1/2 hours. If the night is only a little warm and the AC only runs 25% of the time, we could get 6 hours until our batteries are down to 50%. But if it's a hot night and it runs 50% of the time or more, we'll only have 3 hours of air-conditioning.

But that's on the first night. Because it takes so much generator run time to charge from 80% to 100%, most shut off the generator at about 80% charge. That means on second and subsequent nights, we have 60% of the run times above, i.e. 3.6 hours if the night is only warm, and 1.8 hours if it's hot. And we'd need a 200 amp charger to bring them back up the next day, and an EU2000 won't run that!

This is why it's impractical to run an air-conditioner off batteries through an inverter. In fact, we use two Honda EU2000 generators paralleled to supply that 2000W continuous and in the real-world other things, such as powering the converter to charge the batteries. One EU2000 can't supply the full start-up current needed, meaning the compressor is starting slowly and overheating the motor windings, as well as hurting the generator. DuoTherm says our AC unit needs a 3500W generator.
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Old 04-13-2006, 04:58 AM   #200
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I have seen someone run A/C off batteries and solar power in an Airstream. At the 2004 Lansing International, there was a guy that cooled his vintage Bambi or other small Airstream at the Vintage Open House in just this way. He probably had a small A/C unit (8kW) due to the small size of the trailer. He had many, many batteries (could have easily been 500 lbs. worth) installed in the bed of his pickup truck, and the solar panels on the roof of the truck. He thus had to plug the trailer to the truck to run the A/C. I suspect that after the Open House demo it may have taken days for the solar panels to top the batteries back up.
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Old 04-13-2006, 11:19 AM   #201
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Thanks for the advice everyone. I did a little more research after initially thinking it might be possible to run A/C off of batteries and found some useful formulas.

To find the 12volt amp hour draw of a 110 volt appliance run through an inverter you need either the "AC Watts" or "AC Amps" of the appliance and then plug them into one of these:

AC Watts/12 X 1.1 X hours of use = Amp hours

AC Amps X 10 X 1.1 X hours of use = Amp hours

Yeah... I can see that wouldn't be realistic to run A/C off batteries. Ah well, I guess I'll need a generator if I camp in hot places.

I wonder how long it will be before there will be refrigeration that draws very little power...
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Old 04-13-2006, 08:01 PM   #202
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Hey RoadKing Moe,

thats a very complete analogy and it sounds like you know your watts and amps pretty well .It is correct 1eu2000 cannot start that a/c . 2 in parallell as you have stated will . thats the popular way .batteries on the other hand ,forget about it .I had said in my post 2 eu 2000 not one ,or the 3000 which seems more suited to running the a/c . You cannot run the 2000s on eco throttle anyway so go with the 3000 or generator of your choice .As long as it is pretty quiet like the eu2000s are.
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Old 04-13-2006, 08:06 PM   #203
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HEY ankoruta ,
Use a dual 110 or lp . the dometic in my trdwnd on lp works better an much colder than the 110 . They say campground power losses are common and the 110 is usually less than ,at the panel boxes.lp frees you up for cold ones out in the sticks .Save the batteries for lighting at night or a dvd if you want.

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Old 04-13-2006, 08:26 PM   #204
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Good News

Quote:
Originally Posted by ankornuta

I wonder how long it will be before there will be refrigeration that draws very little power...
A,
The older gas referigerators use a pilot light. The newer units with an electric igniter have solid circuitry that do not use much juice. These operate off a 12v battery quite well I believe. You are learning quickly, asking good questions.
R
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Old 04-13-2006, 09:45 PM   #205
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Holding Tank Holes

So, the people at the RV place told me that I didn't need to use silicone to seal the flexible fittings into my polyethelyne holding tanks. I just drilled the holes, forced the fittings in (with a flange on the inside and outside) and they seem to make a nice seal, but I'm curious if I need to use silicone here as well. Also, do I need to silicone around the ABS pipes that pop into these fittings?
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Old 04-13-2006, 09:46 PM   #206
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Quote:
Originally Posted by fastrob
A,
The older gas referigerators use a pilot light. The newer units with an electric igniter have solid circuitry that do not use much juice. These operate off a 12v battery quite well I believe. You are learning quickly, asking good questions.
R
Thanks Rob! I'm really looking forward to A/C coming out eventually that could run on 12 volt or propane... I think that would be a major leap in technology.
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Old 04-14-2006, 10:01 PM   #207
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I drilled all my tank holes, fitted the flex fittings, put in the well nuts, etc today after work. So, tomorrow... I guess I'm going to bite the bullet and glue all the plumbing together and strap everything down, permanent-style.
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Old 04-15-2006, 07:38 PM   #208
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Milestone: Holding Tanks Done!

So I've finally finished something other than demolition and damage control. I completed the installation of the holding tanks which involved installing the insulation, wires to the well nuts for the capacity sensors, gluing the pipes together, etc. I used that expanding foam stuff in a can to seal up small areas around the tanks and keep critters out.

I installed a black tank washer which I think will be very helpful. I also installed the Valterra valve assembly.

Then, I filled the tanks multiple times, applied pressure and stress, etc and checked for leaks. I found a couple little drips the first time, one of which was addressed with teflon tape on the black tank washer connector and one was on a well nut, which I tightened and applied some silicone to.

Note: When marking black holding tanks and ABS pipes for drilling, cutting, etc, White Out works very well. Being black, the white paint works great. I think my White out markings are visible in a couple of the pictures.
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Old 04-15-2006, 07:53 PM   #209
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Old 04-17-2006, 03:31 PM   #210
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I set my wheel wells and bathroom walls up on the frame to get some final fittings for the shower drain and toilet drain topside locations. It looks like my guesstimations were very close.
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