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Old 04-11-2021, 07:14 PM   #1
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How Many Watts RV Heat Pump

I am contemplating adding solar to my new to us Itasca Cambria. I'm working with a friend who is a retired Electrical Engineer and my plan is to be able to run the heat pump without shore power or generator. My M/H has the Coleman Heat Pump and, so far, I have been unable to find the starting and running watts for that unit. My rig is a 2005 and has the original heat pump unit. Anyone have any idea? Thanks a lot!!

This is my first post, hope my details show up in he signature line!!
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Old 04-11-2021, 08:11 PM   #2
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RV A/Cs use between 12 and 15 amps or 1,440 to 1,800 watts. Starting is roughly three times as much. Let your EE friend run the numbers. It will take a helluva battery bank to cover that load for long.

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Old 04-11-2021, 08:23 PM   #3
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What David said.
More often the issue with running large electro-mechanical loads is how to replenish the power you draw down from the batteries. It would require several thousand amp hours of lithium to run it for a while, and then replenishing it becomes the challenge.
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Old 04-11-2021, 09:09 PM   #4
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You might want to study some of the new RV systems out there like what Winnebago uses on the Travato 59GL and 59KL. They use a 48 Volt Electric Car Style Battery Pack that stores 12.8 Kilowatts of energy, a 48 VDC to 120 VAC 3.6 kW inverter, and a 48V to 12V DC-DC converter to power the RV 12 VDC systems. They recharge using a dedicated 48V output alternator on the vehicle engine.

If you are wanting to use AC/Heat Pump outside of the mid-day full daylight hours, then you would have to size 1.4 kW of LiFe04 battery storage for each hour of AC/Heat Pump operation. For example to run 6 hours would take eight 100 AH LiFe04 batteries. To use AC during day and also recharge batteries you would need at least ten 320 watt solar panels. Just does not make sense on a Cambria. Sorry.
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Old 04-11-2021, 10:35 PM   #5
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Hey thanks Guys!! This was more of a feasibility study and at this point looks cost prohibitive along with a roof size limitation. Well as battery and solar panel technology improves maybe it will work some day. Thanks again and happy trails to you!!
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Old 04-11-2021, 10:56 PM   #6
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My way of thinging -- Plus some questions about alternator charging.

When using a 12Vdc battery to supply a 120Vac inverter you have a power correction of ~10. And by this I mean if you know your air conditioner draws 8A-AC...for how ever long you use it... and for simplicity let's say you run that AC appliance for 1 hour... then you have 8AH of AC current.

But if you use an inverter to power this same AC appliance it will take ~10x that or ~80AH of battery storage to run that AC for 1 hour, plus the another 15% for the inverter efficiency (loss), so let's just round that to 100AH of DC battery storage for every hour of operation.

And so, if you have 420AH of Flooded Lead Acid (FLA) batteries, and you follow the 50% Rule, then that 100AH air conditioner will only run for about 2 hours.

And it will only run if you have a PSW inverter, because as I found out yesterday, when I tried using my Dimensions Quasi-Sine Inverter to power-up a portable AC... it would not start... and it just hums loudly. So, you need a PSW Inverter for sure, but maybe for the OP that's just a given? ...For the rest of us, now we know only a PSW will work on heavy motors like an AC.

What is often overlooked is that you also will PROBABLY need a low frequency inverter too, since I don't think even the best brand of high frequency PSW inverters will not handle heavy loads for long periods of time.

So to avoid a fire, I hope you do a lot of research on the type of inverter you will need to run heavy loads for hours at a time.

For example: Maybe a LF-PSW-4000W inverter will be all you need, but it might also be okay to use a HF-PSW-5000W inverter too. I don't know! I do know all these inverters talk about 2-3x surge capability, but none talk about long term operations at 1600-2000W.

So don't make the mistake of thinking you can run an Air Conditioner off the same inverter that use to power on a microwave, which is a high current appliance, but you only run it for 5-10 minutes.

Note: I did read about some newer portable AC that are Alexa enabled and have "soft start" circuitry. These appliances, like your residential refrigerator, might advertise "inverter technology" and maybe worth looking into, because having a "soft start" built into your portable AC would be a plus.

And, I seem to have read something about DC air-conditioned in India, but I did not find anything available here in the USA. (See YouTube.)


IDK... That's why I will be monitoring this thread.

I think if you have 300AH of LiFeO4 batteries, and you can recharge them to 90%, and on the low end you are supposed to stop discharging them at 20%, then you have ~70% of useful capacity, or about 210AH... just like your 420AH FLA!!!

But, because we are talking about charging LiFeO4 off the alternator, it might be possible to get 200AH recharged in just 3 hours of driving. ...But is that any reason to switch to Lithium? ...No! ...So going to Lithium just to replace FLA does not sound like a major improvement.

* That's why I still think this apprach is bester: If adding more AH is the goal, then why replace your FLA with LiFeO4?

* What about just build a separate 24V LiFeO4 power grid in your RV and dedicate 300AH to powering your portable AC or your residential refrigerator?

All good fun right? ...But don't forget you still are talking about driving 3-4 hours to replenish 200AH and if you just doubled your battery storage by adding 300AH of LiFeO4, then you have to double your driving time to recharge 400AH; or you have to run your generator! ...And then you almost back at square-one; and you just spent $3500-$5000!

* Screw this! ...Just run the generator and be done with it!


I pretty much said, " this green BS, and for fun I just bought a portable AC to run instead of my basement AC in the hot-hot humidity of Texas during the summer.

I have a 40' coach so I have room to store it, but I'm working on a plan to port the 6" hot air exhaust through my floor or side wall. TBD. I may even put it my closet and port it out the back cap, but at every turn there are trade-offs. So I'm still noodling on it for now. (I will post a thread if it works out.)

This will be a good test of my ATS, and my generator, to see if it can handle 3 ACs running at the same tiem.

My guess is that the basement AC will only operate on one compressor, but we shall see.

My hope is that the portable will get the job done on it's own, thereby saving the basement AC from early failure, and added expense for repair, but I may have to go to a 10,000 BTU Portable AC to combat the summer heat. TBD. I first need to test it in 100F weather.

So, I will have to get back to you on this project in another 2-3 weeks when the temperatures in Texas start heading up.

If it works, then I will consider this to be $400 well spent. TBD.


Here's the thing: If you drive 4-6 hours every day, and you rely on your alternator tp charge all your batteries, then I wonder how much of the alternator output makes it to the house batteries?

For example, if a 160A alternator puts out 90A, does anyone know how to estimate the amount of AMPS delivered to the engine battery bank and to the house battery bank? ...and don't forget those DRLs use up a lot of DC amps!

Maybe you Victron people with your fancy bluetooth monitoring device(s) can help us out on this one?

What I would like to know is this: If you have a 160A alternator in a diesel rig, how many driving hours does it take to replenish 200AH of battery storage?

==> I estimate it will take about 5 hours of driving and that sounds about right to me, based on my battery monitoring. So I am saying about 40A gets set to the house batteries? ...But is this accurate?

==> Now if you run the same model on LiFeO4, using the same 160A alternator, how long will it take to replenish 200AH on it? ...And what amount of Amps will the alternator be putting out to a LiFeO4 bank which does not have as much internal resistance vs FLA?

==> Final question: Do you trust the BM inside some of these LiFeO4 battery boxes; or would you always use a Battery Isolator when connecting to a lithium battery bank? [/B]
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Old 04-21-2021, 04:29 PM   #7
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General design rule: Any time you want to heat/cool --> air/liquid for any significant period of time, inverter/battery/solar will not be feasible. Use LP/genset.
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Old 04-21-2021, 08:42 PM   #8
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ou could always consider changing out to a split unit. they tend to draw much less current
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Old 04-21-2021, 11:59 PM   #9
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same as a/c only the gas runs backward if it a pump not strip
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Old 04-22-2021, 04:47 AM   #10
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Originally Posted by n9wdq View Post
ou could always consider changing out to a split unit. they tend to draw much less current
This couple accomplished exactly that. Ingenious if you ask me.
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Old 04-22-2021, 09:09 AM   #11
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our last boondockers have a new split unit that they say draws only about 500 w and use their soar to charge and run it. I may be a bit off on the wattage as that does sound low, but they have desert camped and ran from solar totally for over a week.
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Old 04-22-2021, 02:15 PM   #12
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Originally Posted by RocknRoll View Post
This couple accomplished exactly that. Ingenious if you ask me.
Impressive efficiency. I wonder if a company like Dometic will ever make a super efficient RV specific system.
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Old 04-22-2021, 06:23 PM   #13
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I too saw this Split AC Upgrade 1 month ago and it got me thinking how I can add a Split AC to my Itasca Horizon 40AD and I think I figure out how!

I started looking for a place to mount a slit AC condenser and I think there is space behind my cargo storage and my before my brake cans... under the RV... if you can lay a a Split AC Condenser on it's side?

So if you have a 38' or 40' RV maybe you should look under your coach to see if there is room for a condenser with framing you can easily weld to the chassis frame rails!

I then went looking for a suitable place inside my RV to hang a 36"x12" AC Evaporator & Duct, and I think I found one above my bedroom window, but you will need to come up with another way of opening he storage door where the TV is. ...In my case, the previous owner took the TV out of that cubby and mounted it to a 6' piece of oak and that worked great!

However, I did not pursue this project for 3 reasons:

1) The cost was $1,500-$2,000.

2) MY Coleman Mach (2-ton) basement AC is still working great.

3) I decided to add a portable 8,000 BTU AC to the bedroom and vent the hot exhaust air out the bedroom Tip-Out-Window for $350!

Here's the thread if you want to know more:

So below are pictures of a Portable AC unit I store in my bedroom when I'm traveling; and when I'm camping I just roll it into position so I can access my washer/dryer and closet.

Driving has worked out well. The portable is positioned between the bed and the carpeted lip to the closet, and I added a door stop for extra measure. (No need for a bungie either.)

With the portable AC in the bedroom I will not hear it in the living room either!

Plus my Winnebago roof vents will distribute all the cold air from the bedroom to the front of the RV; so I really think a 8,000 BTU that runs on 8-9A will be sufficient to handle 105F weather this summer. TBD

And if I'm right, I will wire a separate 20A power line so when I have access to both 50A and 20A shore power can can run the Portable AC off the 20A service and not my 50A service in the coach.

And when I'm on generator I will just plug the Portable AC into my existing wall socket and probably only run 1 AC. TBD

Making the window shims was really quite easy! And if I want to roll the portable to the front of the coach, I made a shim to vent the AC out the window over the couch, but I hope to keep the AC in the bedroom so I don't have to listen to it during the day.

We shall see and I will let you know how it goes!
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