A/C Calculations

[caymaanedge]

I’ve read a lot about this running AC in battery/solar, but it seems the calculation details are lacking on the large systems.
So here’s what I’m chasing.
(1) 13,500BTU AC consuming 15amps at start-up and 13 amps when running. Soft start is installed.
My fridge consumes about 2 amps while running.
Let’s say light and other stuff average 2 Amps as well.
So approx. 20amps @ 120v
What are you using for runtime calculations for the AC and Fridge? 100% or say 70%?
At 100% that’s about 5,280 amps @ 12v
How do you size the battery bank and solar? That’s a 220ah average over a day, but no solar in the dark so carrying between sun would be like 12hrs @ 220ah = 2640ah. The big systems I have seen are running 1000-1200ah of LifePO4 which is less than half that.
What am I missing?

For reference I have 1140 watts of solar and 680ah of LifePO4 batteries. Trying to understand what it would take to run one of the AC’s as well.

Thanks

 

[MattiFin]

Fridge is probably running less than 20% assuming it is a compressor fridge.
AC totally depends on your use and situation.

 

[chrisski]

In my RV, if its hot enough to turn the AC on, in the day it is on all the time and never shuts off. As the sum sets it will cycle on and off, and finally shuts off for the night.

Outside temps are a high of 92, with a low of 60 and AC set to 74.

Honestly, for the fridge, I’d run it soon before it gets too cold with a Kil a watt meter installed. You’d get good numbers. This will of course be more in the hotter summer months and cool in the winter months.

============

Sizing the battery is based off a power audit, and since it’s been in the RV about a year, I’ve got some charging data. I have 1350 watts of panels and a 12 volt system and can charge at a rate of 60 amps Because of a FLA 13% limit. I can exceed that limit once the sun is high in the air, so if charging is not done by 10 am, I need to pay attention. The battery bank is 458 amps.

When I built it with 1000 watts, it was good for my needs, but I did not like setting the portable panels up, but more so chasing them down when they blew away, so I put 350 more watts on the roof. So I rarely set the portable ones up, unless its an extreme usage night.

============
For how I plan on AC:

I’m doing a 24 volt upgrade with lithium batteries that will bring my usable power from 2300 wh to about 8000 wh. Once I get that tweaked over the winter, I will fire up the AC and gather some data on that. My pencil calculations say I would want 1300 watts of roof panels (350 watts more) and 800 watts of ground panels (400 watts more), 2100 watts total to. Be able to reliably run the air conditioning unit and push back the 500 watts to 1000 watts I expect the RV 13500 BTU air conditioning to be using. I plan on pushing 1000 watts at least from those panels for about 6 hours a day. THe closer the AC is to 500 watts running and not 1000 watts, the more I will be able to charge.

Before I try the AC next spring I need to have quite a bit of data collected from my Victron shunt to see how my new 24 volt 3000 watt inverter holds up.

If things don’t go as well as planned, I would look at a mini-split install.

 

[caymaanedge]

Thanks for the input. I suppose I could run the AC and see how long the batteries can go, but I really would like more data….
I’m considering doubling my solar to 2280 watts and pushing batteries up to 1020ah. Just want to verify it will meet my expectations.

 

[Short_Shot]

A lot of people toss the junk rooftop ac units in the trash, fill the hole, and cover it with solar.

Then they install a mini split ac.

Uses tons less power.

 

[kevinich]

I usually look at sizing based on kwh. It's easier than trying to figure out how many amp hours, because that's all based on the voltage, so a 12V is twice as much as a 24V. Now an AC unit that is non-inverter (ie. not variable output) will always run at 100% when switched on. So 13A at 120V is going to be 1560 watts per hour. So let's say you duty cycle it at 70% during the day and 50% at night, then you can say 10 hours during the day at 1560w = 10*1560*0.7=10,920wh or 10.9kwh and at night for 14 hours @ 50% equals =14*1560*0.5 =10,928wh or 10.9wkh.

So that's a total of 10.9kwh + 10.9kwh = 21.8kwh

If you have a battery that is in a 12v system. Then you're looking at 21800wh/12v = 1816Ah of power. Now you have to size your battery much higher because you cannot do a 100% depth of discharge on it. So let's say you size it 50% larger, then it will be 2724Ah.

In most cases those top running units are quite inefficient, similar to window a/c units, unless you buy an efficient inverter duty system. So that's why a lot of people are switching to the mini-split systems as it's quite efficient, running at high SEER numbers (usually double what the top mounted units do). In that case you can almost expect a reduction of about 30-50% of energy usage.

 

[chrisski]

A lot of people toss the junk rooftop ac units in the trash, fill the hole, and cover it with solar.

Then they install a mini split ac.

Uses tons less power.

I don’t think a mini split on a 35’ fifth wheel is all that common. I’m sure its been done before. I have never seen a fifth wheel with an AC removed and the hole patched in person.

Problem I’m running into is my AC 13.5K or 15K BTU, runs all day long without shutting off. A 120 volt mini split seems to limit itself to 9k. I have two ACs. I can leave the master bedroom off, but I’m already uncomfortable with the one I have and don’t think it would be better to downsize to a 9k BTU.

Will says in a recent video he found a 120 volt 12k BTU AC. I did not see the link posted.

THere’s problems with putting a minisplit in a fifth wheel also. Mainly where to mount it. That back bumper looks like a great place but bounces quite a bit while driving.

Those are problems I hope I don’t have to deal with.

 

[Short_Shot]

I don’t think a mini split on a 35’ fifth wheel is all that common. I’m sure its been done before. I have never seen a fifth wheel with an AC removed and the hole patched in person.

Problem I’m running into is my AC 13.5K or 15K BTU, runs all day long without shutting off. A 120 volt mini split seems to limit itself to 9k. I have two ACs. I can leave the master bedroom off, but I’m already uncomfortable with the one I have and don’t think it would be better to downsize to a 9k BTU.

Will says in a recent video he found a 120 volt 12k BTU AC. I did not see the link posted.

THere’s problems with putting a minisplit in a fifth wheel also. Mainly where to mount it. That back bumper looks like a great place but bounces quite a bit while driving.

Those are problems I hope I don’t have to deal with.

Mostly because people with those don't seem to mind burning money on battery systems and have room for a ton of solar. Obviously not everyone has that kind of budget though.

Usually they just add more panels and only run it during the day and live with the power consumption.

You can easily get a split phase inverter to get yourself the 230v you need for a 15k btu or larger unit. As for bouncing around on the back bumper, that's pretty much what most people do.

 

[caymaanedge]

I have A 36’ Class A with two 13,500 Btu units with soft starts. No option for a min split so I need to work with what I have.
The RV is inside so I guess I will run it and see how long my 640ah last. Then I’ll put it outside in direct sunlight and do it again. Hopefully that will give me enough real life data to figure it out.

 

[Sojourner1]

I'll run my 15k air conditioner off my solar/ batteries, depending on the solar output that helps to extend longer run times. If its hot out and the A/C will need to be run for longer periods I'll split between the EU2200 generator and solar/ batteries. If it's only to cool it down for a couple hours or so I'll run it off just the batteries with whatever solar is being produced if there is any. Something to think about designing your system is be sure you have proper sized wiring and that there is some sort of ventilation for the inverter because it will be throwing heat from it. Something else to think about running high draw items for long periods of time is if it's after dark you don't deplete so low that system shuts itself down before solar can start to carry loads/ charge the bank again.

Here is some recordings I did back in April of this year that might help some. The right hand column shows what running, outside ambient temps, what solar watts was being produced. The Top column explains the system in sections.



Edit: I should of added that it's been used like this since spring 2020 after adding the micro-air to the air conditioner, not just a short test and then make the claim "it can be done". Long term use with hands on experience not just theoretical paper #s.

 

[McCarthy]

I'd just plaster the entire roof with large, commercial grade 460 watt plus panels. Found mine for 220 bucks locally a piece. Get it done once and for all.