Airstream Forums

Airstream Forums (https://www.airforums.com/forums/)
-   Full-Timing, Winter Living & Workamping (https://www.airforums.com/forums/f459/)
-   -   Can everything, including the AC, be wired to run off the batteries? (https://www.airforums.com/forums/f459/can-everything-including-the-ac-be-wired-to-run-off-the-batteries-191780.html)

Lindenwood 02-03-2019 07:47 AM

Can everything, including the AC, be wired to run off the batteries?
 
We are looking to buy a new (or gently used, if we can find one) FC30FB Bunk for full-time living. One of our desired goals is the ability to boondock in relative comfort (I can tolerate pretty much any temp, but I want to at least have the option of decently-conditioned air for the rest of the family!).

So, specifically, it is my understanding that the Air Conditioners are only connected to the AC side of the trailer's "power grid," and thus cannot be powered by the batteries (if this is incorrect, please school me!). I was wondering if it is instead possible to wire the AC unit to be powered by the DC "grid."

To be clear, I have no expectation of running the Air conditioner (or any high-consumption appliances) purely off the stock or near-stock batteries. The intent would be to simply use the batteries to provide surge power for AC startup and intermittent appliance use.

For example, the 13500 BTU AC should pull about 2700w at startup, but only run on around 1250w. Thus, assuming perhaps a 50% duty cycle at a reasonable setting, we are only looking at maybe 700-800 watt-hours including the startup surges (say, ~2700 watts for 15 seconds every 10 minutes). Thus, a quieter, cheaper, more economic, and much more portable 2000w-class generator should easily be able to provide a net positive charge to the battery throughout the day.

A modest solar setup should make it that much easier to maintain battery charge.

Thoughts on how difficult it would be to set uo the airstream to operate like this?

Thanks!

overlander63 02-03-2019 08:02 AM

You can wire the air conditioner to run off the batteries, using a 3000watt inverter, but be advised that when inverting 12v to 120v, you need to multiply the watt draw by 10x. You'd be drawing 30000 watts, or about 300 amps, to start the air conditioner. Even the biggest, baddest batteries won't hold up long to that load.
Some people have wired their air conditioner to run for a brief period on their batteries, using an inverter, but basically only for a few minutes to take the heat out of the trailer, then it's back to windows and vents.
You would also need a huge bank of solar panels to have any hope of replenishing the batteries between uses.
Also, if you are planning to do this in Florida, be advised it is a state law that any residence is required to be connected to the power grid.

blkmagikca 02-03-2019 08:05 AM

From a practical point of view, forget about running the air conditioner off your batteries (e.g., using an inverter/charger) - you would need an obscene amount of solar panels and LiFePO batteries. It is highly unlikely that you would have enough "real estate" to mount solar panelling to do this. If you install The Easy Start module - see https://www.microair.net/products/ea...nt=30176048267 - you would be able to run the a/c using a 2000 series inverter type generator, such as the Honda 2000 or Yamaha 2000i.

lewster 02-03-2019 08:10 AM

Hi Lindenwood,

It is entirely possible for you to connect your roof A/C (only 1 of your 2 units) to your batteries ( I do this all the time) to allow you to operate the A/C for a specific period of time. The only thing you have to worry about is the power required by your A/C and your battery life.

You will also need a new, larger inverter/charger (minimum of 2000 watts), new, much larger batteries and a solar system that will allow you to re-charge your batteries as they deplete.

Anything is possible, it simply requires the time and money to accomplish and a person who can do the job for you!

Al and Missy 02-03-2019 08:35 AM

Quote:

Originally Posted by overlander63 (Post 2206141)
You can wire the air conditioner to run off the batteries, using a 3000watt inverter, but be advised that when inverting 12v to 120v, you need to multiply the watt draw by 10x. You'd be drawing 30000 watts, or about 300 amps, to start the air conditioner. Even the biggest, baddest batteries won't hold up long to that load.
Some people have wired their air conditioner to run for a brief period on their batteries, using an inverter, but basically only for a few minutes to take the heat out of the trailer, then it's back to windows and vents.
You would also need a huge bank of solar panels to have any hope of replenishing the batteries between uses.
Also, if you are planning to do this in Florida, be advised it is a state law that any residence is required to be connected to the power grid.

One does not multiply the wattage draw by the voltage ratio, only the current. Neglecting, for the moment, inverter efficiency, the wattage at 12 volts is the same as the wattage at 120 volts, but since the voltage goes down by a factor of 12, the current comes up by the same amount plus a little to account for efficiency of the inverter. So a 30 amp starting current becomes 360 amps and a 15 amp run current becomes 180 amps.

It looks like you did the math right, just mis-stated the reason.

OP: An EasyStart can significantly reduce the starting current, as previously stated, but being realistic, you are going to be running the generator whenever you are running the AC.

Al

SuperTrouper 02-03-2019 08:36 AM

Quote:

Originally Posted by overlander63 (Post 2206141)
Snip...but be advised that when inverting 12v to 120v, you need to multiply the watt draw by 10x. You'd be drawing 30000 watts, or about 300 amps, to start the air conditioner. snip

Clarification, the watts don't change.

DC watts to amps calculation formula
The current I in amps (A) is equal to the power P in watts (W), divided by the voltage V in volts (V):

I(A) = P(W) / V(V)

So amps are equal to watts divided by volts.

amp = watt / volt

or

A = W / V

Alternating current calculations are a little more complicated and there are losses in the conversion from DC to AC but the simple calculation is close enough for discussion. So, if the Air Conditioner draws 30 amps at 120 Volts then the power (watts) is 30 x 120 or 3600 Watts. The power required remains the same. If your source becomes 12V then the math says 3600 watts divided by 12 volts is 300 Amps. Given a large battery bank of 300AH (Amp hours) and utilization of only 50% of that (assuming lead acid batteries) you could theoretically run this load for a half hour before the batteries are depleted. In reality, as mentioned in the original post the AC only draws max power at compressor start up and then hums along at 1400 watts or so.

Lewster is the best resource for the discussion here. For us, a MicroAire EasyStart and a Westinghouse 2500 Watt genny is what we have in the case we need AC without hookups but so far, we have not needed the AC here in Northern California our 400 watts of solar and 220AH of batteries have sufficed for our needs. I've only run the generator at home to keep it operational.

kscherzi 02-03-2019 08:58 AM

I've noticed my 15,000 BTU AC draws nearly 2,000 watts continuous at 120 volts according my kill-a-watt meter.

2dabeach 02-03-2019 09:17 AM

Lindenwood....Buy yourself a 3,000 watt Honda generator instead of a 2,000 unit and you should not have a problem running a single A/C.

DeltaRon 02-03-2019 09:42 AM

AC on batteries
 
And Lewster is the guy that help you convert. There’s no better power, solar guy in the country. And he works out of Naples during the winter months. Call him.

switz 02-03-2019 09:49 AM

We installed nine 100 watt solar panels on the roof go our 2014 Classic along with a 600 amp hour lithium battery and Magnum MS2812 charger/inverter plus all the solar controls. All of the trailer AC wiring connects through the Magnum except the original refrigerator (now a Vertifrigo 12Vdc only), the original water heater (now a Truma Aqua Do comfort instant on propane only) and one of the two air conditioners.

Thus all 120Vac outlets and one air conditioner can run off of the battery, However, the air conditioner will suck a lot of amp hours. We have run the air conditioner for a 30 minute lunch stop with no issues.

mykytiukr 02-03-2019 09:53 AM

Boondocking!
 
Do a search on YouTube for “Solar RV Airconditioning”. There are many many videos of people doing exactly what you are asking about. There is one where a guy is using a small window AC that starts with about 1000 watts and runs a about 500.

rchawkins 02-03-2019 10:00 AM

My friend Rob Thilo has a 2016 Classic with the set up you want and it’s for sale. Talk with him

mykytiukr 02-03-2019 10:01 AM

https://www.amazon.com/Frigidaire-FF.../dp/B01B4XUUDI Here is the link to the small AC unit he used.

TheGreatleys 02-03-2019 10:14 AM

Quote:

Originally Posted by Lindenwood (Post 2206135)
We are looking to buy a new (or gently used, if we can find one) FC30FB Bunk for full-time living. One of our desired goals is the ability to boondock in relative comfort (I can tolerate pretty much any temp, but I want to at least have the option of decently-conditioned air for the rest of the family!).

So, specifically, it is my understanding that the Air Conditioners are only connected to the AC side of the trailer's "power grid," and thus cannot be powered by the batteries (if this is incorrect, please school me!). I was wondering if it is instead possible to wire the AC unit to be powered by the DC "grid."

To be clear, I have no expectation of running the Air conditioner (or any high-consumption appliances) purely off the stock or near-stock batteries. The intent would be to simply use the batteries to provide surge power for AC startup and intermittent appliance use.

For example, the 13500 BTU AC should pull about 2700w at startup, but only run on around 1250w. Thus, assuming perhaps a 50% duty cycle at a reasonable setting, we are only looking at maybe 700-800 watt-hours including the startup surges (say, ~2700 watts for 15 seconds every 10 minutes). Thus, a quieter, cheaper, more economic, and much more portable 2000w-class generator should easily be able to provide a net positive charge to the battery throughout the day.

A modest solar setup should make it that much easier to maintain battery charge.

Thoughts on how difficult it would be to set uo the airstream to operate like this?

Thanks!

My rig is wired like that. My relatively large inverter with "pass-through" functionality is wired in-line with my shore power, prior to the breaker box. Turn the inverter on, and it powers everything in the trailer from the batteries. It won't run the AC for very long on batteries before they die, but it will start and run it.

If you want to supplement a low output generator with your batteries, you'll want a "hybrid" inverter, which is designed to do just that. My inverter is not a "hybrid" type, so I can choose to power with either shore power or batteries, but not both at the same time.

All that said, if your goal is just to run your AC with a Honda 2000 generator or something similar, it would be cheaper and easier just to install an Easy Start on your AC unit to lower the startup surge to a level that the generator could handle. Unless you have a very large solar array and/or battery bank, it's not all that helpful to be able to run the AC off batteries.

Lindenwood 02-03-2019 10:33 AM

Thanks for all the great responses!

To be clear, I would only ever try to run the AC with the generator running. So, even at startup, with the generator providing 2000w of that power, less than 1000w would have to come from the batteries. Even basic batteries should be able to handle that ~80A load for the few seconds until it settles down, no?

I will definitely look into consolidating the grid to function like this.

wulfraat 02-03-2019 10:45 AM

Can everything, including the AC, be wired to run off the batteries?
 
5 Attachment(s)
Quote:

Originally Posted by Lindenwood (Post 2206217)
Thanks for all the great responses!



To be clear, I would only ever try to run the AC with the generator running. So, even at startup, with the generator providing 2000w of that power, less than 1000w would have to come from the batteries. Even basic batteries should be able to handle that ~80A load for the few seconds until it settles down, no?



I will definitely look into consolidating the grid to function like this.



You need a hybrid inverter to do this along with some proper batteries (not the interstates that come from the factory). I use the Victron multiplus 3000 hybrid inverter and do this all the time (supplement 8-12A of shore power from a small gender or household outlet with battery power. Your main 15k AC will pull over 1700 watts when running. This approach (hybrid inverter) Works like a champ, especially if you have a large solar array.

I can also run my AC off batteries alone for 2-3 hours.

Like most of us who run the AC of limited power supplies you will want to install an easy start computer controlled soft starter, which dramatically reduces current draw from the compressor on startup.

Lewster did my inverter / batter / solar install. Highly recommend his services.

Here are the full details:

https://www.airforums.com/forums/f539...um-182406.html

Lindenwood 02-03-2019 10:54 AM

Quote:

Originally Posted by wulfraat (Post 2206219)
You need a hybrid inverter to do this. I use the Victron multiplus and do this all the time (supplement shore 10-15A of shore power from a small gender or household outlet with battery power. Works like a champ.

I can also run my AC off batteries alone for 2-3 hours.

Lewster did my install. Highly recommend his services.

Here are the full details:

https://www.airforums.com/forums/f539...um-182406.html

Wow! That is quite the setup!

guskmg 02-03-2019 04:26 PM

Lewster did mine. 3000w, magnum, 800w solar, and 600ah lithium. We really enjoy being grid independent. Add a compost toilet and never need hook ups. Excellent equipment, installation, and service.
guskmg

TouringDan 02-03-2019 07:25 PM

Can everything, including the AC, be wired to run off the batteries?
 
1 Attachment(s)
Quote:

Originally Posted by mykytiukr (Post 2206192)
Do a search on YouTube for “Solar RV Airconditioning”. There are many many videos of people doing exactly what you are asking about. There is one where a guy is using a small window AC that starts with about 1000 watts and runs a about 500.



I have a thread titled “5,000 btu/hr AC and 1,000 W Genny” and dated 5/16/12. I have a 5,000 btu/hr Frigidaire AC unit that is similar to the one you are referring to. My unit looks identical but is just not quite as efficient as it is an older model. It requires 465 watts versus 440 watts. I can operate this unit using my 1,000 watt generator or can operate it for a minimum of 4 hrs using the two BB Lithium batteries I have installed. This works well for us when we need AC. This is a nice unit and is very quiet.

Below is a photo of the “power plant”. It feeds the main panel box and operates all the 120 volt equipment.

Dan

Attachment 332920.

Thonevan 02-03-2019 07:28 PM

Get a generator to run the A/C... Or a lot of fans!


All times are GMT -6. The time now is 01:28 AM.

Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2020, Jelsoft Enterprises Ltd.