Running A/C from Battery Bank

[TinLizzie]

We have a 2017 Winnebago Sunstar LX 35F, 2 rooftop AC units, 4 100 amp hour Battle Born lithium batteries, and cannot run AC units unless connected to shore power or generator...I called Winnebago and they said this was by design...I know you can only run AC for a short time on battery bank but the idea is to get the inside cooled down enough...I have a 2kw Magnum inverter/charger...we are wanting to install full solar setup next year to complement the lithium batteries but now I'm concerned what 'special' modifications we would be required to make. Winnebago said we would have to redo the wiring, but could not give any specifics as to what that meant...I know we have to install solar charge controller, 3kw inverter/charger, probably soft start AC switch and other solar specific wiring...

Has anyone else done a conversion of a rig similar to this or are you able to run your AC for a while from the battery bank? thanks....

[Gary RVRoamer]

Connecting one or both a/c to an inverter supplied circuit isn't all that difficult, but you are woefully short of both battery and inverter power to have a prayer of success. Each a/c uses a constant 1250-1400 watts of power and each time the compressor cycles on there is a brief surge of 50%-100% more. That means a 3000W inverter can barley handle one a/c, and the demand on the battery bank is huge. For example, 2400 watts @ 12v means an amp draw of 200. A 400AH battery bank won't be able to supply that much amperage and still keep the voltage up high enough to avoid an inverter low-voltage shutdown. You probably need an additional 400AH of battery simply to run one a/c unit, and even then it probably won't run more than 15 minutes. A very high amp rate like that discharges very quickly, much faster than the slow 20-hour rate used to calculate the AH rating.

[speed racer]

Do the math. 2KW would probably run one ac unit for a short time but it probably wouldn't let it start because start currant is much higher than run.

[Knightab]

Originally Posted by speed racer

Do the math. 2KW would probably run one ac unit for a short time but it probably wouldn't let it start because start currant is much higher than run.

You are right on the money Speed Racer! I also have 400ah of lithium and a 2000 watt inverter, mine wont even attempt to run AC and even if it did it would drain the batteries pretty quick. using 150 amp minimum from the batteries an hour and I have enough solar to produce 50 amp an hour it will still only be 4 hours and the batteries would be dead.

[TXiceman]

An AC is a very high amp draw load. To run AC off the inverter battery bank will require a huge inverter and even larger battery bank. Be realistic and run the generator for such loads.

Ken

[A Traveler]

Originally Posted by TXiceman

An AC is a very high amp draw load. To run AC off the inverter battery bank will require a huge inverter and even larger battery bank. Be realistic and run the generator for such loads.

Amen! That’s what the generator is there for.

[Jim_HiTek]

By re-do the wiring, I think they're telling you that you need to install heavier gauge wires for what you want to do. Most people that cover the roof with solar panels have to run big thick heavy gauge wires down the refer vent.

Whether or not you could ever reasonably run your AC off of batteries for any length of time to be useful is in doubt. Because you'd need to draw and replenish ~120 amps while it's running. That's ~1700 watts. And since solar panels are usually around 120 watts, you'd need 14 of them and bright sunshine...not sure you can fit 14 on top of the typical RV. Especially one that has rooftop ACs.

How about running your generator? That way you can run the AC as long as the generator runs.

But I'm just guessing...you should contact a solar outfit that does RVs, they can tell you.

[Ivylog]

The ACs are not on the inverter circuit for a reason, they are on the shore/generator circuit because of the high power demand. While the microwave is on the inverter circuit, I still run the generator if going to run it for more than a couple minutes and I have 880AH of batteries. It could take an hour of generator to replenish 10 minutes of one AC or many hours of solar.

[Knightab]

Originally Posted by TinLizzie

We have a 2017 Winnebago Sunstar LX 35F, 2 rooftop AC units, 4 100 amp hour Battle Born lithium batteries, and cannot run AC units unless connected to shore power or generator...I called Winnebago and they said this was by design...I know you can only run AC for a short time on battery bank but the idea is to get the inside cooled down enough...I have a 2kw Magnum inverter/charger...we are wanting to install full solar setup next year to complement the lithium batteries but now I'm concerned what 'special' modifications we would be required to make. Winnebago said we would have to redo the wiring, but could not give any specifics as to what that meant...I know we have to install solar charge controller, 3kw inverter/charger, probably soft start AC switch and other solar specific wiring...

Has anyone else done a conversion of a rig similar to this or are you able to run your AC for a while from the battery bank? thanks....

Richard, they are probably right about the wiring but it depends on how much solar you are going to install. You also have options on how you configure the solar, I have a main bank of 600 watts and wire 2 panels series and then the 3 sets in parallel, this bumps the voltage up to around 40 in great sun and then the inverter (MPPT) will knock it down to a useable voltage and use what ever is left over to put into the batteries. I have a second array of 300 watts with 2 in series and then parallel and have them on a seperate controller also MPPT. I had it laying around and didnt want to mix 75 watt with 100 watt panels so I have 2 arrays feeding the batteries. The reason I did 2 panels series is it cuts the amps to half so you can make use of smaller wire. If you buy a controller than can handle 150 volts you can wire more than 2 in series, downside is if you get shading on a panel it will kill the output so its important to keep them in full sun if in series.

[jcussen]

Can be done, way easier with a 3000 watt inverter or/and a easy-start. On a sunny day, I can run 1 ac for 5 or 6 hours on a combination of solar and battery power. Have to shut it down at night though.

[Jlo11111]

Lot of bad info on this thread. Let's focus on running just one AC unit. You need a more powerful inverter; 3000w or better will work. Your 400ah of lithium batteries should be able to run one AC unit for a few hours assuming you re-wire the coach a bit to be able to do so. Of course, the more batteries you add, the longer you can run your AC. Several RV manufacturers have recently come out with coaches that can run an AC unit for 8-9 hours and they have lithium battery packs in the 800ah range.

[BCam]

I didn't watch the video but this may give you some clues although they're not necessarily dealing with an A/C that has the same requirements in terms of amps, etc.

https://www.thefitrv.com/rv-tips/so-...battery-power/

Note: The above article characterizes their battery bank as 11,600 watt hours. This is the same as 967 amp hours (11,600 watt hours/12v = 967 amp hours). This is almost 2.5 times your 400 amp hour batteries.

[creativepart]

Until more efficient A/C units make it into use in the US and LiPo batteries drop 50% in price your dream of running the A/C in your coach for more than 45 min is just that, a dream.

It’s not a Winnebago problem or issue, it’s simply an issue of energy storage vs energy demand.

And a 2,000w inverter is at least 1,000w under powered to start and run one RV A/C unit.

[jcussen]

Before I got a 3000 watt inverter, ran one ac on a 2000 watt inverter by using this:

https://www.youtube.com/watch?v=cjLzqmUmTcM