Adding Second A/C to 50 Amp TT

[thegabrielles]

Hi All!! My family are getting back into the RV scene after getting away for a few years. We purchased a 2022 Cruiser Aire 28RKS. This is a 32'-9" trailer with one slide that runs the length of the Kitchen and living area. The camper came with a single Dometic A/C in the living room that is ducted. We have only been out a few times but one of our trips it was pretty warm with no shade trees. The A/C didn't keep up very well and it was especially warm in the Bedroom. The RV came prewired for 50Amp so adding a second AC shouldn't be too complicated... except finding one. The specs on the ceiling where the wiring is state: 110-125Volt, 60Hz, and here is my problem 16Amps Maximum. I am struggling to find an AC that will meet the 16Amp minimum (especially on start-up). I am looking to add heat to that AC as well. I would appreciate any advice or point me in the right direction.

2022 F150 Powerboost Platinum (purchased Nov 2022, ordered May 2022)
2022 Cruiser Aire 28RKS Purchased Aug 2022

[deadticket8]

The breaker is designed to take a surge on start up. It will trip if it continues to draw an excessive load, which means you have a problem somewhere.

[BB_TX]

ken56 wrote:
Wait, let me throw my wrench into the works here. A 50 amp unit consists of 2 legs of 110 volts coming into the unit. The distribution panel is like one in your home. Every other finger on the bus bar is taken off one side or the other so hooking up any 2 pole breaker will be staggered.....right?
….

Some have a breaker panel with the main 50 amp breaker at the left side and all sub breakers to the right. In that case the slots alternate on hot 1 and hot 2. Like a house.
Some have a breaker panel with the main 50 amp breaker in the middle. In that case the sub breakers on the left are on one hot and the sub breakers on the right are on the other hot.

[enblethen]

Depends on the style of the panel. Some panels have the busses run sideways from the main breakers, while others are more like a residential panel with alternating breaker locations.
We should not be talking two pole breakers as the majority or RVs have no 240-volt items.

[ken56]

Wait, let me throw my wrench into the works here. A 50 amp unit consists of 2 legs of 110 volts coming into the unit. The distribution panel is like one in your home. Every other finger on the bus bar is taken off one side or the other so hooking up any 2 pole breaker will be staggered.....right?

I have a 37 foot TT and only has one 15,000 AC in the living area with ducted into the front bedroom. Mine gets hot too when it faces into the sun and on hot days. That front cap isn't insulated all that well is it. I've considered the Colman Polar Cub, a 9,000 btu unit for the front bedroom.....I know nothing yet of the requirements for it weather or not it's a 220 AC or a 110 unit, all I know is it's expensive therefore I will try the AC mod before I invest in a new air conditioner.

[Grit_dog]

This thread is turning into nonsense real quick.
This is simple. Your camper is pre wired for an AC. Install one and hook up the wires and you’re done, y’all stop rvnetting it!

[dodge_guy]

What I would do is buy a 15k AC and install it where the existing 13.5k is, then move that 13.5k to the new spot. And yes, you want each AC to be on its own leg, no reason to overload one line. Especially with how they wire RV’s. But it should be wired properly already.

[BB_TX]

ScottG wrote:

BB_TX wrote:

thegabrielles wrote:
….
I will check the power on the RV, just and assumption but wouldn't the manufacturer spread the current out evenly on a camper that is prewired for 50amp service... I know what assume means. 🙂

You would like to think that wouldn’t you? I think most are on separate hots but you would not be the first to report them both on the same hot.

Interesting discussion. I still don't see why there is any need to balance. A 50A leg can easily handle 2 AC's even if something like a water heater is running. All three of those running at the same time would still be less than 5000 running watts - well below the 6000 avail. The RV's panel doesn't care - you could max out one leg and have nothing on the other leg without any heat, etc.
………..

The NEC standard is for the normal connected load on a circuit breaker should be no more than 80% of the breaker rating. Two ACs, a water heater, and an outlet or two could easily exceed that.

[thegabrielles]

ScottG wrote:

BB_TX wrote:

thegabrielles wrote:
….
I will check the power on the RV, just and assumption but wouldn't the manufacturer spread the current out evenly on a camper that is prewired for 50amp service... I know what assume means. 🙂

You would like to think that wouldn’t you? I think most are on separate hots but you would not be the first to report them both on the same hot.

Interesting discussion. I still don't see why there is any need to balance. A 50A leg can easily handle 2 AC's even if something like a water heater is running. All three of those running at the same time would still be less than 5000 running watts - well below the 6000 avail. The RV's panel doesn't care - you could max out one leg and have nothing on the other leg without any heat, etc.
How about those large class A's out there with 3 and even 4 AC's purring along in Las Vegas? Do they never run three or 4 at once? It sure sounds like they do when you walk past them..

If I'm missing something, I'd enjoy learning.


EDIT: found this old thread that suggests running three at once (so 2 on one leg) is no problem: Linkaroonie

Although I tend to agree on some Ways my particular case is different, and it may be for some others as well. My truck is a Powerboost, it’s a Hebrides F150 that uses the electric motor to charge up a 1.5KWhr battery, then an inverter. Inverts the signal into 2 3600watt legs. So my generator is 7.2KW on the truck but output is limited to 2X 3600watts. If the two AC are on the same leg I most certainly won’t be able to run both at the same time. A simple rewire to have them on different legs would definitely make sense in my situation.
That being said I can not possibly think of very many situations that I would need 2 AC while boondocking. If I have a power failure and move into the RV for a bit, maybe, but that’s doubtful as well because I wouuohook the truck directly to power my house.
My goal is to find out all the possible solutions, research them all and then make the decision that will work best for me.
I do appreciate everyone’s insight. I’ve learned a lot with all your help already.

[ScottG]

BB_TX wrote:

thegabrielles wrote:
….
I will check the power on the RV, just and assumption but wouldn't the manufacturer spread the current out evenly on a camper that is prewired for 50amp service... I know what assume means. 🙂

You would like to think that wouldn’t you? I think most are on separate hots but you would not be the first to report them both on the same hot.

Interesting discussion. I still don't see why there is any need to balance. A 50A leg can easily handle 2 AC's even if something like a water heater is running. All three of those running at the same time would still be less than 5000 running watts - well below the 6000 avail. The RV's panel doesn't care - you could max out one leg and have nothing on the other leg without any heat, etc.
How about those large class A's out there with 3 and even 4 AC's purring along in Las Vegas? Do they never run three or 4 at once? It sure sounds like they do when you walk past them..

If I'm missing something, I'd enjoy learning.


EDIT: found this old thread that suggests running three at once (so 2 on one leg) is no problem: Linkaroonie

[BB_TX]

thegabrielles wrote:
….
I will check the power on the RV, just and assumption but wouldn't the manufacturer spread the current out evenly on a camper that is prewired for 50amp service... I know what assume means. 🙂

You would like to think that wouldn’t you? I think most are on separate hots but you would not be the first to report them both on the same hot.

[enblethen]

Yes, manufacturer would separate load. The ac A/c unit may not be connected to the 120-volt distribution panel. It maybe coiled in void behind panel. That is why I commented earlier on ensuring it gets connected to the opposite buss. Yes, two A/cC units could be on same side, but along with other appliances and converter could overload. That is "could"!

[thegabrielles]

Awesome, great info! I understand the start up spike on AC units. But did not realize that wasn't measured. Just assumed the rating was the max. Interesting that it wouldn't trip a breaker spiking that high, even for a moment. Again, not an electrician. Just trying to figure this out.
I will check the power on the RV, just and assumption but wouldn't the manufacturer spread the current out evenly on a camper that is prewired for 50amp service... I know what assume means. 🙂

[JBarca]

thegabrielles wrote:


Snip...
The RV came prewired for 50Amp so adding a second AC shouldn't be too complicated... except finding one. The specs on the ceiling where the wiring is state: 110-125Volt, 60Hz, and here is my problem 16Amps Maximum. I am struggling to find an AC that will meet the 16Amp minimum (especially on start-up).
I am looking to add heat to that AC as well. I would appreciate any advice or point me in the right direction.

2022 F150 Powerboost Platinum (purchased Nov 2022, ordered May 2022)
2022 Cruiser Aire 28RKS Purchased Aug 2022

Hi,

I would say you may have miss read/understood the max amperage sticker. The sticker is normally talking about the max constant draw. And are you sure it does not state 15 amp? 16 amp seems odd for wiring size.

I have found "most" RV air conditioners will peak over their normal operating max current upon startup. The inrush current on the compressor will go over for a fraction of a second. The AC units have a hard start or other internal capacitors to help deal with this starting spike. And even then, the startup inrush current will still peg almost double or more over the nameplate max operating current of the AC for a fraction of a second.

For example, many campers, even on a 30 amp camper, come with a 20 amp breaker for the AC unit. I can tell you the AC unit will not pull all 20 amps constantly, but the inrush on a 13,5000 BTU RV AC (older Dometic Brisk Air) can be in the 37 amps range. Yet, the measured normal operating amps are 11.5 amps. If you want to see an amp probe measuring what I am talking about, see my post here on the Sunline forum where I cleaned the AC coils.https://www.sunlineclub.com/forums/f71/cleaning-the-ac-coils-lots-of-pics-10405.html

Here is something you can also do. With the power off, measure the wire gauge in the ceiling for the 2nd AC hookup. It may be 14 AWG which is standard for a 15-amp circuit. If it is 12 AWG, it would be for a 20 amp circuit.

The circuit breaker has a slight time delay in it that helps cover quick large inrush currents. This is why the 37 amp inrush of a 13,500 BTU AC unit that only runs on 11.5 amps normally starts up just fine, that and the addition of hard start capacitors on the compressor. Slow blow fuses (the old screw-in type) can have longer time delays than circuit breakers. This can be why they picked a 20 amp breaker to power an 11.5 amp constant draw AC unit. The wire in the camper had to be 12 AWG, but the normal current was only 11.5, yet the inrush was 37 amps but was fast enough not to trip a 20 amp breaker. In this case, a 15 amp breaker may have tripped as the inrush is too high for the time delay. They breakers are rated at X times higher than the stated constant current.

Hope this helps

John

[BB_TX]

I added a second AC (13.5k) to my 35' 5er. Living in TX and most of my travels in the south/southwest means long travel days in 100 degrees are common. And the trailer would be quite warm after 6-8 hours on the road. The second AC greatly improved the cool down time after setting up. But by bedtime we would shut off the second AC and rarely start it back up on subsequent days at the same location even in very hot temps. Once the trailer was cooled the main 15k AC would keep it cool.

And I agree with comments above about which hot leg to connect the second AC to. Balancing is the key. And if the "other" leg already has several heavy loads (microwave, water heater, converter, kitchen outlets for coffee pot/toaster, etc) it may make more sense to put the new AC on the same leg as the other AC if that hot leg does not have much else on it. 50 amps on each leg is more than enough to run two ACs. And if you happen to have to connect to 30 amp it doesn't matter any way.