Adding Second A/C to 50 Amp TT

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"!

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. :)

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

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.

Thanks everyone for the great answers. I'll definitely look into the mod on my current AC and check the ductwork. Maybe if I can make that system more efficient I wont have to worry about adding an AC.

GottaRunGottaCamp wrote:
here is a mod, that will improve your AC unit
clicky

OP, I have a 32' with a large slide and only 1 15K AC unit as well. We have always struggled in the hot humid summers to keep up with cooling. The AC would be on all the time in the summer at the lake without tree cover. We put reflectix in the windows to prevent as much heat coming in and we got the window screens on the outside to prevent heat as well. It was better, but the AC would still run all day long and it would be cooler, but never got to temp during the day.

Last spring I did this mod and it was an amazing difference. It was so effective that my FIL asked me to do his, and we camped with friends in Tennessee and they asked for help modding it too.

The AC is so horribly designed, you get plenty of cold air that dumps into that box, then loses air pressure and doesn't go into the ducts and ultimately cool off the camper. Putting in those channels isn't perfect, but greatly improves the airflow and reduces the turbulence and noise from the box that it used to dump air into.

When we were at the lake this past summer after the mod, I came in at one point and the AC was off. I thought one of the kids might have messed with it, but I looked and it had just cycled off because it had hit the set temp. I was amazed, the mod really helped!

That said, if you add a second AC, I would also recommend that you add the Soft Start capaciter to your existing and your new unit. They will really lower the startup draw of the AC unit. It puts a lot less stress on your wiring and your AC.

afidel wrote:
Before investing in a second AC I'd tear apart the ducts, look for missing tape, disconnected hose segments, etc.

Check things like this

A Second A/C is easy to install. Here's my installation project

here is a mod, that will improve your AC unit
clicky

Before investing in a second AC I'd tear apart the ducts, look for missing tape, disconnected hose segments, etc. There's a very good chance your AC can keep things cool if it's properly installed, is just probably not installed correctly. A 20' cheap boroscope will allow you check to see if the vent is cut, kinked, or otherwise damaged.

In short you probably don't need to brute force your cooling with a second AC, you probably just need to use the cold your current AC can produce more efficiently by fixing the piss poor assembly job done at the RV factory.

Thanks for the responses. This AC would not be ducted. The wiring is indeed there, I checked today. I only need a unit to keep the bedroom and bathroom cooled (or heated) in extreme temps. I think a smaller unit may be lighter as well. Hard to find ones with a heat pump though.
totally sure where that leg goes to in the Power Distribution. There would not normally be an issue unless I am using my truck to power it. The truck has a 7.2KW inverter built into it. Technically it works as two 3600 Watt generators. The more balanced the load the better chance I would have with the truck keeping up. I highly doubt there would be a need for that but another Hot weekend in Talladega and I may want it... but need, not really. Outside is where we want to be.