2 A/C's on 30 Amp Service Question

[spsiever]

So just brought home my new 2017 Rockwood Ultra Lite 8335BS TT and I have (2) ducted factory A/C units.
How do they both work or do they not both work when on 30 Amp service. We are going to a state park that only has 30amp

Thanks in Advanced!

[wmtire]

Originally Posted by spsiever

So just brought home my new 2017 Rockwood Ultra Lite 8335BS TT and I have (2) ducted factory A/C units.
How do they both work or do they not both work when on 30 Amp service. We are going to a state park that only has 30amp

Thanks in Advanced!

Howdy spsiever and welcome to the forums. Usually on 30 amp service (which will require an adapter for you to plug your 50 amp RV into, in case you don't already have one), you will only run 1 air conditioner at a time to keep from overloading circuits.

Hold on a sec and I will edit this post with a lot of useful information.

[B and B]

I beg to differ WMTIRE. First hand experience is that you can run two 15 kbtu AC on a 30 amp service. Start fans on both, low. Turn one compressor on let it run for 15 minutes then add the second compressor. You will be around 25 amps, as low as voltage is not to look it can work. No Microwave, fridge and water heater on propane.

[wmtire]

The below is a copy and paste, and I usually recommend it to those just starting out. Some of it, you may already know, or may not be applicable to your particular RV. You will be able to filter out what pertains to your situation or not. I would read the electric threads and energy management first.

You can just peruse at your leisure:

Basic electric:

Basic RV Electricity - RV Information (RV Maintenance)

RV Electric

I am adding this link for you to explain the TRUE difference between 30 amp (3600 watts) and 50 amp (12,000 watt) service as it's often misunderstood. This link will also explain the adapter I referred to in post #2, to allow you to connect to a 30 amp outlet.

https://www.rvtechmag.com/electrical/chapter3.php

Your very important converter:

RV Converters and Amp Draw - RV Information (RV Maintenance)

Suburban water heater (if applicable to your RV):

http://www.forestriverforums.com/for...tml#post327988

http://www.forestriverforums.com/for...ml#post1527599

Water Heater bypass/crossover valves:

http://www.forestriverforums.com/for...st-103381.html

And the newest addition to help understand what constitutes a true full cylinder in refilling vs exchanging propane cylinders

http://www.forestriverforums.com/for...ng-133760.html


Hope this helps.

[lbrjet]

Would not recommend attempting to run both.

[TheWolfPaq82]

Originally Posted by spsiever

So just brought home my new 2017 Rockwood Ultra Lite 8335BS TT and I have (2) ducted factory A/C units.
How do they both work or do they not both work when on 30 Amp service. We are going to a state park that only has 30amp

Thanks in Advanced!

Is your Rockwood equipped with the "Power Control System" ? My 2018 Cherokee has two AC units that run off 30 amps.
When both are running the PCS...(power system) will shed power to Water heater, refigerators, and AC compressors as needed. I run water heater on propane to take it out of the equation, but FR decided it would be cost effective to add 7 outlets to the refrigerator circuit (which the PCS manufacture does not understand), so when the PCS sheds that circuit, I lose both televisions and all the 120 outlets in the trailer...except for the 3 GFCI outlets.

[elind]

Originally Posted by B and B

I beg to differ WMTIRE. First hand experience is that you can run two 15 kbtu AC on a 30 amp service. Start fans on both, low. Turn one compressor on let it run for 15 minutes then add the second compressor. You will be around 25 amps, as low as voltage is not to look it can work. No Microwave, fridge and water heater on propane.

I agree. I have run my 13.5k & 15k at the same time , just space out the starting and turn off everything or switch it to propane. If the voltage drops my EMS will shut it down.

[ependydad]

Supposedly the Micro-Air EasyStart helps with this. As indicated above, the biggest issue is the start-up of the compressor. If you can mitigate that, supposedly you can run 2 A/Cs on 30amp service.

[aceinspp]

You maybe able to do this but not a good practice as things will go wrong telling new folks you can. Let your conscious be your guide. Later RJD

[gordonsick]

I made a posting on the Berkshire forum at http://www.forestriverforums.com/for...ml#post1573259 on this topic.

In short, I've been able to make it work once and it failed another time. I suspect that the difference is that the time it failed, the campground wiring was undersized and there was a big voltage drop.

But, when it did work, I was able to run both 15K Btu ACs, my Whirlpool residential fridge and an ANOVA sous vide cooker that can draw up to 15 Amps. And, the voltage held up at 110 V.

So, you might want to check the voltage at the campsite to see if there is a power sag.

–Gordon

[Whalenss]

My Isata 5 is 50 amp with 2 a/c. Running both pulls almost 30 amps when under load.

[markb5900]

There is a reason when you have 2 ac's that they make it a 50 amp plug.
You probably 'CAN" make it work, if a, b and c and the moon and stars are aligned perfectly.
Personally if all I have is a 30amp circuit, I just run one AC at a time and don't take the chance of burning up a compressor on one or both of my AC units.

[DouglasReid]

Originally Posted by TheWolfPaq82

Is your Rockwood equipped with the "Power Control System" ? My 2018 Cherokee has two AC units that run off 30 amps.
When both are running the PCS...(power system) will shed power to Water heater, refigerators, and AC compressors as needed. I run water heater on propane to take it out of the equation, but FR decided it would be cost effective to add 7 outlets to the refrigerator circuit (which the PCS manufacture does not understand), so when the PCS sheds that circuit, I lose both televisions and all the 120 outlets in the trailer...except for the 3 GFCI outlets.

What that means is that 30 Amps IS NOT capable of fully supporting your RVs electrical needs. But a Smart Control system is deciding what and when to turn off your individual appliances.

The posters who said that a 30 Amp service will not support two AC units is correct! Each uses 20 Amps and that exceeds the 30 available. Even if starting them up on a time delay sequence when they cycle on and off they aer going to overload and trip the main breaker in the camper or on the pole

Personally Id prefer 50 Amps and not have to worry about what I turned on or when.

[spsiever]

Thanks All, I do have the power control unit, but we will stick to using 1 unit at a time, when the park doesn't have 50 Amp service!

[formerFR]

you absolutely 'CAN' run both AC units, IF you turn them on at separate times, but that does not mean that you 'SHOULD' do it.... but it IS possible. Tripping a breaker is the only negative outcome if the power unit cannot handle both.

of course, most of us experienced RVrs know the limits of our coaches, and mostly only use one AC unit at the time when on less than 50a(100a total) service.... but it IS possible if you almost NOTHING else pulling any power.

[BuzzWolfAR]

Originally Posted by markb5900

There is a reason when you have 2 ac's that they make it a 50 amp plug.
You probably 'CAN" make it work, if a, b and c and the moon and stars are aligned perfectly.
Personally if all I have is a 30amp circuit, I just run one AC at a time and don't take the chance of burning up a compressor on one or both of my AC units.

Totally agree with this. I don't want to be an electrical engineer. I retired to \

[gordonsick]

Originally Posted by Whalenss

My Isata 5 is 50 amp with 2 a/c. Running both pulls almost 30 amps when under load.

Whalenss,
That is a pretty hefty draw. How did you measure it? Was it while an AC unit was starting or when both were running?

There is a heavy draw when the AC starts, and that is why the front and back AC units are coordinated so that they don't both start at the same time.

The sticker on my 15K Btu Dometic doesn't give a lot of the traditional information that one sees on other electrical items. I attach a photo of the sticker.

The sticker says that the unit is 12.9 Rated Load Amps (RLA) under cooling or heating. From The Professor: Compressor Amperage Data | 2011-03-07 | ACHRNEWS I gather that this is the maximum continuous current draw for the compressor with a big 44% to 55% over-capacity.

The sticker also says that it is a 1/4 hp motor, which is 186 watts at 100% efficiency, which amounts to less than 2 amps at 110v. We could suppose that the motor is some old design that is only 25% efficient and take that to 8 amps, which is consistent with the claim that 12.9 RLA includes excess capacity.

Finally, the sticker says that the unit should be on a 20 amp circuit, and that should be more than enough current to start the compressor. It doesn't say what the actual current draw is when starting, since it presumably depends on ambient temperature, compressor temperature (if it ran recently) and some other factors.

So, if one AC unit is running and the other unit is starting, we could theoretically get up to 20 + 12.9 = 30 Amps, which would blow the breaker. But, as you will note, there are fudge factors all over the place in this calculation, so it is unlikely that you will never get anywhere near 30 Amps in the situation where one AC is running and the other is starting, which is be highest load you can expect with two coordinated AC units. And, there is ample evidence in this thread that they are coordinated.

But, there is a final caveat. This all assumes that you are able to maintain 110 volts in all of this, or perhaps have a small drop in voltage. I see two reasons why you may have trouble maintaining 110 volts:

1. You are running a very long power cord to your unit. Perhaps you have an extension cord, or the campground has a very long run to your post without running oversized wire. For longer runs, you need bigger wire, and #10 wire would be the minimum. Since I have 50 amp wiring, I'd have way more than that, with #6 wiring on the three conductors and a smaller #8 for ground. Thus, if there is a long power cord with only #10 wire, it must be the campground wire.

2. The campground could be feeding a lot of circuits from one transformer, which are all running air conditioners, and it hasn't enough capacity to feed them all 30 amps, even though they are each rated at 30 amps.

If you are getting less than 110 volts, then your compressor motor could try to pull more amps than its rating, or the electronic controls could throw a fault and shut off the air conditioner. That is how I got my E7 fault when two AC units didn't work.

This is a long and windy post. The bottom line is that you can run two 15K Btu AC units on 30 amp power, as long as your wiring and the campground wiring is big enough for the distance it is covering, and the campground transformer is capable of delivering 30 amps to all its circuits simultaneously. To confirm that the wiring is good enough, you could start one of the AC units and watch the voltage with a multimeter as you attempt to start the other. I'm not sure how low the voltage can go before you get into trouble. That would be an interesting fact for us to learn with testing. If the voltage doesn't dip much below 110 volts, then you are safe to run two AC units on 30 Amps.

–Gordon

[twdenman]

Originally Posted by spsiever

So just brought home my new 2017 Rockwood Ultra Lite 8335BS TT and I have (2) ducted factory A/C units.
How do they both work or do they not both work when on 30 Amp service. We are going to a state park that only has 30amp

Thanks in Advanced!

Jayco is putting two 11,000 btu A/C units in their 30 amp Class A's. Some kind of "Power Management System", that controls the rear A/C compressor when another "load" is turned on. ie microwave. The fan remain on but the compressor stops until the load is turned off. Maybe something new?

[Flybob]

Most of those that said you can run two 15K ACs at the same time have qualified that statement by saying you need to start them at different times. The problem with this is that after the initial start this is virtually impossible to do unless you want to be up all night turning ACs on and off. The first time both try to start close to the same time, the breaker will trip. As much as we would like to defy the basic laws of physics, we can't. Compressor and fan draw about 15A ea

[TheWolfPaq82]

Originally Posted by gordonsick

I made a posting on the Berkshire forum at http://www.forestriverforums.com/for...ml#post1573259 on this topic.

In short, I've been able to make it work once and it failed another time. I suspect that the difference is that the time it failed, the campground wiring was undersized and there was a big voltage drop.

But, when it did work, I was able to run both 15K Btu ACs, my Whirlpool residential fridge and an ANOVA sous vide cooker that can draw up to 15 Amps. And, the voltage held up at 110 V.

So, you might want to check the voltage at the campsite to see if there is a power sag.

–Gordon

It's not so much for the voltage drop as it is for..."Amperage Spike" The trailer is wired to only handle so much amperage...30A / 50A you keep hammering away spiking the Amps all the time, you'll be looking at degradation of the wiring over time.