Auxiliary power for air conditioners

[Bob Nodine]

This in not a post about adding a second air conditioner and is as the title says auxiliary power for the two air conditioners. We ordered our 2022 Quantum JM31 with two 11K BTU air conditioners and a power management system. When the air conditioners are operating with both compressors running they add a total combined ampere draw of about 18 amps to the 30 amp total. If other high current devices are turned on with the air conditioners and the total ampere load exceeds 30 amps the rear air conditioner is shed. The front unit will also shed if the load continuers to rise keeping the total below 30 amps. This works well when the weather is not hot but when the wife starts using the washer/dryer, microwave, and induction cook top and the outside temps are in the nineties, cooling is limited. We often camp in hot weather and almost always have a 50 amp connection at the pedestal. We started thinking about how we could modify the motorhome electrical system to put the two air conditioners on the second leg of the 50 amp service but still leave the power management system in control of the air conditioners if we only have a 30 amp service. This has been an ongoing project for over a month and we recently completed it. We are pleased with the outcome and have documented the modification in our blog. It is a long description so we are not posting it here but if you are interested in the details please go to our blog in the link below. We understand that most owners would not want to go to these extremes but tinkering with RV's is our favorite hobby and pass time.

[paulwadley]

Hi Bob

Good write up in your Blog. I read the entire article.

Paul

[Bob Nodine]

Originally Posted by paulwadley

Hi Bob

Good write up in your Blog. I read the entire article.

Paul

Thanks Paul.

[10scDust]

I read it all too, now I am going to copy it for future reference if I decide I need to do the same. Right now we don't travel enough during the warmer weather because the DW has not reached full retirement yet, her decision,=.

[TurnerFam]

right, and without reading 'all' of your details, I suppose you have basically created a 'secondary' shore power inlet option, providing power to ONLY the two air conditioners, separately, from each 'leg' of the 50amp power(which is a double-pole 50amp 240v breaker/outlet, the same at most any rv park), and using the 30amp campground outlet for the RV's other uses thru the 'normal' 30amp shore cord.

[ducksface]

I haven't yet read the blog, but I will.
My ac unit is on a switchable circuit.
It has two 20 amp breakers in case I decide to add a second ac unit later. A flip of a switch and it's all segregated from the transfer switch.

A bit of an aside:
I'm fairly certain it Will be a minisplit we add if we do add a second a.c..
24.1 has room under the bed for the head unit and room in the trunk(or under the coach or on the bumper for the outside unit.
Maximum effeciency, minimum noise and easily to buy and easy to fix.

[OldWEB]

Wow! I applaud you for all that time and energy. Nice job.
There are some nifty ideas in there.

My concern would be that you now have a 50A breaker (pedestal) protecting the majority of wiring/equipment, that is not how The Code was written.
If/when I want to install a second A/C unit, it would be wired to a #12 cabtire that I would plug into the 20A receptacle on the pedistal. Also, with a washer/dryer and induction cooktop, why was a 50A shorepower not installed?

[Bob Nodine]

Originally Posted by OldWEB

Wow! I applaud you for all that time and energy. Nice job.
There are some nifty ideas in there.

My concern would be that you now have a 50A breaker (pedestal) protecting the majority of wiring/equipment, that is not how The Code was written.
If/when I want to install a second A/C unit, it would be wired to a #12 cabtire that I would plug into the 20A receptacle on the pedistal. Also, with a washer/dryer and induction cooktop, why was a 50A shorepower not installed?

I knew someone would bring that up. Circuit breakers are sized to keep the wire from overheating. You are correct that if we were drawing 50 amps from either leg the 10-2 wire would overheat as it is rated for only 30 amps continues duty in open air. On the main leg the coach has a 30 amp breaker so if the current draw exceeds 30 amps that breaker will disrupt the current long before the 50 amp breaker at the pedestal has a chance. On the other leg with the two air conditioners each one has a 20 amp breaker that will trip. If there is a short circuit between the 30 amp and the 50 amp or the 20 amp and the 50 amp the 50 amp breakers will trip. There can be no long term current above 30 amps that will overheat the wire.

[Chance]

Originally Posted by Bob Nodine

....cut.... When the air conditioners are operating with both compressors running they add a total combined ampere draw of about 18 amps to the 30 amp total. ....cut....

That’s impressive if they can run on +/- 9 Amps each. Did you measure that yourself or take it from Coleman specs?

Two 11,000 BTU/hr air conditioners seems an excellent option for RVs where 15,000 BTU/hr just isn’t enough.

[Bob Nodine]

Originally Posted by Chance

That’s impressive if they can run on +/- 9 Amps each. Did you measure that yourself or take it from Coleman specs?

Two 11,000 BTU/hr air conditioners seems an excellent option for RVs where 15,000 BTU/hr just isn’t enough.

The air conditioners are made by Dometic and they look like Brisk Airs. The current reading was a live reading from the Hughes Watchdog 50 amp pedestal monitor. It is a Bluetooth device and we monitor it with our phone. Here is the screen capture from my phone while both air conditioners were running with the compressors on on Line2 of the 50 amp service in my garage.

[Chance]

Originally Posted by Bob Nodine

The air conditioners are made by Dometic and they look like Brisk Airs. The current reading was a live reading from the Hughes Watchdog 50 amp pedestal monitor. It is a Bluetooth device and we monitor it with our phone. Here is the screen capture from my phone while both air conditioners were running with the compressors on on Line2 of the 50 amp service in my garage.

Thank you for information Bob. I was not aware Dometic had an energy efficient A/C in the 11,000 BTU/hr range that competed with the Coleman Power Saver series. The Coleman PS1 is rated at just under 10 Amps at 95 F outside and 80 F inside with 50% relative humidity.

Your Dometic may be even better depending on temperatures at the time you took reading. Power requirements change quickly at different inside and/or outside temperatures. Inside humidity also affects power consumption.

Thanks again, I’ll look at Dometic specs for comparison. Really glad to see A/C manufacturers trying to make air conditioners more efficient. There is still opportunity for improvement, but for now it’s a welcomed start.

[Bob Nodine]

Originally Posted by Chance

Thank you for information Bob. I was not aware Dometic had an energy efficient A/C in the 11,000 BTU/hr range that competed with the Coleman Power Saver series. The Coleman PS1 is rated at just under 10 Amps at 95 F outside and 80 F inside with 50% relative humidity.

Your Dometic may be even better depending on temperatures at the time you took reading. Power requirements change quickly at different inside and/or outside temperatures. Inside humidity also affects power consumption.

Thanks again, I’ll look at Dometic specs for comparison. Really glad to see A/C manufacturers trying to make air conditioners more efficient. There is still opportunity for improvement, but for now it’s a welcomed start.

Here is a photo of one of the units on our Quantum:


The specifications on the Dometic 11K unit , Model B59530.71X which we have, claims a CRLA of 8.6 amperes and a fan current of 2.5 amperes. That tells me the current draw could be as high as 11.1 amps depending on conditions. Our garage is at 74 degrees so when we tested the air conditioners with the thermostat at 70 degrees the head pressure was probably not very high. That could explain the low current we measured.

Here is a link to the Dometic 11K unit:
https://www.dometic.com/en-us/outdoo...k-ii-air-20784

Here is the specifications from the manual and a photo of one of the units on our Quantum.

[Chance]

I found the following specs for an 11,000 High Efficiency Dometic Brisk II Evolution and it’s listed at 1,316 Watts. The Coleman 11,000 BTU/hr Power Saver is listed at much lower power requirement (see below). However, I don’t know how new this data is for either unit. I’d want to know that if buying.

https://www.dometic.com/en-ca/outdoo...specifications

Also, the Dometic power consumption is based on ISO 5151, whereas Coleman use A.R.I. to determine running Watts. If I recall correctly, the two tests are similar, just that one is more popular in Europe and the other in North America.

Dometic mentions their unit is quiet, but I haven’t seen sound data to compare.


.

[Bob Nodine]

Originally Posted by Chance

I found the following specs for an 11,000 High Efficiency Dometic Brisk II Evolution and it’s listed at 1,316 Watts. The Coleman 11,000 BTU/hr Power Saver is listed at much lower power requirement (see below). However, I don’t know how new this data is for either unit. I’d want to know that if buying.

https://www.dometic.com/en-ca/outdoo...specifications

Also, the Dometic power consumption is based on ISO 5151, whereas Coleman use A.R.I. to determine running Watts. If I recall correctly, the two tests are similar, just that one is more popular in Europe and the other in North America.

Dometic mentions their unit is quiet, but I haven’t seen sound data to compare.


.

The two units seem close on specs and it all depends on how you read it. The Coleman states 1316 watts if the inside temp is 72 and the outside temp is 120 which places it in the same range as the Dometic. I do see the Coleman states 10.0 amps at full throttle and the Dometic 11.1 amps. Don't know how they would compare on noise and don't see any data on that. We once installed a 9000 BTU Coleman on a Scamp fiberglass camper and it would run from our Honda 2000 generator. My guess is the Coleman is not as noisy as the Dometic. I can tell you that we installed the Wackoo silencers and when using the generator cannot hear the air conditioners over the generator. We were out doing some testing yesterday running on the generator and when I walked back to the bedroom had to get very close to the rear unit to tell it was running.

[Chance]

Either air conditioner model would likely trigger the same load shedding conditions you made modifications to avoid, so probably doesn’t make much difference anyway.

The standard RV is limited to 30 Amps, or 3,600 Watts (less than generator rating at sea level), so if you have both Dometic pulling 1,300 Watts each, or 2,600 Watts combined, it doesn’t leave enough excess (1,000 Watts) to power the microwave or even a typical hair dryer.

If Coleman only pulled 1,075 Watts each, it would only leave 1,450 Watts free (3,600 — 2,150) assuming nothing else was running, and that’s still not enough for microwave, hair dryer, or some coffee makers.

Since RV shouldn’t pull 30 Amps for very long anyway, the concept of running both air conditioners on 30A service or 4,000 Watt generator is essentially conditioned on very little else running at same time.

I personally like the 2 X 11,000 BTU/hr A/C design concept on 30A service, but know it wouldn’t work for everyone. It would not bother me if one A/C turned off for a few minutes while I nuked dinner or made coffee, but understand why you modified the system. Nice job, and thanks again for sharing information.


P.S. — Perhaps air conditioners that were just a bit more efficient and a slightly smaller microwave like now used on some compact motorhomes would make a big difference. In milder weather when A/C require less power, it may already work fine as is. I’ll be interested in hearing what you discover/experience when limited to 30A service.

[vjb1950]

Originally Posted by Bob Nodine

This in not a post about adding a second air conditioner and is as the title says auxiliary power for the two air conditioners. We ordered our 2022 Quantum JM31 with two 11K BTU air conditioners and a power management system. When the air conditioners are operating with both compressors running they add a total combined ampere draw of about 18 amps to the 30 amp total. If other high current devices are turned on with the air conditioners and the total ampere load exceeds 30 amps the rear air conditioner is shed. The front unit will also shed if the load continuers to rise keeping the total below 30 amps. This works well when the weather is not hot but when the wife starts using the washer/dryer, microwave, and induction cook top and the outside temps are in the nineties, cooling is limited. We often camp in hot weather and almost always have a 50 amp connection at the pedestal. We started thinking about how we could modify the motorhome electrical system to put the two air conditioners on the second leg of the 50 amp service but still leave the power management system in control of the air conditioners if we only have a 30 amp service. This has been an ongoing project for over a month and we recently completed it. We are pleased with the outcome and have documented the modification in our blog. It is a long description so we are not posting it here but if you are interested in the details please go to our blog in the link below. We understand that most owners would not want to go to these extremes but tinkering with RV's is our favorite hobby and pass time.

I see no place to get to your blog to read

[Bob Nodine]

Originally Posted by vjb1950

I see no place to get to your blog to read

It is the link at the bottom of my signature and should appear in each post I make.