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Old 03-20-2013, 07:55 PM   #1
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Running 2 ACs on 30 amp w/ auto select?

I read awhile back online about a device that could be wired inline with both AC-1 and AC-2 that would cycle them automatically so that neither compressor ever started at the same time. I guess you could describe it something like an automatic single pole double through device that keeps the power from never spiking and blowing the breakers on a 30 amp shore side system. I have searched and searched, and don't seem to be able to come up with the right terminology to find this simple device again. Any help would be greatly appreciated.
Thanks, Airdoc
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Old 03-20-2013, 08:32 PM   #2
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Are you saying that it prevents the two ACs from cycling on at the same time, but allows both to run together?

Wow, OK, the peaks aren't together, but still, I would have thought that there's more current draw than one 30A circuit could take.
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Old 03-20-2013, 08:38 PM   #3
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I recall seeing that system a loooong time ago. To me, it doesn't allow for any extra cooling, it simply moves the cooling from front to rear in a timed cycle.

When I added a second AC, I went for a second power inlet. I run the standard 30A for the trailer and main air, plus a 20A for nothing but the rear. In HOT weather, both Airconditioners run almost all of the time.
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Old 03-20-2013, 08:45 PM   #4
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Quote:
Originally Posted by airdoc View Post
I read awhile back online about a device that could be wired inline with both AC-1 and AC-2 that would cycle them automatically so that neither compressor ever started at the same time. I guess you could describe it something like an automatic single pole double through device that keeps the power from never spiking and blowing the breakers on a 30 amp shore side system. I have searched and searched, and don't seem to be able to come up with the right terminology to find this simple device again. Any help would be greatly appreciated.
Thanks, Airdoc
There is an automatic device that does just what you are seeking. It is from Intellitec, and IIRC is called the Auto Energy Selector Switch. You can run 2 loads thru the switch from a single breaker. Large motor homes use this device when they run out of breaker space and still want to add more circuits.

PM me if you want the part number.
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Old 03-20-2013, 08:46 PM   #5
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Originally Posted by airdoc View Post
I read awhile back online about a device that could be wired inline with both AC-1 and AC-2 that would cycle them automatically so that neither compressor ever started at the same time. I guess you could describe it something like an automatic single pole double through device that keeps the power from never spiking and blowing the breakers on a 30 amp shore side system. I have searched and searched, and don't seem to be able to come up with the right terminology to find this simple device again. Any help would be greatly appreciated.
Thanks, Airdoc
No way in the world is that practical.

If it was, you would not be able to use a single light bulb, as well as having to shut off the Univolt.

Running 2 AC's is OK, but wire for it properly.

Andy
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Old 03-20-2013, 09:10 PM   #6
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As I recall all the device did was cycle from one AC unit to the other, but only one was on at a time. So the distribution of air may be better, but the capacity is the same, effectively one AC. Since most running AC units take in the range of 14 amps, two at the same time on a 30 amp circuit with any additional load like the refrigerator, the converter/charger etc would push the system over the edge and trip the main breaker. It is not just starting load you have to be careful with. The total usage of energy is also a factor.

Some Airstreams I have had used a manual switch to allow you to either operate the microwave or the AC unit, but not at the same time. The 310 motorhome I had only allowed the rear AC unit to run when the generator was on, a really stupid design. There was not even an option to run the back AC on shore power at any time.
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Old 03-20-2013, 10:12 PM   #7
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Hi, I was going to get one of these years ago when I had my "Mac Tools" truck; It had two air conditioners and when running both at the same time, It was a huge load on my generator when they both cycled at the same time.
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Old 03-20-2013, 10:26 PM   #8
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The Dometic A/C units have a "compressor disable" wire pair to facilitate energy management.

I've thought about setting up something simple to do this and found a current-sense relay at Grainger that could be wired into the circuit for the front A/C (there's just a window that the hot wire goes through, much like an ammeter), and when the current exceeds some limit -- 5A or so -- indicating that the front compressor is on, close the circuit for the compressor disable line to the rear A/C.

Never done it because we aren't camping in the summer on 20a as often.

You can sometimes run both A/Cs on 30a if they are on low fan and you shut off everything else including the fridge and the converter.
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Old 03-21-2013, 06:19 AM   #9
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The Dometic A/C units have a "compressor disable" wire pair to facilitate energy management.

I've thought about setting up something simple to do this and found a current-sense relay at Grainger that could be wired into the circuit for the front A/C (there's just a window that the hot wire goes through, much like an ammeter), and when the current exceeds some limit -- 5A or so -- indicating that the front compressor is on, close the circuit for the compressor disable line to the rear A/C.

Never done it because we aren't camping in the summer on 20a as often.

You can sometimes run both A/Cs on 30a if they are on low fan and you shut off everything else including the fridge and the converter.
Jammer,

You must be referring to the 2 yellow 'load shed' wires found in the wire bundle when you install the unit. These are for use in a 'Smart Energy Management System' also made by Intellitec, which is a load sense-driven load shed relay board. This is generally installed at the breaker box, or comes installed with Intellitec's Smart EMS breaker board and will not allow certain loads to over-draw the set parameters of the system. It determines the load using the neutral of the feed into the main breaker as it passes thru a current sensing ring

In large motor homes, this system keeps the amp draw below 50 amps on rigs that have 3 roof A/C units, washer/dryers, electric water heaters and other high load appliances.
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Old 03-21-2013, 03:00 PM   #10
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Lew,

Yep, those are the wires.

Just for fun, here's the relay I was going to use:

https://new.grainger.com/product/DAYTON-Relay-15V827

Who knows, I still might end up doing it. Poor man's energy management, I guess. The hot wire to the front A/C goes through the donut, then there are hot and neutral connections to terminals 1 and 2 that power the electronics in the relay, and terminals 3 and 4 (or maybe 5 and 4 -- one's n.o. and the other's n.c.) go to the yellow load shed wires. I think it could be shoehorned into the breaker box, and since the yellow wires carry very little current it would be easy to run 24 gauge wire right across the ceiling for those.
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