Unless you have a high dollar diesel pusher with a litany of electrical appliances and air conditioners, a 30 amp shore
power connection is adequate with the exception of running air conditioners. When we ordered our Quantum JM31 we added the optional two air
conditioners and energy management system because years of experience using
an RV in hot weather has educated us. This option deletes the 15K BTU air conditioner
in the front and replaces it with an 11K BTU unit and adds a second 11K BTU
unit in the rear. The energy management system monitors the overall current
draw from either the shore power connection or the generator and sheds
the rear air conditioner if the current exceeds 30 amps. The front air conditioner
can be shed if the current demand again exceeds 30 amps while the rear unit is
shed. The majority of the time we are at a campsite with a 50 amp connection and when the weather is hot would prefer not to shed either
unit when the wife is using the washer/dryer, the microwave, or the induction
cooktop.
We thought about how to modify the electrical system to power the air conditioners from a second leg of the 50 amp pedestal connection without affecting the standalone 30 amp system. The following block diagram shows what we came up with. Because all the power to the motorhome would need to be off while making the connections, we did not want to make this modification until we had everything on hand and could do it in one day. So this has been an ongoing project for over a month ordering parts and making mods that did not require the power to be turned off. The modification is now complete and we are pleased with how it turned out.
Do not connect the bare wire safety ground on the second 30 amp power cord.
The plan was to install a second transfer switch to connect the other leg of the 50 amp pedestal defaulting it to the main 30 amp input. In that manner the coach would operate in the original configuration as long as the second 30 amp bulkhead connection was not used. To make the circuit work the way we wanted we had to install a two circuit breaker box with two 20 amp circuit breakers to serve as the breakers for the two air conditioners. The original two 20 amp circuit breakers in the power distribution center were repurposed as two 20 amp duplex outlets to be used in the winter for an electric blanket and a space heater. We were not able to find a flush mount two circuit breaker box and had to modify a surface mount version to be flush mountable. Since it was important to keep the power management system ampere monitor in the circuit when the air conditioners were operating in the normal 30 amp mode a junction box was necessary. The junction box allowed the 30 amp feed to be split between the power distribution center and the second transfer switch placing both after the ampere monitor. We were able to locate and purchase a 30 amp twist lock bulkhead socket just like the factory installed one. That made the modification aesthetically pleasing and continued the factory theme of preventing insects from entering the RV via the power cable.
All the modifications had to be confined to under the bed or the outside compartment near the shore power inlet. Space is limited with the fresh water tank and other items already installed there. Removing the panel near the shore power connection proved that area to be the best location for the transfer switch. The upper run of 10-2 Romex is coming from the junction box near the power distribution center and provides standard 30 amp power to the shore input of the transfer switch. The connection below that is the generator input of the transfer switch and is connected to the second 30 amp bulkhead socket on the exterior of the motorhome. The output of the transfer switch goes to the breaker box with the air conditioner 20 amp circuit breakers.
The area around the bottom of the bed is framed and then covered with luan. There was an opening of the frame near the power distribution center that was perfect to fit the breaker box for the air conditioners. We first cut a piece of 1/2 inch plywood that would fit in between the framing and then mated the breaker box to that plywood.
On each side of the bed we installed a 20 amp duplex outlet fed by the original 20 amp air conditioner breakers. We re-labeled the breakers CKT #1 and CKT #2.
First we ran the system with only one power cable connected to the main 30 amp shore power input and turned on both air conditioners with the thermostat set to 70 degrees to insure the compressors would run. Our garage HVAC is at 74. The Power Control System displayed a current draw of 20 amperes. Not enough to cause the rear air conditioner to shed but a clear indication the current monitor is seeing the air conditioners.
The next step was to turn off the air conditioners and connect the second leg from the Bulldog to the auxiliary 30 amp connector. We waited for the transfer delay and after hearing the switchover turned the air conditioners back on. You could hear the compressors running but the Power Monitor System was only showing 4 amperes total current draw from the main 30 amp shore connection. The total air conditioner load was removed from the standard shore connection and moved to the second leg of the 50 amp pedestal connection. If we remove the second 30 amp connection the transfer switch will place the two air conditioners back on the standard 30 amp shore power connection and the entire motorhome again operates from a single 30 connection.
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