When I got to my customers 28′ Studio ATC Toyhauler, he had already purchased and installed some products in his trailer but was having issues. He installed the SPS (Smart Phase Selector) unit from AM Solar, Multiplus 3000, BMV 712 battery monitor and upgraded the stock solar charge controller to a Victron 100/30. Neither of the AC units would run off the Onan 5500 generator or inverter, the breakers on the generator would trip and the existing 200 watt solar panel would not keep the batteries charged when not in use. When running high demand loads like the AC or microwave the inside lights would flash and inverter would fault out with low voltage notifications.
Additions were to include my 700 watt solar package and a Color Control GX inside the RV for the display, control and data logging. I was able to use the midnite circuit breakers on both solar charge controllers in the same baby box. I didn’t like the way the inverter was mounted with wood so that would get secured better. I like to mount the sensitive electronics above the water lines as it is too easy for a small leak to form and take them out. The 6ga wires going into the inverter are critical to make sure there is no loss of voltage. There are better choices than the stereo grade buss bars when looking for long lasting tight connections. The biggest issue, so I thought was the battery wiring, there was some 2ga and some 4ga completing the circuit and knowing the inverter could pull a continuous ~250A it all needed to be 4/0. Since I was redoing the wiring I also cleaned up the stock DC wiring that was left to accommodate most battery configurations by ATC.
1st Test Run
So I proceed to test the system with AC unit for a load, no low voltage alarms but still not right. The load would make the inverter and SPS unit go into studder issue and the compressor would not start. I tried running the Onan and then starting one AC unit with same issue, the generator would not carry the load? I played with the system limiting the amperage from the Onan to 30A allowed the SPS to start the first AC unit, then setting it up to the 42A that the 5500 Onan can provide allowed the second AC unit to start. So I get online and dig deeper, the SPS unit is designed to run whole trailer on one inverter but has fine print that states that the AC units require EZ starts to operate. I was not able to get confirmation that this is the problem.
After completely removing the SPS from the system everything works like it should and did prior. The AC will start and run from battery or Onan and there is no more stuttering from the inverter. The customer had the existing batteries and that is the weak link of the system now. Batteries that will run an inverter need to be Lithium or Deep Cycle. What Battery is best for my RV?
To SPS or not to SPS?
The SPS (Smart Phase Selector) is meant to have a one leg inverter power both legs of the trailer. It is advertised as a solution to power every outlet. The price of the SPS is $600 and then you will need to install an EZ start $320 on each AC unit. There are options and I think I would consider an inverter on both legs before the SPS as they are very similar in cost. When I add an inverter to a trailer I will either put in on one leg or convert the whole trailer to a one leg system, my trailer has been set up this way for over 2 years without issues.