Inverter subpanel question

[handirifle]

So I installed my inverter in my RV. Currently has 2 batteries, soon to have 4, running it. The inverter is currently set up so that I plug a cord into the outlet on the inverter, and through adapters to my 50amp inlet on the side of the RV. I eventually want to add a sub panel and separate the circuits I use with it from those I do not. At present I have to shut off things I will not/can not use, like AC units, converter, etc.

I am thinking I can add a 30 amp sub panel and move the breakers I WILL use, from main panel to the sub panel, and power them through a 30 amp breaker on the main panel when connected to shore panel and from the inverter through a DPDT manual switch, like this one P&S 1228-I : SW MAN CONTRL 30A 120/277V (DPDT) MAINTAINED CONTACT | Gordon Electric Supply, Inc..

I have read of issues of back feeding concerns ruining the inverter, so I am asking on here. If I use a switch like this, I am thinking of running a common ground to the existing ground connection, and running the single hot and neutral lines through the manual switch. This switch is a 3 position, that is either open, or connected to one set of leads or the other, I believe.

If I am thinking this through correctly, I can have the power and neutral from the main panel on one side, going to the sub panel, and the power and neutral from the inverter, going to the sub panel, on the other side, and never the two shall meet . Both panels would be grounded to the same source in the RV.

Am I missing anything?

Before you ask about auto transfer switches, I am leery because I have read a lot of warnings where these can allow the back feeding I am concerned with and frying the inverter.

 

[Mendonsy]

I suspect it all depends on the inverter that you have. Our Xantrex 3kw has both DC and AC inputs. It acts as a charger for the house batteries and also supplies power to the outputs when plugged into shore power. The manual specifically says that you should never connect the shore power directly to the inverter outputs.

 

[handirifle]

Mine is not a charger and has no connection for any AC input. I am strictly talking AC output from inverter to the panels. Two seperate power sources for the trailer, sepersted so only one supplies at once.

 

[Mendonsy]

It seems like your idea should work OK as long as the inverter output can never be connected to the shore power. That DPDT switch should solve the problem as long as it can handle the inrush current of the 30a panel.

 

[handirifle]

Its rated for a 2hp motor so it ought to be ok. 30amps constant. I want to make the transition as seamless as possible. Right now it is plug in the power cord (dry camping only) to the inverter, turn off unwanted breakers, and turn on inverter.

This way I will leave inverter output plugged in, and control with DPDT switch. That way even if the inverter accidentally got turned on when plugged into shore power, it would do no damage. The inverter powered circuits will only have ground wire in common with main.

 

[Mendonsy]

Yeah, I think it should work OK. That switch just appears a bit small for a 30 amp, but if that's what they are rating it at then it should be fine.
Motors draw a lot of current while starting, but it's a "soft" load because it takes a few cycles for the magnetic fields to build up. It's the solid state stuff which starts up as a dead short for the first half cycle that is hard on switch contacts.

 

[handirifle]

I don't anticipate starting it up with a load on it. Things will come on only as needed. Biggest draws for this will be the microwave, on occasion, and the wife's hair dryer.

 

[Tractor Seabee]

Maybe you should work out a wiring diagram on how you plan to do this. We can better analyze for any pitfalls or problems and add to the ideas. Basic premise I always use is KISS. Keep it simple shipmate.

I had a 40' motorhome once! It had only a 30A shore power cord, two AC units, and only 4 circuits. Crazy, always shifting loads and tripping breakers and could only run ACs one at a time. I installed a standard 100A panel with 50A main in a closet and a 50A shore power cord. Then had 10 circuits. End of problems except when on generator, back to load shedding. Luckily the generator was a 240V output using only one side pf it so that helped. The original was you had to plug the SP cable into the generator manually. Needless to say I installed a transfer switch.

Ron

 

[handirifle]

I tried to draw it in Word Draw but it had about 100 "objects" and tried to select them all and accidentally deleted it. Not going to try it again. If I can explain. DPDT switch, will have common (center) contacts with hot and neutral from the inverter. Depending on switch position, these will connect to hot and common circuits of either the sub panel (on one side) or the main (on the other side). Ground will be common to all three.

 

[plowhog]

I plug a cord into the outlet on the inverter, and through adapters to my 50amp inlet on the side of the RV.

I don't understand that at all. You are using the inverter like it is shore power, heating up all the plugs and appliances in your RV?