Transfering between the inverter and the generator

I have a '97 class C motorhome. I've updated my electrical system as the budget allowed, doing most of the work myself. I spend most of my time off shore power. My power modes in order of frequency of use are:

1) battery power (I have almost no use for 120V power, so this is about 98% of the time)
2) whole house inverter (only used a couple of times a week to power external hard drives for backups, print, vacuum, and use my spin dryer for laundry)
3) on board generator (new addition, will be mostly used for charging and the odd treat of AC on a hot day)
4) shore power

My MH doesn't have a transfer switch. To use the genset, I plug my shore power cable into an outlet in the cable compartment. To use the inverter, I plug the shore power cable into a heavy duty 120V 15A extension cord that runs to my inverter and I turn off the breakers for the converter, fridge, AC, and microwave.

My generator didn't work until a few days ago and wasn't in the picture. So my default mode was shore power cable plugged into the inverter extension cord and excess breakers off. I'd turn the inverter on when I needed it so that it wouldn't draw down the batteries.

Now, the generator works and I'd like to use it during those grey stretches when the solar panels aren't enough. Running outside to unplug and replug the shore power cable when I have inside starters for the genset and inverter is going to get old. But I am especially concerned about flipping breakers regularly as I know they should not be used as on-off switches.

I'd like a manual device that can switch between my inverter and generator from inside the rig and also kill certain circuits when I pick the inverter. I don't like anything automatic and wouldn't want a transfer switch that automatically picks the best source of power for me (yup, I never switch my fridge to auto :) ).

I've looked at some wiring diagrams and think that my best bet involves a sub-panel from my main electrical panel, but all the diagrams I see use shore power as the default mode when it is a very rare occurrence for me.

So I'm looking for some wiring diagram and parts suggestions. I don't know yet if I'll do this work myself or hire out, depending on the technical nature of the work to be done.

Thank you for any insight,

Rae

time2roll
Nomad
Jul 26, 2013
Just plug the shore power into the generator to power the entire panel.

Then move the circuits you want inverter only to a subpanel. The main panel and inverter will feed the transfer switch sending power to the sub panel.

If the inverter needs to only power one or two circuits you could just use one transfer switch for each branch circuit.
Golden_HVAC
Explorer
Jul 26, 2013
There is a automatic transfer switch, about $75 for a 30 amp single pole breaker. You might want a 50 amp two pole breaker that is a bit more expensive - say $120 to $150. With it, you can also control a 20 amp breaker to feed the battery charger while on shore power or generator, but leave it off while on inverter power.

You can install a new 20 amp receptacle to plug in the converter to. The shore line and generator can go into the transfer switch via your stock cord. Then the inverter can go in the "Gen" side, that goes through without the relay being energized. (this saves power). With a two pole transfer switch, have the "Hot" go to both inlets on the "Shore" side, and one output to the RV panel, the other to just the converter new receptacle. The other input goes to the inverter, and do not connect to both sides, so it will not power the converter/battery charger.

By the way, you can use the circuit breakers as switches. It is not the "Best" thing for them, but especially while not under load, it will not harm them. So if the A/C is not running, it is fine to turn on the CB and off all you want to.

Fred.
pianotuna
Nomad III
Jul 26, 2013
Hi,

Shore power--->breaker panel--->items to be powered
Generator with transfer switch feeding the shore power cord. That will default to inverter when the generator is off.

I often use my inverter when on modest shore power and also when drawing heavy loads from the generator. For example the generator can't quite power the air conditioner and the electric water heater at the same time. But it can power the air conditioner and the converter. The converter sends power to the batteries and the batteries power the inverter which powers the water heater.

gen-->shore power cord-->loads (air, fridge and converter)-->battery bank-->inverter-->water heater.

I also have a dedicated inverter outlet in the kitchen which I use almost every day that I cook.
MrWizard
Moderator
Jul 26, 2013
walk into any commercial building
gas station, auto repair garage, machine shop etc..

you will that the MAJORITY of lighting and automated circuits are turned on/off by the CB in the power panel

everytime I see that statement about can't use a CB as a switch, i do a "HUH ?"

and i speak as a 'commercial industrial and residential electrician'

i don't know where that old wives tale came from
but i have replaced a lot more worn out 'switches' than i ever did circuit breakers

if the 'device' is not running at full load, CB make great switches

i wouldn't use it to the turn the roof top A/C on off with full compressor load, instead of the proper controls

but turning of the fridge or the water heater etc, no problem

HECK if you turn OFF the Auto-mode and manually set those to LP only, you never have to worry about them , and don't have to flip the CB, you only have to watch out for the 'converter'
mena661
Explorer
Jul 26, 2013
MrWizard wrote:
w
i don't know where that old wives tale came from
but i have replaced a lot more worn out 'switches' than i ever did circuit breakers
Wow! Excellent info!!!
TravelingRae
Explorer
Jul 26, 2013
Wow, thank you very much to everyone who has chimed in. Right now, I'm mostly worried about using my breakers as switches.

If that's true about the breakers being okay to use as switches, then I really don't need to do anything since I'll only be using the genset once a week or so.

Another thing I'm considering is making my shore power cable accessible from inside. It's right below my converter, which is in my office where all my power use happens. If I could install a hatch over the compartment, I could just bend down and plug the cord in where needed without having to go outside and around the rig. Heck, I could get all fancy and put the outlets on the wall. Wonder if that would be easier than rewiring my circuit panel?

Rae
MEXICOWANDERER
Explorer
Jul 26, 2013
I figure it this way, if I have to do something ten times a day, then I think about maybe making it automated or remote. Otherwise a little exercise is excellent for me. DPDT relays are not expensive and 2 of them connected in parallel gives me sixty amperes switching on both L1 and neutral. If the inverter has a "seek" circuit, three different color LED's allow me the luxury of seeing what is happening in the power department.
mlts22
Explorer
Jul 26, 2013
You might see about buying "SWD" (switch rated duty) breakers and installing those. That way, there would be no worries about using the breakers as primary switches.
TravelingRae
Explorer
Jul 26, 2013
Oh, I like the idea of getting those SWDs! Thanks!

I have no problem with exercise. But I am going to want the genny when it's pouring outside. :)

Rae
pianotuna
Nomad III
Jul 26, 2013
Hi Rae,

Who will start the generator when it is pouring outside?

TravelingRae wrote:
But I am going to want the genny when it's pouring outside. :)

Rae