I have an older RV without a transfer switch. I have a hard wired 30A cable in a compartment. It can be plugged in three ways:
1) to a shore power outlet
2) to the generator outlet
3) to the inverter outlet
My main power source is the inverter with the generator being my backup and shore power being a treat.
It is going to quickly become a pain to have to go outside to unplug the shore power cable from the inverter outlet and plug it into the generator outlet. Moreover, my electrical panel default position is a bunch of breakers off, so I have to switch them on before running the gen set. It is not good to use breakers as on/off switches with any sort of regularity.
So it looks like it’s time to consolidate all of that and get a transfer switch. I am looking at my options and see that most offer only two sources of power rather than three, and most are automatic. I also see that some electrically-minded folks have designed their own systems. I’d love to go that route.
What I am envisioning is something that would plug into both the genset 30A outlet and the inverter 15A outlet and into which I could plug the shore power cable. It would also give me an option of which circuits to have live.
The device would be accessible from inside and have a manual switch that would let me pick either the generator or the inverter, but would not start either automatically. So I could put it to inverter, walk to the living room, turn on the inverter, and only my inverter-friendly circuits would come on. If I picked the genset, I’d walk to the kitchen, flip on the remote generator starter, and all my circuits would be live.
Another thought is that surely a 30A splitter must exist? Something I could plug my shore power cable into and which I could then plug into two different outlets, only one of which would be live at a time?
I’m obviously not an electrically-minded person. 😀 But I’m starting to think I need to find myself an RVing forum so I can find some electrically-minded people to bounce ideas off of.
Here’s what I have done with my class C.
I left the 30A cable as is to switch between shore power or genset. In transit or boondocking, of course the cord is plugged to the genset at all time. Call this source of power the “external power”.
At the breaker panel, I identify the circuit breakers for various appliances and outlets, and regroup the wires as needed. The circuits that I want to run with the inverter are wired to switches that lets me select between “external power” or the inverter. My inverter is a pure sine wave 2kW job that can run the microwave, hence I want to be able to switch the latter also. I also include the fridge circuit among the switchable ones because I occasionally have enough power, and want to save on propane.
The circuits that are always on the “external power” are for the AC and the smart charger. It’s because the AC takes way more power than a conventional battery/inverter combo can handle. The smart charger, if left on the inverter, would cause a dumb lossy circular loop by using the batteries to charge themselves.
So, what is/are the switch(es)? One can design a home-built multiple auto switch that powers up with the inverter, or use simple manual double throw switches.
One can use 3 or 4 independent wall switches (available at Home Depot, called a 3-way switch) to switch each circuit breaker separately.
Better yet, one can use a 3PDT or 4PDT industrial toggle switch that does 3 or 4 circuits in one. However, it may be tough finding one with a 15 or 20A rating for each pole.
The inverter output is wired to the above manual switch(es) in parallel.
I hope the above is enough to allow an engineer/technician/electrician friend to help you wire it up. Cost is minimal.
I saw a similar setup when I was Googling last night. I found several reasons NOT to use ordinary light switches.
One thing I’ve figured out is that I’m not like most RVers in that my order of power use is:
1) batteries
2) inverter
3) genset
4) shore power.
So my default mode needs to be shore power cord plugged into the inverter, excess breakers off. I think a sub-electric panel will be the way to go.
Linda, I have no idea how long it will take to kill your breakers. I’ve been using them as switches, too, knowing that you’re not ‘supposed’ to. I think that since I’ve been doing it so rarely it can’t possibly be a huge deal. But now that I have the genset, it’ll happen more often so I need a better solution.
Hmmm. So I should stop using my breaker switches for the microwave and water heater as on/off switches when boondocking? Or I should stock some backup switches to have on hand when I kill mine?
I realized that I might have caused some confusion in the earlier post.
The original breakers in the RV remain in place, and are left on all the time.
One can buy simple 3-way wall switches for a couple of dollars at Home Depot, and use them as manual transfer switches. Wire them in, with one switch per circuit breaker.
Or better, get a 3PDT or 4DPT industrial switch, which can do 3 or 4 breakers at the same time. It is smaller and easier for mounting to boot.
The 3-way wall switches or the single 3PDT or 4PDT toggle switch are added to the circuits, and allow one to route either external power or inverter power to these circuits. One must find a place to mount them.
In my case, as the breaker panel/converter box is mounted in the dinette seat, I have nearby spaces to innocuously mount the switch.
With this arrangement, I can even leave this new switch(es) in “inverter” position all the time. This means that even when I run the genset to charge the batteries, my internal AC outlets are still fed off the inverter.
All I need is to hit the genset “start/stop” button.
In other words this means the inverter is feeding of the batteries at the same time the latter are getting charged. It’s OK if the load is small. If the power usage is high such as the microwave, then I would flip the switch to take the load off the inverter/battery.
I should add this caveat.
The person doing this wiring must know what he is doing. Accidentally connecting the inverter output, even when it is off, to the live output of the shore power or the genset will kill the inverter instantaneously. Its output transistors get blown out in microseconds, faster than any fuse can react!
They were possibly worrying that the 3-way switch may have contact fusing, causing the inverter to get shorted against the other power source. If that happened, that would certainly destroy the inverter.
I am curious if the common switch can fail this way. I need to disassemble one to see its internal construction. Depending on the switch and relay, if a contact fuses, the mechanism is stuck and it would not transfer anyway.
But they may be using this switch to transfer an entire 30A circuit, which is beyond the rating of the switch, while I would switch only the lower power circuits and avoid the higher-amperage circuit for the AC.
For the electrically minded person, this is similar to ensuring a relay used is of the type “break-before-make”.
The way I set it up, all of my outlets can be run off the big 2KW pure sine wave inverter, while the genset or shore power is powering the AC and the smart charger. This protects all sensitive electronics, because the pure sine wave output is electronically regulated and super clean. The batteries act as a buffer to keep any spikes of the shore power or genset from reaching the electronics plugged into the outlets.
I am not a full-timer, but in my travel, I like to minimize the genset use when I camp. My setup allows me to fire up the genset momentarily whenever I need to run the AC or to help the solar system top off the battery, all with the “start/stop” button and nothing else. No need to move any cable, nor flipping any breaker or switch.
I have 1,000W pure sine wave inverter so I can run just about everything except the clothes iron, the AC, and the microwave off my batteries in terms of wattage. I also can’t run the fridge on AC because I don’t have enough amp hours. I really think the genset is going to be more for supplemental charging than actually giving me power. I just don’t see myself becoming one of those people who starts the genny to use the microwave. I do think that I will appreciate having the option to run the AC if I need it.
“The person doing this wiring must know what he is doing.”
Agreed. This isn’t like messing with 12 VDC. 120 VAC at high amperages can easily kill not only your inverter, but you. Get a professional to do this job.
I’d suggest using a Parallax ATS301, which is the 30-amp automatic transfer switch (ATS) that’s most commonly used in class C RVs. It’s about US$80 from Amazon. You’ll still need a separate 30A switch to select inverter or generator. Make sure that it’s a “break before make” type, to avoid cross-connecting power sources with disastrous results.
It’s really hard to find someone short of a really expensive RV tech who meets the trifeca of knowing 12V electricity, knowing 120 electricity, and understanding my electrical setup and needs. And the RV techs I’ve known tend to be very dismissive and not willing to concede that I’m not a complete idiot.
The fact at this point is that I have the technical knowledge to do all my electrical work myself (with appropriate research beforehand). I’m just not comfortable with the execution of it yet. So I need to understand this before I can ask someone to do it for me.
Forget automatic transfer switches as I wouldn’t trust them and they don’t meet my needs anyway. I don’t need a computer to tell me what source of power I should be using or starting my devices for me.
If cutting a hole into my office floor wasn’t such a difficult prospect (1″ marine grade plywood over a 1/4″ steel subfloor), I’d put a hatch over my shore power cable compartment and just plug and unplug from inside. Moreover, a couple of apparently electrically-minded people have told me it’s possible to replace my breakers which ones that can be used as switches. So that’s the route I’m looking at now.
No, the ATS301 will not be starting up the genset or the inverter for you. Nor do other so called “automatic transfer switch” in the same class. One does not get the same functionality as the control boxes in the fancy class As that can do true automatic power management. I also do not, nor want it with my simple setup.
I now realize that the way I rewire my motorhome may be a bit unique, and may be difficult to explain without being in person. However, I think I have described enough for a technically minded person to do the same if he/she desired.
Oh, I’m mixing up my apples and oranges. Thank you for the clarification.
Our rig already has an automatic transfer switch. I installed my 2500 watt inverter in the same compartment as my shore power cable. It was more than big enough. I plug my shore cable into the inverter as i go down the road or if i boondocking. When i start my gen the autotransfer makes sure i dont put 110 into the inverter. My converter plugs into its own outlet. I wired up a second outlet contoled by a switch being powered from the converter outlet. When i turn on my inverter i turn the power off to my converter. Hope this makes sense.
Rob, when the transfer switch cuts in the inverter, if the AC is accidentally left on, does it hurt your inverter?
I have not attempted to do a “stress test” on my Xantrex inverter to see what it will do when it gets severely overloaded. Hence, I wired my manual transfer in such a way that the AC (and also the converter/charger) could never get power from the inverter. Call me paranoid.
The plan is to turn the inverter off before the genny is started. But i have forgot a couple of times and have had no issues. Since i plug the shore cord into the inverter i will never have an issue of shore power and the inverter on at the same time. Since i had the transfer switch factory installed my mod only cost me $10 for the boxes, outlet and switch.
No, what I meant was that, it is possible to accidentally feed the air conditioner with the inverter. You can leave the air conditioner on, then power up the inverter. Would the overload hurt the inverter?
My wiring is such that the above situation can never happen.
About the inverter feeding the AC, I get what NWBound is saying. I think in my case I’d be okay as the inverter shuts off when I give it too big a load, but I wouldn’t take any chances! I’d wire it like NWBound says.