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Old 11-23-2006, 11:30 PM   #1
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Inverter transfer switch help

I am installing an inverter to power the AC system when boondocking (will only be used very short periods so as not to kill battery).

I want to install a manual transfer switch. Simple, eh?

Where can I obtain a 30A transfer switch that isn’t bulky and doesn’t cost more than the inverter did?

This switch would have main shore power wiring to one pole, inverter power to other pole, feeding out to main AC circuit breaker panel.

A heavy duty 30Amp, double pole/ double throw switch should do it.

All I can find are marine grade, generator type, AC selector switches that sell for $140 (West Marine part # 5426630, BLUE SEA SYSTEMS, Mfg # 9009).

Anything sold as MARINE seems to be $$$$$$.

Can I use an automatic transfer relay out of an AS motor home?
How do these determine which line is hot? Are they reliable? What happens if someone switches inverter on while shore power is still connected?


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Old 11-24-2006, 12:59 AM   #2
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The issue of running big inverters comes up once in a while on the forum and I wonder if anyone has done what you are looking at doing. The reason I ask is the amount of power requires to generate that much current. I found this chart which shows the battery life based upon the amount of current created. Unless you are going to carry a bunch of batteries, I don't see how this could be pratical.
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Old 11-24-2006, 01:15 AM   #3
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I was wondering the same. Has anyone tried wiring in and using a big (ie. 1750w) inverter)?

Thanks, the chart is helpful.

I got the inverter cheap. I know electrically you can't get more out than goes in, V=IR and all. Don't want to toast the battery.

I just like toast.

Thanks, Walter
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Old 11-24-2006, 05:52 AM   #4
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They do make DPDT 220V wall switches. They are kind of hard to find. Try an electrical supply company. I doubt HD or L will have them, but you can look. They may not handle 30 amps though. I had one on a 220v well pump, so I know they exist.
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Old 11-24-2006, 06:10 AM   #5
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cost prohibitive

That inverter will cost you much more in other costs than what a Yamaha or Honda quiet generator would...and the generators have multiple use scenarios, while the inverter would definitely be a dedicated item along with $2000 worth of batteries!
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Old 11-24-2006, 10:07 AM   #6
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My onboard inverter powers two outlets in the trailer. One by the writing desk and the other by the TV. No Transfer switch. THere is a transfer switch for the generator hookup though.
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Old 11-24-2006, 10:41 AM   #7
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Has this ever been done?

So switches are available. You ask about use for short periods -- and it is certain that is all you'd be able to do. And then what? You'll not want to use more than 60% of your battery capacity or else you'll diminish their service life significantly. And then you'll not be able to use anything electrical until you replenish your batteries. This sounds like a clear case for a portable generator and not going thru the middleman (ie, batteries).

[on edit: Adding more batteries to make this even occasionally practical will severely push the dynamics of trailer loading, hitch weight, GVWR, etc.]

Recharging batteries with anything short of a home or campground electric hookup or 110v generator will be slow. Two rather slow options are thought of commonly -- solar and your tow vehicle's alternator. The latter supply line is thin, long, and can take 2-300 miles of driving before your batteries are topped off for instance. Using the umbilical and tow vehicle batteries in this way risks having your tow vehicle "wake up dead."

The more common quiet Honda eu2000i doesn't put out quite enough amps to start up the AC. The compressor requires about 20-22 amps at startup IIRC (less when up and running). Many threads out there in Forums on this topic ... Solar battery recharge (not running the AC!) is a very expensive option for what you get -- slow, occasional, and maybe not ready when you are.


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