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Old 04-03-2014, 08:08 PM   #1
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AC circuit powered from 2 sources


good day everyone what im wanting to do here is to build a sort of bypass system for my rv. im installing an inverter but only want to energize certain circuits ie tv stereo computer type of thing. i dont want to install dedicated plugs so i am planning on putting in a dpdt 40amp power relay. i know how to wire it as a transfer switch breaking the hot and neutral but this way i would need 1 relay for each circuit. is there a way i can just break the hots and feed the neutral from the inverter into the rv panel. i would need a way to prevent feedback to the inverter and this is where im stuck. any thoughts or suggestions on how to do this efficiently would be greatly appreciated thanks.

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Old 04-03-2014, 09:04 PM   #2
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AC circuit powered from 2 sources


Would suggest talking to the local Camper/RV place, that would better tell you. Or just use a small Honda Genset. Computer I would go with a laptop, vs. desktop. And also install an SSD hard drive in the computer, not use a Platter unit.

TV's, especially small LCD flatscreens, say 24-29", do not use that much. Batteries have to be recharged. You will only get so much power out of them. Say 1-2 hrs max, unless you are using a large bank of Marine Deep Cycle.

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Old 04-03-2014, 09:20 PM   #3
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AC circuit powered from 2 sources


thanks for the reply but the rv places have all said that i need to buy a fancy expensive inverter with passthrough which mine doesnt. like i said in the original post its easy to use a dpdt power relay to isolate circuits but i dont want to have to buy a relay for each circuit if i dont have to. thanks
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Old 04-03-2014, 09:26 PM   #4
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AC circuit powered from 2 sources


my rig has 4 deep cycle 6volt marine batteries in a series parallel config.
giving me 300 amp hours. given a 60% depletion rate for the batteries leaves me with 180 amp hours. my tv/dvd draw approx 5 amps so i could run this for 36 hours before requiring a recharge. i do have an onboard 5500 watt onan generator but dont always want to be running it.
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Old 04-03-2014, 09:36 PM   #5
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AC circuit powered from 2 sources


That is a lot of dead weight to be hauling. Plus over kill for what you are wanting to place on it. The problem with relays is that they can short out in an open state, causing you to end up overloading the circuit, or end up frying and not working. You would need to make sure that you keep extra ones on hand.

Personally I would just get a breaker panel for RV's, and use that with a breaker or switch as a transfer switch. You could build your own, include an Amp & Volt meter in it, to watch what is going on with the batteries.

You did not include your location, so there is no way of telling where you live. There has to be someone around you, that has a setup for what you are wanting to do. (ie local Sprint Racing guys/gals, Construction guys, etc.).

There are forums devoted to off gridding. Have you checked in there to see if anyone has designed a panel like you are wanting.
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Old 04-03-2014, 09:45 PM   #6
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AC circuit powered from 2 sources


havent had much luck with rv forums so far. this is a constant contact 40amp dpdt relay im using now designed for continuous duty same make as what comes in a commercial rv transfer switch but they arent cheap. the wife wants autonomous setup when the inverter is on certain circuits get energized when the genny runs the entire panel powers up. currently the entire panel gets lit up when on inverter or genny and we sometimes run into issues with say forgetting to turn hot water off electric or shut off the converter. i know its a convenience issue more than anything but i know there has to be a way.
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Old 04-03-2014, 11:30 PM   #7
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AC circuit powered from 2 sources


seperate the circuits,
one sub board for genny loads only
another sub board for invertor loads
instal a DPDT contactor on invertor sub board supply side.
in normall condition supply comes from same supply as genny,
But when invertor is tearned on power from invertor goes to coil
of the contactor, which now switchs the supply from invertor sub
board from genny to invertor.
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Old 04-03-2014, 11:36 PM   #8
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AC circuit powered from 2 sources


so if im understanding you correctly i would just need 2 dpdt contactors in order to achieve this or do you mean 2 panels main & inverter with 1 contactor
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Old 04-03-2014, 11:51 PM   #9
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AC circuit powered from 2 sources


You could break up your existing panel into two panels.


So it would really be two small panels (not really subs),

and one DPDT contactor.

After the main switch split the supplys to the various circuits
genny supply vs invertor supply.

It's common practice here in Australia
when instaling gennys, it acts like an automatic load shedder.
Only your using it for a slightly different reason
but its the same system.
its automatic and almost idiot proof !

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