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Open Roads Forum  >  Tech Issues

 > DIY 30 amp transfer switch with parts from Home Depot

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kevink619

Santee, CA

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Posted: 08/21/11 01:03pm Link  |  Print  |  Notify Moderator

Hi,

Is there any way I can build an inverter/shore power transfer switch with 30A light switches from Home Depot?

I'd like to safely wire my inverter to the built-in 120V wall outlets in my trailer, but I don't have $150+ to spend on a fancy transfer switch.

Manual operation is fine - I just want to safely connect my inverter to the built-in outlets.

Is there something I can do with a combination of 30A 120V light switches that I can purchase at Home Depot - not some electrical supply house that is only open during the week (when I'm at work)?


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Golden_HVAC

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Posted: 08/21/11 01:41pm Link  |  Print  |  Notify Moderator

Hi,

It might be possible to get a 3 way switch that has off in the center, and use that for a transfer switch. But it would be much safer to just use a portable inverter, mount it near where you want the power, and run a heavy duty #10 gauge wire to that, plug in via a cigarette lighter. The problem with a 3 way switch is they don't have the ability be stuck in one position, when you try to transfer, so you might have a un=intened backfeed situation. With a transfer switch, if the contacts weld themselves together, it will not transfer to the other position. However with a 3 way switch, if the contact to one position welds itself to the common side of the switch, and you move it to the outher input, you will have a short circuit from both inputs to the common, backfeeding the inverter and possibly destroy it.

The portable inverter will work up to about 300 watts, and is what I use more often than my built in inverter charger, because it is more energy efficient than running the large inverter.

And if you are powering the whole power panel in the RV, you would have to shut off the circuit breaker feeding the converter/charger when on inverter power. Better to order a transfer switch online. A 30 amp transfer switch should only be about $90. You would also need a auxillary contact that will shut off power to the converter/charger when on inverter mode, to make it totally automatic.

Fred.

smkettner

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Posted: 08/21/11 03:46pm Link  |  Print  |  Notify Moderator

How many branch circuits? 15 amp TS $50

If you keep the transfer switch after the panel it does simplify a few things.

You would need one of these for each branch circuit.


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smkettner

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Posted: 08/21/11 03:48pm Link  |  Print  |  Notify Moderator

Or here is the basic 30a relay: http://www.rvpowerhouse.com/product.php?id=152

You would need an electric box and it would not have the delay circuit. (not needed for inverter)

Leviton also makes a 30a SPDT or DPDT light switch but that is 50 to $80 also.

* This post was edited 08/21/11 04:09pm by smkettner *

Gdetrailer

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Posted: 08/21/11 04:04pm Link  |  Print  |  Notify Moderator

kevink619 writes "Is there any way I can build an inverter/shore power transfer switch with 30A light switches from Home Depot?"

Simple answer, no.

The switches you will find at Home Depot, Lowes or other box store are not designed for the use that you are intending.

For example, a 3 way light switch is a single pole double throw (SPDT) switch, it only switches the Hot wire. These light switches also are rated for 15A or 20A which is too light.

In a transfer switch both the Hot and Neutral lines are switched, this requires a Double Pole Double Throw (DPDT) switch. The only switch that Home Depot has which would meet that spec is a toggle switch but it is only rated for 20A, not 30A as you are needing.

Not sure as to what you are attempting to do, but as a poor mans transfer switch you simply plug your RV shore cord into a gen or inverter when no shore power is available. If you have a power hatch you can put a 30A socket inside the power hatch and then plug your shore cord into the socket. The other end would be routed to your inverter or gen through the trailer.

wa8yxm

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Posted: 08/21/11 04:42pm Link  |  Print  |  Notify Moderator

Short answer .. I don't know.. (That is I don't know if Home Depot carries the needed switch)

I had one circuit I wished to switch between a "Mains only" (Shore or generator) and "Inverter" circuit.. I went to a local electrical supply (I will give the actual name so you know the type of name to look for: Brightmore Electrical Supply)

They had a switch, cost 50 bucks as I recall, It is a 3-position (on/Off/On) break before make transfer switch.. Sold AS a transfer switch, manual.


Even lower cost option.

Somewhere where it will not bother you put 3 outlet boxes.

in the box on the left use a black or white or whatever color is common in your coach outlet and cover.

The middle box gets one of the covers with a hole in it and a pigtail with a plug (same amprage as you wish to switch)

The one on the right gets another outelet.. this one is Red or Orange.

Plug and outlets are "Mates" (that is 15 20, or 30 amp whatever you wish to switch)

Simply "Transfer" the plug from the "Mains" (Common color) to the "Emergency Inverter Powered" (red or Orange) outlet.

I call that a "Poor man's transfer switch" Please note that at one time this is how many RV's were designed.. The generator did not feed a transfer switch but an outlet somewhere nearby, you plugged your shore cord into the generator outlet to "Transfer" over.

Same theory exactly.. Same in practice too.


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Dutch_12078

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Posted: 08/21/11 05:17pm Link  |  Print  |  Notify Moderator

I suspect that by the time you purchase all the pieces and parts needed to assemble your own, you'll have come pretty close to the $80 price for a Parallax ATS301 automatic switch from Amazon.com.


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09FLSTC

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Posted: 08/21/11 06:02pm Link  |  Print  |  Notify Moderator

Her's one for $50 I don't see how you can build one for much less.

kevink619

Santee, CA

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Posted: 08/21/11 06:19pm Link  |  Print  |  Notify Moderator

09FLSTC wrote:

Her's one for $50 I don't see how you can build one for much less.


Wow. Can't get more affordable than this one. I think this is the transfer switch that I'll order.

Thanks everyone.

RoyB

King George, VA

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Posted: 08/21/11 06:41pm Link  |  Print  |  Notify Moderator

If you want to live dangerously just manually back feed a circuit breaker in your panel with your generator output. Then open the main circuit breaker to disable the shore power source and then throw the breaker your generator is connected to and it will then become the power source for the panel.

Please NOTE: This is unsafe - not in electrical code by any means - dangerous - but does work - and you asked....

One big downside is you will never know when the shore power has returned back on-line and you definately dont want to turn on your main breaker to see if it has unless you open the breaker first the generator is connected to. Im afraid the shore power source will probably win-out over the high dollar generator if both of them was on-line at same time... Eventually you will forget the most important thing not to do and the next sound you will hear is your generator groaning real loud for a couple of minutes... Then you gotta call Mayberrys again to get another one.

It has to be contactor (relay) controlled to be in code like 09FLSTC posted.


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