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Old 01-06-2007, 04:29 AM   #15
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I think the combination of the two things you're showing in that diagram has the potential to be dangerous and I would definitely not do it that way. You're running two circuits in the same breaker box and also having one of those circuits connected to a loose plug in a cupboard.

If you made a mistake inside the breaker box and wired the "inverter outlets" circuit to the "city power" circuit you might not easily be able to detect it - after all, the outlets would still work on city power, and you'd still need to plug in the inverter when not on city power - but that loose plug you're using to change power sources would be hot when on city power. There's the obvious potential for shorts or electrocution from that, and you could also end up plugging in the inverter and outside power at the same time which would be very bad.

If you don't want to power all outlets from the inverter by wiring it in before the main breaker box, I would put in a sub-panel (you can get a very small box with just one 20A breaker) just for that circuit, and put the switching mechanism before that. But running two circuits that must remain isolated for safety inside the same box - in a way that is not at all standard - I think is a very bad idea.

If you don't have the two circuits in the same box, the plug-switching is fairly innocuous, but transfer switches are pretty cheap and foolproof once wired correctly. If you use a transfer switch for the whole 30A service, use 10-gauge wire. If you use it just for one 20A circuit, use 12-gauge.

If you get everything right, the diagram you show would probably be reasonably safe - for you. But maybe not for the next owner, or the electrician you call in 10 years from now because you've gotten old and lazy, or maybe you after you haven't used the trailer in 5 years and you forgot how it works. One of those guys - maybe you - is trying to work out why half the outlets don't work (because someone left the plug connected to the inverter), sees that one of the circuits in the breaker box isn't connected to city power and "fixes" it by connecting it... then he reaches into your switch cabinet and finds the loose - now hot! - power plug. Not a happy day.
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Old 01-06-2007, 08:05 AM   #16
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Transfer switch

I agree with Lew and like the idea of a transfer switch. This one found on EBAY 130065491625 is the one I have in my home that is used with a generator.
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Old 01-06-2007, 09:32 AM   #17
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There's nothing wrong with implementing a "Bubba Transfer Switch" as long as you label the two boxes and plug, and implement it safely. The drawing attached gets the wire splice in the "plug wire" circuit out of the main breaker box into it's own isolated box, and provides protection for the outlets and their wiring.
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Old 01-06-2007, 11:53 AM   #18
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Thanks for the feedback everyone.

Finally Maurice helped get my implementation idea across. Thanks! Just call me Bubba...

John, I like the idea of that transfer switch on eBay. Maybe I'll research something like that as well.

BTW- just a warning. I know there are people who try to use a DPDT switch to make a manual cut-over by switching the hot and neutral. This has the opportunity to arch across the contacts, or a cheaper switch may make the one side, before breaking the other. Either case blows your inverter.
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Old 01-06-2007, 08:51 PM   #19
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Use a transfer switch to avoid a learning curve with costs that will happen at some point. This is one of those things that new owners of pre owned Airstreams ask themselves, "what was the 'po' thinking when they put this thing together".
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Old 01-06-2007, 09:02 PM   #20
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What Size/type of Generator should be used?
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Old 01-06-2007, 09:51 PM   #21
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Tim.
Here is one more idea to think about. Why not just leave the few items on the inverter all the time? It sounds strange to convert ac to dc and back to ac when you are attached to shore power, but it would be much simpler. No additional wires to run, no switches to fail, no chance of error and the only cost is a bit of extra power to invert. Since you would be on shore power it would not be a big deal. I like the KISS thing...
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Old 01-06-2007, 10:35 PM   #22
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Interesting idea. To do that I'd have to run new AC wiring the specific items I want to run w/o power....

I got it installed today. My inverter has an optional spot to wire a romex internally. So I have it ran back into the closet waiting for the *plan* of switching the AC side.

I think I'm going to go the electical supply and get a 20 amp contactor with a 115vac coil. I'll wire the inverter power to the coil so its only energized when the inverter is on.

The contacts in the contactor (relay) will auto switch the leads to the wall outlets from the AC breaker to the inverter power.

So the system will be automatic.
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Old 01-09-2007, 08:19 PM   #23
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Don't want Bubba...

Ok guys....

Today I picked up a 30 Amp double pole, double throw relay to do my inverter power transfer.

The one I got has a 120vac coil to activate it so I'm going to wire it as shown in the attachment.

Basically when the inverter is off, the relay is off and will transfer AC current from the breaker box to the outlets. When the inverter is switched on, it will power the 120vac coil on the relay and engergize it which will transfer the hot and neutral wire over to the inverter to power the outlets.

So to get the outlets on the inverter you simply turn it on and it will switch then automatically. Only downside is the wasted inverted power to power the relay. Not sure how much that will be. The coil measures about 290 ohms so the waste could be around 45 watts.

The other way to do it would be to wire it so that in the relaxed position the power is on the inverter instead of the line. However, the majority of the time I'll be on line power and I don't want to wear out the relay by running it 24/7.
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Old 01-09-2007, 08:26 PM   #24
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Good Job!

Quote:
Originally Posted by Safari Tim
Ok guys....

Today I picked up a 30 Amp double pole, double throw relay to do my inverter power transfer.

The one I got has a 120vac coil to activate it so I'm going to wire it as shown in the attachment.

Basically when the inverter is off, the relay is off and will transfer AC current from the breaker box to the outlets. When the inverter is switched on, it will power the 120vac coil on the relay and engergize it which will transfer the hot and neutral wire over to the inverter to power the outlets.

So to get the outlets on the inverter you simply turn it on and it will switch then automatically. Only downside is the wasted inverted power to power the relay. Not sure how much that will be. The coil measures about 290 ohms so the waste could be around 45 watts.

The other way to do it would be to wire it so that in the relaxed position the power is on the inverter instead of the line. However, the majority of the time I'll be on line power and I don't want to wear out the relay by running it 24/7.
Tim,

Looks suspiciously like the basis of a home-made transfer switch to me!! That is the heart of the big models used in the MoHo's. No worries now!!
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Old 01-10-2007, 04:58 PM   #25
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I like that a lot better than the loose power plug! One more question though, and I really don't know the answer to this one, if this switch transfers almost instantly might some electronics be affected by the inverter not being in sync with the shore power? I doubt it's a problem, but maybe someone knows for sure.

The expensive inverter/chargers have built-in automatic transfer switches which are nice, but then that's why they're expensive. I want a Prosine 2.0 but I may settle for a cheap inverter for a while.
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Old 01-11-2007, 08:28 PM   #26
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Got 'er done!

Got the transfer relay installed. It works great. When the inverter turns on it powers the relay which transfers the inverter power to all the curbside outlets. When the inverter is on w/o any AC stuff on, the inverter AND transfer relay draws 0.9amp from the battery according to the tri-metric. I find this perfectly acceptable for the convience.

Slight bummer, which I already knew, is the 110vac lights in the trailer are also on this circuit. So we can power the 110vac lights off the inverter which is somewhat of a waste . We'll just have to make sure we use the 12vdc ones.

My inverter is installed under the bed. It has a remote power button accessory for it, which I just ordered. So I'll be able to put the remote on/off at my central control panel. So when we need inverter power we simply turning it on and it will transfer the outlets automatically.

BTW for an interesting test, even though the inverter is rated for 800 watts, I plugged in a 1500 watt heater for fun. The inverter can surge for several minutes and it has overload protection. Anyway it ran the heater and was drawing 92 amps!
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Old 01-11-2007, 08:50 PM   #27
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hello Safari tim , looks good there ,a great job as usual your doing .I myself
will be happy with the good original electrical system on my 60 trdwnd .
I will agree that a good affixed diagram and schematic of your electrical
system conversions should be all log in a binder notebook as well as a
similar schematic attached inside a closet door or affixed someplace for
future trouble shooting when needed. It is not hard to forget how you wired
A Y and Z circuit to B G and C connectors or whichever it may be .I have similar diagrams of all the original umbilicle wiring and battery hookups and all
to reference later when my mind goes or is going seemingly sometimes .
anyway, So many components there to figure out ,takes a person that
knows whats up as you do ,thats for sure.

Scott
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Old 01-11-2007, 08:57 PM   #28
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Good point Scott.

I intend to label this box and the breakers as well. I'm also going to keep a *manual* of all the DC fuses and what they do, etc... As you say easy to forget!

I needed to update the Ambassadors electrical because of the appliances changes I'm making, airconditioner, convection mircrowave, twintemp, etc...

The inverter is mainly for the purpose of running the LCD TV's when dry camping. :-)
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