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Old 08-23-2011, 07:11 PM   #1
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Complete Rebuild of Electrical System

I am trying to design the electrical system on the trailer. I want to be able to do the following:

1) Power an LED TV and DVD player, maybe a laptop or two and a couple phone chargers. This capability should be available at all times. My calculations show that as around 175-200 Watts.
2) When shore power is available, which is rarely for our camping, I want to run the fridge on 110V. Haven't picked a model, let's call it 300W (really won't affect anything in this discussion).
3) Everything else in trailer (LED lights, water pump, CO/LP detectors, tank level system, are all 12V and I've got a handle on.
4) I really don't want to have two separate AC outlet systems for inverter power v. shore power. My trailer is only 15' interior, and I only plan to put in 4 outlets. Also, I would rather not have to switch the TV power cord back and forth.

I plan to buy the PD4045 charger/converter AC breaker / DC fuse panel combo and probably for the battery bank a 200 amp-hour 6v system in series)
I plan to take the 110V inlet to the system from a Marinco 30A on the side of the trailer. That way, I will either just connect up to campground power if available, or when we eventually spend $500-$1000 on a generator, from it instead.

Now here's where I'm not quite sure what to do. To fulfill requirement 1, I want to install an inverter to take the power from the 12V system and run the TV and other goodies whenever I want (inverter will be modified sine wave, 300W continuous minimum). But if I install it on the 30amp AC inlet line so that it services the converter and all the breakers, I am scared that it will create some overload loop between the converter and inverter unless I turn off the converter every time I turn on the inverter, which is annoying, and relies on human interaction for proper operation. I want to keep it as idiot-proof as possible.

So do I jumper in to the AC lines that go to the 4 breakers with parallel wires from the inverter 110V outlet, and then install some sort of giant diode upstream on the circuit at the PD4045 inlet, but after the breaker for the converter? (I think of everything in chemical engineering terms--with the electrons flowing through a check valve).

Some solutions I see are using a transfer switch or an inline inverter with one built in. However, it is hard to justify spending $100 or more on the transfer switch when I really only need a $50 inverter for my needs. And the cheapest inline inverter with AC in that I can find is over $200.

So does anyone know of any alternative options or would that diode work?
I suppose I could wire the shore power to a breaker panel with the fridge and one dedicated outlet (like over the sink for electric kitchen appliances), then the rest to the PD4045 AC inlet, but then all the other outlets would always be running off of an inverter, even on shore power, which seems plain silly.

Wow that was a lot of typing. If you actually read that all, Thank you.

- Peter
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Our Adventure Blog - Documenting our backpacking, hiking, camping, and Airstreaming
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Old 08-23-2011, 09:04 PM   #2
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So you are concerned about an out of phase shift between your shore power 120v and the 120v output from you inverter? Say your shore power was at 0Deg and the inverter output was at 15Deg in the 60cycle phase..
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Old 08-23-2011, 09:08 PM   #3
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30amp SPDT relay with a 120vac coil

Wire the coil to the shore power side and when it is energized ( shore power present ) it disconnects the inverter output from the AC loads, and connects the shore power to the AC loads
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Old 08-24-2011, 12:54 AM   #4
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Quote:
Originally Posted by Darkspeed View Post
So you are concerned about an out of phase shift between your shore power 120v and the 120v output from you inverter? Say your shore power was at 0Deg and the inverter output was at 15Deg in the 60cycle phase..
Well that among other things. I only had one class of electrical engineering. Most of my electrical is in learning ABYC regulations for boat wiring and reading through diagrams on my SUV to wire in various accessories cleanly.
I guess it's also because the idea of an inverter powering a system that then runs a converter that charges a battery that runs that same inverter seems inherently wasteful. And why use modified sine wave if I don't have to?

Quote:
Originally Posted by Darkspeed View Post
30amp SPDT relay with a 120vac coil

Wire the coil to the shore power side and when it is energized ( shore power present ) it disconnects the inverter output from the AC loads, and connects the shore power to the AC loads
Thanks Dark, this sounds like it should work perfectly, and it's cheap. You even got it the way I would like it with normal position of the switch being for the inverter.

I don't know the intricate details of relays and have used them <10 times, so if I use something like this pool and spa one, where should the outlet side of the coil go? Does it make a difference where it's return path is?
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Old 08-24-2011, 01:39 AM   #5
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Well
your shore power hot / neutral would go to the two coil terminals

Your trailer loads hot would go to relay common

Your shore power hot would go to relay NO - normally open

Your inverter output hot would go to relay NC - normally closed

Your shore power neutral, inverter neutral, trailer loads neutral would all be tied together on the neutral bus

If you were clever you would have a portable ground rod for boondocking tied to the ground bus

Double check the relay, some label the NO/NC withe the relay energized, some de-energized
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Old 08-24-2011, 10:16 AM   #6
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Quote:
Originally Posted by Darkspeed View Post
Well
your shore power hot / neutral would go to the two coil terminals

Your trailer loads hot would go to relay common

Your shore power hot would go to relay NO - normally open

Your inverter output hot would go to relay NC - normally closed

Your shore power neutral, inverter neutral, trailer loads neutral would all be tied together on the neutral bus

If you were clever you would have a portable ground rod for boondocking tied to the ground bus

Double check the relay, some label the NO/NC withe the relay energized, some de-energized
OK, perfect. I assumed hot to neutral on shore for the coil, but I didn't want to mess it up.

Neutral ground bus I've already got on the PD4045 unit from what I understand. Technically a ground bus as well but yes I do plan to at least install a larger ground bus or maybe even a portable rod. I'll probably just do what fuel trucks and pumping trucks have, with a grounding clip on a spring loaded cable reel, and then I can clip to grounded objects at campgrounds or just clip on to a portable rod.

Now I'm even more anxious to finish my frame and subfloor so that I can start installing all this.
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Our Adventure Blog - Documenting our backpacking, hiking, camping, and Airstreaming
(still updating, haven't gotten to the Airstream trips yet)
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