Switching between shore power and Inverter power for 120 AC

[MtnDon]

To keep a maximum voltage drop of 10%, that means

Wow! I just have to comment... Ten percent drop on a 12 volt nominal system means the voltage going into a high amp unit like an inverter would already be so close to the low voltage alarm on most that it is a virtual certainty to go off with moderate use. But more than that inverter electronics do not like low volts; they shut down to protect the electronics. When designing for off grid we make all out efforts to keep maximum voltage drop to 3% and prefer to be less than 2%. All the more reason to keep the cables from the battery as short as possible and as large as the wallet will permit. We used 2/0.

[Socal Tom]

I would expect that in a large RV. It's a little surprising to me in a TD.

Unfortunately, DC doesn't travel well. That's especially true when you're trying to move the 125A that a 1500 W inverter needs from the tongue box to the galley and back. I was looking at mounting mine in the galley cabinet of my 4X8 build but the routing quickly added up to 25' to the batteries and back. To keep a maximum voltage drop of 10%, that means 4AWG cable.

That part I understand.

What I meant was, that in the Generic Benroy ,the AC outlets are all within 4 ft of each other, whether they are in the cabin or in the galley. If I had to mount my inverter in the front to keep the DC run short, I would have been inclined to install a separate pair of AC outlets for the inverter power. A quick look on Amazon found the cheapest ATS switch at $80, so it would be cheaper and probably take less space to install one inverter outlet in the cabin and one in the galley, near the shore power outlets. In an RV you have power outlets spread accross 40 feet of RV, so it would be silly to duplicate them, and the cost would probably be less for the ATS vs replicating all the outlets and extra wiring.

I think we can agree the OP was correct, it would be bad karma to plug your battery charger into the inverter. It would probably drain the batteries pretty quickly.
Tom

[RetchedOne]

The Inverter will be within a foot or two of the batteries.
I understand voltage drop/wire size etc. AC can go far, DC doesn't travel well.

I'm looking at powering ONLY a small dorm fridge with in inverter.
Possibly a spare (Inverter powered) outlet for a blender.. lets be honest.. a gas powered margarita blender sounds cool.. but who wants to start it after 3 drinks.
Odds are we will be on shorepower most of the time, or running a small 3500 watt Honda generator a few times a day.

We do plan 300-400 watts of solar power

SO, with all that in mind...

Can I put a ATS AFTER the PD4045, inline with the ONE circuit that will power the mini fridge (Wet bar)?
Possibly one perfectly sized inverter for teh fridge, and one separate inverter for the "Margarita outlet"

Power comes in from the "Shore plug" (Camp power or generator) into the PD4045.
Power leaves the PD4045 headed to the fridge.. Stops at a ATS...
The ATS is fed from the PD4045, AND the inverter...
When no shore power, the inverter works... to power the fridge.

I'd still need to make sure they don't both come on... And would want a way to easily turn the Inverter off, as I don't want it running while travelling down the road

This keeps all teh outlets off the inverter except the one/two I want
- I dont want the rooftop AC running off the inverter, or my wife's blow dryer...
It doesn't "Loop the system"


Thoughts?

ATS -
http://www.progressivedyn.com/transfer_relays.html

[Shadow Catcher]

I hooked mine up with a 30A DPDT switch That takes the 120 AC from the external plug and routs it to the PD 4500 power center or 120AC from the inverter bypassing the PD charging circuit.

[RetchedOne]

I hooked mine up with a 30A DPDT switch That takes the 120 AC from the external plug and routs it to the PD 4500 power center or 120AC from the inverter bypassing the PD charging circuit.

How do you bypass the charging circuit?

[RetchedOne]

Looking at the diagram of the 4045, kinda see how you could wire up a DPDT to do that... Hmmm...

As I think I only want an inverter on the fridge primarily, I may see if the idea of wiring up one 120v circuit to a ATS will work

[PaulS]

I just got a 1000 watt pure sine wave and am considering using a 15 amp DPDT relay with a 120 vac coil. Wiring this into my circuit for my frige and microwave so when I plug into shore power that energizes the coil and changes the circut from inverter to shore power. What do you guys think?

[MtnDon]

PaulS, it seems that what you propose is exactly what a store bought ATS does. It uses a relay to switch the power. They usually use a 20 - 30 second delay to effect the change over. That is handy when using a generator as shore power as that lets the generator get to speed, warm and stabilize a little before demanding power from it.

[PaulS]

Good point to consider MtnDon. I just already have the relay and that is allready a 15 amp circut. I don't want to power the whole trailer with the inverter

[pmowers]

I looked at using a DPDT switch to control the inverter with the idea of running my refrig off of it, deciding the it was not worth it I just used an Igloo electric cooler running off of the 12 VDC.
One thing that you need to watch is the starting current for something like a refrigerator. When I was in the Army, our Biomedical Equipment specialist determined that we needed a 500W backup for our blood bank refrig. He designed a system using an inverter and a battery tender along with about 300 lbs of batteries. The system failed miserably, as he forgot to account for the nearly 2000 W startup draw, not the 300 W to run.

[Gold5one]

Just a bit of battery information for those contemplating a 1000 watt inverter - working a few times as an RV tech, I saw a lot of 1000-2000 watt inverter systems. Two size 24 or 27 RV batteries were used for a 1000 watt inverter and 4 batteries ( usually 4- 6volt for 24vdc) for 2000 watt inverter. The issue for us small trailer owners, is a single RV battery is designed for about 25 amps max output, enough for 300 watts AC inverter power. If that is enough, you are good to go.
For a higher wattage ( 500w), single battery inverter system, I would use a marine dual purpose, ( ie, Exide Stowaway) that is designed for high starting current and still does the longer loads (trolling motor), not a deep cycle RV battery.
Those 1000 watt inverters sold at truck stops do work for truckers- installed in a rig that has two 80lb starting batteries.