Boondocking 12 VDC electrical with 110 VAC dependent stuff

Boondocking 12 VDC electrical with 110 VAC dependent stuff Jul 27, 2023 15:16:18 GMT -8 WhitneyK likes this

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Post by davesshasta16sc on Jul 27, 2023 15:16:18 GMT -8

VTT Peeps and Professionals,

I have been working hard on researching the best plans for my electrical system in my 1972 Shasta 16-SC. It seems the trailer was re-wired for 110 VAC only from shore power. So, I am going to be re-wiring a 12 VDC system except for the appliances. When on Shore Power I will be pushing 110 VAC to my converter and 110 VAC dependent appliances, directly. I am going to use a dorm fridge, a counter top Breville toaster oven and a media center PC with monitor. All will run on 110 VAC only and therefore, can run on shore power when available and the inverter will need to be off. When boondocking, those same 110 VAC dependent appliances must pull power from an inverter and so the converter needs to be off.

	Shore Power	Boondocking
Electrical Input	110 VAC	12 VDC
Inverter Status	Off	On
Converter Status	On	Off

There was a similar thread posted regarding this back and forth here:

vintagetrailertalk.freeforums.net/thread/12684/ac-dc-back-again

Now there are some pretty fancy and expensive Transfer switches for this situation but I kept coming back to the same question:
When on shore power, the 110 VAC will go to the converter, then the fuse box. Then it will go to the inverter, which will try to send 110 VAC to the 110 VAC dependent outlets. But those outlets will already be getting current from the shore power. Converse is true when boondocking. The Inverter will pull 12 VDC from LiP04 battery and send it to the 110 VAC only plugs. The converter will receive 110 VAC from one of those plugs, so it needs to be off when the inverter is on so it does not take the 110 VAC from the inverter and try to send it back into the 12 VDC system.

Q: Instead of a Transfer switch, can I put in two simple on-off switches for the converter and inverter? Turn off the converter and the inverter on when boondocking and turn on the converter and the inverter off when on shore power. Then the 110 VAC dependent outlets will only receive one current source, and the converter will not try and take the 110 VAC coming off the inverter and feed it back into the system as 12 VDC.

I think that actually does make sense.

Here is my diagram, I included Vikx Frame Junction Box, which I will install and my plans for Solar re-charging of my battery as well as the two switches:

The White Whale_Electrical Diagram_Planned by David Porzio, on Flickr

I believe all the components are there.

I do have one other question in regards to the hot charge wire going from the Frame J-box to the Hot side of the battery. I presume that is to charge the battery while towing the trailer? If so, does there need to be some sort of charge regulator or controller between the Hot Charge line from the Tow harness and the trailer battery to manage charging a LiP04 battery? I believe VIKX diagram (see below) was done under the presumption the battery is Lead Acid.

VK Lee Frame J Box Wiring by David Porzio, on Flickr

I hope what I am asking makes sense:
1. Does this wiring diagram look correct?
2. Can I install simple on-off switches instead of a transfer switch to control converter and inverter when drawing shore power vs Boondocking/Battery Power
3. Do I need a charge controller between Hot charge wire from tow vehicle and the Trailer LiP04 battery?

Thanks in advance

Framing about done almost ready to put on skin and roof.

Dave's Shasta 16-SC

Boondocking 12 VDC electrical with 110 VAC dependent stuff Jul 28, 2023 12:24:19 GMT -8 WhitneyK likes this

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Post by vikx on Jul 28, 2023 12:24:19 GMT -8

Most vehicles won't overcharge a battery while on the road because the charge line is quite long and of lighter gauge. I think you will need a charge controller for a LiPo battery when on shore power. They can be extremely sensitive to overcharging so better safe than sorry. (some newer converters may have a built in LiPo charger) Inverters can also have built in chargers. Research this issue with knowledgeable people.

A transfer switch would probably be better than two on/off switches but they will work. The reason for the transfer switch is to prevent future problems with new owners.

Be VERY CAREFUL doing the tow wiring. I use a 4 way ribbon from the front j box to the rear for tail and brake lights but switch to the 7 way universal color code at both J boxes.

WHITE= ground
GREEN= running and tail lights
BROWN= right turn and brake
YELLOW= connected to RED for left turn and brake

It is easy to mix up the 4 and 7 way color codes. (wonder how I learned this??) A properly wired 7 way cord and plug at the front insures proper trailer to vehicle connection. (Newer vehicles equipped with a 7 way receptacle use the universal code)

The diagram looks correct except the amount of amperage used. Using 30amps wiring and connections to the inlet and breaker box is good. The toaster oven would be better on a 20amp dedicated circuit with the other fixtures on another 15amp circuit. If you decide on an air conditioner, the 20amp circuit could be used, as long as the toaster isn't on at the same time. An air conditioner can be powered by the campground pedestal, bypassing the trailer wiring. You may need a "twin" breaker if the box will only support 2.

You should not need a fuse in the interior fuse box for the clearance lights unless you plan to switch them on while disconnected from the tow vehicle. This line would be OFF when towing. In other words, you wouldn't want the exterior lights getting power from 2 different sources. Depending on the wiring, your tail lights will also be on with the running lights. An easy solution is to remove the running lights from the circuit and power exterior lights only.

Keep in mind that most converters and inverters require a dedicated ground to the trailer frame, as well as the 110 breaker box. Solid copper is recommended.

Hope this helps.