Pro Power on Board 7.2K to Trailer - While Driving

[EricR]

OK, I think I have figured out how to run power from our truck's PPOB 7.2K to our travel trailer while driving. This will allow our trailer's Lithium batteries to be charging and the refrigerator to be running while towing.

The parts are starting to come in and I will post a write-up with pictures when I have everything put together. For now, here is a summary of my plan.

I have chosen the watertight Leviton Wetguard connectors and "10/3 SOOW SO Portable Power Cord Cable UL Approved" to transfer the 30A 110V AC from truck to trailer.

Parts for the truck, starting at the PPOB 30A outlet:

1. 28W74 plug (L14-30P)
2. 2-3 FT of the wire mentioned above
3. FDBX1 Box, with 99W47-S Outlet (L5-30R - to be mounted under the truck, near hitch receiver)

Parts for the trailer, starting at the hitch:

1. 28W47 plug (L5-30P)
2. 20-25 FT of wire
3. In the trailer: add a Power Transfer Box, or replace the existing converter with an Inverter/Charger (haven't decided yet)

So in addition to the standard 7-pin connection between the truck and trailer there will be second connection for the 110V power using the watertight NEMA L5-30 connectors.

Using another 28W47 plug, a 29W47 socket, and 25-30 FT of wire I will make an extension cord. This will to go between the truck and trailer to allow the truck to be positioned further away while we are camping.

Also, I am considering building a couple of short adapter cables (aka dogbones) to allow the extension cord above to connect to the standard RV park 30A service. Thus, we would only need to bring one long, heavy cord.

The first adapter would to connect from the RV park 30A power-post to the extension cord. It would consist of a Camco 55283 plug (TT-30P), 6 IN wire, and a 29W47 socket.​

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The second would connect from the extension cord to the trailer 30A inlet. It would consist of a 28W47 plug, 6IN wire, and a Marinco 305CRCN.VPK socket (L5-30R) with watertight hood and twist-on ring.​

These watertight connectors are industrial grade and are expensive, but I wanted to do this right and have no worries (like killing someone cutting through our campsite on a rainy day). I saved quite a bit of money buying on eBay. They are available from other brands as well (Pass and Seymour, Hubbel, Woodhead, etc.) that seem to sell for less on eBay than the Leviton. The part numbers I've listed seem to be common across brands. I don't know if the different brands are interchangeable so I stuck with all one brand to make sure the connectors are really watertight when mated.

The wire came from Amazon.

I really hope this works.

BTW, I'm just a rookie at this.

So all feedback, thoughts, input, corrections of dumb things, etc. will be greatly appreciated!

Stay tuned for updates!

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[dhrandy]

Sounds like a great idea. Your Lithium batteries should be charging from the 7 pin connector, unless it's not wired correctly. The fridge is another story, that's why I prefer 3 way fridges. But I know that's not always possible when purchasing a camper.

 

[EricR]

... Your Lithium batteries should be charging from the 7 pin connector ...

Let me start by saying I'm no expert. Here is what I have learned. I am moderately sure it is correct. Always willing to learn more!

Yes, the 7-pin from the truck will charge a LiFePo4 battery - but not very well. These batteries typically need between 14 to 14.6 volts to charge to full capacity and for the internal BMS (battery management system) to be able to balance the charge level of the individual cells.

Also, these batteries can accept/draw large amounts of current (eg. 100A). I have seen many recommend not using the 7-pin and to install a DC/DC charger along with another set of wires from the truck to the trailer to protect/isolate the truck's alternator. To be fair, others report they are using the 7-pin with no harm to their truck or alternator. It's a risk I choose to avoid.

We like dry camping over RV parks, so the plan was to add a solar system with rather significant capacity - until we decided to buy the 2021 Powerboost with the PPOB 7.2k. Now the plan is to forgo the cost and complexity of installing the solar system and use the PPOB. See how much money we saved by buying our new truck!

So I decided as long as I "need" to run another wire-set from the truck to the trailer it might as well be 120V AC. It allows the the refrigerator to run and the LiFePo4 batteries to be fast-charged at 50+Amps with the correct voltage - while towing. Also, the higher voltage of 120V AC also has the benefit of needing a much smaller gauge (eg. less expensive) wire than the equivalent 12V wire run.

-Eric

 

[EricR]

As an example, here are pictures of the Leviton Wetguard box and connector that I will mount near the truck's hitch receiver.

 

[Notallthosewhowanderarelo]

I think it's a crazy idea, but I am looking forward to your updates on this project!

It's too bad most of our electrical connections on our RVs are near the rear.

 

[EricR]

I think it's a crazy idea, but I am looking forward to your updates on this project!

Haha! I've been very focused on the details of how to do this well, and now you cause me step back for a moment and look at the project as a whole with new eyes. And yes, you are probably right -- it is a crazy idea! ?

It's too bad most of our electrical connections on our RVs are near the rear.

Yes, my 30A inlet is 3/4 the way back on the driver's side. But your comment has me thinking I could run the 120V wire underneath the trailer to where it would be in line with the shore power inlet and then use an 90 degree connector to plug into the the inlet. This would eliminate the need for a transfer switch. On the other hand, I would have to devise a way to clip/snap the 90-degree connector under the trailer when it is not in use.

-Eric

 

[EricR]

Here is my revised thinking. Hat tip to @Notallthosewhowanderarelo for thoughts that fueled my further thoughts!

Parts for the truck, starting at the PPOB 30A outlet:

1. 28W74 plug (L14-30P)
2. 6-8 FT of 10/3 wire
3. 29W47 socket (L5-30R)
4. The 29W47 socket will be thrown over the tailgate and held near the hitch receiver with a bungee cord)

Parts for the trailer, starting at the hitch:

1. 28W47 plug (L5-30P). This will be at the trailer tongue to connect to #4 above.
2. 20-25 FT of wire run from the tongue along the underside of the trailer.
3. FDBX1 Box, with 99W47-S Socket(L5-30R - to be mounted on the trailer frame, just below the trailer's RV park power TT-30P inlet)
4. A 2-3 FT cord to go from the FDBX1 box to the trailer's RV park power inlet. It will have a 28W47 plug at one end, and a 90 degree TT-30S at the other end.

The advantage of this over my original plan is not transfer switch needs to be installed inside the trailer. The cool thing about PPoB is with a simple adapter it is pretty much the same as plugging in at an RV park (that is, 120V 30A power).

So with the above configuration our trailer won't know the difference between being plugged in at the RV Park from rolling down the road connected to our truck's PPoB!

We'll notice the difference though:

• Our lithium batteries will be fully charged upon arrival (great for boondocking)
• Our refrigerator will be 100% cold - without having to use propane while rolling down the road.

More to come!

-Eric

 

[EricR]

It Works!

See this thread with pictures:

https://www.f150gen14.com/forum/thr...-on-board-7-2k-to-trailer-while-driving.6462/

Thanks for the input!

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