Running trailer electrics off 12V umbilical

[fishboat]

We recently acquired a year-old 6x12x7h, single axle, CTC..but the trailer type doesn't matter for my questions.

I've been doing a TON of research primarily here on tnttt on all facets of building up and powering a camping trailer. This place is such a treasure-trove of info..you folks are great.

With respect to electrics, both 12Vdc & 120Vac..

120Vac: The trailer has a 50A service installed(previous owner, Wells Cargo install) and has 120V plugs installed inside, as well as 120V lights & AC/Heater.

12Vdc: No 12Vdc is available yet inside the trailer, however it is wired for 12V LED lights in the ceiling (Wells Cargo factory install, powered/wired through trailer pigtail running lights)


I'll be building cabinetry in the v-nose of the trailer, but have a concern about excessive tongue weight if I add battery(s) and a high efficiency chest refridge (truckfridge, engel, arb, dometic..etc..) to the v-nose area. I haven't determined the curb and tongue weight yet..but let's shelve that discussion for the moment.

Now my questions.

1) Has anyone run their trailer off a 12V umbilical from the tow vehicle? I'm thinking of having the 12V fridge, battery(s), batt charger, and solar controller in the back of the tow vehicle and then running a heavy gauge 12V extension cord to the trailer. Maybe a 20 foot cord. I'm aware DC power is subject to voltage drops. The cable would be sized accordingly. I'll probably be using a 100W suitcase solar setup to charge the batts.

Trailer 12V loads would be a ceiling vent-fan(7 hrs at night, probably a low-draw computer-server fan), minimal LED lighting for less than a hour a day, and charging phones(primarily), occasional topping off a laptop battery...that's about it. We're long-term tent campers and don't use much power in primitive campsites.

2) When we do camp at a site with 120V power (probably 1 in 5 or 10 trips) I'd plug into 120V power and have a 12V converter inside the trailer for all the 12V loads. The fridge, batts, batt charger, and solar controller would still be located in the truck.

Seem reasonable?
I'm thinking having the main 12V load, the fridge, and batts in the tow vehicle solves any potential tongue weight issues and allows easy vehicle charging of the (AGM)batts when we make a run in the truck somewhere as well as charging the (AGM)batts and running the fridge while were traveling during a trip. The suitcase solar panels can be plugged into the controller in the vehicle. I'd probably build some sort of power-station box for the truck to hold all the components. The back hatch of the truck is always open when we camp.

[GTS225]

I surmise the first question should be "How many batteries are you planning, and what type of batteries?"
If you're going over two, deep-cycle lead-acid, I suggest you plan a compartment/bench straddling the axle, so as to keep the weight centered over the suspension. A fridge isn't going to weigh much, but add in the batts and shelving up front, I think your tongue weight concern is valid.

OK, just noticed that you specified AGM batts. That'll help out, but again, how many?
I do like the battery pack in the TV idea. One could build a "module", if you will, that would fit into a rear corner, between the fender well and the tailgate, with permanent wiring from the front to the module for charging purposes. If you're planning to use a relatively compact battery, you could probably squeeze three into the module, along with the charge controller, and have it "plug-and-play" with quick connect sockets to match both the TV wiring, and the solar panel.

Roger

[John61CT]

Yes keeping all batts and charge sources in the TV simplifies things, long as you don't need the trailer powered while TV is absent.

Empirically measure the actual "12V" voltage of your bank when it gets to 50% SoC

also the maximum current drawn by your devices,

determine if any cutout from low voltage

then use a good voltage drop chart

I like Blue Sea Circuit Wizard

to size those fat wires.

Make sure crimped well, robust connectors

maybe order custom from genuinedealz.com

proper fusing, wire supports, etc

Won't be cheap, but a once-off and done right good forever.

[Ottsville]

Sure it can be done and previous posts all give some good points.

Here's a couple of random thoughts though. Make sure your batteries are separated from your automobile battery so that any draw doesn't kill your automobile battery as well.

I prefer to have batteries on the trailer for ease - one less thing to have to load every time you decide to head out plus you have power to trailer when the truck isn't there.

If you're worried about tongue weight on the truck then having battery, charger, and fridge in the truck is actually worse than having them on the trailer because the weight is shared by the tongue and the axle if they're forward of the axle versus all on the rear axle of the truck plus the tongue weight. If your tongue weight concerns relate to towability then you possibly could move your axle slightly forward or rearrange your loading to compensate for more weight in the front.

[fishboat]

Thanks for your thoughts.

I'd probably run no more than two batts if 6V or just one 12V.

I just looked up the suggested wire gauge for a 1% voltage drop over a 20 foot, 12V umbilical..cough..I didn't realize 12V voltage drop was so bad..yikes. The calculator suggested 0 GA wiring(8 amps, 20 feet, 12Vdc, 1% drop), 4 GA for a 3% drop..that's not going to happen.

OK..possibly time to look into an alternate plan. Possibly hauling the refridge and batt(s) secured over the trailer axle while traveling and moving them into a "camping position" during camp setup..installed on drawer slides in v-nose cabinetry. Or the fridge into the v-nose drawer slide and the batt(s) into a tongue box. I was trying to minimize setup work, but then there's reality.

For reference..the batt(s) would weigh in at 75-120 pounds, depending on Amp-h rating and whether I use two GC 6V batts or a 12V 110 amp-hr-ish deep cycle. If I had to move the battery during setup I might lean toward two 6V GC batteries as they are smaller and lighter separately than one larger 12V. The 12V high-eff fridge weighs about 50-55 lbs empty..which it wouldn't be. It may weigh in at around 75# with food and beverages in it (50ish quart model).

(p.s. All this matters now as I'd like to draw-model some v-nose cabinetry and I can't do that until I know what has to be stored/installed in the v-nose area)

[GTS225]

I'd have to advise you to drop the dual 6V battery idea now. If you're set on dual batts, run two 12 volt batteries. Dual 12's will not really weigh much more than dual 6's, and give you twice the amperage availability, for a longer run time.
As for cabling, if I'm not mistaken, you can still get a good sized pair of jumper cables for a decent price. That will give you high-amperage cable for less than hitting up your local Home Depot.

OK, maybe I'm not following your thought processes. You're planning for a 1% voltage drop over 20', but that is also dependent on amperage draw through that same cable. As the draw goes up, so does the voltage drop, as the wire size is the "choke point", if you will.
Just how much amperage do you anticipate pulling from the tow vehicle?

Remember, your starter motor in your tow vehicle pulls 130-200 amps, and those cables really aren't that big.

Roger

[Aguyfromohio]

...I just looked up the suggested wire gauge for a 1% voltage drop over a 20 foot, 12V umbilical..cough..I didn't realize 12V voltage drop was so bad..yikes. The calculator suggested 0 GA wiring(8 amps, 20 feet, 12Vdc, 1% drop), 4 GA for a 3% drop..

Are you sure you typed that in correctly to your online calculator?
When I check a couple of my favorites and enter 12 VDC, 20 ft run, 1% voltage drop , 8 amps out, I see at most 4 AWG, and that uses the total round trip length of 40 ft.
Zero gauge seems awfully big for 8 amps running 20 feet, and 1% seems rather small for a max voltage drop, 2% seem fully acceptable to me (11.76 VDC)

No harm in buying extra copper as long as you don't mind fighting with a stiff and heavy umbilical.

[fishboat]

...I just looked up the suggested wire gauge for a 1% voltage drop over a 20 foot, 12V umbilical..cough..I didn't realize 12V voltage drop was so bad..yikes. The calculator suggested 0 GA wiring(8 amps, 20 feet, 12Vdc, 1% drop), 4 GA for a 3% drop..

Are you sure you typed that in correctly to your online calculator?
When I check a couple of my favorites and enter 12 VDC, 20 ft run, 1% voltage drop , 8 amps out, I see at most 4 AWG, and that uses the total round trip length of 40 ft.
Zero gauge seems awfully big for 8 amps running 20 feet, and 1% seems rather small for a max voltage drop, 2% seem fully acceptable to me (11.76 VDC)

No harm in buying extra copper as long as you don't mind fighting with a stiff and heavy umbilical.

Different calculators are offering different results..I just checked what sites I went to this morning..the calc may have been done on a UK solar site.

Looked again on

http://wiresizecalculator.net/#calc_goto

and I'm seeing the same results as yours, sorry. In any event..20 feet of 4 or 6 GA dual conductor cable..meh..that sort of takes the glow off the TV-power station option. I'm thinking I'm going to have to take a hard look at the tongue weight and see if I can afford to (maybe) build the fridge into the v-nose cabinet on a drawer slide and carry the batts (two 55ah 12V (as suggested above) at 40# each) back toward the axle. Then relocate the batts up front (v-nose cabinet or tongue box) for use while camping. I'm leaning toward the two-battery route to keep the individual battery weight down as my girlfriend needs to be able to set things up on her own. Overall, I'm trying to avoid adding a quick 150# (fridge + food + batts) to the tongue. Building the cabinets and power accessories plus gear storage in the v-nose will already add tongue weight. There will only be about 50-60 pounds of gear loaded in the trailer behind the axle to offset added tongue weight. The rear of the trailer will remain open for hauling gear and the bed area. The trailer is below..

[fishboat]

Sure it can be done and previous posts all give some good points.

Here's a couple of random thoughts though. Make sure your batteries are separated from your automobile battery so that any draw doesn't kill your automobile battery as well.

I prefer to have batteries on the trailer for ease - one less thing to have to load every time you decide to head out plus you have power to trailer when the truck isn't there.

If you're worried about tongue weight on the truck then having battery, charger, and fridge in the truck is actually worse than having them on the trailer because the weight is shared by the tongue and the axle if they're forward of the axle versus all on the rear axle of the truck plus the tongue weight. If your tongue weight concerns relate to towability then you possibly could move your axle slightly forward or rearrange your loading to compensate for more weight in the front.

All good points.

I'm trying to keep the tongue weight in the 10-15% of trailer weight guideline. I assume it's in that range now and adding a couple hundred pounds to the v-nose area (fridge + contents + batt(s) + cabinets + gear) doesn't sound like a good idea. I'll need cabinets up there so that's sort of a fixed added weight. The fridge + contents and batt(s) are variables that may be located and used up front in the nose while camping, but could be carried elsewhere while towing on the road. There will be minimal weight behind the trailer axle to offset added tongue weight.

Adding the weight to the back of the tow vehicle just puts the weight over the truck axle and on the tow vehicle payload capacity..which I have plenty of.

[fishboat]

I'd have to advise you to drop the dual 6V battery idea now. If you're set on dual batts, run two 12 volt batteries. Dual 12's will not really weigh much more than dual 6's, and give you twice the amperage availability, for a longer run time.
As for cabling, if I'm not mistaken, you can still get a good sized pair of jumper cables for a decent price. That will give you high-amperage cable for less than hitting up your local Home Depot.

OK, maybe I'm not following your thought processes. You're planning for a 1% voltage drop over 20', but that is also dependent on amperage draw through that same cable. As the draw goes up, so does the voltage drop, as the wire size is the "choke point", if you will.
Just how much amperage do you anticipate pulling from the tow vehicle?

Remember, your starter motor in your tow vehicle pulls 130-200 amps, and those cables really aren't that big.

Roger

Two 12V (smaller) batts in parallel is a good idea. Keeping individual battery weight down is helpful (it looks like I may be abandoning the TV power station concept due to umbilical cabling needs). I'd only be pulling 5-10 amps occasionally.

[KTM_Guy]

What is your tongue weight now?
What’s the TV?
Do you need battery power for weeks on end or just to last a weekend trip?
Do you need the back of the trailer to be clear to hall stuff?
Water is another high weight gain. Do you need to carry it and how much? Where will you carry that?

For us we are going the trailer route over the tent because we want to be able to say let’s go and grab some clothes, some food and head out. The last thing I want to do is have to load a bunch of stuff in the TV.

If no option in the trailer I would look into welding brackets off the frame behind the fenders and mount a battery box there.

Todd

[Ottsville]

What is your tongue weight now?
What’s the TV?
Do you need battery power for weeks on end or just to last a weekend trip?
Do you need the back of the trailer to be clear to hall stuff?
Water is another high weight gain. Do you need to carry it and how much? Where will you carry that?

Good questions especially the first one. Don't assume that your trailer weight distribution is accurate to that 10 to 15% range from the manufacturer. Weigh it. And if your tow vehicle is sufficient, I wouldn't be concerned about going up to 20%.

Remember that weight added forward of the axle doesn't necessarily equal the same weight weight change in tongue weight. We're talking levers here. Play around with this calculator:

https://www.engineersedge.com/calculato ... vers_3.htm

[John61CT]

I just looked up the suggested wire gauge for a 1% voltage drop over a 20 foot, 12V umbilical..cough..I didn't realize 12V voltage drop was so bad..yikes. The calculator suggested 0 GA wiring(8 amps, 20 feet, 12Vdc, 1% drop), 4 GA for a 3% drop..that's not going to happen.

Why? I very commonly use 00 or even thicker when needed.

Compared to managing a separate (consumable) bank, having to buy an expensive (more fragile) DC-DC charger, $500+. . .

The wiring will likely pay for itself in 5-7 years

[troubleScottie]

Remember the trailer is a lever. Adding weight to the back (beyond the axle) compensates for weight in the front. Your current image basically has NO weight in the back - no mattress, no galley, no water, nothing. If you add everything to the trailer in front of the axle, all of it is going to be on the tongue. As stated many times, tongue weight 10-15% of the total towing weight. Sum( each object's weight x distance to axle) for the front of the trailer should be equal to the same measurement for the objects in back plus 15% of the total weight.

Batteries could go over/behind the axle under the floor or on the floor/cabinet over/behind the axle with appropriate vents. Your spare could be relocated.

Also the axle seems to be pretty far back -- could/should be moved forward.

I would be concerned about having to rearrange anything once you arrive. Especially electrical stuff. Much of the reason for the TD/trailer/5th wheel/motor home is that you can park and you're done. Having to move things around immediately just so it is usable is not a great plan. Think 2AM arrival in a driving rain after a 8 hour drive. How much do you want to have to do to go to sleep. Same goes for leaving from home or the camp - how much stuff do you have to put away before you leave - again think in the dark in the rain?

There are many designs here with similar trailers that have all of your issues. Look up the builds for them and see how they addressed the problems. You are definitely not the first one seeing this problem.

[John61CT]

The best battery value by far is Duracell (actually Deka/East Penn) FLA deep cycle golf cart batteries, 2x6V, around $200 per 200+AH pair from BatteriesPlus or Sam's Club

It is much harder to find 12V batteries that are true deep cycling.

Certainly not usually sold in auto or big box consumer channels.

And definitely more expensive per AH @12V.

Avoid sealed batts unless you really need them.