Expo Trailer Power Umbilical

[SAR_Squid79]

Electrical, by far, is the thing that I am least confident about when it comes to wrenching.

I'm building an Expedition Trailer currently, and instead of going with a stand-alone battery box in the trailer, I just want to do dual batteries in my truck, and run a power umbilical to the trailer (which will have lighting, and a fridge, etc.).

Can someone please tell me if this wiring diagram is safe and makes sense, or is it retarded? Also - what gauge wiring should I use, and what size fuses?

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**Edit**

This is completely independent of the Trailer's Tail Light/Brake Light/Turn Signals/Marker Lights - I know how that works.

 

[SAR_Squid79]

*Note:

I will probably use a Vector 750 watt Vector Inverter with 2 outlets. 1 of the outlets will be full-time dedicated to the Engel MT45 fridge.

Also - would it be unsafe to wire the female outlet on the truck - STRAIGHT - to the battery with no relay, and no switch?
Maybe using one of these: http://www.amazon.com/Superwinch-1520-Trailer-Wiring-Kit/dp/B00008PWWJ

 

[ntsqd]

I'm not quite tracking on the desired results. One is obviously power to the fridge, what are the other(s)?

FWIW if the fridge will run on DC I'd do it that way. Converting to AC is usually less efficient unless it has been proven that the fridge's AC operation is enough more efficient than it's DC operation that it can offset the loss of the inverter. Which would surprise me.

On fuse/breaker ratings & wire sizes you need to know what your maximum amps will be and the distance of the wire run. The Anchor Marine catalog used to have a chart for figuring out the wire size based on this. Mine is an old copy (& at home), no idea if the current ones have this or not. A book on marine 12VDC systems most likely will. There's a recent thread around here where some informed book recommendations were made. The tables that I've found so far on-line are for house wiring and those have assumptions built into them that really don't apply.

If the amps required put you into battery cable sized wiring those Anderson connectors used in the Superwinch kit are a good option. However, you can buy just those connectors from McMaster or Grainger and then you're not limited by their cable length. Search for fork lift charging connectors or plugs. Found this link in a couple recent posts here: http://www.powerwerx.com/ another source for those & other plugs.
Just to be safe I would consider something like the MEGAfuse at/near the battery. One of those cables shorted to ground can pull a lot of current and make a nasty mess.

750 watts of 120VAC is roughly 6.25 amps, so including inverter losses I'd venture the amps required by the inverter would be about a 10 amp draw. An inverter is going to be sensitive to voltage drop, so given a choice I'd use the 2-3% drop tables rather than a 10% drop table. This will result in a wire gauge that would typically be one to two sizes bigger than the 10% drop table would call for. Even at that I'm guesstimating that for the run a 10ga. or 8ga. wire could be enough.

 

[Robert Bills]

You may want to use a constant duty solenoid rather than the relay shown in your diagram. Available from any trailer supply, NAPA, etc.

Your diagram shows a 110v outlet. I would not use one of these under any circumstances, lest someone plug a 110v extension cord into your trailer by mistake.

I recommend the same connectors that "ntsqd" recommended. The advantage to these is that you can modify your jumper cables to use the same connector, put another connector on the front of your truck, and not only be able to power your trailer with any 12v battery but be able to provide a jump for a buddy without ever needing to lift your hood or reorient your vehicle.

Finally, I would add a fuse to your trailer circuit. It may not be necessary since the power lead will be fused on your truck, but what if you use another battery or 12v power source?

 

[SAR_Squid79]

FWIW if the fridge will run on DC I'd do it that way. Converting to AC is usually less efficient unless it has been proven that the fridge's AC operation is enough more efficient than it's DC operation that it can offset the loss of the inverter.

The fridge is AC/DC and will run off of both 12V & 110.

Thanks for the Powerwerx link, and good call on that MegaFuse!

Your diagram shows a 110v outlet. I would not use one of these under any circumstances, lest someone plug a 110v extension cord into your trailer by mistake.

That 110v outlet in the diagram was just for illustration purposes. I didn't actually intent to use one of those.

And thanks for the tip on the constant duty solenoid. I didn't think the type of relay I had pictured would do the job, I just didn't know what else to use.

 

[Robert Bills]

You might also try this website for switches, relays, connectors, battery isolators, dual battery wiring kits, etc.

http://www.wranglernw.com/

They are very knowledgable were quite helpful when I was wiring the onboard air system and auxilliary circuits in my jeep.

 

[ntsqd]

Have a look at the const. duty solenoids. The one I'm familiar with was rated to 200 amps, which is about 1/2 of what some starters or likely receiver socket mounted winches can draw. If planning to do the jump-start cables (A good call IMO) or a receiver winch you may want 2 in parallel.

Trying to use the Ford type starter solenoids may or may not work. Conventional wisdom says that since they are intermittent duty that they won't live very long in such an application, yet I have heard of folks claiming success. I mention this much more for options awareness than endorsement of that approach.

Heading off on a tangent:
A clever thing might be to use a starter solenoid in parallel with both the MEGAfuse and the const. duty solenoid. Wire it so that you can energize it only when winching or jump-starting. That preserves the fuse rating for normal use, yet allows more current than fused on demand.

 

[SAR_Squid79]

See - now you're getting way over my head! I told you guys that I'm a little bit of a moron when it comes to electrical...

Without a diagram, I don't understand ANY of what you just said.

 

[ntsqd]

Sorry. I was afraid that might happen.

Constant duty solenoids have a max rated power that they can carry. The one I've used in the past was rated for 200 amps, but they're not all the same so what ever one chosen should be looked at & confirmed to carry enough current. If you never expect to winch or jump start off that plug on the rear of the truck then I'd expect 200 amps to be way more than enough. By about 10 times.

If jumping or winching is possible/probable, then you need to select parts that can carry more like 400 amps to at least the rear plug on the truck. One constant duty solenoid would fry if used like that. Two of them hooked such the each had a terminal connected to the battery and their opposite terminals were connected to the plug could handle that higher current level. That is "parallel wired", each carries part of the total current flowing.

Keep in mind that the loads determine the current amounts, not the wiring. If you wire 4 gazillion amps to an LED light it will still only draw it's tiny amperage.

Ignore the lower part of what I said above ("Heading off....") until later, if at all.

 

[Robert Bills]

Have a look at the const. duty solenoids. The one I'm familiar with was rated to 200 amps, which is about 1/2 of what some starters or likely receiver socket mounted winches can draw.

The constant duty solenoid you need looks like this:

It is available from NAPA (part no. PHI54140) for $27.99. These are the same solenoids used for lift gates, Warn winch motors (at least on my 8274), etc. I use one on each of my tow rigs for the 12v power feed to the trailer, and another to power my 1/3 hp 12 volt compressor in my jeep's onboard air system.

If you go to If planning to do the jump-start cables (A good call IMO) or a receiver winch you may want 2 in parallel.

I don't think that parallel 12v power lines will be necessary (although I've been wrong before). If you go to http://www.wranglernw.com/, you will find a "battery to grill" jumper cable kit. You can wire your own (front and rear) from component parts if you don't want to buy a kit. Call them and ask how you should wire your system. They won't steer you wrong, and will have everything you need.

Trying to use the Ford type starter solenoids may or may not work. Conventional wisdom says that since they are intermittent duty that they won't live very long in such an application, yet I have heard of folks claiming success.

Don't bother with a starter solenoid. It will work for a while, but will "pop" when it gets hot. It is not designed for constant duty. I used one on the recommendation of a friend when I first wired my onboard air system (which uses a much stronger 12v compressor than Viair, etc.). It worked fine in my driveway, but failed the first time I used the compressor to air up tires at trails end. I replaced it with the solenoid pictured above, which has worked fine for 9 years.

 

[SAR_Squid79]

The constant duty solenoid you need looks like this:

It is available from NAPA (part no. PHI54140) for $27.99. I use one on each of my tow rigs for the 12v power feed to the trailer, and another to power my 1/3 hp 12 volt compressor in my jeep's onboard air system.

AWESOME! Thanks!

I don't think that parallel 12v power lines will be necessary (although I've been wrong before).

I would not use this setup for winching. I really like the Jumper cables idea. But I, too, don't see why running the parallels would be necessary to jump someone off.

 

[SAR_Squid79]

SO - is this revised wiring diagram about right?

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Should I run the ground wire from the plug on the Truck side, to the negative battery pole?

 

[Robert Bills]

Should I run the ground wire from the plug on the Truck side, to the negative battery pole?

You don't need to run an additional ground wire the entire length of your truck. However, you should add a ground wire to the trailer chassis.

 

[SAR_Squid79]

It's also been suggested that I use 6 ga. wire instead of 8.

 

[ntsqd]

You don't need to run an additional ground wire the entire length of your truck.

I disagree IF this is to be a high current (jumpstart/winch) capable plug. That is a situation very similar to moving the battery to the trunk in a race car. In doing that hard starting/slow cranking is the frequent result without a full length ground wire. BT, DT & learned from it.
Keep in mind that you can wire the truck for future uses without also needing to wire the trailer for that same high current. That is to say that the battery to the plug can be 0 or 00 and from the plug to the inverter can be a wire size appropriate for the current. If that isn't a goal for you, then none of this applies.

What is the 6ga recommendation based on? If only going to run the inverter and some incidental stuff then that size is large overkill while still not being big enough for jump/winch uses.

Diagram looks good to me.