Power Jack - battery source power?

[Schiappiv]

2016 Airstream classic
If trailer batteries are removed will the power jack run off of my tow vehicle battery when the trailer and tow vehicle are electrically connected?

[AlinCal]

I dont think so, the jack power comes off the batteries directly and with them out it will not complete the circuit. if you jumped the battery charge line to the jack power it would.
Disclaimer, I don't have that trailer but referred to your wiring diagram. I think all the units that have tongue mounted batteries are wired this way

[Schiappiv]

Thanks for the reply - appreciate it

[lsbrodsky]

I think the answer is maybe. I can tell you how it was connected on my trailer. There is a terminal strip inside the trailer where the charge line from the 7-way connects. That same strip has a 6 ga wire that goes to the battery positive. Attached to the battery clamp is another wire that runs to the fuse holder on the jack post. That is the positive supply to the tongue jack. If yours is connected the same way, there will be voltage to the jack since the circuit is complete and the ground is through the jack base plate.
However, the wire from the car alternator is long and not very big so I really cannot comment on whether there is too much voltage drop to run your jack.
Larry

[uncle_bob]

Hi

Seven way goes to a bus bar through a thermal breaker. Bus bar goes to battery cable through another thermal breaker. As long as the jack is connected to the battery cable ( = you left it connected) it will get current from the TV.

Now, will what you get through a monster long bunch of wire have low enough voltage drop to run the jack well? Maybe yes / maybe no.

Bob

[Schiappiv]

Thanks all for the replys

[A W Warn]

Originally Posted by Schiappiv

2016 Airstream classic
If trailer batteries are removed will the power jack run off of my tow vehicle battery when the trailer and tow vehicle are electrically connected?

Possibly. It depends on a few things.
I'll explain and then provide my answer at the end of my post:
Look at the 12v wiring diagram in your owners manual on page 8-18. Find the following four Bold Print items listed on that diagram and look at the wires that connect them:
Find M1 (7 way plug) and follow the 10 ga charge wire that connects to M4 (the 12volt + positive copper bus). This wire connects to circuit breaker CB3 then feeds current out through circuit breaker CB1 (when the tow vehicle is providing power). The positive battery cable is connected to CB1 and goes directly to the (+) positive terminal clamp at M2 (the battery).
Now find M10 (the hitch jack). Note that the (+) wire that feeds it is also connected to the exact same positive terminal on battery M2 where the positive battery cable comes from the (+) copper bus bar. How these two wires connect to the positive battery terminal clamp is key in how this works.

Now the answer:
If those two wires that connect at the positive terminal clamp at battery M2 are connected to each other, so that current can flow through, the jack will work with the trailer batteries removed while connected to a tow vehicle.
Even if those two wires are separated, if someone is knowledgeable enough to hold those wire in contact, the jack can be easily be made to work while connected to a tow vehicle, even with the trailer batteries removed.


If you are considering this for security, I suggest going one step further. Remove the 30 amp fuse that is in the wire between the jack and the battery. That fuse is a special slow blow fuse that most thieves will not have. Most people do not even know the location of that fuse holder. When/if you take it out, take that opportunity to purchase a spare. They can be really hard to find at the most inconvenient times.

PS
One other caution from my personal experience: If you remove the positive battery cable and leave it loose in the battery box and the trailer is connect the tow vehicle, that terminal will arc to the aluminum if it comes in contact. The spark created can instantly burn a hole in the aluminum skin before a fuse will blow or a breaker will trip.

[A W Warn]

The PS in my prior post also should have included:
When the power cord is connected to shore power a loose lying battery cable can also provide power from the converter to burn a hole or start a fire if shorted.

Since having this experience I cover a loose battery cable with rubber from an old innertube and then wrap that with electrical tape.

I'm sharing my stupidity.
Hope someone else will benefit from it.

[cazual6]

Short Answer: 99.99% NOT likely.

[david.steed]

How about an alternative but elegant solution? My Airstream didn't come with a battery in the box at the front, so I took a leap and ordered a Lithium-ion car starter battery, which I use primarily on the power jack. It works PERFECTLY. I can raise and lower it many times without losing 1 light on the 5 light gauge. It also came with all the adapters to charge phones and so on. This one costs about 85 Swiss francs (about the same in USD) and is similar to mine: https://www.trend-24.ch/product_info...xoC5NMQAvD_BwE

[uncle_bob]

Originally Posted by cazual6

Short Answer: 99.99% NOT likely.

Hi

I guess I must be in that 0.01% since I've done it and had it work ....

Bob

[Schiappiv]

Thanks again for the replys

[A W Warn]

Originally Posted by uncle_bob

Hi

I guess I must be in that 0.01% since I've done it and had it work ....

Bob

Me too, many times.