Does it matter if the wires go "through" or "to" the battery?

[robf]

Maybe this is a simple question, but I keep second guessing myself.

I need to install a new 7-pin plug - I bought a nice moulded plug with a junction box.

I'm not sure if I need to keep the original arrangement where the power wires essentially go "through" the battery (as in the top drawing in the attached picture), or if I can put all the connections inside the junction box, which would be much tidier, and just have a little tail out "to" the battery (as in the bottom drawing).


Is there effectively any difference, as long as the tails aren't too long? I would guess that as long as my truck battery is pushing (electrons) harder than my trailer battery then the battery will charge while I'm driving.
(I have an electrician friend who said he will help me out in a couple of weeks, but I see there are lots of experts here who could probably tell me right away!)

[AC0GV]

Originally Posted by robf

I'm not sure if I need to keep the original arrangement where the power wires essentially go "through" the battery (as in the top drawing in the attached picture), or if I can put all the connections inside the junction box, which would be much tidier, and just have a little tail out "to" the battery (as in the bottom drawing).

The 4-pin was never hooked to the battery. It only ran the DOT required lights on the outside of the RV. Pin #4 on the 7 pin runs 12 VDC to the battery for charging, but most tow vehicles do not charge all that well and your converter will give it the best charge. You must also disconnect the tow vehicle 12 vdc from the RV when it is not running. This can be automatic, or you can just pull the 7- pin plug when yu park. I'd put every thing in the junction box, but that will be up to your electrician.

[Defenestrator]

There's a difference, but it may or may not matter in your case. Basically, you have two paths for power coming in/out of your battery now instead of one. First, that means you need a fuse per path rather than just a single combined fuse. Second, it means you can't use the more accurate "Coulomb counter" type battery meters because all power in/out has to pass through a single shunt for them to be accurate.

Consolidating to the junction box is fine, just make sure the wires going from the battery to the junction box are big enough.

[Jann Todd]

Originally Posted by AC0GV

The 4-pin was never hooked to the battery. It only ran the DOT required lights on the outside of the RV. Pin #4 on the 7 pin runs 12 VDC to the battery for charging, but most tow vehicles do not charge all that well and your converter will give it the best charge. You must also disconnect the tow vehicle 12 vdc from the RV when it is not running. This can be automatic, or you can just pull the 7- pin plug when yu park. I'd put every thing in the junction box, but that will be up to your electrician.

All of our tow vehicles have kept our batteries fully charged when driving as long as the fridge was not on 12V. We very seldom plug into electric for charging the battery unless we are there for several days. You can also put an isolator in the vehicle to prevent the tow vehicle battery from discharging when parked with the cord still hooked up. It also helps if something shorts out to not let the all the wiring burn up on the trailer and tow vehicle. Without an isolator then you must pull the cord from the tow vehicle and plug it in after starting the vehicle. Not a great idea to me. We always pull the cord when parked overnight though in case something goes wrong.

[Lynn Eberhardt]

Best/easiest answer: "Consolidating to the junction box is fine, just make sure the wires going from the battery to the junction box are big enough.:

[k0wtz]

I have mine hooked up for the battery but it doesn't help much. Next time I wont mess with it!

Now some try to run their fridge while running and go so far as to hook up nr 6 wire to the battery.

Whatever you want to do I guess!

bob

[robf]

Best/easiest answer: "Consolidating to the junction box is fine, just make sure the wires going from the battery to the junction box are big enough.:

Too true! Thanks for all the replies - I know there are lots of subtleties, but I just don't have enough background to make sense of them. (The wires will be 10 gauge and less than 2' long, so should be plenty).

...you have two paths for power coming in/out of your battery now instead of one. First, that means you need a fuse per path...

I don't really understand how there will be two paths - ? The reason I am doing all this is because my old junky plug got wet, shorted, and the black and white wires melted a foot back from the battery and a few inches back from the plug. The fuses inside the trailer should protect everything beyond that end, it's just if there was another short closer to the battery, say in the junction box...

[Defenestrator]

Sorry, to be clear - going "through" the battery requires two fuses. "to" the battery just requires one.

[robf]

Originally Posted by Defenestrator

Sorry, to be clear - going "through" the battery requires two fuses. "to" the battery just requires one.

Ok, thanks! ...maybe I am starting to figure it out.

[gordon2]

Originally Posted by robf

..., it's just if there was another short closer to the battery, say in the junction box...

Any wire carrying current from the battery that is not a ground potential should have a fuse as close to the battery terminal as practical. In other words, on the wires that connect to the positive post (except for the rare case of positive grounding). Visualize where the wire(s) from the positive post could touch anything at ground potential... usually the other battery post and it's wire(s), the trailer's frame and any metal attached to the frame. Understand that if not protected by a fuse, the wire will burn up if the insulation fails (or something worse can happen). Therefore you need to have a fuse between those potential contact points and the battery.

Often that fuse is about ten inches from the battery post. But even that might be too far. But if is so close that the fuse and fuse holder are inside the battery box, that will eventually lead to its failure from the corrosive environment in the box if its a regular wet cell type of battery.

One of the best and safest fuses for our batteries is pictured below. You cant get a fuse any closer to the battery post then on the post itself!. Thats what I have and I use an AGM battery so that it will not corrode the fuse and fuse holder for a number of years (or the ring terminals on the wiring). If used with a regular unsealed battery I would plan on doing R&R on it annually.

Mount and fuse sold separately:
https://www.amazon.com/gp/product/B0019ZBTV4
https://www.amazon.com/gp/product/B00198FP8Y

[thrifty bill]

I installed a seven pin connector on my Trillium, even though it does not have brakes. I got the weatherproof J box, placed it on the tongue near the battery. Works well. Now the TV charges the battery while I am traveling. I needed the seven pin connector on my TV anyway with the Escape 19. The battery on the tongue also makes hooking up my portable solar very easy. And since my Escape 19 has the battery on the front box, it easy to hook up the portable solar there too.

[Peder_y2k]

Assuming your diagram has red for positve and black for negative, any fuses should be on the positive red side/s. Also, like previously mentioned, a battery isolator (around $30) should be used on the tow vehicle in case you forget to disconnect for any length of time. **** happens when you least expect. Don't be a disaster looking for a place to happen!

[robf]

Originally Posted by Peder_y2k

Assuming your diagram has red for positve and black for negative, any fuses should be on the positive red side/s. Also, like previously mentioned, a battery isolator (around $30) should be used on the tow vehicle in case you forget to disconnect for any length of time. **** happens when you least expect. Don't be a disaster looking for a place to happen!

The red/pink in the drawing represents white wires, black is positive.
I believe our truck - 2017 Tacoma - has an isolator built in with the tow package. I'll have to follow up on that.

[robf]

All done! (Except for attaching the junction box to the frame with more than just hose clamps - once I'm no longer social isolating and can get some help.)
Thanks for all the input.