Help Installing Trailer Charge Wire - Page 2 - Fiberglass RV


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Old 04-25-2014, 04:44 PM   #15
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Name: Gina
Trailer: 1975 Boler
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If you have a large gauge wire like 4,6,etc compared to a 10 or 12 it will charge the same exact time. Larger wire does not necessarily mean faster charge. It all depends if the smaller gauge wire will not fail like melt or blow fuses. So if the smaller gauge wire won't fail then it will charge at the same rate as larger gauge wire. The resistance from the batteries is what dictates charging current.
Yes if the charge line is 12.6 volts the secondary battery can get a slightly higher charge then line but not much. I'm sure there is an equation for this but I'd rather not ask.
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Old 04-25-2014, 05:46 PM   #16
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Originally Posted by aznative View Post
If you have a large gauge wire like 4,6,etc compared to a 10 or 12 it will charge the same exact time. Larger wire does not necessarily mean faster charge. It all depends if the smaller gauge wire will not fail like melt or blow fuses. So if the smaller gauge wire won't fail then it will charge at the same rate as larger gauge wire. The resistance from the batteries is what dictates charging current.
Yes if the charge line is 12.6 volts the secondary battery can get a slightly higher charge then line but not much. I'm sure there is an equation for this but I'd rather not ask.
I think the reason for the higher gauge is voltage drop means voltage will not be enough over battery voltage to push full charge. Voltage under the hood is 13.8 - 14.2 but running wire length of TV may create enough voltage drop to provide less than 12.9 voltage required to push a full charge into the battery. Fridge running on circuit will cause some drop in line voltage reducing it further.

My understanding is mostly from what I have heard or read here. I do know that what you say about too small a wire will melt or blow the fuse is true from my own experience.

The wickedest example I ever ran across was a little corrosion on the clip for a barrel fuse that was drawing fair amount of power. End of fuse got hot and instead of blowing fuse in the middle it burned through at the end back under the metal cap. Every wire was connected AND the fuse looked fine so how come no power? Was not until I did a continuity check across fuse that I discovered how I had wasted a few hours looking in the wrong places.
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Old 04-25-2014, 07:51 PM   #17
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The voltage drop on the charge wire is proportional to the current flow. If there are no other loads on the charge wire, then the battery will charge quickly, at first. It will draw more current, so the voltage at the battery terminals might be substantially lower then at the alternator. As the battery charges, and the current flow falls, so do the losses on the charge wire. When current flow is zero, then the voltage at the alternator, and the RV battery is the same.

But all bets are off if you are running your fridge, or some other power hungry appliance. Then the current flow on the charge wire will cause a voltage drop that, if the charge wire is not sufficiently large, may be so bad that the RV battery to drains to feed the fridge. Leaving you with no lights at the camp site.
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Old 05-26-2017, 12:45 AM   #18
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Trailer: 1979 boler 1700
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Really good information throughout this discussion. On my boler 17 I have just replaced my charging system and used 4 gauge wire from my battery to the trailer switch positions and bus bars. The thought is to maximize current flow and reduce voltage loss in charging and when drawing from the batteries. I think that heavier cable will always give you more options.
Good luck with the wires. If your boler is anything like mine, the original wiring is interesting to say the least.
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Old 05-26-2017, 01:21 AM   #19
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2005 Dakota with factory tow package.
direct from the battery to fuse block, through a 30amp fuse to 7 pin connector. 10 awg wire teflon (cross link) insulation.
No diode, or other items. When the trailer is plugged in both the truck battery and trailer battery are connected together.

A simple diode will not do a good job of isolation. Point one way and you wont get any charge to trailer battery, point the other way and all you've done is add a .7volt drop between the batteries with the trailer battery getting lowered voltage.

I don't run the fridge on battery, when I'm towing there's no draw from the trailer other than what it takes to charge the trailer battery. I unplug the cord when if I'm not unhitching. Of course when I unhitch to cord gets unplugged too.
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Old 05-26-2017, 05:26 AM   #20
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hmmm good information and got me to thinking that I will run a heavier guage wire back to the battery for charging.
Right now I just use the factory wire from TV and is small.
It is fine while just going on short trips, less then 2 hours on the road, but on longer ones I do want my fridge to run on 12 volt and not propane.
If I understand right, it will just charge the battery and maintain it to the Max of 12.7, which is what my meter shows is the current at hitch.
I am going to run a heavier guage wire to back and check with meter again and see if current is greater, and install if it reward is worth the work and cost of a good isolator ... (around $35)
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Old 05-26-2017, 07:55 AM   #21
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Originally Posted by Byron Kinnaman View Post
2005 Dakota with factory tow package.
direct from the battery to fuse block, through a 30amp fuse to 7 pin connector. 10 awg wire teflon (cross link) insulation.
No diode, or other items. When the trailer is plugged in both the truck battery and trailer battery are connected together.
Exact same setup here. Except I'm using a relay as an isolator, which is controlled by the ignition key.
Relay is closed when the key is an ON.
Relay is open when key is at START or OFF.
It's a continuous-duty relay, sold specifically for this.

On the trailer side, from the 7-pin connector I'm running 6 awg wires direct to the trailer battery (fused at the positive also).
I'm using 6 awg since I was able to get some for cheap, otherwise 8 awg would have worked good ok.
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Old 05-26-2017, 08:24 AM   #22
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My '99 Frontier/2010 13' Scamp truck wiring setup I did myself (thanks to etrailer.com kits/etc.) I ran a 10ga wire w/40A breaker to the truck's 7-pin. With that wire/pin, I run my small Dometic 1.9 Cu Ft fridge on 12v while on the road maintaining 40+ deg. I've pulled as much as 6-7 hours with this setup with NO problems- even stopping to eat breakfast with the trailer/tow still connected and the fridge still on 12V! For what ever reason, not all can do this but it's worked for me. So 10ga has been MORE than enough wire for me.

FWIW, my ole '99 Nissan Frontier with a 4-cyl engine has the stock alternator and is still the original one from the factory.
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Old 05-26-2017, 08:53 AM   #23
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Originally Posted by aznative View Post
If you have a large gauge wire like 4,6,etc compared to a 10 or 12 it will charge the same exact time. Larger wire does not necessarily mean faster charge. It all depends if the smaller gauge wire will not fail like melt or blow fuses. So if the smaller gauge wire won't fail then it will charge at the same rate as larger gauge wire. The resistance from the batteries is what dictates charging current.
Yes if the charge line is 12.6 volts the secondary battery can get a slightly higher charge then line but not much. I'm sure there is an equation for this but I'd rather not ask.
A #12 AWG solid copper wire can carry approx 150 amps before the wire melts. The main problem with DC is voltage drop .
Due to the American belief that bigger is better , people run overly large charge wires at a much greater cost with little or no gain.
A #10 charge wire will allow you to charge your trailer battery.
There are many more limiting factors and increasing the wire size is not the only answer.
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Old 05-26-2017, 12:19 PM   #24
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Originally Posted by aznative View Post
...Then on the trailer side I am going to use 10 gauge again with no fuse to the trailer battery.
TOAD-CHARGE Dinghy Vehicle Battery Charger/Maintainer
I believe it's important to have a fuse at the trailer battery also. Imagine getting a short in your wiring, and the fuse on the tow vehicle blows. You have cut off the current from your tow vehicle battery, but since the cause of the short is still there, your trailer battery will now be providing power back to that same shorted circuit.
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Old 05-26-2017, 03:36 PM   #25
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Name: Gordon
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I believe it's important to have a fuse at the trailer battery also. ...
I'm tempted to say DUHHH! LOL

Anytime you add a charge wire, brake controller, etc and are adding wiring going to the tug's battery, it should be fused as close to the battery as physically possible. Something like this is not a bad way to do it.

https://www.westmarine.com/buy/blue-...lock--16932840
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Old 05-26-2017, 04:18 PM   #26
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All wiring should have overcurrent protection at the source of power. One of the only times you can over fuse a conductor is when it feeds a fire suppression pump . If the building is on fire you don't care if the wire or the pump burns up because that's the least of your problems.
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