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Author Topic: Wiring battery combiner from tow vehicle to trailer  (Read 539 times)

Mp funfinder

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Wiring battery combiner from tow vehicle to trailer
« on: February 25, 2018, 09:08:36 PM »
Hi to all. Newbie to this forum as well as forums in general.

Wondering if someone can walk me through a project they have done. Dos/doníts etc. Looking at using a Citrix 12/24 120 amp model. 2014 Ford F-150 5.0 liter pulling 2011 funfinder210x

Thank you

Lou Schneider

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Re: Wiring battery combiner from tow vehicle to trailer
« Reply #1 on: February 25, 2018, 10:46:40 PM »
Welcome to The RV Forum!

First, you may not need a battery isolator.  If your truck sends 12 volts to the trailer connector when the ignition switch is on and doesn't when the switch is off your batteries are already isolated and you're good to go. 

You can verify this with a test light or multimeter connected between Pin 4 (looking into the truck socket, the upper right contact) and ground.

« Last Edit: February 25, 2018, 10:51:12 PM by Lou Schneider »

Mp funfinder

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Re: Wiring battery combiner from tow vehicle to trailer
« Reply #2 on: February 26, 2018, 08:41:49 PM »
Hi Lou, thank you for your reply.

Little confused, Iím looking to charge the house batteries while in tow using the trucks alternator. I assumed the power from the 7 pin trailer connector supplies nowhere near enough amps to sufficiently charge the house batteries.

Iíve read about this set up in motor homes and van conversions, but not so in truck and travel trailer configuration. This would be in addition to a battery and small solar upgrade as well. Any info/insights anyone wants to provide it would greatly appreciated.

Roy M

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Re: Wiring battery combiner from tow vehicle to trailer
« Reply #3 on: February 26, 2018, 09:23:26 PM »
Lou is correct, the truck alternator should maintain the trailer battery, This is necessary to ensure power is available to activate the brakes in the event of a break away.  If it is very low or dead the truck charging system won't be enough to bring it back.

Jim Godward

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Re: Wiring battery combiner from tow vehicle to trailer
« Reply #4 on: February 26, 2018, 09:25:28 PM »
Wondering if someone can walk me through a project they have done. Dos/doníts etc. Looking at using a Citrix 12/24 120 amp model. 2014 Ford F-150 5.0 liter pulling 2011 funfinder210x

This can and is done often.  That said the voltage drop can be a problem so you need to use sufficient wire sizes.   In the past I used a No 6 stranded wire from the truck to the trailer.  However I believe a No. 8 wire would be adequate.  Many years ago I was on an RV tour with the then Trailer Life/Motorhome magazine GURU and that is what he was recommending. 
Jim
Jim & Pat Godward
AC7PO & KD7ZDM
Hillsboro, Oregon

grashley

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Re: Wiring battery combiner from tow vehicle to trailer
« Reply #5 on: February 27, 2018, 07:04:53 PM »
The 7 pin connector does contain a "hot" wire to maintain / charge the TT battery.  HOWEVER, it will only give excess amps to the TT, and the wire is often such a small gauge that the charging is not as much as one might expect or hope.  Jim's comment on wire gauge is excellent advise.
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tslarson

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Re: Wiring battery combiner from tow vehicle to trailer
« Reply #6 on: March 01, 2018, 10:22:13 PM »
A few things come to mind. If this were a boat or a motorhome, the batteries would be close together, and there is an advantage to having the batteries combined (like one big battery) during charging, as the alternator will see the combined voltage and charge at the rate needed to charge all batteries. The charge will favor the battery that is the least charged. When the batteries are not being charged, the combiner separates the batteries, then the house and starting batteries are separated so there is always one in reserve for starting. Not so-or needed on a TT as the TV is disconnected while camping.
On a TT the battery is 25+ feet from the alternator (really 50+ feet as you need to run a ground wire back to the battery, or a ground wire from the TT battery to truck frame and one from the TV battery to the TV frame). There will be a lot more resistance in that loop of wire, even if it is 8 gauge, than the loop of wire from the TV battery to the starter and alternator (about 6 feet total). The big problem here is that this resistance difference will cause the voltage regulator on the TV alternator to favor seeing the voltage in the TV battery and charge accordingly. If the TV battery is totally charged, the alternator puts out very little and even less can get back to the TT battery. In my opinion this is the main cause for the TV not charging the TT battery, not wire size, but the smaller wire size in the TV charge wire makes this condition even worse. I see no big benefit to using a combiner to connect the two batteries, maybe a larger gauge charge
wire loop and a larger amp capacity relay. Much cheaper. If you really want to charge your TT batteries quickly from your TV you will need a dual output alternator and a increased capacity charging circuit. Thats how we do it on boats.
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Mp funfinder

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Re: Wiring battery combiner from tow vehicle to trailer
« Reply #7 on: March 05, 2018, 07:33:53 AM »
Big thanks to tslarson,grashley, and Jim Godward for your help and input. Thinking now that Iíll stick with the Citrix combiner. But wire it in such a way so that iím using 8 or 6 gauge (with budget in mind) from the tv battery to the hitch then use a quick disconnect (like the ones used for jumper cables) between the tv and the tt. This would be totally independent of the 7 way hitch plug.

As an aside, Iím planning on upgrading to two 100/110 ah group 31 ages on the front of the tt. Down the road, would like to add solar,but not in the budget just yet. We do mostly long weekend trips only one hour or two from home. Sometimes we are on a hookup but more often are not. Thank you gents

Jim Godward

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Re: Wiring battery combiner from tow vehicle to trailer
« Reply #8 on: March 05, 2018, 03:36:31 PM »
An additional comment, be sure to fuse both ends of the wires and you will need both a positive wire and the negative wire. 
Jim
Jim & Pat Godward
AC7PO & KD7ZDM
Hillsboro, Oregon