Help Installing Trailer Charge Wire - Fiberglass RV


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Old 04-17-2014, 09:10 PM   #1
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Name: David
Trailer: Scamp
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Help Installing Trailer Charge Wire

Here is the SitRep:

in August bought a '93 13' Scamp. Been fixing it up, including rewiring the entire trailer with a round 7 pin(flat pin) umbilical. I am VERY please with how this went.
I am presently using only 4 of those 7 with long term plans of putting an axle on the scamp with Electric drum breaks.
Short term plans include using the charge wire to charge the battery on the tongue of the Scamp as we travel.
We have a 2011 Honda Odyssey with a tow package, but that only includes a flat four connector. Honda doesn't offer a round 7pin option for the Odyssey (Boo!).
I have the following round adapter coming for car side (LINKED HERE). It will allow me to A) use the trailer round-7, and allow me to connect to a 12V batter supply from the vehicle side.

HERE IS MY QUESTION: Where should I get my 12 V supply from the car/van side?
an obvious solution is right from the batter, but this would require proper wire, fuse, diode, and properly running the wire to the back of the vehicle.
Since this Odyssey is wired so well, COULD I GET THE PROPER SUPPLY FROM THE BACK OF THE VAN AND THE WIRES AND FUSE PANEL THAT ARE THERE?


SUB QUESTIONS:
I know that I am trying to get a 12V supply to the trailer to charge the battery, but how many amps does that supply need to be?
you will see in the pictures below that there is a 12V "light" plug in in the back of the van. Can I just piggy back on that - assuming that I would never use it for double purpose when in use by the trailer?

Thanks. David
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Old 04-17-2014, 09:31 PM   #2
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Important detail: I have no refrigerator in the scamp and will have no other load drawing while traveling other than charging the battery.
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Old 04-17-2014, 11:07 PM   #3
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I recently wired a 2010 Honda CRV and I connected my charge wire directly to the battery, then to a 40 amp circuit breaker and then routed it back to the 7 pin plug. I used #8 stranded wire.

You can't use the existing circuits, especially the utility socket, because they are all fused to low and have small wires that won't carry the 25-30 amps the battery can draw when it's low. What will happen is that you will just blow fuses... and replacing them with larger fuses with small wire isn't a good idea.... in fact it's a bad idea.
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Old 04-18-2014, 06:24 AM   #4
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Some have described wiring it such that when the car is off it can't draw from the battery. Did you do this? How?
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Old 04-18-2014, 07:04 AM   #5
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Use a battery isolator or solenoid designed for the purpose.
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Old 04-18-2014, 07:49 AM   #6
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This is my understanding ab TV/trailer connectors regarding to 7/4pin adaptors: This only works if TV already had 7pin connector installed, not the other way around. To modify it becoming a 7pin from installed 4pin, one should follow schematic for harness wiring, i.e. run extra wires exactly as it is required, especially a power line runs directly(with fuse) to towing vehicle battery. To determine size of this wire and fuse, get info on enet or right at suppliers when you buy the wire. To charge trailer battery from towing vehicle's cigarette lighter/extra 12VDC supply is improper due to the size of its wire and fuse...Just my thought.
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Old 04-18-2014, 09:05 AM   #7
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Here is a complete write up but sorry no pictures
odyssey wiring
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Old 04-18-2014, 09:29 AM   #8
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Quote:
Originally Posted by Thinh View Post
This is my understanding ab TV/trailer connectors regarding to 7/4pin adaptors: This only works if TV already had 7pin connector installed, not the other way around. To modify it becoming a 7pin from installed 4pin, one should follow schematic for harness wiring, i.e. run extra wires exactly as it is required, especially a power line runs directly(with fuse) to towing vehicle battery. To determine size of this wire and fuse, get info on enet or right at suppliers when you buy the wire. To charge trailer battery from towing vehicle's cigarette lighter/extra 12VDC supply is improper due to the size of its wire and fuse...Just my thought.
As seen in post #1, many 7 pin connectors come prewired with a plug-in 4 pin connector and pigtails for the remaining wires. If you use the plug-to-plug connector, be sure to wrap it well to prevent water damage over the years.
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Old 04-18-2014, 09:33 AM   #9
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Originally Posted by DaMScampers View Post
Some have described wiring it such that when the car is off it can't draw from the battery. Did you do this? How?
Solenoid type isolators are inexpensive and easy to install.

However, while they resemble some starter solenoids, the latter are not designed for continuous use, may draw more current, and are more prone to failure as many motorhome owners have discovered.
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Old 04-18-2014, 10:03 AM   #10
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David, if you haven't already found it E-trailer has a video on how to connect your wiring harness correctly to your Honda Odyssey. I don't have a Honda but I did have to run a charge and brake line for my Subaru as it did not come prewired with either of those - just the lights for the trailer where prewired and where connected inside the vehicle via a similar harness. Had to run the charge line directly from the vehicle battery and fuse box.
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Old 04-18-2014, 10:30 AM   #11
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Dave Tilson offered a couple of links to specific relays in this post.
Voltage on TOW Connector

One relay reads the battery voltage and automatically turns on when the vehicle is running. Senses the higher voltage of the car charging system providing power.

The other is the less expensive and is wired into an accessory circuit that turns it on only when the car is on.
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Old 04-18-2014, 10:32 PM   #12
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Thank you all for your help so far!
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Old 04-25-2014, 03:25 PM   #13
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So I am going to tackle this project soon as well. So I am going to use 10 gauge wire from the battery with a 30 amp relay (activated only when truck is on) also a fuse. This wire will connect to my 7 pin harness on my tow vehicle. Then on the trailer side I am going to use 10 gauge again with no fuse to the trailer battery. I am in the exact situation you are. Looking to only top of my battery during travel. Plus I spend a long time listening to my husband (electrical) engineer talking about draw power, resistance, blah blah blah. Funny thing is I was going to do this same setup just oking it thru him.
This looks like a nice product too.
TOAD-CHARGE Dinghy Vehicle Battery Charger/Maintainer
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Old 04-25-2014, 04:06 PM   #14
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At one point someone suggested I check at the scrap metal recyclers for wire so I could run heavier 8 gauge back to the plug and get it for cheap.

I followed up on that suggestion and if one does not mind a little looking the yard I checked had a good supply of wire much cheaper than buying it from big box store. They had tail end of spools of wire where the wire is brand new.

I want 8 gauge because battery is charged by the difference between the line voltage and the battery voltage. Less voltage drop from heavier wire so faster and more complete charge. The other reason is if I ever want to run my fridge on 12 volt going down the road, reports are that 10 gauge won't keep up and it will tend to run the battery down.

One of the EE types might answer a question that has been bugging me. Can a battery "accumulate" a charge? If charge line has say 12.6 volts will the battery ever reach a full charge of 12.9 volts? My (limited) understanding is that current flows into the battery better at higher voltage, but wondered if it could deliver any charge if not above battery voltage.
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