Help Installing Trailer Charge Wire

[DaMScampers]

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

[DaMScampers]

Important detail: I have no refrigerator in the scamp and will have no other load drawing while traveling other than charging the battery.

[Bob Miller]

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.

[DaMScampers]

Some have described wiring it such that when the car is off it can't draw from the battery. Did you do this? How?

[Roy in TO]

Use a battery isolator or solenoid designed for the purpose.

[Thinh]

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.

[Dudley]

Here is a complete write up but sorry no pictures
odyssey wiring

[Bob Miller]

Originally Posted by Thinh

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.

[Bob Miller]

Originally Posted by DaMScampers

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.

[Carol H]

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.

[RogerDat]

Dave Tilson offered a couple of links to specific relays in this post.
http://www.fiberglassrv.com/forums/f...tml#post452993

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.

[DaMScampers]

Thank you all for your help so far!

[aznative]

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

[RogerDat]

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.

[aznative]

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.

[RogerDat]

Originally Posted by aznative

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.

[David Tilston]

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.

[Bolerpete]

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.
pete

[Byron Kinnaman]

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.

[Gerry]

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)