vehicle chraging trailer battery parts question

[Roberto]

I want to add a deep cycle battery in my CDN M101 trailer to run stuff when camping and want to be able to charge it from vehicle when driving but not sure the part/ parts I need to purchase that charge while your driving when trailer lights pigtail is plugged into vehicle power? Can anyone tell me what it is I should be looking for?

thanks
Rob

 

[Rubiconcruiser]

A 7 pin connector is a good choice, 5 will work but it isnt a standard. The 7 pin has a red or black depending on your setup. this connected to the main vehicle battery is all that is required to maintain a charge on the system. An isolator in the system is a great addition this going on if you run dual batteries. Fused at 30 or 40 amps dependent on wire size, and wire size being a #8 or larger wire is preferred, smaller will work but overload is at a higher potential. Some commercial trailers use a #10, this is ok but use it hesitantly.

 

[western flyer]

A 7 pin connector is a good choice, 5 will work but it isnt a standard. The 7 pin has a red or black depending on your setup. this connected to the main vehicle battery is all that is required to maintain a charge on the system. An isolator in the system is a great addition this going on if you run dual batteries. Fused at 30 or 40 amps dependent on wire size, and wire size being a #8 or larger wire is preferred, smaller will work but overload is at a higher potential. Some commercial trailers use a #10, this is ok but use it hesitantly.

^ Concur.

I just added a 7 pin connector to my 80 series LC. mainly to charge the battery in my pop up trailer. I used a 30 amp circuit breaker and a solenoid (both purchased at a trailer supply place for that exact purpose) mounted near the LC batt. I used 4 ga. Ancor cable, but you likely can get by with a smaller charging cable, such as 8 ga.

 

[Roberto]

so a 7 pin pigtail on trailer and some wires go from it to my tailights and also my deep cycle battery in trailer? so a heavy gauge wire from breaker and solenoid from main vehciel battery back to hook up and gets wired into reciever plug?

Rob

 

[western flyer]

Either of these will convert your 4 pin connector to a 7 pin connector on the tow rig:
http://www.etrailer.com/Wiring/Curt/C57674.html
http://www.etrailer.com/Wiring/Tow-Ready/30717.html

You would run your 8 ga. (or larger) cable from the tow rig battery and fuse/curcuit breaker back and connect to the black wire on that 7 pin connector (now mounted at the rear of the tow rig). White to ground. The blue wire is for brakes, the yellow is AUX; tape these up if you will not use them (yet). I assume you already have a traditional 4 pin connector on your tow rig. With this new 7 pin connector hooked up as I described it, you now have added a positive connection from the tow rig battery that is ready to charge a trailer batt.

------------------------------

Then you would wire this to the front of your trailer (I used that exact one):
7-Way Molded Trailer Wire Connector, 8' Long Hopkins Wiring H20046

I suggest you connect the old trailer wiring to the new 7 way trailer wiring molded connector in one of these boxes (I used this exact box): Trailer Wiring Junction Box Hidden Hitch Accessories and Parts 38656

From this junciton box you would then run your positive cable (connected to the black wire terminal in the box, which is now connected to the black wire of the 7 way molder trailer connector) to the trailer batt. And ground the battery and connect the ground to the junction box, etc.

Does that help?

 

[skersfan]

10 gauge is all that is necessary. Ever RV manufacterer uses 10 gauge, no need for more. Isolator is a good idea if you stay in camp for days upon days, or leave the trailer hooked to the tow vehicle, otherwise not necessary. If you can run down your truck battery in less than 4 days you have another problem

 

[ntsqd]

10 ga can likely handle the current, but if the length of the run is large it may not have an acceptable voltage drop. When a fully charged battery sits at 12.6 and a 50% discharged (max most mfg's recommend) is 12.04 volts it doesn't take much voltage drop to result in a battery that never gets fully charged and as a consequence will live a shorter than expected life.

I have a table in a catalog that I use to calc voltage drop and I've read of on-line calculators. Before settling on 10 ga. I would measure the length of the run and determine how much drop you're willing to allow, then figure out what wire or cable size will yield that.

 

[Roberto]

thanks so much fellas, gonna do some ordering from Etrailer, thanks

Rob

 

[skersfan]

As stated, every single RV manufacturer uses 10 gauge, and normally have longer runs on all fifth wheels than any trailer built by a private individual. I have a crew cab dually with a 42 foot fifth wheel behind it, still only 10 gauge. Have never had a failure due to wiring.

I have built more than 400 hundred trailers from jet ski to huge goose necks, and never used higher than 10 gauge wire. It is total over kill and serves no purpose. 20 amp fuse in line, isolater if desired, nothing more.

Every single pigtail for 7 pin connectors uses 10 gauge wire.

Most large RV 5th wheels have multiple batteries. Depend heavily on them. 10 gauge wire is adequate for those.

 

[ntsqd]

Just because it's how everyone in the biz of building trailers does it does not mean that it's the best way to do it. Being the jaded person that I am I'd argue that because they do it that way is a very good reason NOT to do it that way without more information.

According to my Ancor Marine catalog's chart a 10ga. wire at a 20A rate exceeds a 3% Voltage Drop beyond 15 feet of circuit length - that includes the ground path, so 7.5 feet of + wire. 3% Voltage Drop is what I'd consider to be the max allowable for a charging circuit. So a larger gauge cable does have a purpose and is worth looking into.

Though it's specifically pointed at solar charging, some suggested reading: The RV Battery Charging Puzzle HandyBob's Blog

 

[TobyB]

The answer on this is, 'it depends'.

If the trailer draws significant current while it's being towed, maybe
heavier gauge is a good idea. But let's say you've run your
60AH battery to 80% depth- of- discharge, and now you're
going to tow it 4 hours home. When you plug it into the truck,
it'll pull a pretty high amperage at first- and the 10 gauge wire will
limit the maximum draw. Resistance of 10ga is 1 ohm per
thousand feet, per wikipedia, so if we guess 20 feet in the tow
rig and 20 feet on the trailer, that's about .04 ohms IGNORING the
resistance of the connections and assuming a perfect ground.
Your trailer's at about 12v, your
land cruiser's at 13.5- so it'll try to charge at 60 amps, roughly,
limited by the resistance of the wire. Which should take about
an hour, and that wire is going to be toasty. Well over 100c,
per the same Wikipedia page.
But the trailer battery isn't a perfect load- it'll pull up to 12.5 volts
pretty quickly, and current drops to 40 amps. Now the wire's
just running at 90c, and the battery will be charged in about an
hour and a half.
But wait- the battery pulls up to 13v in less than an hour, current drops
to 20 a, and now, it's STILL going to take an hour plus to charge
that trailer battery fully.
An hour later, it's pulling less than 10 amps....
...and so on. Eventually, you get home, the battery on the trailer's
at 90-something percent charge, and that's your weekend.
You tow out a few hours in a few weeks, the battery tops off, and
you're a happy camper.

Probably OK. Not ideal, and especially if it's cold, the battery wants a bit more.

But, same scenario, if you only tow home for an hour, headlights, rear defrost, heater
fan on, radio, maybe some extra driving lights.... your alternator has a hard time holding 13v,
the battery only gets maybe 50% of a charge, and if you go out a month later, towing only an hour,
you've MAYBE got 70% of a charge.

So big batteries, heavy usage, short charge periods, cold weather, bad grounds-
all can add up to a system- using 10 gauge- that's a bit marginal.

My car trailer that uses the battery only for the winch and
break- away could probably function fine on 12ga, as I take MAYBE
10% out of it winching the car on and off, and tow for hours to get
to the track and then hours to get home.

If you think you're going to use a LOT of juice, heck, run 8 gauge-
but you might need some sort of current limiter to save the
system. Or just a big fuse or breaker.

I think most of us will be fine with 10.

I ran 6 to the back of the truck, and 10 on the car trailer, since
the car trailer battery will never be a 'house' battery.
But I have an Anderson connector on the back of the truck, and
a set of clips to use it as jumper cables, winch supply, etc.
It has an 80a marine breaker on it, and I've never popped it.

It's a fun set of problems...

t

 

[Rubiconcruiser]

Toby,, you sent a great idea to the masses of us who are still in the dark, you have shed light where there has been none and I say thanks, If I can understand it anyone in this group can DUH ( Homer Simpson)

 

[3D FJ]

I have an m416 that i am currently building up. I'm in the planning stage now and came across this thread. I plan on placing an auxillary battery in the tongue box to run lights while camping. If i have a 7pin connector at the back of my truck already, am i correct that all i would have to order is this?

http://www.etrailer.com/p-H20046.html

And then connect the 10ga 12V wire from that harness to a junction box and then to the aux battery in the tongue box and then it's charging? What am i missing? This is basically post #5 above correct?

If i don't plan on unplugging the 7-pin from the truck while parked, will I need an isolator?

 

[titanpat57]

I have an m416 that i am currently building up. I'm in the planning stage now and came across this thread. I plan on placing an auxillary battery in the tongue box to run lights while camping. If i have a 7pin connector at the back of my truck already, am i correct that all i would have to order is this?

http://www.etrailer.com/p-H20046.html

And then connect the 10ga 12V wire from that harness to a junction box and then to the aux battery in the tongue box and then it's charging? What am i missing? This is basically post #5 above correct?

If i don't plan on unplugging the 7-pin from the truck while parked, will I need an isolator?

Toby does a great job putting that in an understandable form.

Me personally...I would still hook it up as is, and run a seperate charging cable back to the battery, with a 30 or 40 amp circuit breaker screwed to the fender or wheel well http://www.etrailer.com/dept-pg-Accessories_and_Parts-sf-Wiring-pc-Circuit_Breaker.aspx Then run a wire through the truck battery to the trailer battery neg and pos...then your sure of a good direct link. http://www.amazon.com/Superwinch-1551-commercial-terminals-capacity/dp/B0009PD5R6/ref=pd_cp_e_3

This is a great read... http://www.marxrv.com/12volt/12volt.htm

 

[rusty_tlc]

In my 25 years in electronics I've never said "Gee I wish I had used a lighter gauge wire for that design."

 

[John E Davies]

In my 25 years in electronics I've never said "Gee I wish I had used a lighter gauge wire for that design."

LOL. I agree about trailer wiring. Go bigger, at least from a 10 AWG to 8 AWG. The cost is negligible and the results will be better. The only real issue is when you can't use common connectors and splices.

I personally would wire a separate charge cable and ground from the truck battery to the rear bumper, and use a set of 75 amp winch disconnects. Then add equal sized wiring, including ground, to the trailer battery. I don't like the idea of high current going through those problematic trailer light connectors. You can get generic high current spade connectors from NAPA. Be sure to install a breaker at the firewall and possibly an ignition switched relay, in case you are forgetful about unplugging at the campsite. ALSO a breaker at the camper battery, in case that hot wire gets shorted to ground. Unless you install a battery shut off switch at the trailer battery, that one wire will be hot as long as the battery has a charge.....

John Davies
Spokane WA USA