Adding a battery

[Mark V.]

As one of the first mods to my new Boler, I want to add a battery.
I've built a tray to hold the 20# propane cyl. and the battery box on the tongue but the wiring has me stumped. Where can I tie into the existing wiring and how can I have my vehicle charge the battery while driving (future requirement).

I've Googled for about an hour and can't find a decent explanation... Even a hard copy of Trailer Life's RV Repair & Maint. doesn't describe it.

The ground seems straight forward - Just tie into the white wire somewhere under the front bunk.

The positive wire (black) doesn't appear to be so simple, can someone please explain it to me?

TIA,
Mark

[Darnelle]

My trailer battery is charged via the 7-pin plug that is wired directly to the TV battery (positive side). I used 10-guage wire with a solinoid-type battery isolator and 30 amp resetting circuit breaker. (Directions are in the package.)

This enables charging ONLY when the truck is running. Otherwise you risk having your trailer drain your vehicle battery. (You could also unplug your trailer from the vehicle when you stop for any length of time, but I like things to be dummy proof. Unplug your umbilical and then forget to plug it back in means towing without lights and perhaps dragging the line and ruining it.)

Both my vehicle and the trailer are grounded to their respective frames. The 7-pin connects these grounds together. I do not trust grounding only via the ball hitch. My brake controller grounds directly to the battery, per its instructions.

Vehicle-end and trailer-end plugs come complete with instructions, but you will have to watch the color codes as all vehicles are not the same. 6-pin = brake lights, running lights, left blinker, right blinker, ground, battery charging. 7-pin adds electric brakes.

[Casita Greg]

I may not be interpreting your post correctly...When you say you want to add a battery, am I correct in assuming that you already have an existing one (for a total of two trailer batteries?) If this is correct, then the following may help. Also, does your trailer presently have a converter installed? If you just want to add a house battery where none currently exists, then this probably isn't what you're looking for, but if you already have one battery installed then this is what I would recommend. So, for what it's worth, here goes...

One thing to keep in mind is that your TV's alternator most probably will not be capable of charging three batteries at one time. It isn't even really all that effective at charging two batteries. (Tow Vehicle battery, main trailer battery, and now an auxiliary back-up trailer battery as well = way too much demand on your poor little alternator.) Not recommended.

You'd be better off installing a battery selector switch {Batt #1/Batt #2/Both/Batt Off} in your trailer's already existing charging circuit (+), then select the battery you want to use, but stay away from trying to use or charge both simultaneously.

Wiring should be minimum 10 gauge, but larger is always better.

Note: Only the positive wires are connected through the switch, the trailer ground is common bond to the converter's ground.

[Mark V.]

I may not be interpreting your post correctly...When you say you want to add a battery, am I correct in assuming that you already have an existing one (for a total of two trailer batteries?) If this is correct, then the following may help. Also, does your trailer presently have a converter installed? If you just want to add a house battery where none currently exists, then this probably isn't what you're looking for, but if you already have one battery installed then this is what I would recommend. So, for what it's worth, here goes...

One thing to keep in mind is that your TV's alternator most probably will not be capable of charging three batteries at one time. It isn't even really all that effective at charging two batteries. (Tow Vehicle battery, main trailer battery, and now an auxiliary back-up trailer battery as well = way too much demand on your poor little alternator.) Not recommended.

You'd be better off installing a battery selector switch {Batt #1/Batt #2/Both/Batt Off} in your trailer's already existing charging circuit (+), then select the battery you want to use, but stay away from trying to use or charge both simultaneously.

Wiring should be minimum 10 gauge, but larger is always better.

Note: Only the positive wires are connected through the switch, the trailer ground is common bond to the converter's ground.

Funny, when I wrote the post, I thought it was clear but seeing your responses, I see that I failed to mention that my trailer currently *does not have* a battery installed. Also there's no indication that it ever had one. The trailer is in good shape and doesn't appear to have ever been modified, so the wiring is all original.

The wiring on the TV side seems pretty straight forward - especially if there would be instructions with a solenoid. It's the trailer-side wiring that eludes me.

I've already replaced the 7-pin connector as the original one had damaged contacts, and the original metal casing freaks me out. A plastic 7-pin connector housing just seems like a safer option.

I have some 10 gauge wire (black & white) and a 30 amp self resetting breaker, I just don't know how to connect the battery to the existing trailer wiring!

-M

[Donna D.]

This is for a Scamp, but since Bolers and Scamps are kissin' cousins it may help: Wiring Diagram - Scamp

[peterh]

OK, here's a picture of how I would do it.

• I would put a standard fuse with a slightly higher value at the tow vehicle's negative battery pole in case the thermal resettable fuse fails.
• I would place fuses of the same value on the positive lead at the TV's positive pole, at the trailer's battery tray, and just inside the trailer wall.
• You should wire the two trailer battery terminals positive-to-positive and negative-to-negative
• The two batteries should be of the same type and approximate age.
  • This prevents a battery with a different storage lifetime and peak/float voltage from parasitizing (draining) the charge from a partner battery with a different peak/float voltage or which can hold its charge longer.
  • You can have two "wet cell" batteries or two AGM batteries, but not one "wet" and one AGM battery.
  • Battery ages should be within a year or so of each other.
• If you add a solar panels and charge controller, I'd put the charge controller on its own fuse with the "wiring just inside trailer wall."

I would not be too concerned about your tow vehicle's alternator and charging capacity. Even base-model economy cars have alternators with 65-Amp or better capacity; more than enough to operate your car's running lights and charge both your car's starting battery and two batteries in the trailer. A bigger worry would be making sure you don't hook your car an trailer together before you get your car started when the trailer batteries are really, really low. When your trailer batteries are near dead it's better to treat the situation like you would when you jump-start a friend's car: get you car running, then hook connect to the other vehicle with the dead battery.

[Mark V.]

OK, here's a picture of how I would do it.


Attachment 28902

• I would put a standard fuse with a slightly higher value at the tow vehicle's negative battery pole in case the thermal resettable fuse fails.
• I would place fuses of the same value on the positive lead at the TV's positive pole, at the trailer's battery tray, and just inside the trailer wall.
• You should wire the two trailer battery terminals positive-to-positive and negative-to-negative
• The two batteries should be of the same type and approximate age.
  • This prevents a battery with a different storage lifetime and peak/float voltage from parasitizing (draining) the charge from a partner battery with a different peak/float voltage or which can hold its charge longer.
  • You can have two "wet cell" batteries or two AGM batteries, but not one "wet" and one AGM battery.
  • Battery ages should be within a year or so of each other.
• If you add a solar panels and charge controller, I'd put the charge controller on its own fuse with the "wiring just inside trailer wall."

I would not be too concerned about your tow vehicle's alternator and charging capacity. Even base-model economy cars have alternators with 65-Amp or better capacity; more than enough to operate your car's running lights and charge both your car's starting battery and two batteries in the trailer. A bigger worry would be making sure you don't hook your car an trailer together before you get your car started when the trailer batteries are really, really low. When your trailer batteries are near dead it's better to treat the situation like you would when you jump-start a friend's car: get you car running, then hook connect to the other vehicle with the dead battery.

Thanks to both DonnaD and PeterH,

Between the two, I've determined what I need to do trailer side. Now looking at the tow vehicle, I'm not convinced that the dealership wired my 7-pin connector adequately. There's a 20A fuse at the battery, and a factory harness at the rear. My question is about the wire gauge. It's nowhere near the 10 gauge I used trailer side but as it's a factory harness I can't simply pull a new positive wire and attach it. Does this look adequate? Am I protected by using the smaller 20A fuse than the 25A that PerterH suggeseted?

See attached for pictures from each end with a penny for scale.

Note: On the first image, the positive wire is the black one between the green and yellow.

[peterh]

As you reduce the wire size (gauge) it's capacity goes down, and the fuse capacity has to drop down with it. 12g wires with a 20A fuse is a fine combination and quite adequate to the application. You're also fine just having the one fuse; two fusible elements is overkill unless you have a resettable fuse in the mix.

Running 10 gauge from your battery to your fuse panel is a good idea, too. Using a larger wire reduces power loss due to the wiring's internal resistance when you're drawing lots of power, but 12 (or even 14) gauge wire with matching 20 (or 15) Amp fuses from your panel on out to your trailer lighting and other devices is, once again, all you need. (The only exception would be wiring up an inverter or battery charger/converter/solar charge controller. I'd stick with 10g to and from those devices.)

[Tom U]

Originally Posted by peterh

OK, here's a picture of how I would do it.


Attachment 28902

• I would put a standard fuse with a slightly higher value at the tow vehicle's negative battery pole in case the thermal resettable fuse fails.
• I would place fuses of the same value on the positive lead at the TV's positive pole, at the trailer's battery tray, and just inside the trailer wall.
• You should wire the two trailer battery terminals positive-to-positive and negative-to-negative
• The two batteries should be of the same type and approximate age.
  • This prevents a battery with a different storage lifetime and peak/float voltage from parasitizing (draining) the charge from a partner battery with a different peak/float voltage or which can hold its charge longer.
  • You can have two "wet cell" batteries or two AGM batteries, but not one "wet" and one AGM battery.
  • Battery ages should be within a year or so of each other.
• If you add a solar panels and charge controller, I'd put the charge controller on its own fuse with the "wiring just inside trailer wall."

Peter,

Some questions:

Can battery #2 be located on the opposite side of the trailer? If so, 10 or 8 gauge wire?

Can a single solar controller charge both batteries when hooked up this way? I saw a controller that has circuitry and output for charging two separate batteries but a single hook up would be more simple.

Will a group 29 @ 120AH and a group 27 @110AH work together as a bank? Both are 12v deep cycle wet marine batteries.

Thanks - btw "thank you" emoticon not in new 'Smilies" list

Tom

[Con]

Of all the vehicles I have bought or leased over the last 35 years I have only had one the had the charging circuit or brake circuit in the factory harness. That was my 2003 Chevy Silverado. All others, even when I ordered them with the tow package, I had to run in my own 10 ga. wires and add the solenoid and circuit breakers. Taking it to a dealer, forget it. They don't know what the hell they are doing. I had to tell them how.
I would suggest you learn how and then when there is a problem, you will have a good idea on how to fix it.
As matter of fact I have the components sitting on my work bench to install in our new 2010 Hyundai Santa Fe. Again, the tow package doesn't have everything it should.