12 volt charge line for towing? Need advice

[Titan Ken]

I have the Big Tow package and looking at the trailer plug connector there is a "12v +" on the connector. I checked it with a volt meter and indeed it is an ignition switched 12 volt connection. Is the amperage and wire gauge suitable to provide sufficient battery charging to my travel trailer when towing?

I'm asking this, because on my previous vehicle (2000 Tundra without tow package), I had to have a charge line, with relay and circuit breakers installed and wired to the tow plug connector.

Is this factory installed 12 volt line properly fused?

Thanks, Ken

[titanjbc]

Looks like someone who has access to the service manuals has to answer that one. I, too, have been looking at that, since I'll be picking up the trailer next week. My first instinct would be "yes", you could use that as a charge line, but my instincts have been wrong before.....

[bestatchess]

Originally Posted by Titan Ken

I have the Big Tow package and looking at the trailer plug connector there is a "12v +" on the connector. I checked it with a volt meter and indeed it is an ignition switched 12 volt connection. Is the amperage and wire gauge suitable to provide sufficient battery charging to my travel trailer when towing?

I'm asking this, because on my previous vehicle (2000 Tundra without tow package), I had to have a charge line, with relay and circuit breakers installed and wired to the tow plug connector.

Is this factory installed 12 volt line properly fused?

Thanks, Ken

How many amps would you be drawing ?

[Titan Ken]

I don't know how many amps I would be drawing, and not sure how to find out. My travel trailer has two 12v deep cycle batteries, which the charge line provides current to, to keep them charged, as I understand it.
My previous vehicles (without factory tow wiring) had to be wired specifically for a charge line.

Ken

[bestatchess]

Originally Posted by Titan Ken

I don't know how many amps I would be drawing, and not sure how to find out. My travel trailer has two 12v deep cycle batteries, which the charge line provides current to, to keep them charged, as I understand it.
My previous vehicles (without factory tow wiring) had to be wired specifically for a charge line.

Ken

Is there any manual or anything that gives the specs of the charger in the trailer?

A good side car battery will be rated at about 60 amp-hr. Charging circuits vary all over the place as far as the amps supplied to charge the battery, many are in the range of from 2 to 15 amps. You can even get tiny little 1.5 amp chargers to "trickle charge" stored batteries. As an example of charger function, a charger that provides 6 amps will take 10 hours to charge a 60 amp-hr battery. Deep Cycle (in case you didn't know) batteries are designed to be deeply discharged prior to charging. This will shorten the life of an ordinary battery. Some chargers have circuitry to vary the provided amperage over time, depending on the charge state of the battery.

Without knowing the specs of the charger in your trailer (what would be critical is the maximum current draw with both batteries fully discharged) it is impossible to say whether the stock wiring would be adequate. Anothing thing to be considered is the voltage drop caused by the resistance of the wire (V=IR) which will be greater with a longer wire. A bigger diameter wire will have less resistance.

If you are using some low draw charger, like this:

http://www.lslproducts.com/ToadChargePage.html

then the existing wiring may be adequate.

However if your trailer is setup to use the towing vehicle's alternator to charge the batteries, you will need to add additional wiring, problem something heavy like 8 guage fused at 50 amps.

[cttitan]

Originally Posted by Titan Ken

I have the Big Tow package and looking at the trailer plug connector there is a "12v +" on the connector. I checked it with a volt meter and indeed it is an ignition switched 12 volt connection. Is the amperage and wire gauge suitable to provide sufficient battery charging to my travel trailer when towing?

I'm asking this, because on my previous vehicle (2000 Tundra without tow package), I had to have a charge line, with relay and circuit breakers installed and wired to the tow plug connector.

Is this factory installed 12 volt line properly fused?

Thanks, Ken

This is a copy of the TT harness wiring. The power line is fused with a 30A fuse.

[Titan Ken]

Thanks for the trailer tow wiring diagram. Knowing it's a 30 amp fuse, makes me think it is indeed adequately designed for its purpose of charging the trailer batteries - - at least as well as the wiring I've had installed in my previous tow vehicles.

Ken

[stevemis]

Originally Posted by cttitan

This is a copy of the TT harness wiring. The power line is fused with a 30A fuse.

Just because the fuse is 30 amps doesn't mean the circuit is capable of delivering that kind of current for an extended period of time.

Bestatchess is right, you will likely have significant voltage drop. It's Ohm's Law, a function of the amount of current, the voltage, the length of wire and it's guage (thickness).

Anything less than 13.6 volts will NOT properly charge a deep cycle marine battery. You will likely get under 12v if you try to pull 10a through the tow connector.

I have two deep cycle marine batteries on my boat - one for starting, and one for accessories. The starting battery is maintained by the alternator, and I have an on-board 120v charger for the accessory battery. This charger is rated at 10 amps, and it will supply between 9.5 and 10 amps to the battery when discharged. I'm sure a 15 amp charger would supply 15 amps.

The more your battery is discharged, the more current it will "want". Your voltage will drop as the current demand gets higher.

I would strongly advise against charging a battery from the trailer wiring.

Please consider a proper 12v <-> 12v charge controller with a current limiter and automatic "float", wired per the manufacturer's directions.

-Steve

[Titan Ken]

I didn't mean to say I am trying to "charge" the 2 batteries on the travel trailer when towing. I'm under the impression the charge line through the tow connector merely provides adequate voltage to "maintain" the batteries while towing and to provide a 12 volt source for the refrigerator thermostat electronic module (refer running on LP while traveling). I understand the charge line should be heavy gauge wire to prevent voltage loss. My two previous tow vehicles were wired with a charge line in addition to the standard tow wiring. I was merely curious if anyone actually knows if the wire gauge is sufficient.

Thanks, Ken