Battery Charging Wire?

[Sitah]

Hey Gang,

I'm just about finished with the electrical in the Chubby Bunny. We bought a new tow vehicle that has a battery charging wire (black). Now, my question is, how do I connect that to the battery for charging? I just don't know. Is there some mechanism or whatnot that goes between that wire and the batter? I ASSume there is, but I don't know. I've looked in the forum archives, but haven't seen anything concrete. Thanks!

[Suz]

Chris are you asking how to attach it to your car battery or your trailer battery?

[Suz]

That may sound like a silly question, but my suv came all set up for towing, except that I had to connect the red wire under the hood before it would actually charge my trailer battery.

[Sitah]

That may sound like a silly question, but my suv came all set up for towing, except that I had to connect the red wire under the hood before it would actually charge my trailer battery.

Well, my new vehicle has a 7-pin connection; I've changed the trailer's connection to 7-pin as well. The "battery charger" pin on the vehicle is hot, so it must be connected already. I want to know how to connect that wire to the trailer's battery for charging. It's not necessary, but it might make things easier. Right? Could a wire leading to the trailer's battery overcharge it? I don't know. Ask me about Shakespeare and T.S. Eliot, not about RV wiring! Thanks.

[Frederick L. Simson]

but haven't seen anything concrete.

Well, of course NOT. This IS fiberglass...


(I'll be in my room.)

[Frederick L. Simson]

Well, my new vehicle has a 7-pin connection; I've changed the trailer's connection to 7-pin as well. The "battery charger" pin on the vehicle is hot, so it must be connected already. I want to know how to connect that wire to the trailer's battery for charging. It's not necessary, but it might make things easier. Right? Could a wire leading to the trailer's battery overcharge it? I don't know. Ask me about Shakespeare and T.S. Eliot, not about RV wiring! Thanks.

All [b]I did was make a connection from the appropriate pin of the trailer's 7-pin plug to the positive terminal of the trailer's battery. What will happen (I think) is that your tow vehicle's alternator or generator will recharge both the tow vehicle's starting battery and the trailer's house battery together at the same rate.

[Benny K]

The wire that is being used as a charge wire should be at least 10 guage to handle the current and be fused at 30 amps or have a 30amp circuit breaker, either manual reset or auto reset, near the alternator connection or a remote 12V take off point, to protect the wire and your tow vehicle and trailer....the other end can be hooked up directly to your trailer batterywith a lug onto the positive (+) post.....I would also put inline, in the engine compartment, a relay capable of more than 30 amps, controlled by the ignition switch circuit to open the circuit when the ignition is turned off, so that you don`t kill the tow vehicle battery if you drain the trailer battery and haven`t unplugged the trailer connector...i.e. leaving electric fridge on for too long if touring a museum or just sightseeing....Benny

[Sitah]

[quote]
The wire that is being used as a charge wire should be at least 10 guage to handle the current and be fused at 30 amps or have a 30amp circuit breaker, either manual reset or auto reset, near the alternator connection or a remote 12V take off point, to protect the wire and your tow vehicle and trailer....the other end can be hooked up directly to your trailer batterywith a lug onto the positive (+) post.....

Thanks for the information. So, the trailer's battery won't overcharge? As long as I have a 30 amp circuit breaker, I should be safe? I'll get it wired this morning.

Ever poked your fingers with those little copper wires when doing wiring? Ouch!

[Benny K]

Your alternator has a regulator built into it , if it`s newer than about 35 yrs old....so no problem.....and the ouch would be ouchier if you were working with steel cables with a broken strand.....the relay that I mentioned is the type used for fog lamps, etc., and is a black cube about 1" square and can come with a mounting flange...they`re cheap....and the circuit breakers are about half the size and the resetable ones come with a button on the side for manual reset and the auto resets work like your headlamp ones which reset themselves....so if you hear something clicking at the breaker there is a problem in the system and it`s kicking on and off......good luck.. .....Benny

[Gerry]

Your alternator has a regulator built into it , if it`s newer than about 35 yrs old....so no problem.....and the ouch would be ouchier if you were working with steel cables with a broken strand.....the relay that I mentioned is the type used for fog lamps, etc., and is a black cube about 1" square and can come with a mounting flange...they`re cheap....and the circuit breakers are about half the size and the resetable ones come with a button on the side for manual reset and the auto resets work like your headlamp ones which reset themselves....so if you hear something clicking at the breaker there is a problem in the system and it`s kicking on and off......good luck.. .....Benny

[indent]This is all good things to do but I read somewhere that by not installing a Battery Isolator you run the risk, if you have drained your trailer battery too low, as soon as you turn on ignition the tow battery will send what ever power it has to the trailer battery to even out the power, thus, you may not have enough power to start your vehicle.

[Byron Kinnaman]

[indent]This is all good things to do but I read somewhere that by not installing a Battery Isolator you run the risk, if you have drained your trailer battery too low, as soon as you turn on ignition the tow battery will send what ever power it has to the trailer battery to even out the power, thus, you may not have enough power to start your vehicle.

I don't thing the charge wire can carry enough current to make any difference. If would take a couple hours for the TV battery and the trailer battery to equalize.

If you're ever really concerned, just start the TV then plug in the trailer.

[Benny K]

Suppose if the trailer battery was near dead or dead and tried to pull high current it would trip the breaker that is in the circuit....I`ve been using this system in RV use for 30 years without a problem.....Benny

[Fred Bell]

Suppose if the trailer battery was near dead or dead and tried to pull high current it would trip the breaker that is in the circuit....I`ve been using this system in RV use for 30 years without a problem.....Benny

I too have upgraded my tow vehicle ('06 Nissan Frontier) and installed the factory wiring harness for towing and here's my situation. Before I had a '99 Chevy Astro with the old style 4-pin wiring harness so this 7-pin stuff is new to me. I'm confused about function of the pin on the TV marked "+ Battery". I metered the pin and found 0 volts when parked, 12.7 V with the key in the ignition turned to ACC, and 14.1 V with the engine running. I traced the mating wire through the harness of my Scamp and found that it splices into the trailer's main battery wire. The wiring looks correct according to Scamp's schematic.

I peeked inside the factory wiring harness and found a red, blue and white wire that look about AWG 16. The other brown, black, yellow and green wires look about AWG 18 or smaller. There's no AWG 10 gauge wire suitable for charging. Without risking damage to the connector I couldn't tell which wire was connected to which pin. In addition, Nissan tells me that the truck is not set up charge the trailer's battery. They also told me that if I attempt to charge the trailer's battery with the truck's alternator that I may damage the alternator, violating the warranty. Maybe the 12 volts supplied by the TV is only for accessories inside the tralier like the 12 volt heater element for the fridge. You mentioned relays, and I remember installing 2 relays under the dash, but I thought those were for the brake, reverse, turn and running lights.

Any ideas would much appreciated.

Fred

[Pete Dumbleton]

Ask someone else at Nissan -- If the truck positive battery is connected to the trailer connector, then the trailer battery will be charging (but not very fast because of the wire size) -- Nissan engineers shouldn't be ignorant of the typical RV wiring -- It's highly unlikely that your alternator would be damaged because it should be seeing the average voltage of both batteries and charging at a lesser rate.

Personally, to make battery charging more efficient (it's a long way from the front of the TV to the trailer battery in feet), I run my own charging wire (#8 or even #6) from the TV battery, thru an autoreset circuit breaker, and then back to the trailer connector -- That way I get a minimum voltage drop and faster charging.

However, if I bought a new vehicle that was wired to supply + battery to the trailer, I might be lazy and live with it...

[Frank Campbell]

Just a word of caution, I recently added a seven pin plug to my Boler so I could charge the battery while travelling. I was leary of hooking up the isolator system myself on my 2003 Dodge Dakota so took it to an RV dealer and had it done. Cost me $85.00 including parts, cost them $650 to have a Chrysler dealer diagnose and repair the ABS warning light was on after they did the work. They had accidentially shorted out a $350 dollar part.
Frank C

http://bolerlife.com

[Fred Bell]

These ain't old pick-up trucks, any more!

I'm going to take my Nissan back to the dealership and get someone who really knows there stuff to explain things to me. Until then, I'll just keep the battery disconnected.
I'll also ask them about the isolator system, too. However, it's been my experience that dealers get nervous about giving advice on adding after-market stuff that they don't sell.

Thanks for the tip.

Can anyone make a guess on how much amperage a battery depleted by half will draw once it's connected in parallel with TV battery/charging system?

Also I looked for a specific fuse for the + battery connection to the trailer and couldn't find one. It's not mentioned in the manual, either. Maybe there's a fuseable link buried deep somewhere in the wire harness.

[Capt Ron]

I too have upgraded my tow vehicle ('06 Nissan Frontier) and installed the factory wiring harness for towing and here's my situation. Before I had a '99 Chevy Astro with the old style 4-pin wiring harness so this 7-pin stuff is new to me. I'm confused about function of the pin on the TV marked "+ Battery". I metered the pin and found 0 volts when parked, 12.7 V with the key in the ignition turned to ACC, and 14.1 V with the engine running. I traced the mating wire through the harness of my Scamp and found that it splices into the trailer's main battery wire. The wiring looks correct according to Scamp's schematic.

Any ideas would much appreciated.

Fred

Fred,

The voltages you report are about right. On a good digital volt meter, a fully charged 12V battery (at rest after 24 hours or so) should read 12.72 volts. A typical automotive alternator will charge that same battery at 14.1 volts because the voltage regulator built into the alternator is set to cut out at that voltage. That voltage is called the 'float' voltage ... if the battery was a little flat, say the resting voltage was 12.5 or so, then the alternator should kick the voltage up to 14.3 or so until the battery voltage reaches 14.1 then it will reduce the charging voltage to 14.1.

This system is intended to recharge the vehicle starting battery, after starting the machine, by putting back the charge just removed by the start-up process. That job is different than charging a camper's deep cycle battery where the battery may be run down to 50% charge (maybe 12.3 or 12.4 volts) before recharging.

Generally the wiring of your tow vehicle won't be heavy enough to support charging the RV battery efficiently. Also the two batteries will attempt to equalize charge states and given enough time a flat RV battery could drain the TV battery. That's why folks put isolator diodes between the batteries. They allow current to flow only one way ... but they also cause about a .5 volt drop in charging voltage.

There is no perfect solution here but your TV charging circuit should provide enough juice to eventually bring your RV battery back up without much risk of overcharging. 14.1 volts will recharge the RV battery but it will take a while maybe 6 or 8 hours of driving or even more depending on the discharge level of the RV battery. 14.1 volts is also below the threshold where the electrolyte will boil off... it takes 14.3 or more to get the battery fluid boiling. That also explains some of why folks go to auxiliary charging systems like generators or solar panels to recharge the RV battery. A good RV charging system could replenish a 50% discharged deep cycle battery in an hour ... but that's an entirely different subject.

Just don't leave the RV plugged into the TV for very long without the engine running and make sure to check battery fluid levels.

[Pete Dumbleton]

In Fred's case, it should be noted that since he gets 0 VDC on the charge wire with the truck key off, he has an isolation system already functioning (apparently part of the factory package) so there's no risk of running down the truck battery from the trailer's electrical system.

[Fred Bell]

Hey guys, thanks for the input.

I finally found someone at the Nissan dealership who knows something about this stuff. He told me that the aux. +12V power on the 7-pin connector is rated at 30A. There's a 30A fuse/relay block in the engine compartment fuse box. He defended the size of the wire for a 30A circuit even though it's not AWG 10, and said that the truck has several circuits rated at 30A using AWG 14 wire.

All is still good, however. I never intended to charge the trailer battery with the TV. I usually only go for 3 or 4 nights and a fully charged battery easily gives me all the juice that I need. I plan to run the fridge's 12V heater while driving and that only draws 8 amps. I now know more about what the TV is capable of and the rating and location of the aux. 12V circuit fuse.

I'm thinking that for now, I'll disconnect the trailer battery while driving so that only the fridge is drawing off the aux. circuit.

Thanks again.

[Pete Dumbleton]

If one disconnects the battery while running, and has brakes, the breakaway brake switch likely won't turn on the brakes (unless one has a dedicated brake battery).

Also, if the ground/return wires are disconnected from the battery, the electric brakes may not work unless they are grounded to the frame.

If one looks at the wiring under the hood on a typical vehicle, one finds fairly small gauges of wire in the charging system, yet the alternators are typically capable of producing multiples of 30Amps -- The wiring is likely sufficient for the load in terms of safety, but the voltage drop may be enuf to prevent a 100% charge on the trailer battery.

Were it my truck and trailer, I wouldn't disconnect anything while running and would rely on the ignition-isolation to protect the starting battery from draining.