Help! Battery Charger in Trailer

[innovlight]

Hello All,

I have a couple of questions. I am interested in wiring up a battery charger/and battery inside my trailer, so that I can run some lights. I was looking at the plug on the trailer to see if I could charge the battery off of a 12V connection on there, but will this be enough to charge a decent size battery?

Do you think that I should hard wire the 2nd battery to the altenator? I want to be able to run the lights when the trailer is unhooked. The wire in the plug does not look like a very high gauge, so I'm assuming this would not work to charge say a 100 Ahr battery.

Anyone's help is appreciated.

Thanks.

 

[MrJimi]

You haven't said much about what you have but if you have a 7 way connector, there is a provision just for that.
And welcome

 

[innovlight]

Well, I have an old Fedex trailer, and yes it has a 7 way plug, with the SAE J560 standard. I have found the 12V + and -, but does anyone know if it will be able to charge say a 100 AHr 12V battery?

 

[Mickey_Fx]

You haven't provided much info about the trailer or tow vehicle and I'm assuming, which is dangerous, that is how you plan on charging the battery from the stated connector. I think it is not a case of IF but how long if the trailer is wired to charge a battery.

To be able to charge at a decent rate I'd want to see at least 10 ga wiring from the egine compartment all the way back to the battery on the trailer.

If you intend to keep the connector connected while using the battery, you need some kind of isolator to prevent draining the tow vehicle battery.

 

[Soundguy]

Ditto that.. the 7 way plugs do have a provision for trailer power..

soundguy

 

[Farmerford]

I agree with Mickey Fx: it is a question of how long it will take to charge the battery, not whether it will charge it at all.

But consider the size of the wiring. The 12V circuit in the 7 way plug may be designed only to operate a couple of interior lights in the trailer, in which case the wires could be relatively small, say 18 AWG. That size wire is rated for only 20 amps and a fully discharged 100 Ah battery will draw well over 20 amps. So, you might exceed the capacity of the wire (if your alternator or other source has the capacity), which would cause the wire to overheat and, at some point, melt the insulation and perhaps short out and start a fire.

If you can reach and measure the wire you will know how many amps it can carry. Otherwise, I would put a 20 amp fuse in line and then try it with a battery that was at least partially charged. If that works okay and the wire does not appear to get more than slightly warm to the touch, but blows the fuse when the battery is being charged from a highly discharged state, then increase the fuse to 30 amps and try again.

 

[Soundguy]

There should be a fuse or circuit breaker inline with the power wire on that trailer plug.. unless it was installed by 'bubba'.

Remember.. power running back there is intended to charge a break-away device.. etc.

If there is much question on the charge capability / load.. then just don't 100% discharge the onboard battery....

soundguy

 

[laurencen]

The positive wire in the plug is intended to charge a break away system, this is usually a small lead acid cell, if your battery is fairly charged and running lights the wireing should be fine, I recomend putting a circuit breaker on the positive line before the battery just in case however unless you drain the battery it will be fine

 

[Soundguy]

There should already be a load protection device in the truck.. I know my dodge came with a SRCB, and my gm and ford uses maxi-fuses unde rthe hood.. there is actually a slot for them in the oem fuse box..

soundguy