Electrical help needed please

[Rovertrader]

Although I am a Civil Eng, I do not 'get' electrical/wiring, so pardon my simplistic question. But, I have a F250 and planning a bed mounted battery(in a box) and possibly an inverter(which I already have). The question is, can I simple tie into the hot lead (not the brake, but + lead which is keyed) on my 7 pin wiring to act as a charger for said bed mounted battery? I have read if the batteries are different sizes, it can potentially drain the 'new' battery trying to charge the factory batteries(diesel, hence two). Also, the wire is aprox 8-10ga - will this work for a 'charging' situation, or do I need the big zero gauge as if running in series? Since the + lead is keyed, it would prevent draining the main batteries when parked.
All I am trying to accomplish is mounting a rear battery for the bed, and facilitate having it charged when the truck is running, without the whole dual battery solenoid setup. Thoughts from those who know?? Seems to me it should work, as campers being pulled utilize a similar approach, and are being charged from the same lead I plan to tie into...
Thanks

 

[rambrush]

The wire should do just fine in my opinion as it was meant to charge the trailer battery, it would not care where the battery is actually located.

 

[Hilldweller]

There's a difference between "work" and "work well".

How well do you want it to work?
What kind of battery is your primary, your new one? What kind of load will you be imposing on the new battery? How old is the primary? How many amps is your alternator?

 

[Jim K in PA]

As Bill says, it will work. The issue is the rate of charge that you can get across the fairly light gauge wire, as well as the actual voltage it sees. That 12v pick from the trailer harness should be fused already to protect the circuit. Don't be surprised if you burn a fuse when charging a deeply discharged battery. You are correct in that when switched off, the remote battery will be isolated from the main/house battery.

Keep in mind that the 12v lead in the harness is NOT intended to recharge a trailer house battery. It is intended to charge the small backup "break away" battery for electric brake setups. That little battery is MUCH smaller than the typical camper battery.

 

[Rovertrader]

Okay, a little more research, and it appears I can charge the third battery from said wire. However, I was advised I should add a 30amp fuse just in case the two primary batteries ever get low, and the truck tries to use the third battery to start- in other words, reverse use of current. The starter circuit is aprox 175 amps, and would obviously create havoc should it be called upon for such duty with a 10/12 gauge wire...
The vehicle is an '11 F250 diesel, hence two new HD primary batteries in the truck. I am adding a new HD deep well battery for the rear of the truck- lights, Ingel, a/c converter, rear/trailer winch if needed, etc. The trickle charge from the main battery will suffice my needs, as I will also have the option of shore power when parked- if available, and the converter also doubles as a charger for the third battery. And the truck supply being a keyed circuit, I will not chance draining the primary batteries.

I did not realize the 'hot' circuit was to simply charge the breakaway battery on the trailer- I thought it powered/charged the primary trailer 'house' battery? Are you sure of this?
Thanks as always
Dale

 

[Hilldweller]

Can you hump in an 8 gauge wire, Dale?
And I think a diode on the circuit is what you'd want to prevent juice from going the wrong way.


That charge circuit isn't just for the break-away, per se. But it's not for charging a deeply discharged battery for sure. I use mine for charging both Optimas on the trailer and it works.
But I have a Power Wagon...

 

[Buliwyf]

No. The trailer plug pin/circuit is best for recharging the trailers break-away brake battery. It's a nice 2011 Superduty. I recommend taking your time and installing a good system with a manual override instead. That circuit will work ok, and some campers are setup that way, but we can do better.

I like the auto solenoid/relay setups. But I plan on just using a continuous duty relay and 4 gauge car audio wire to connect + and - to the trucks main battery. (yes I avoid chassis grounds for non-factory system) That way I can put all my non-factory accesories on the aux battery and isolate them from the truck with one flick of a switch.

Essentially I'll keep the electrics in my truck stock. We add a ton of goofy electronics. Parasitic draw becomes a problem as components age or break down. I've been stranded a few times, and killed a couple Optimas because I've left stuff on or things that were supposed to shut down on thier own didn't.

Also keep in mind that your engine alternator won't recharge your aux battery fully if it's connected to your main battery. That's why the auto relay setups switch back and forth. But I don't want to switch back and forth. I want to make sure my main is recharged completely, then I'll connect the aux battery. If the aux battery never gets a full charge, I could care less. But I never want anything switching my batteries back and forth automaticly.

I plan on using two 12v 6a small potted battery chargers for "shore power". With two battery chargers each battery will get charged completely and seperately, even if they are connected. Kohler and Katolight both offer fine 120/12v 6amp chargers. I'll bet this is the same charger:
http://www.sears.com/shc/s/p_10153_...21x00003a&ci_src=14110944&ci_sku=SPM512177001
I'll mount a reverse 120v outlet near the grill on my truck for my "shore power" extension chord.

There are many good ways to do it. That's just my plan.

I have no idea how I'm going to secure and cover a group 31 battery to the inside of my bed.

30 amp fuse is a good idea, but won't prevent reverse flow of current. You'll need a diode to do that.

 

[Rovertrader]

Bill- does that mean in spite of having a PW it works? ;-) I do miss mine except at fillups...

Thanks again for the help. I have considered going the manual solenoid route, but really doubt the third battery will get lower than what the 'trickled' charge the existing + would compensate. I can always put a full charge prior to a trip via the shore power/converter.
I do believe the diode would be a good insurance policy as well.
Any other issues I am missing?
Thanks all!!

 

[kjp1969]

We have a hard sided RV camper trailer that uses two 6v golf cart batteries in series as house batteries. The charging circuit on our '04 Sequoia charges the house batteries when under tow. I have no data to judge how "well" it does this, but after an hour or two under charge, even when moderately discharged, the house batteries show significant improvement.

 

[Hilldweller]

We have a hard sided RV camper trailer that uses two 6v golf cart batteries in series as house batteries.

I'm curious.
I've been telling Stumpy to put a pair of these on his trailer to replace his ailing batteries.
How many amps do you have on tap? Golfcart batteries are notoriously robust and full of potential...

 

[kjp1969]

I'm curious.
I've been telling Stumpy to put a pair of these on his trailer to replace his ailing batteries.
How many amps do you have on tap? Golfcart batteries are notoriously robust and full of potential...

To be honest with you, I have no idea. I bought them at Costco for $70 or $80 apiece, and they usually last 3 years or so- I change them when we no longer have enough capacity to dry camp with all the amenities for 4-5 days without a charge. During that time, typical weather is low 35F, high 65F and we run the furnace all night at around 64 degrees. We also run lots of incandescent lights, a propane fridge, and a water pump. For our purposes, they are the greatest, cheapest solution that I've found. We run them into the ground, probably lower than we should, but they keep on trucking.

To the original poster, look at it this way: if you had a slide in truck camper, the house batteries would be charged one of two ways, via shore power or by that same 7-pin circuit. I would go for it- its the simplest, easiest, cheapest solution. If it doesn't work well enough for you, then reevaluate. But I suspect it will be fine.

 

[DesertXJ]

You will be fine using the charge line from your 7 way, its already fused in your main power distribution center in the truck. The charge line is to charge trailer batteries. Big travel trailers both bumper pull and 5th wheel and Tent have big deep cycle batteries. They don't have break away batteries because they use the house batteries as a substitute for the break away battery.

Using 6 volt deep cycle batteries is the way to go if you have the room. Many of your big huge 5th wheels use them and also your Big motorhomes.

 

[Rovertrader]

so, two 6V wired + to +, and - to - I assume? And the golf cart batteries are preferred? I can see them working well as they have a long life and tons of reserve.
Thanks again!!

 

[Hilldweller]

so, two 6V wired + to +, and - to - I assume? And the golf cart batteries are preferred? I can see them working well as they have a long life and tons of reserve.
Thanks again!!

+ on one to - on the other. Then take the leftover +/- and use them as the working terminals.
Series.

 

[DesertXJ]

was just going to reply to that.

so, two 6V wired + to +, and - to - I assume? And the golf cart batteries are preferred? I can see them working well as they have a long life and tons of reserve.
Thanks again!!

This called a parallel circuit which will only give you 6 volts

+ on one to - on the other. Then take the leftover +/- and use them as the working terminals.
Series.

This is a series circuit and will give you 12v


Then there is a Series Parallel circuit which you would use if you had say four 6 volt batteries and only wanted 12 volts