Charging spare battery

Garand · 09-10-2012, 08:08 AM

After a recent dry camping trip I realized I need to add to our current electrical set-up (pun intended), and I need some advice.

I want to carry a spare battery tied-down in the bed of our truck and charge it from the 7-pin connector when we are not towing. I suspect I need some kind of regulator or charge controller between the 7-pin and the battery to avoid overcharging. I’ve looked online and found lots of references to solar set-ups but no direct information regarding what I want to do.

Does anyone have any advice?

Thanks!
Dave

Jim Bennett · 09-10-2012, 10:39 AM

Dave, all you need to do is to get a plug, and only hook-up the 12V feed and a ground to this plug with some 10G wire (buy a short chunk of 10/2 cab tire, the good quality black rubber coated stuff), and put alligator clips on the other end of the wire to connect to the battery. No regulation needed, as it is provided by the charging system of your truck.

You would have to make certain that the positive alligator clip was protected from coming off and grounding out, and that nothing could, or would, fall against it.

So all you need is the male plug end, a short length of 10/2 cab tire, and two alligator clips.

dave macrae · 09-10-2012, 10:50 AM

Having the postive wire protected with in line fuse is a good idea. the fuse should preferably be near the point where the wire goes into the seven pin. also don't forget that when the battery is removed those aligator clips will be live so you will want to make sure you unplug from the seven pin before you unplug the battery.

Jim Bennett · 09-10-2012, 10:58 AM

The charge line to the connector should be fused, but it can't hurt to add another, maybe even a lower wattage as the draw won't be that big. Good idea on disconnecting, doing the plug first would be key.

Garand · 09-10-2012, 11:52 AM

Thank you both for the prompt replies! What I like best is that my normal inclination to over-complicate things was wrong.

Dave

Jim Bennett · 09-10-2012, 11:55 AM

Over complicating an issue, methinks we can all suffer from that from time to time.

My biggest fault is over analyzing purchases, finding reviews and looking at alternatives. People who just go an buy what they need without shopping around suffer much less anxiety. I do kinda like researching stuff though.

Garand · 09-10-2012, 12:05 PM

I'm with you on the research aspect Jim. Half the fun for me is digging around, weighing compromises and getting the product I want at the price I want to pay.

Dave

cpaharley2008 · 09-10-2012, 01:41 PM

I assume your trailer is hooked up. Then it would be better to purchase a battery charger and plug it in at the c/g and charge the battery. If you are not hooked up, then you do not have a source to charge an extra battery. The on board converter is a poor battery charger, you will be quicker and better results using a 3 or 4 stage charger to charge an extra battery.

Garand · 09-10-2012, 03:18 PM

Quote:

Originally Posted by cpaharley2008 (jim)

I assume your trailer is hooked up. Then it would be better to purchase a battery charger and plug it in at the c/g and charge the battery. If you are not hooked up, then you do not have a source to charge an extra battery. The on board converter is a poor battery charger, you will be quicker and better results using a 3 or 4 stage charger to charge an extra battery.

Hi Jim;
No, we carry the spare battery only when we are dry camping. It serves (via inverter) to run chargers for the various electronic paraphernalia, cameras, flashlights and other stuff we tote along. This preserves the trailer batteries for pumps, lights and the ever-so-nifty marine fan that cools us at night.

Dave

cpaharley2008 · 09-10-2012, 04:25 PM

So you want to be able to charge the extra battery using your trailer plug on your tow vehicle? Here is what Etrailer says

Can the 12 Volt Outlet on Trailer Connector Adapter, # HM47675 Charge or Maintain a Trailer Battery
Question:
1994 F250 Camper / Towing package Can the 12V accessory plug on this item be used to charge or maintain a battery in the towed trailer?
asked by: Mike

Expert Reply:
The 12 volt outlet on the Hopkins Multi-Tow Trailer Connector Adapter, # HM47675, can be used to maintain a trailer battery but it will not be able to charge it. The gauge wire used to provide power to the 7-Way is too small to effectively charge a battery, but it will provide enough power to keep it from draining.
expert reply by: Michael H

Have a question for the experts? click here.

Jim Bennett · 09-10-2012, 04:46 PM

I have successfully charged lots of batteries in trailers while hooked to the tow vehicle. In fact, doing most of the camping I have done with a trailer in the past, I have had little opportunity to hook up to 120V to run the converter for charging, and have had to rely on this charge while driving to top the battery up. The charge rate will only be improved with a larger gauge wire from the vehicle alternator, and I always used a 10g wire for the charge wire.

Basically, as long as there is a higher voltage on the wire leading to the battery than the battery itself has, it will take a charge until these two voltages equalize.

dave macrae · 09-10-2012, 05:06 PM

As long as the battery is not fully discharged the 10 guage charge wire will top up and maintain a full charge very well this is provided the connections in the circuit are in good condition, one area most people don't ever think about is the connections on the back side of the trailer 7 pin connector, the after market generic type are not weather sealed and generaly corrode very quickly causing a large voltage drop across the circuits. The factory ones with a weather pac style connector can still corrode causing the same problem. The other proble most neglect to realize is that the ground is more important than the power circuit and the ground side of the circuit needs to be at et least as big as the power side, It is after all a loop, what goes in must be able to go out.

Garand · 09-10-2012, 05:28 PM

Interesting discussions.
I've got 10g red and black wires to run to the battery (about a 5 ft run) and intend to bolt (wingnut) the connections in place on the battery to ensure they don't come adrift.

As to the plug, I plan on wiring the 12v and ground wires in place and then sealing the open end of the plug with "liquid electrical tape" followed, once that has dried, with Goop sealant. That should both prevent corrosion to that part of the plug and waterproof the connections.

Dave
(thinking of changing my signature to ("if it ain't over-engineered, it's no fun")

dave macrae · 09-10-2012, 07:57 PM

A good friend of mine has a saying that i like " Anything worth doing is worth overdoing!! " I truly like it and borrow it.

Jim Bennett · 09-10-2012, 08:29 PM

You guys probably did some of the home renos on the places we go and work at. In a few cases things are scary underbuilt, but in the majority of cases things are excessively overbuilt. 20 nails in a board where 2-3 would suffice, doubled up studs where not needed, etc. Though Momma used to always say "Better safe, than sorry".

gbaglo · 09-10-2012, 08:53 PM

My take on all this is that my Honda 1000 generator weighs half what a 12V battery weighs. It's available on demand and although I have to carry gas for it, I am comforted that, if my tow runs out of gas, I have a spare five liters. ( although, I must admit, last time I went to fuel the generator, the gas can was empty ).

I can charge the battery direct from the generator, but lazy as I am, I've just plug into the AC and charge through the trailer. I will admit it's not as quiet as a spare battery...

baglo

dave macrae · 09-11-2012, 07:01 AM

To be honest I have a honda 2000 aswell. The original justification for it was that with it it takes the risk of running out of power and being cold with out a furnace. This senario only happened once a long time ago but it wasn't much fun with a child in the trailer. The good quality ones like honda and yamaha are very quiet when just running to charge the batteries. Our set up with dual 6v and solar panels and then the generator for back up works very well for us but just having a spare battery would certainly be less expensive

Garand · 09-11-2012, 07:19 AM

Guilty as charged, Jim. As I said on another forum, "after taking about 8 total hours to install our new dishwasher, 'at least I know its done right'" No one will ever see the careful routing I used for the supply and discharge lines, but I know that somewhere behind that mundane dishwasher lurks plumbing art.

I'm not guilty of using 20 nails where 3 would do, but I am guilty of using screws more often than nails when building things.

This house has been our home for 20+ years and I've often referred to it as a "hobby house" (like I don't have a few other hobbies as well). Whoever buys this house will get a lot of quality work lying under the multiple coats of paint. In fact, I claim we've painted so many times here that we're beginning to lose floor space as a result.

Dave

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