Two 12V Batteries?

rmdrifter · 08-31-2012, 03:43 PM

I want to mount two 12V batteries on the hitch of my 186SPT. Question: Using parallel wiring, will my truck alternator charge both batteries while I drive without any additional modifications or parts? And I assume that if the answer is "yes", then when I'm hooked up to shore, that both batteries would be charged as well Now it does a fine job of charging one. Thanks!

LadyWindrider · 08-31-2012, 03:49 PM

The answer to both question is yes, the truck will charge both. That is a long run for wiring, so make sure it is large, about 6 gauge or better. Tie them down good also, (not a bungee cord), as it is amazing how much bounce they will get on that hitch. Make sure also you don't bounce any acid out.

**Herk7769** · 08-31-2012, 03:57 PM

Quote:

Originally Posted by windrider

The answer to both question is yes, the truck will charge both. That is a long run for wiring, so make sure it is large, about 6 gauge or better. Tie them down good also, (not a bungee cord), as it is amazing how much bounce they will get on that hitch. Make sure also you don't bounce any acid out.

The standard charge wire in the Bargman 7 pin connector is heavy enough for your a 2 battery set up. No need to change anything.

OldCoot · 08-31-2012, 04:04 PM

Quote:

Originally Posted by herk7769

The standard charge wire in the Bargman 7 pin connector is heavy enough for your a 2 battery set up. No need to change anything.

X2, been using it for years that way.

rmdrifter · 08-31-2012, 04:20 PM

Thanks guys, always appreciate the timely and accurate replies.

LadyWindrider · 08-31-2012, 05:35 PM

I was talking about a wire all the way under a camper. I assume a trailer, with battery in nose or on tongue. The battery would be hooked to the converter. Now, to add battery on the trailer hitch, again I assume that would be on the rear, over 20 feet of wire. That is where I was suggesting a large wire.

Agree, adding a larger wire to the trailer connector is useless, the contacts are the limiting factor on current.

rmdrifter · 08-31-2012, 05:57 PM

Actually plan is to move battery box on front of hitch over and slide in another box next to it with parallel wires--both should fit and will be mounted with 4 tap screws each through crossbars as is current box.

crasher · 08-31-2012, 05:58 PM

I put 2 Trojan 225's on my tongue on my SP189.

They fit in a Group 27 box - two of them, but it had to trim the boxes and the lids with a Dremel to get them to fit. Two group 24 boxes mayfit, but probably need to trim a bit too. Looked, but could not find a "double" box.

So I suggest doing some measuring first.

rmdrifter · 08-31-2012, 06:09 PM

I'm using two 24s--smaller box size--which will be enough amps for my purposes. Also couldn't locate a dbl 24 box, only dbl 6V boxes available. I eyeballed and measured situation pretty carefully and think I can fit both boxes on front hitch of 186. Regardless, I'll make sure they are absolutely secure before taking off. Will complete project Sunday PM...will let Forum know if there are any mounting issues.

LadyWindrider · 08-31-2012, 06:36 PM

Now I get it. Just so you will know, the front of the trailer is the tongue, or the pin on a 5th wheel, not the hitch. The hitch would be on the back, like the one on your tow vehicle. Some campers do have them. Glad I'm not confused anymore, forget what I mentioned above.

As to your comment on post #9, "I'm using two 24s--smaller box size--which will be enough amps for my purposes." Parallel batteries don't give more amperage. You are still limited by the max amp hour per battery. The amps won't add, but the time will double, assuming two matched batteries.
In other words, 50 amp hours will still be 50 amp hours, it will just double the time to 2 hours, and then you will have two dead batteries.

Hope this makes sense.

**Herk7769** · 08-31-2012, 06:56 PM

Quote:

Originally Posted by windrider

Now I get it. Just so you will know, the front of the trailer is the tongue, or the pin on a 5th wheel, not the hitch. The hitch would be on the back, like the one on your tow vehicle. Some campers do have them. Glad I'm not confused anymore, forget what I mentioned above.

As to your comment on post #9, "I'm using two 24s--smaller box size--which will be enough amps for my purposes." Parallel batteries don't give more amperage. You are still limited by the max amp hour per battery. The amps won't add, but the time will double, assuming two matched batteries.
In other words, 50 amp hours will still be 50 amp hours, it will just double the time to 2 hours, and then you will have two dead batteries.

Hope this makes sense.

I think you need another beer my friend.

12 volt batteries in parallel doubles amp hours but not volts.
Two 6 volt batteries in series doubles voltage but not amp hours.

Two 50AH 12 volt batteries will provide 100 amp hours of capacity at 12 volts.

lswartz · 08-31-2012, 07:16 PM

Quote:

Originally Posted by herk7769

I think you need another beer my friend.

If it is cold, I'd like one too.

I am having a heck of a time finding a container for my 2 6 volt golf cart batteries (& yes, you get 12 volts with the amp hours of the weakest battery). The Walmart battery boxes are not high enough for golf cart batteries. the same for their tool boxes. I am going to try a Rubber Maid box tomorrow & then visit Lowes and/or Home Depot. Maybe Sears as well. I may just have to find someone to weld some new angle iron on top of the hitch to give me some more space.

**Herk7769** · 08-31-2012, 07:19 PM

Quote:

Originally Posted by lswartz

If it is cold, I'd like one too.

I am having a heck of a time finding a container for my 2 6 volt golf cart batteries (& yes, you get 12 volts with the amp hours of the weakest battery). The Walmart battery boxes are not high enough for golf cart batteries. the same for their tool boxes. I am going to try a Rubber Maid box tomorrow & then visit Lowes and/or Home Depot. Maybe Sears as well. I may just have to find someone to weld some new angle iron on top of the hitch to give me some more space.

I made my battery box out of two restaurant "bus" trays.

lswartz · 08-31-2012, 07:27 PM

That is a nice clean setup. I don't have that kind of space but it would be nice to have them inside vs. on the hitch behind the propane tanks. It might be the trade off of a smaller trailer.

**Herk7769** · 08-31-2012, 07:47 PM

It is the front compartment of my 5th wheel.
It was all open when I bought it.
I built the power compartment out of plywood.

rmdrifter · 09-01-2012, 02:45 PM

Interesting comment Windrider, and thanks for the education on terms. All I'm interested in is doubling the time, so from what you indicate above using two batteries will achieve that end. Just curious though as to how it actually works: Do the batteries drain simultaneously and equally when wired parallel...correct assumption?

**Herk7769** · 09-01-2012, 04:22 PM

Quote:

Originally Posted by rmdrifter

Interesting comment Windrider, and thanks for the education on terms. All I'm interested in is doubling the time, so from what you indicate above using two batteries will achieve that end. Just curious though as to how it actually works: Do the batteries drain simultaneously and equally when wired parallel...correct assumption?

It actually depends on the batteries and how you wire them.

In order for them to work properly (charge and discharge together evenly) they must have equal resistance (including internal resistance) from the charge point to the ground point (called a "CELL".

In order for the internal resistance to be equal:
1) The batteries must be from the same manufacturer
2) The batteries must be the same type and size
3) The batteries must be the same AGE (the same number and depth of charge/discharge cycles)
So, buy them as a set and change them out as a set.

In order for the external resistance to be equal:
1) The red wire from the camper must go from the positive of the first battery in the cell and the ground wire must go to the last battery in the cell.
2) The inter connecting wires inside the cell MUST be identical in resistance. That is the SAME length, gauge, and termination (lugs).

This is so the charging and discharging current flows evenly through the stack of batteries. If the resistance in one battery is lower than the other (due to any violation of the above rules), the current into and out of that battery will be higher than the one with the higher resistance.

This will result in the lower resistance battery being discharged deeper than the other and be charged up faster that the one with higher resistance. As a result, the weaker battery will work harder; lose electrolyte every charge; and fail earlier. This effect will be worse the wider the resistance difference between the batteries.

Adding batteries to the cell beyond two must follow the same rules as above as shown in the top photo.

rmdrifter · 09-01-2012, 05:13 PM

Thanks Lou for taking the time to make such a detailed explanation--very clear.

HONDAMAN174 · 09-01-2012, 05:57 PM

So that's what I'm doing wrong. I have them hooked up wrong...again! I have both trailer leads coming off of one battery and the parallel cables hooked to the second. So I have one nearly dead unit and one fully charged at the end of dry camping. Thanks for the info!

**bikendan** · 09-01-2012, 06:46 PM

if everyone visited the "12 volt Side of Life" website, where a lot of Herk's pics come from, there would be a lot less questions like this.

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