Relocate batteries to reduce tongue weight

[RTBabich]

I would like to reduce the tongue weight of our 2009 WW FB2100. There are currently 2 6v batteries mounted on a rack on the tongue. There is enough depth at the rear to mount them under the bed of the trailer in the center near the spare tire. I can make access plates in the bed of the trailer for 2 drop in battery boxes. The boxes would be vented underneath and I know the requirements for cable sizing. I've been searching for an in-floor mount/drop-in style battery box, but haven't found much. Has anyone seen anything like that? In a few weeks I'm going to set up a lever scale to measure the tongue weight and shift the batteries to the rear for a second measure before cutting any holes. I'm thinking moving the batteries from 11ft in front of the wheels to 4ft behind has got to have some effect. It would be a more secure location for the batteries and still be accessible.

[misterpowertool]

RTBabich wrote:

misterpowertools wrote:
... The first trailer had a 758# TW on a 3330# empty TT. The second TT had a 864# TW on a #4300 empty TT. Excessive for both. I have borrowed a 1000# scale to find this out. First TT got a group 31 diehard platinum under the sink, barely fwd of the axles. Second TT got 2 Exide group 31 AGMs in a rear storage compartment. ...

What were the tongue weights after the rework?

First TT 758 to about 680lbs had two 24s, got one 31
Second TT 864 to 740 lbs had two 24s, got two 31s

Those cheapy 24s were OK for a friends trolling motor, one went to an enclosed trailer, another is the starting battery in my gas golf cart.

[RTBabich]

misterpowertools wrote:
... The first trailer had a 758# TW on a 3330# empty TT. The second TT had a 864# TW on a #4300 empty TT. Excessive for both. I have borrowed a 1000# scale to find this out. First TT got a group 31 diehard platinum under the sink, barely fwd of the axles. Second TT got 2 Exide group 31 AGMs in a rear storage compartment. ...

What were the tongue weights after the rework?

[big_buford]

Strabo wrote:
I towed our 5vr yesterday to the repair shop, it was empty.

No water
No Rhino
No food
No firewood
No clothing, gear

I was surprised how heavy it still felt...

The trailer itself was much lighter, but a properly designed fiver (toyhauler) the pin weight goes way up when unloaded. Mine is the same, it is a wierd feeling.

[misterpowertool]

I did nearly the same thing to my last 2 travel trailers and will likely do it to my current toy hauler before spring. On the travel trailers, I ditched the el cheapo batteries that came with them and bought some nice sealed big AGM batteries. The first trailer had a 758# TW on a 3330# empty TT. The second TT had a 864# TW on a #4300 empty TT. Excessive for both. I have borrowed a 1000# scale to find this out. First TT got a group 31 diehard platinum under the sink, barely fwd of the axles. Second TT got 2 Exide group 31 AGMs in a rear storage compartment. Neither were hard at all to rewire and I did upsize the wire even though they moved closer to the converter. For what you might spend on access doors and undermounts, you might be close to the cost of some sealed batteries and save yourself some work.

[Strabo]

I towed our 5vr yesterday to the repair shop, it was empty.

No water
No Rhino
No food
No firewood
No clothing, gear

I was surprised how heavy it still felt...

[FireGuard]

If you want precise calculations you need to find the center of balance C/B of the trailer.
Then take the weight and multiply it by the distance from the C/B to get the moment.
The C/B wont be the axel location, it will be much farther forward.
I was a Loadmaster on a C130 cargo plane and made these computations many times.
In my opinion, I don't think it would be worth the effort.
Now, in my case to keep the A/C within limits we had to, but for a trailer I wouldn't worry about it. Just carry all the stuff in the rear and watch how full your tanks are.

[1L243]

It looks like your guessing on the TW with what the trailer plate says? That figure could be way off. You really need to weigh in now (fully loaded) before you do an modifications to reduce TW. At 750lbs of TW (after moving batteries) and a almost 9000lb trailer is going to be flirting with sway issues. Weigh in get your numbers then you will know where you stand... Relocate the batteries for security or access but not to reduce TW. It could actually make towing worse. If the Expy is dragging due to TW make your mods there not in the trailer. Airbags would be my choice...
http://www.youtube.com/watch?v=WMYyA4w0kAs

[RTBabich]

Hap Hazard wrote:
... I strongly suggest you (he) locate a pilot and do some calculations. Every pilot must know weight and balance for his aircraft. They measure the distance from the center of gravity to the location of the weight. Using a formula they can determine the new center of gravity. By proper loading they can shift the center of gravity forward or back.
It sound like you’ll be removing nearly 100% of the weight from the forward position but only shifting a small portion of that weight behind the axle. To be most effective you should move that weight as far back as you can to accomplish your desired hitch weight.

I used to know a few pilots. I worked on the F-14 software for many years. It is correct that 100% of the weight would be removed from the forward position and another 100% would be removed from the tongue if I could put them 11ft behind the axles. However, there is only 4ft behind the axles. Even 80lbs off the tongue would be good. This is not an airplane, it's a teeter totter. I was only looking at a possibility for lowering the tongue weight on my Expy as it is close to it's max in case loading for a trip is different than normal. I have done approximate calculations and it looked interesting. When I get the trailer loaded normally after a couple of trips I will weigh the tongue, then place the batteries temporarily in the back and reweigh. That will give me exact info.

[Hap_Hazard]

There’s more to this story. RTBabich states he wishes to move the batteries from 11 feet ahead of the axles to 4 feet behind. I strongly suggest you (he) locate a pilot and do some calculations. Every pilot must know weight and balance for his aircraft. They measure the distance from the center of gravity to the location of the weight. Using a formula they can determine the new center of gravity. By proper loading they can shift the center of gravity forward or back.

It sound like you’ll be removing nearly 100% of the weight from the forward position but only shifting a small portion of that weight behind the axle. To be most effective you should move that weight as far back as you can to accomplish your desired hitch weight.

Hap

[RTBabich]

otrfun wrote:
... Curious, what is the current length and gauge of cable from your converter to your batteries? Will the length increase or decrease by moving the batteries? FWIW, cable size (gauge) is typically undersized (restrictive) on most OEM installations. If you’re going to rerun the cable I would consider using a larger gauge cable. This could reduce electrical losses and decrease charge times.

The converter is an Inteli-Power 9100 40A. The output has 2 wires. One wire is 8ga which goes to a fuse block with six 12ga leads from it. The other is 10ga going to the batteries about 10ft long.

[Doughboy12]

And that is what they call "the rest of the story."
I would put some helper springs (or the like) in before I would modify the RV that much...to save very little.

[RTBabich]

Steve76eb wrote:
... I imagine it has to do with the Expedition....

Yes, it has everything to do with the Expedition. The kids are all in college and have their own cars. The 2000 Tige wake board boat is pulled by an '89 Itasca Class-C with a dog of a 460 engine. The Itasca has a double bed and tiny bath so camping is not fun. After getting my parent's '06 Corolla the Expedition sits getting about 1k a year on it. It is a great full-size SUV that will carry 8 nicely and came equipped with the heavy duty tow package. The trailer was a great deal, has 2 queen beds in the back and a large bathroom in front. We want to camp local, light and with no toys once a month or so. It is fairly level around here. The trailer specs show a tongue weight just over 800lbs and the Expedition is rated at 880lbs. The 2nd gen Expedition has 30 more Hp (5.4L) and the tow capacity went up 800lbs to 8900lbs, but I wouldn't want to get even close to that. Our trailer shouldn't be much over 6k with our use. After replacing the 4" foam beds with mattresses the tongue weight may not be as close. Maybe in a couple years we'll look at a used truck, but right now everything is paid for.

[Dirtclods]

Have you weigh your tongue weight with the trailer loaded yet?

[Steve76eb]

Seems like a lot of work for nothing. Just to keep them out of the sun or being stolen. There must be more to this to go through all this work. I imagine it has to do with the Expedition. At one time I used to use my 1997 Expedition to tow a 4000 pound 22ft Nash trailer. It did fine, but nothing I would brag about. I wouldn't want to tow anymore weight with it. You are twice the weight of my Nash, but I doubt your newer Expy is rated to tow twice what my 1997 could. I bought a brand new 04.5 Dodge Ram with the Cummins and didn't even know that trailer was back there. The sketchy mountain driving with the Expy was a thing of the past. I still have that Expy with 280K miles on it and still run it 60 miles a day. I relegated it back to what is does best...moving people....not trailers.

The comment of moving up in truck was a wise one as I believe that's what is prompting the move of the batteries. The short wheelbase Expy is best left to towing the wakeboard boat to the local lake and taking the kids to school. Good luck in sorting the weight issues out. My first choice for a tow vehicle would not be an Expedition since I have been down that road already. Its easy for me to say to upgrade to a better towing platform, but tow vehicles are not cheap and sometimes you have to try and make work what you already have.