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Old 08-30-2015, 10:45 AM   #1
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Twin Bed Internal Battery Location

Planning to convert my Classic 25fb queen to twin beds. I'm thinking about moving my battery location to under the twin beds to reduce tongue weight. I will replace my two Interstate Grp27s with AGM, either Grp27 12v or two 6v.

The curb side has the bath, pantry and kitchen so I suspect that side is the heaviest side. The street side has the fridge and shower. The curb twin will have the converter.

Weight for these batteries are from 124lb to 136lb. Should I split the batteries so ther is one under each twin bed to distribute the weight? With the curb side heavier should I put both batteries under the street twin. I want to place the batteries as far to the rear as possible.

I don't want to go to a larger size battery sinc I would antipating having to lift them up and out of the twin bed area and 70lbs is about my safe limit to lifting.

Kelvin
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Old 08-30-2015, 10:58 AM   #2
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Make sure the new batteries are as far back under the twin beds as possible to help reduce tongue weight. But also remember to keep at least 10% of the GVW on the tongue for towing stability.

The battery position would also be constrained by the location of the charger. If you have or contemplate a solar system, then the battery setup has to as close as possible to the converter/inverter.

We had a 25FB International and the curb side rear tire carried 200 more pounds than any of the others. A friend commented on my observation that that specific tire was replaced nearly twice as often on their older 25FB than the other three.

Before the modification starts, I would make the effort to get the individual wheel weights so you know which wheel currently carries the greatest load.
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Old 08-30-2015, 11:45 AM   #3
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I'm not anticipating getting roof solar as I have a portable 200 watt solar panel. I may modify it so the controller is inside the trailer rather than being on the panels.

I would imagine filling up the fridge for longer trips could make up some of the slightly higher weight on the curb side.

If I were to put the batteries on the street side I would have them located against the shower wall under the twin. I'd probably make use of the pneumatic struts from the queen bed to lift the street side bed up so I could pull the batteries out. That would place the 135lbs 7ft back from the current tongue location.

My current hitch weight is between 1100lbs to 1200lbs. It changes when I load two bikes on my Arvika biker rack located over the propane tanks. For extended travels the bikes will always accompany us. So I don't think I'll ever reduce the hitch weight to under 750lbs even if I moved the batteries and the spare tire under the A frame.

At a CAT scale can you get the individual axles weighed?

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Old 08-30-2015, 12:29 PM   #4
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Are the battery cables, that route into the interior of the Airstream directly terminated to the converter/charger? I think they terminate to the electrical area where the Store/Use relay is located then positive/negative wires then route to the other side of the bed where the converter/charger is located.

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Old 08-31-2015, 08:13 AM   #5
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Cat scale positioning usually generates front axle, rear axle, and the combined trailer axle weight. If it is a slow day, one can get permission to drive the other way onto the scales and put the trailer axles on the two different segments usually for the tow vehicle tires. That trip would also provide the opportunity to detach from the trailer, move the tow vehicle off the scales and get the tongue weight at the same time.

I understand the weight issue from the literature tongue weight to the reality. Our 2013 25FB International (GVW of 7,300 pounds) had a literature tongue weight of 833 pounds and an actual tongue weight of 1,150 with the Hensley hitch head attached, dealer installed street and rear awnings and a 155 watt solar panel on the roof. That was before I even left the dealership. Loaded for camping and after moving the load around, the tongue weight was 1,175 pounds.

From my memory of the wiring under the front bed on our 25FB, the contemplated modification relocating the main power panel, an inverter if installed, and all the other wires coming in may require several electrical junction boxes to extend wires that can not stretch to their new location.

Our twin Classic has a night stand with a single drawer and a power outlet below that drawer between the beds and the external access storage area is nearly the full width of the trailer under the head board area.

Going to the Airstream support area and downloading parts manuals for several generations of trailers that offered the twin options may provide some ideas how the factory placed the electrical parts.
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Old 08-31-2015, 08:31 AM   #6
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I did this for my 26' '64 Overlander. I actually have 3 gel cell batteries. Had the belly pan open so I ran the shielded charge cords under the trailer and back up to the back where the converter was, making the trip as short as possible. I think it was #4 or #6 wire. Can't remember. More solid wires than say the fine stranded stuff in a jumper cable.

Anyway, you big concern is making sure to strap them down well. I used t-nuts from underneath, and then framed in the batteries at the base, with a strap running over the top. On the opposite side, I have the fresh water tank. On a double axle, all this weight is between the axles. Since the original setup was a heavy univolt and batter at the far rear, I feel like I've added some tongue weight, plus I have 2, 30 lb propane tanks up front - though they are aluminum.
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Old 08-31-2015, 10:19 AM   #7
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I wouldn't put them as far back as possible, but near the trailer center as possible. Two reasons.

They are sitting on a unsupported cantilever back there, subject to many g-forces when traveling. Hard on the trailer shell/frame structure over time.

In the event of a sway condition, weight at the extreme ends is very hard to reverse, bring back to centerline. The sway will be amplified. Airstream cautions against heavy weight at the rear and limits hitch weight to 1,000 lbs, most probably due to this dangerous condition.

On the other hand, they warn you have 10-12% of your total weight on the hitch to keep the trailer stable. They build these with the heavy stuff near the center so it's a good idea to stay with that concept.
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Old 08-31-2015, 10:27 AM   #8
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In the case of the Hensley/ProPride hitches, the truck receiver is actually carrying the hitch head. I can see two (or more) points of view whether this should be considered tongue (hitch) weight. I don't think it is, but it depends on what and why you are weighing.
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Old 08-31-2015, 11:06 AM   #9
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I probably have closer to 15% on my tongue currently so moving the batteries shouldn't have an adverse affect.

When the vinyl and carpeting is removed can you see bolts that attach the subfloor to the frame. I would imagine the subfloor would be bolted down to every frame support out to the shell perimeter. If I mount the batteries under a twin bed would screwing down a sheet of plywood that extends between the frame supports on to the subfloor, to serve as a base for the batteries, to strengthen and distribute the weight of 124 to 136 lbs of batteries?

How does AS support the subfloor under the fridge. You can put a lot of weight in a fridge and its located out from the center.

I may abort having the batteries moved back if I risk damage down the road.

Kelvin
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Old 08-31-2015, 12:33 PM   #10
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I should have said Airstream puts the heavy appliances over or near the axles, rather than centered in the trailer. So the suggestion to avoid moving them too far back.
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Old 08-31-2015, 08:53 PM   #11
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If the goal is to reduce tongue weight, you could switch to Optima gel cell batteries which have less weight than conventional lead acid batteries. I am contemplating the opposite in our '67 Overlander. Having the single battery under a twin bed makes it difficult to service the battery and in our case, there is not enough room in the battery compartment to parallel two batteries which limits ability to boondock.
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Old 08-31-2015, 11:20 PM   #12
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Optima vs. Golf Batteries

Quote:
Originally Posted by Jacob D View Post
If the goal is to reduce tongue weight, you could switch to Optima gel cell batteries which have less weight than conventional lead acid batteries. I am contemplating the opposite in our '67 Overlander. Having the single battery under a twin bed makes it difficult to service the battery and in our case, there is not enough room in the battery compartment to parallel two batteries which limits ability to boondock.
I've never heard of the Optima Battery, but it looks good. Anyone know if they are better than using two 6V golf batteries? Less weight? The Optima website says they are not gel, but advanced AMG batteries that last longer.

Thanks,

Lyle
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Old 09-01-2015, 09:36 AM   #13
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Our 300 amp-hour AM Solar lithium iron phosphate battery has a foot print of 14.5" x 11.25" and it requires about 11.25" of vertical space. This battery weighs 84 pounds which is less then the two stock standard factory installed Interstate batteries we removed.

Two other foot print configurations for this battery are 7.25" x 22.5" or 5.625" x 29".

One configuration for the 400 amp-hourm configuration could be 11.25" x 19.375" and would weigh 112 pounds.

We can safely use 80% to 85% of the capacity which means there is 255 amp hours of usable power. The battery will absorb all the power we can throw at it when charging, but does require an intelligent programable charger.

We mounted the battery just in front of the street side wheel well with the Magnum MSH-3012 charger/inverter along side.
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Old 09-01-2015, 10:15 AM   #14
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Quote:
Originally Posted by ltorgy View Post
I've never heard of the Optima Battery, but it looks good. Anyone know if they are better than using two 6V golf batteries? Less weight? The Optima website says they are not gel, but advanced AMG batteries that last longer.

Thanks,

Lyle
Optima batteries are lighter simply because they use less lead inside the battery, which provides less battery capacity. They have the footprint of a group 24 battery which typically has an 80 amp/hour capacity. An Optima has a mere 55 amp/hours of capacity. Folks generally want to increase their battery capacity, not decrease it.

Do a bit of research on present remarks about Optimas. They were once well rated, but now that they are manufactured in China, buyers are experiencing many problems with them.

There are many other battery solutions available.
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