Another inverter project, maybe a custom battery rack for under the coach.

plans for the battery "box" are coming together, google image search "suspended cradle" for an idea of what's coming

the (2) current batteries sit 3' from the hitch, the (4) batteries, replacing the 2, will sit 10' from the hitch, I would like to know how to calculate the reduction (if any) in tongue weight mathematically, before installing it all, and mechanically measuring

supermanotorious said:

the (2) current batteries sit 3' from the hitch, the (4) batteries, replacing the 2, will sit 10' from the hitch, I would like to know how to calculate the reduction (if any) in tongue weight mathematically, before installing it all, and mechanically measuring

Click to expand...

It's just the ratio of each distance to the overall length between the hitch and the axles (the centerline between two axles).

For example, if the weight is at the hitch you'll have all the weight there and none on the axles.

If you move the weight back 1/4 of the distance, 75% will be on the hitch and 25% will be on the axles.

Put the weight halfway between the hitch and axles and 50% of the weight will be on each.

excellent point, thank you

here is the basic idea for the battery cradle and it's starting to come together, it will hang from eight 5/16" grade 8 bolts with nylon lock nuts, all the holes in the cradle are drilled first, undersized, then passed on to the RV frame rails, then expanded to size for perfect alignment

also, the motorcycle jack is showing you exactly where the batteries will be

I could still use some advice on fishing the remote wire for the inverter

getting the angles to mate was kinda of a PITA but it was also kind of fun, that is the fabricator's conundrum! pics might be a little misleading: the bars are perfectly parallel and the ends are of identical length and exact same angles

i'm SO on the fence with this project, this box will certainly hang low and i cant tell you if it's too low or not but i'm afraid it might be, the problem is my driveway slopes away from the house and the trailer is backed in, so the rear of the trailer is close to the ground while the tongue is several feet above so it sits level in these pictures and when it's level on level ground, this box will be closer to the ground

i'll continue making this cradle, at least tacking the rough frame together then hitch it up for a test drive, a big indicator will be simply having the tow vehicle wheels come off the sidewalk on to the street, if it bottoms out then, it's not good

since i was concerned, i decided to re-weigh the tongue, with the 2 batteries on the tongue i'm at 1,172 lbs, with out at 1,100, i'd really like to be under 1,000 as a basis then adding weight before/after the axles to fine tune afterwards, at a minimum this tells me i can not add more batteries (weight) to the tongue

if the cradle doesn't work for clearance reasons, i'll consider some vented boxes in the rear most part of the only storage compartment although that will still require some tongue weight measurements, first world problems i guess

on a slightly related note i'm making a custom drop shank for my truck since the Harbor Freight shank in the weight distributing hitch barely (if at all) makes it level, I'd like to tip the scale a little and have it barely level on a too high note, so that extra height should help as well

coming along, my little helper approves ha ha ha ha

Looks more like you just added a bit more sleeping capacity to the trailer instead of more battery space!  ;D

if I pulled that stunt mom would shoot me ha ha ha

supermanotorious said:

getting the angles to mate was kinda of a PITA but it was also kind of fun, that is the fabricator's conundrum! pics might be a little misleading: the bars are perfectly parallel and the ends are of identical length and exact same angles

i'm SO on the fence with this project, this box will certainly hang low and i cant tell you if it's too low or not but i'm afraid it might be,

Click to expand...

Yes fabricating stuff like that can be a PIA.
IMHO that is pretty low.  Looks like its about the same height as your dump valve.
If if this does ever hit; the damage could be catastrophic.  Unlike the dump valve which is only plastic so will break and can be relatively easily repaired. :-\

yeah I know, I'll have to do some tests, maybe a skid plate or wheelie bar, may have to remember to visually inspect going through ruts

but the steel is already paid for, so its just my time going forward, I'll def take the test ride before finishing with sheet metal, and before installing batteries

and for your delicious viewing pleasure, I'll have a gopro underneath filming it!

can't wait for my 3/4" bit to show up so I can wrap up this shank!

got to get creative to get the shot!

I say it's a GO!

https://www.youtube.com/watch?v=pN9tBAjk3Qc

Would have been a better video if your helper was holding the camera....lol
Looks good; a few looked kinda close?

yeah it's kind of hard to see just how much clearance there is over some bumps, I'll probably go back, park it over one and measure

But that wouldn't include your camper's momentum bouncing over the speedbump. I think I'd duck tape a piece of balsa wood so it extends 3 inches or so (whatever you're comfortable with) under the rack and take the rig for a real ride over speedbump and curb city. Then keep on extending it until you recognize its exact limitation.

Fantastic thoughts, supermanotorious, and I don't see why it won't work as long as you're aware of its exact limitations.

For a level road, just subtract the height of the bump from the clearance from the rack to the road.

Of more concern is travelling over uneven terrain.  You need maximum clearance midway between the axles and the hitch point to clear random bumps and dips and it looks like your battery bank is pretty close to there.

I'm going to look for some photos, of a custom roller bar I made for an industrial winch I build for some hydro-geophysicists that I'm considering making for this rack to help protect in those moments

ah ha, found them this bar is basically a roller for a fairlead, I could make it again to help roll over obstacles

If I get what you are saying; its a bad idea IMHO.
#1 it would make you even lower.
#2 even though it could roll, the entire weight of the trailer would be on your battery tray contraption which would likely bend and break trailer parts, not just bend or tear off battery tray. (Ok not entire weight of trailer, but a lot of it.)