Tongue box & solar mods in progress: build thread -- advice & insults welcome

Discussion in 'Cargo Carriers / Bike Racks / Other Storage Option' started by unclemark, May 13, 2015.

  1. unclemark

    unclemark Overland Park, KS

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    After thinking about it for nearly a year, I've gotten started building a tongue box of sorts, although it is more of a pair of front boxes. It's tall, 23 inches, and wide, 71 inches.

    Here is the plan:
    [​IMG]
    Here is the developing reality, still unglued, without tops or doors on the side cabinets:
    [​IMG]
    On the left will be tool boxes and the miscellaneous stuff that collects in that extra tub that I'm tired of hauling to camp. I bet I'll add a shelf.

    On the right will be a solar charge converter, an inverter, various switches and circuitry for the independent 12V system that I currently lack because, well, I have no battery. Here also are the levellers, the chocks, and the crank handle because this is the driver's side and it will be the first place I go after I've backed into the campsite and hopped out. Shelf is likely here too.

    Here's the rationale for building tall:
    --Bear with me, but I've already bought a solar panel, and I went big: 200W, 36V.
    --Only one brand of charge controller can really optimize this panel's performance: The 150V-TriStar-MPPT-30. It is 11.25 inches tall, it must be mounted vertically, and it requires 6 inches of air space above and below to avoid overheating. That's 23.25 inches. I'm a quarter-inch short. See? It's not so tall after all.
    --Considering the expense of the controller, I will probably want to have the flexibility to charge my battery over the road using solar to get the full benefit of all that power pouring into the panel on sunny days. You may disagree, but from what I've read charging off the TV's alternator is simply not a robust option without automobile modifications that I'm trying to avoid (like really fat wire running from under the hood to the tongue to preserve as many amps as possible).
    --I don't have anyplace large enough inside the trailer to install that space-hogging controller, especially with the camper closed.
    -- I've thoroughly researched most of the other MPPT controllers, and it's pretty clear that even if I spent more money, I couldn't get a unit as reliable and aggressive at pushing volts into my battery. Frankly, I'm not sure that any other true MPPT controller exists. Ah geez. I just had to go there.

    Here are other features I'm contemplating:
    -- Doors open to the front, piano hinged on the inside edge, latched on the outside edge.
    -- In center, propane tank goes on the left and 1 Group 24 Trojan 12V battery and box on the right.
    -- I probably can't add two batteries because of weight and my inconvenient tongue jack, which has charms that need not be explained for this conversation.
    -- I'll be removing chunks of the 3/4 inch plywood back to lighten this sucker up. But that's a load-bearing wall for the wings of this structure, so I can't remove the center back section completely.
    -- Doors will likely have thinner 1/4 inch inserts to lighten this sucker up.
    -- But security will be a big deal with that pricey controller inside this box. So I'm thinking about lightweight options for impregnability.
    -- Gonna need tight-sealing doors, especially that door on the right protecting that electricity.
    -- Also thinking about an RV "porch" light on outside of each door, dome light inside each box.
    -- I've got a 24x42 sheet of aluminum diamond plate that I'm dying to work into this project.

    So fire away with your tips, cautions, insults, and wisdom. I'll be grateful.
     
  2. speckhunter80

    speckhunter80 Well-Known Member

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    You are going to all this expense I sure as heck would not install a group 24 battery. It only holds 80-85 amps. If you can only get one battery then go with something like this http://www.trojanbattery.com/product/j185h-ac/ it has 225amp hours
     
  3. JeffC

    JeffC New Member

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    I'm not getting the controller and panel size with one group 24. Seems like way too much for the storage capacity unless you're going to be running big loads during the day. I just got a Bogart solar charge controller so I can charge my two batteries and wondered if that wasn't overkill. I'm gonna wait to get my panel until I see how much juice I use with the Trimetric.
     
  4. unclemark

    unclemark Overland Park, KS

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    Thanks, I appreciate the suggestion. The weight of that battery is a lot for this little trailer and for my TV. The tongue jack is particularly vulnerable because of its weak wheel design.
    http://www.popupportal.com/index.php?topic=86444.0
    And my Escape suspension is pretty soft. Still, I'll give this some thought. Thanks.
    Yeah, I got the cart before the horse when I saw this for sale locally at a buck a watt:
    http://www.solarelectricsupply.com/canadian-solar-200-watt-solar-panel-cs6p-200p-310
     
  5. ~erik~

    ~erik~ Active Member

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    Sounds like you made some good choices re. the solar components. I went with a 150 watt panel from Amazon.com as the free shipping made it the cheapest I could find.

    You didn't mention how or where you would mount your solar panel. I attached mine to the roof of my Aliner, am interested in seeing how yours works out.

    Nice work with the boxes on the tongue. Look forward to seeing the finished product.

    I second what others have stated about battery size. I went with the Trojan T1275. It was on sale at my local battery store. Only downside is the 82 lb. weight.
     
  6. jmkay1

    jmkay1 2004 Fleetwood/Coleman Utah

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    I don't know much about this so forgive me if I'm wrong. If the propane and battery are going to be inside this box I would think they will need lots of air flow and ventilation. Also thinking that you would want to be able to quickly turn off propane if there was an emergency. Or is this box not covering up the middle section.
     
  7. rabird

    rabird Howdy!

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    panels tilt is far more important than MPPT. direct connect works well, one just has to disconnect if the batt ever gets full. Will your battery ever be discharged enough to take 16A?

    If at home you use utility power to maintain the battery, the controller set points are almost worthless and any cheap A controller with 'normal' set points works very well.

    why would you even consider MPPT?
    'Frankly, I'm not sure that any other true MPPT controller exists.'
     
  8. unclemark

    unclemark Overland Park, KS

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    The middle section will be open. Venting all three components (propane, battery, MPPT controller) has been a puzzle. The battery can't occupy the same space as the controller because the battery gases corrode the metal, for example. I finally settled on an open section for the tank and a battery box.
     
  9. unclemark

    unclemark Overland Park, KS

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    Thanks for your comments. (edit): Regarding the mount, I'm working on a tilt-up design with knob tightener, angled aluminum, screws and glue.

    This morning, I mentioned to DW the bigger battery at 2x the cost of the what we'd previously discussed and she said, "Well it's good you asked on the forum" instead of "Honey, just give me the debit card and I'll hold onto it until December." Thanks for the suggestions. I've noticed my local battery store has better prices on Trojan and other name brand batteries than I see online.
     
  10. unclemark

    unclemark Overland Park, KS

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    Direct connect from a 36V panel? (edit): I am dreaming of a tilting mount, in fact I'm buying materials today.
    I'll have to do more research before I can articulate this, but getting from 36V to 12V apparently requires MPPT. I'll try to figure out why this is. Thanks for the challenge.
     
  11. vinmaker

    vinmaker Member

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    I love your idea.

    My Highwall does not have a front storage bin and I would love to add something like this so I can store items that I would rather not put inside the camper. My A frame set up is a lot like yours. I never thought of building a large front box. But now that I see what you did, I am inspired to give it some serious thought.

    Just thinking aloud with first thoughts. I wonder if I could construct the box out of 1/2 plywood and then bring it to a metal shop to have them fabricate a skin for the box out of diamond plate. It would basically be a custom diamond plate box. I would have them fabricate a one piece top that would hinge open. Hmmm.... But what about my LP tanks?....Hmmm....

    Very interesting.

    Thanks for sharing. I will be following your progress closely. Please post lots of pics for us. :)

    Vin.
     
  12. unclemark

    unclemark Overland Park, KS

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    Thanks. I'll get back to this after work this p.m. and try to put in a few more specs.
     
  13. rabird

    rabird Howdy!

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    Direct connect, a panel matches the load so if direct connected to 12.324v batt, the panel would put out amps associated with 12.324v. you'd need to disconnect once the batt gets to the desired voltage.

    Your panel has a Vmp of 29v, at 36v it makes NO watts. see the IV/power curves in your controller manual.

    MPPT is needed since PWM doesn't use buck converter (transformer).
    PWM direct connects to the battery, MPPT finds the Pmp (max power) and transforms this watts at ~29v in your case to battery voltage.

    Higher voltage panels or series connected allows for smaller wires since the amps are lower @ higher volts (same watts), voltage drop in wire is based on amps.

    Your panel is rated ~7A and that is the current between the panel and controller in good sun, between the controller and batt might be as high as 16A.

    Here's my 3 pt (from the panel specs on the back) of an IV and power curve.

    [​IMG]

    At zero volts and 21v it makes NO watts.
     
  14. bondebond

    bondebond New Member

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    vinmaker, skip the plywood box. If you're going to have a metal shop build a "skin" for it, just do that instead. It will be waterproof, no chance of burning the wood underneath during welding and you subtract the now superfluous weight of the wood.
     
  15. vinmaker

    vinmaker Member

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    True. But I would prefer to fabricate the wood box so as to make it idiot proof. That way the fabricators have an easy 3 dimensional image of what to build. This way they can take the measurements as they see fit and then just make it up.

    The wood box would also allow myself to visualize what it looked like and to see if it is actually as functional as I envision. If if was not what I envisioned then I could scrap the project with little cost. I would not want to pay for fabrication and then ditch it. Too wasteful.

    Great point on the wood weight. I guess you could simply ditch it and that would just be a scrap cost of fabrication.

    Vin.
     
  16. chipperone1

    chipperone1 Member

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    A good fabricator only needs a simple sketch - a napkin doodle if you want to call it that - and some dimensions to make EXACTLY what you want. A plywood mockup should be useful for you to determine what it is that you want/need.

    When I go solar my plan is to use a Tristar MPPT and flat mounting a large panel and getting what I can from the sun.
     
  17. JeffC

    JeffC New Member

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    I'm not going to mount my panel. I want to be able to move it where it gives me the best bang. I camp in the woods mostly so making sure my lid is in the sun would be too limiting. Plus I don't want another potential place to leak. I can see where the aliners would be a great place to mount them, but what happens when your panel is facing north?
     
  18. rabird

    rabird Howdy!

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    less sun is collected by the panel. Same as flat, fixed tilted, etc. This means bigger panel for the same result as tracking. Same as low light and shorter days.

    There are plenty of compromises like budget [LOL]
     
  19. JeffC

    JeffC New Member

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    That's no kidding! I'm hoping to be able to,get away with a smaller suitcase panel and use the portability to make up for the size. Once I get it figured out I may start a thread with results. The Trimetric should give some good info.
     
  20. lifespeed

    lifespeed Member

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    A good approach, the Trimetric really informs one as to what is going on. Installing this first is a great idea, then your solar and battery decisions are well-informed.
     

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