Off Grid Power Supply

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Introduction: Off Grid Power Supply

About: I'm an inventor / maker / designer based in the Bay Area. My background is in residential architecture, film set design, animatronics, media arts, exhibit design, and electronics. I use digital design and fa...

This project is quiet, indoor friendly alternative to a gas powered generator. If you're charging devices, using lamps, or even running an electric motor for a limited time, this off grid power supply is a great companion for camping or emergency situations.

Step 1: Tools + Materials

Shapeoko XXL by Carbide 3D

    This is a great CNC machine for furniture-sized projects. It's got a 33"(X) x 33"(Y) x 3"(Z) cutting area and it's fully compatible with Fusion's CAM tools. The post processing in Fusion seems to work very well with all the tests I've tried.

    Or Be Your Own CNC...

    If you don't have a CNC router, all you need is a hand drill, a jigsaw with a metal cutting blade, a large format print from a print shop, and some patience. Here's a link to my Digital Fabrication by Hand instructable, showing you how to be your own CNC machine: http://instructables.com.mevn.net/id/Digital-Fabrication-By-Hand/

    I'll provide PDF drawings in the next step that you can use as templates to cut out your own parts by hand with a jigsaw.

    3D Printing

    I use a Creality CR-10 for just about everything. It's the best bang for your buck, in my opinion. The trim piece for this project pretty much takes up the whole bed footprint.

    • Use this coupon code at Gearbest to get it for $339: 1111CR10

    3D Print Filament

    • I used Matte Fiber HTPLA from Proto-pasta for this project, but pretty much any filament will work. I like this stuff because the finish looks really good.

    Electronics

    Total: $210 (not counting wood and 3D print filament)

    Hardware

    All of the following hardware can be substituted for smilier hardware available in your location and on your budget, but the CNC files are designed with these parts.

    • 1 1/2" wood screws
    • 1" Ø tubes for cross bars. I used some carbon fiber tubes that I found laying around in the shop, but any PVC tube or wooden dowel will do. These should be cut to 8 5/8" long.

    Materials

    Software

    Fusion 360 is free and it's awesome. I use it for everything I design and fabricate. If you have access to a CNC machine, it's about as good as it gets when it comes to easy and fast CNC programming.

    Student / Educator License (renew free every 3 years)

    Hobbyist / Startup (renew free yearly)

    Step 2: Design + Fabrication

    Just like everything else I make, I designed this project in Fusion 360. I love it because it's so easy to make CAM setups of the things you design, as you'll see in the Fusion archive that's attached here. If you take a look at the parameters list, you'll notice that I'm using a material thickness parameter. This is important because the interlocking parts (held together with screws through pilot holes) can be automatically updated if you're using a different material.

    The STL files are for the end caps that hols the cross bars. The capMid piece is meant to be a connection piece for the side panels, but I ended up not using them because I glued the sides onto the box.

    The DXF files are vector files that can be used for CNC or laser cutting.

    The PDF files are printable files that can be used at templates for hand cutting. They should be printed at 100% on whatever sheet size they'll fit on.

    Layout.PDF is for 1/2" material.

    Face Plate.PDF is for 1/8" material.

    Step 3: Parts Assembly

    The battery and charger fit into slots on the insert piece and are held down with zip ties and screws with washers as seen in the photos. The inverter is fastened with screws through pilot holes in the side of the box.

    The diagrams above show where the parts in the face plate belong. I used power pole connectors to connect all the electronic parts, but you could easily do it all with screw-on wire caps from any hardware store.

    Step 4: Chassis Assembly

    The assembly is basically just a box with X-shaped side pieces. These pieces protrude past the main box and make feet that have carbon fiber cross bars. These bars make good handles for moving the power supply, but the idea is that they also can be used to attach it to a roof rack or something like that.

    I used 2" wood screws to attach the end caps to the X-shaped panels as shown in the diagram. The caps were a bit snug, I would probably make the tolerance bigger for those pieces if I were to do it again.

    Step 5: Go Off the Grid!

    I ran a shop vac off of this power supply for about an hour before the inverted started beeping (warning me that the output was going below 10V). We used it at a cabin in the woods for a weekend charging phones, bluetooth speakers, and fluorescent lamps, and in 48 hours we still had power.

    I'd like to try charging it with solar panels to get a sense of how well it would work with that kind of system. Let me know what you think in the comments!

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      We have a be nice policy.
      Please be positive and constructive.

      4 Tips

      I forgot to finish another thought before I posted my last message. Even if there is no back on this the battery should still be sealed off from the other electronics. As the inverter heats up and the cooling fan comes on it will circulate the gasses through the unit and other electronics. Even people that were just charging the battery in their car in an open garage have had the battery gasses explode, burning the car and the garage down. If you really need to use a lead acid battery it would be better if the battery was separate from the rest of this unit. Just be careful.

      Just one problem with this, if you are going to have everything all together in this one box you need to do something to separate and seal the battery off from the rest of the components, it also needs to be vented. Even if it is a sealed maintenance free deep cycle battery it will give off corrosive gasses that will destroy your inverter and other electronics, you also have the makings of a bomb, if battery gasses build up in an enclosed space they can explode. Batteries put off a lot more gas while charging. This is why they tell you not to put the inverter in with the batteries in a trailer, camper or RV.

      I agree that it is wise to vent the battery separately - it would be easily accomplished and allows the cheaper, larger, vented batteries to be used. The idea behind the venting is not only for safety so no gases can build up, but because of corrosion.

      But the 'bomb scare' stuff is over-hyped. If someone had a battery start a fire, it was because other things were around, not due to the battery. I have experienced a battery explosion, but the apparent failure mechanism is that the battery fails internally by rapid discharge which caused a gas build up in one or more cells. When the car's starter was engaged, the bridge that was causing the discharge, arced and ignited the gases which blew the top of the battery off. There was acid all over the place, but it was mostly low concentration though it bubbled pretty ferociously in a base bath of baking soda (I think I used), but the acid was not strong enough to burn my fingers as I carried the spent battery into the shop to buy another. It happened in front of an auto store. The employees were scared to death to touch it!)

      The gases are generally recombined as they are produced from H and O to H2O, but over-charging causes an abundance of the gases so much so that they don't recombine rapidly enough. Even so, an explosion is an anomaly - it is not normal, a malfunction caused by rapid charge (overcharge) or discharge (short) and will probably happen regardless of the venting used. AGM is the best way to prevent it for this kind of use - and buy the deep cycle variety.

      I second the separate compartment for the battery. The out gassing could also corrode the electronics. I would also use a separate float charger on the battery to maintain the battery when not in use.

      1 Questions

      What is the diameter of the carbon fiber rod you are using for the 4 arms? Thanks!

      95 Comments

      I tried several times to open the "trimNew.stl" file in Utimaker Cura to create gcode for the print but only a few small boxes are shown. Is the file bad or is it me? Thanks!

      5 replies

      You might be having a problem with units. Small boxes sounds to me like the trim is there, it’s just tiny. Do you get a units option in Cura?

      I think you'll want to scale it up from 1 to 25.4 (25.4 mm in an inch...).

      It is there as you said but the units are scaled down. X is 9.1584mm, Y is 1.2362mm and Z is 8.6024mm. Should I scale it up to 838.2mm (33") for X? Still, though, the lengths for X and Z while similar aren't the same. I'm a newbie at 3D printing so I'm asking basic questions. Thanks!

      I realized that the X value shouldn't be 33". It should be around 7.6". I'm just not sure how much to scale it up.

      Cura doesn't seem to have a units option. However, it does have a scale function where a model can either be increased in size by a percentage or X, Y and Z values.

      I will make 1 same for myself. Good for use for example when city off electric. Silent and power) nice !

      I think this would be an amazing system to add solar panels to. With a slight redesign you could probably turn the top surface into a solar panel and incorporate 2 flip-up side panels for a 3 panel top surface while leaving the front open for charging and the handles available for carrying. I'm not 100% certain how the attachment would work with all these other things attached but I think if you ran your solar panels through a charge controller right to the battery terminals, that it would work just fine. In fact that'd be a pretty awesome product that might be worthy of a Kickstarter.

      4 replies

      this is a standard configuration for an "off grid" system without really being off grid considering that he has an AC-DC converter in it. the only difference is that he made a nice enclosure for it. so why would it be a product "that might be worthy of a Kickstarter"? is it the enclosure that caught your attention?

      No, I'm talking about a modular portable power system that is DIY from a kit. I like the option of adding a 12v car charging port, or a usb port, or 4. Maybe I want solar panels, or maybe I only want to plug it in to charge. Maybe mine has wheels or a camping lantern built right into the side. If you know that something like that already exists, point me in the right direction.

      Yeah, I love that idea. I think the design would be a bit different, but it would be good to know what the solar panel options would be and how many you would need to charge the battery in a reasonable amount of time.

      if u use a solar panel you will need a charge controller... this is a DC_DC charger with a MPP (Maximum Power Point) controller to suck out the max power from the solar panel into the battery. so this device goes between your solar panel and the battery. also remember that the panel is a lot bigger than the box that you made. what you made is a battery back up unit with a massive battery and a novel enclosure. you will need a big panel to charge that battery. you have to decide how quickly or slowly you want to charge the battery and buy the panel with that amount of capacity. 35 AH/ 5 hours means 7 amps from the panel for the full day. here is So Cal we have an average of 5.5 hours of sunlight/day.

      What does this do that a portable backup starter system for automobile use doesn't do? I didn't check the actual figures, but what it sounds like is the designer put together standard products into a cute (and well designed) box in order to make use of his toys (kudos for that) but otherwise nothing spectacular nor even special. For about $100 you can go to Walmart or the like and buy a portable car starter. The only thing it is missing is an inverter. Buy a 400 w inverter for $50 and you can mount it inside the original box by pulling the cords out and wiring the inverter into the opening. Along with it you would receive a flashlight and an pretty good air pump to boot. And you would be likely to keep on top of its maintenance because you have it with you in the vehicle all of the time - I would arrange to have it charged from the 12 v of the car.

      Optionally, you could build the pretty (cool) box and install all of the guts out of the automotive backup starter system along with the inverter with a little ingenuity. What do you think about that possibility?

      1 reply

      I think the main difference would be the size of the battery. You make a good point though, you could purchase one of these backup starter systems, rip out the guts and add a nice big battery and put it into a nice looking box as a nice alternative for having to buy the parts separately. If someone was extra clever they could probably find a way to expand the capacity and keep the form factor of the original. I like it.

      I don't see a free hobbyist / startup option for Fusion 360, am I missing something? I see $40 month/ $300 a year, free 3 year for student, or free 30 day trial.

      1 reply

      Just wait until your 30 day trial is up- you'll see an option to continue for free as a hobbyist / enthusiast / startup (I forget what they're calling it now). You'll be prompted to renew yearly for free.

      OK my experiences in making these.

      .

      Once upon a time the local power company had power lines, that could only be described as termite food but the food had run out and the termites had move on.. Power was regularly going off - sometimes many times a day. So I had to make a "battery based 240VAC 10A power supply from 2 big car batteries, a charger and a UPS, especially modified for continuous running (model specific).

      .

      1. Lead Acid batteries DO vent and can leak - the fumes / mist / liquid is corrosive and it roones nice electronics - like in your inverter etc. They need to be kept in a separate TOP VENTED plastic container - to let the hydrogen gas leak out - via the holes in the top. (One 8.00mm hole in each corner). Preferably a battery container - made for such things.

      .

      2. I'd also put wheels under it. While car batteries usually are not that heavy, lifting things like that, that are very low to the ground - you either have to squat to lift it OR your leaning over and possibly doing your spine in.....

      .

      3. I'd also be inclined to make a 2 separate compartments, and a circuit board, rather than loose wires in the box. Also the ventilation slot is NOT properly sized - for the inverter's intake, and there is NO cross ventilation on the charger, seated as it is side on vent blocked underneath it, and the exhaust vent for the container, also looks to have many SMALL holes, which isn't the same flow area as many LARGER holes.

      .

      One of the things about axial flow fans is that they DO move air, but at very LOW pressure, and if you have things that restrict or obstruct flow, especially a very restricted intake, and a restricted exhaust - your in real danger of choking the COOLING airflow to internal parts, that need cooling, and this can lead to component failure and or unforseen problems.

      .

      I mean I think some "stylistic designers" with their bullshit trend setting air vents, well I have a dim view of them. But when what you do makes it way worse, then your placing yourself in a position of great hazard. The other thing that needs to be noted is that if you look at the OLD style transformer based welders, without cooling fans, is that they had ventilation slots that allowed generous amounts of convective cooling to happen. You have NON of these natural features and all the "HOT" is inside a wooden box. Like ply is not a super GOOD insulator, but it is MORE than good enough to encourage the starting of fires from OVERHEATED components on the inside.

      2 replies

      Dude, thanks for the solid advice! I've got some holes to drill...

      Well it is a good idea..... If your in a place where the power is non existent, irregular and or you only need a small power supply, for a small amount of things, I can understand that...... a 5W LED lamp for several hours and charging up a phone is a good thing... easier than firing up a generator.

      .

      Always try to design from the natural fall back position.... like if there was no cooling fan, how could we cool this? and then any cooling fans on top of this, would be degrees of redundancy.

      .

      Like I really doubt that this would catch fire.... but funny things happen in unforseen or unexpected ways....

      .

      Assuming that all the internals of the inverter, were rated to 80*C... if the ambient temperature was say 40*C and the fan was working. In say 5 years time, there was a build of fluff around the bottom vent. And the blocked off air vent meant that the integrated circuits were running at 120*C, and slowly by slowly the dust coating on them built up until one went "pop" and spat out a small spark that landed in the fabric fluff on the base air vent and that caught fire and blew a little flame onto the carpet... and slowly that spread up into the curtains etc.. and there goes your house - up in flames.

      .

      When most things overheat, they dry out and or just plain cook or blow a thermal fuse, and if they do catch fire, the circuit boards either do not burn or are extraordinarily difficult to ignite etc., etc., etc..

      .

      It's just those situations that set up the fairly obvious prerequisites for failure, and putting hot running electrical gear inside a small wooden box, with completely inadequate ventilation, is sort of setting up the power supply for the very big problems that can arise from over heating....

      .

      The smart way to design is for generosity in good design and unforeseen circumstances....

      .

      Like kitchen dining tables. How many idiots design them with hard, sharp corners and square edges? How many kids brain themselves when they go head first into them? Duh. Rounded corners with generous radius's prevents the cutting open of the head when an impact does happen. No split open head, no hospital visit, no hospital visit, no huge medical bills.... etc.

      You could use a dynamo and convert it to wind as an alternative to soar would cost you about 50 bucks just an idea

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