Introduction: Off Grid Power Supply
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
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: https://www.instructables.com/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.
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.
- Power Inverter: ($61) 800 Watt Continuous / 1600 Watt Peak Power
- 12V Deep Cycle Battery: ($64) Be sure to use a deep cycle battery, a car battery will run out very quickly!
- 12V AC Battery Charger: ($54) This charges the battery from a wall outlet when it's available.
- AC Power Socket: ($7) This connects to the AC battery charger. Be sure to use one that has a fuse!
- Cigarette Lighter Terminal: ($6) This terminal connects to the battery and can be used for DC charging, such as with solar panels.
- 12V Battery Meter: ($15) This gives you voltage and percentage of battery power.
Total: $210 (not counting wood and 3D print filament)
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.
- 32" X 32" 1/2" thick MDF sheet. Any 1/2" material will work with the files I'm providing.
- Glossy Epoxy resin for waterproofing
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!
We have a be nice policy.
Please be positive and constructive.
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.
What is the diameter of the carbon fiber rod you are using for the 4 arms? Thanks!