And now for something completely different. In pure wood working terms this is a dovetailed box. This one however has a twist, its not just built using unplugged techniques, it provides unplugged power!
We often camp out and needed a power source to run some LED lights and charge up phones etc. This is was an ideal chance to both practice some dovetails and make something useful:- A portable, rechargeable self-contained 12v power supply.
Constructed from standard hardware store pine, this uses simple dovetail carcass joints to make the box with a lapped butt joint for the base. The lid is butt jointed and hinged. The box dimensions are set to keep the batteries tightly fitted for transit. Its a snug fit so they don’t need any additional brackets to hold them in place. The two handles on the face are there to protect the switches and charging leads during use and transit. The lid needs a rethink. It shrunk and warped in the sun as the wood has dried out! This could have been avoided by more careful selection and use of stock. I’ll remake this in a later post and explain how to choose wood based on its intended use.
It can run 2× USB sockets and a cigar type socket. Charging can be from mains power, solar panels or from our vehicle. We’ve used it for up to three days without a problem, which is fine for our purposes. The batteries are 2 x 7 Ah (amps per hour) 12v sealed lead acid batteries. You’ll need to calculate your intended electrical load before you buy your batteries. There are some easy to use battery calculators available online (one is here). An iPhone uses 1 Amp and the LED strip light uses 0.6 Amp so we’ll get nearly 9 hours use out of this set up between charges. If you need more get a stronger battery. You risk damage to the battery by over discharging, we recharge at 12.4v to avoid this. Fully charged it shows 13.4v on the display.
This is the brains of the device. A solar charging regulator. This manages the incoming power to ensure the 2 x 7ah 12v batteries are efficiently charged. 
There are plenty of different regulators available very cheaply. This one cost around £12 online.I found the regulator underestimates the voltage by 0.3V, so there is a different reading on its display than the external one. There is a fuse box installed inside. Everything is routed through this to protect the circuits and batteries from power surges.
All the power is delivered to the sockets on the external face. I have also fitted an internal cut off switch to prevent battery discharge in storage (not shown).
Final point on the power supply. Make sure any solar panels attached have a diode installed. This prevents the battery trying to charge the solar panel in low light conditions!
This is the power supply in use.
There are numerous different socket types you can use, just choose some based on the devices you are going to regularly use.
In the left hand picture you can see an LED light strip test rig I set up. This puts out enough light for a tent. The white cable is an IR remote control sensor. 2.1mm CCTV power sockets are used as connectors, they come in ready made lengths from 500mm to 50m, so are ideal for an adjustable set up.
The LED strips have now been attached to wooden battens with inset magnets to allow them to attach to our tent poles or vehicle.