Mega power bank
Here's a super-sized power bank, able to keep all your gadgets charged many times over. It offers both USB charging and a 12V accessory socket - with a suitable inverter you can even power small mains devices. It also features a digital voltmeter, to allow the state of charge to be judged.
The design here includes a rugged, waterproof case, with a storage compartment for leads and accessories. It's ideal for a camping trip, particularly when paired with a solar panel for recharging.
Step 1: Collect the components
The main components for the build are:
- An (empty!) ammunition box. The one I used was a .30 (7.62mm) calibre ammo box, measuring 25 x 8 x 18cm approximately. These are readily available from Army Surplus stores or a number of eBay sellers.
- A 12V sealed lead-acid (SLA) or valve-regulated lead acid (VRLA) battery. This needs to fit in your ammo box with plenty of height to spare. I used one measuring 15cm x 6.5cm x 9.5cm approx, which is a common sized replacement for UPS units. Typically these have a 7Ah or 9Ah capacity rating.
- Panel-mounting 12V socket, USB charger, and DC voltmeter set. These can be found on Amazon searching for "12V three hole panel". The three sockets are attached to a plastic mounting plate, but can be removed if required. In this design they are attached directly to the front panel and the mounting plate is not needed.
- A chunky toggle switch - this can be bought from many electronics suppliers, or a car or caravan accessory shop.
You'll also need:
- Wood for the front panel - this should be a decent (10-12mm) thickness as it's a structural part of the whole design - and a number of other offcuts of thin sheet plywood or similar.
- A short length of aluminium angle.
- Wire, solder, and battery terminal connectors (these are often supplied with the panel socket set).
- Thin foam for battery mounting - the stuff I used was saved packaging from a laptop case.
- Nuts, bolts, wood screws, and double-sided adhesive tape.
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