A quick scour of Amazon reveals that your average Celestron Powertank, a portable battery box for astronomers, varies in price from around £50 for a 7ah model, through to £130 for a 17ah model, to £150 for a Lithium Ferrite beasty.
Blimey, astro manufacturers know how to hit astronomers right in the bank balance! SCREW THAT. I’ll do it DirtyAstro style!
Total cost for this version: £120
Build time: an hour
Tools: Drill, hack saw / oscillating multitool / dremel
Weight: Down to choice of battery. For this one, lots!
NB: *Links below updated late-2018 to something-similarly-available seeing as wire and switches were from the now-defunct Maplin…
- Socket set – 12v cig lighter, 2x USB, Voltmeter – £8
- Fuse lines – not strictly necessary, but safety n’ all that shiz – £4 (or slightly more pricey Bus Box – £10)
- 12v DC connector pack – £10
- Leisure battery box – choose to suit size of battery – £18
- Battery! I went with a 110ah Leisure battery as want it for many purposes beyond astro… £56
- *AND, 2 colours of 6A-10A equipment wire (or use domestic 3 core mains cable).
- *and 2 differing colours of these on/off switches…
- *and one of these pushbuttons or similar…
Strap it all together, wire it all up and you have what should last an entire weekend from a full charge of 12v goodness, fully switched and fused.
See attached pics!
Wiring is effectively thus: red on battery [+] to FUSE to POWER pole of switch. ACC pole of switch to + terminal on cigarette socket / USB socket accessory we want to switch. Black from battery [-] to GROUND pole of switch. Black from battery [-] to – terminal on cigarette socket accessory.
Repeat for remaining switch & socket.
For the final pushbutton and voltmeter, red [+] on battery to FUSE to + pole on pushbutton. – pole of push button to + pole of voltmeter. – pole of voltmeter to black [-] on battery.
Just follow the wiring in the Rat’s Nest pix below and the above should make sense.
Bottom left, momentary switch for centre voltmeter. Top left, on/off switch for left hand cigarette socket. Top right, on/off switch for righthand USB sockets.
Other end of rat’s nest… (the two black wires disappearing off down beside the battery are the quick connector for my maintenance charger)
Voltmeter… on a 2A fuse
Momentary switch on rear for voltmeter… hold for a reading.
Left hand switch is power on/off for left hand locking cigarette socket, on a 10A fuse.
And Right hand switch is power on / off for right hand pair of USB sockets, on a 5A fuse