Build your own torch     my current preferences



Basic specification

Umbilical - 12V, 20W dichroic lamp - overdriven to 19.2V

Probably use a dimmer modified for reed switch operation as recommended


Batteries

16 x 3.8Ah 7/5AF cells from Budget Batteries = £64
I've got them now and they're actually 3.7Ah - hmmm never mind, that's probably less than production tolerance in any case


Lamp

12V, 20W dichroic

Planning to use IRC type for best efficiency - I've got hold of some Philips Masterline ES and an Osram Decostar to try


Battery housing

Acetal C or Delrin construction
Silica gel sachets seem like a good idea to protect the batteries from any moisture so I'll drop some in




Lighthead

compact aluminium body with good heatsinking properties
heavy borosilicate or soda glass
easy lamp replacement




or maybe . . . .



Switching

Reed switch in lighthead and relay or dimmer circuit in battery housing
Reliable safety mechanism to avoid accidental switch on . . .


Umbilical and connectors

5 core umbilical - not all cores used initially - room for development

Probably choose an in-line connection using Bulgin Buccaneer Standard or Subconn connectors
The connectors are probably a weak point and it seems likely that an in-line failure would be less catastrophic than a leak directly into a housing


Battery charging

Slow charging at 0.1C = 370mA for these cells


Circuits

to follow