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Updated (12-MAR-03)  Current Preferences

Build your own torch


A casual enquiry about the feasibility of a DIY torch started a 'flood' of posts from many of us who had been thinking along the same lines
I've tried to summarise the many suggestions and tips put forward

General Specification Ideas:

basic type general preference is for a 12V, umbilical, suggested circuit, lamp overdriving also seems like a sensible option
interchangeable heads use connectors for a choice of heads depending on the dive, or for an extra battery pack, or . . .


drop a sachet of silica gel inside the housing / lighthead - to absorb moisture and stop things from condensing and going gammy

Aluminium Minimum 1/4" wall thickness. I’m using 6" OD tube ; which allows enough material after cutting your internal thread. It also allows you to machine an exterior 'step' if you wish to attach the lid by toggle-latches. The latches can sit under the step and be held in place with a standard jubilee clip. This avoids any through-hull holes

The best thing to make a cannister from is the barrel and 2 rear end caps from a pneumatic cylinder. If you can find a scrapper somewhere then you are onto a winner. They have grooves, holes and various mounting options which makes fitting it to your kit a piece of cake. Takes the pressure too

I also had a quote for a canister made new by a pneumatics manufacturer - £111 for an 80mm bore x 275mm long cylinder barrel and 2 end caps with the ports blanked off. Would be cheaper in quantities but the cheapest way would be to find a pair of scrap 80mm bore cylinders and take the rear end caps off those. They come ready anodised as well, saving you that bother

SLA's are bulkier so the 6 cells amount to similar length as 10 x Nimh. Might be possible to produce a standard cannister which would hold either type

Cannister will end up long so possibly worth considering a wider, stubby canister and packing cells in banks of 2 or 3

Aluminium tube and blanks: Best to ring round your local non-ferrous stockists and ask for off-cuts- they usually have some and will sometimes let you have them for free, especially if you ask for a root in their scrap bin

Delrin / Acetal engineering plastics as used by Halcyon etc.
Glass lens several reports of implosion if too thin

use borosilicate, tough and heat resistant, 80mm dia piece up for about a tenner - to seal it, the best way is to machine a step into the end of the torch with an O-ring in it so the bigger the pressure, the better the seal. You don't need to thread the end then, just use a stainless or plastic circlip

Got the borosilcate glass from a local glass stockist - just ring round to find a suitable supplier for your design. The glass is used for fire fronts and inspection ports so is quite common

I used a sealed dichroic and was planning to not have a front glass. No idea what depth a dichroic will collapse at so I was going to take one into Stoney some time and find out
- I took one to 35m at Stoney - it didn’t implode, it just let water in - water got in around the front glass on my cheap Homebase lamp - doesn't look like this will work. I think it probably leaked at 1m

Glass Precision Engineering

Lighthead maybe if the light head were made a with a DIN screw, a standard plastic dust cap type design could be used to protect the exposed connections? - ref. disconnecting the lighthead to prevent accidental switch-on

Possibly would have to be turned out of solid as tube walls might be too thin to provide lands for O rings

modified Maglite ? - sounds costly and complex . . . . purpose made head would be better

Maglite (2 x D cell) for £17 - maybe not so costly . .

modified cheap dive torch ?

Hozelock garden pond light – only £11 from TLC - verified ok to 40m - that’s some pond !!

a few alternatives – mostly more expensive but some worth a look:

       Lunaqua    Noma    Aico    Mariner    Acorn    Halley    Maplin ?


Overdrive with high V Overdrive the lamp for greater efficiency. Filament lamps provide whiter light and more light per watt at higher filament temperatures - maximum efficiency is reached just below filament melting point. There is a compromise between efficiency and lamp life. Most dichroics are rated for a life expectancy of around 4000 hours - it makes sense to sacrifice some of that life for much better efficiency

From Osram’s LV Halogens pdf (link below) the following 'rule of thumb':

        05% increase in voltage (from rated voltage) results in:

        50% loss of lamp life
        15% increase in luminous flux
        08% increase in power
        03% increase in curent
        02% increase in colour temperature

I ran some overdriving tests a while back
The following table shows measured currents at various voltages and a few life-test results. The R and W values are calculated

The lamps were mainly on all the time during test, I just switched them off – allowed to cool – and switched back on a few times a day. Expected life in a torch with more on-off cycles and lots of knocking about would probably be less than shown here
Brightness levels were generally very impressive at these higher voltages. The lamps were clearly uncomfortable when the voltage exceeded 21V - getting very hot and giving off some pretty nasty fumes, but seemed ok below 20V.

        test results table

* I suspect that my psu went berserk and blew this prematurely – the onboard wobbly Voltmeter was showing 28V when I found the lamp dead. The psu itself died only a couple of hours into the next test . . . . . . Either way, I’m fairly happy that 19.2V is going to be OK and have bought 16 x 7/5AF batteries. I can’t do any more testing anyway and if it proves too much I can just take a cell(s) out of the circuit

Dichroic cheap, good choice of reflector angle / beam width / power    lampholder

IRC = Infra-Red Conserving - an energy-efficient lamp construction. A coating on the halogen capsule reflects much of the radiated infra-red energy back onto the filament so reducing the energy requirement to keep the filament at operating temperature. Reports vary from 30-40% savings - sounds optimistic but what do I know . . . . I’ve ordered some Philips Masterline ES to try

Philips Masterline ES IRC axial filament lamps from Philips: Masterline

note: unusually, the glass front on these lamps domes out about 2-3mm, might need to consider this in lighthead design

Osram LV Halogens Osram lamp data - (4.4Mb but loads of info inc. Xenophot)

Describes that Xenophots should not be overdriven – they already operate at higher temperature than standard halogens

Osram’s IRC axial filament lamp:   Tru-aim general   Tru-aim detail

GE Lighting GE technical catalogue.pdf

HID Airspeed Press HID Update

probably too complicated and risky (expensive) for the amount saved


General Drawing comparitively large currents from the batteries requires a good connection between the cells, not just touching as in normal torches. Batteries can be got in pre-made sets ie. 6 or 12V with welded connections

or buy tagged cells and solder them up yourself

To connect your battery pack to the rest of your lamp (inside the canister) use a connector for radio controlled cars- they click shut, so they won't come undone, and can take the amps running through them

Stick an in-line fuse into the system to stop everything going pop if there is a short - Will need to be quite a high value time-delay fuse as the normal switch-on surge will be high

all sorts of odd batteries available here:

Sealed lead acid bulky, steep discharge curve, but cheap and robust

voltage decays so light will dim with time. Characteristic voltage is 2V so need 6 cells to get 12V. A set of 8Ah Cyclons from the CPC catalogue = 6x £8 = £48. Will run a 45 watt bulb at full brightness for approx 1 hour, possibly longer. I have a torch which uses 5Ah Cyclons and it runs a 45W bulb for about 45 mins before it yellows

      12V, 5Ah for £48

NiCd need care to avoid memory effect, flatter discharge curve to maintain brightness, 1.6Ah D cells from Budget @ £1.70 each
nb. according to budget battery info these particular NiCd’s do not suffer from the memory effect

      12V, 1.6Ah for £17

NiMH powerful, can be expensive but probably a good investment, 2.2Ah D cells @ £3 each, or 7Ah D cells from Budget @ £6 each look very good value. Tagged cells are a better option for high currents: 7Ah tagged D cells @ £8.60 each, or 9Ah tagged D cells @ £9 each

      12V, 2.2Ah for £30
      12V, 7Ah for £60
      12V, 7Ah for £86 (tagged)
      12V, 9Ah for £90 (tagged)

2Ah AA cells from 7DayShop for £5.75 for a 4-pack

      12V, 2Ah for £18 (with 2 spare cells)

With the new ideas on overdriving I’ve opted for these more compact 3.8Ah 7/5AF cells @ £4 each

      19.2V, 3.8Ah for £64 - (they've arrived - they’re actually marked 3.7Ah)


Reed and relay keep housing penetrations to the minimum

relays from Maplin relay1   relay2,      reed switch from Maplin reed,     magnet from Maplin magnet

Toggle switch cheap and simple

Protection ? accidental switch-on prevention idea - an in-water switch as shown here:

don't mess about with in-water detection, just have a positive lock on the switch for transport or disconnect the light head and shield the exposed connector to avoid shorts

Automatic battery protection - if you deep discharge those expensive NiMH batteries too many times then you'll end up buying new ones
Low battery warning - gives you a chance to dim it to extend burn time before it's lights out, Sooty
Starts the bulb off gently rather than full power straight away.Most bulbs blow when you switch them on - the LVR dims the bulb up stopping this
Connection was extremely simple - 2 power wires to the LVR, one feed from the LVR to the lamp head and another from the lamp head to the battery -ve.
The LVR comes with a switch pre-mounted which I changed for a magnetic reed switch. The great thing about this switching arrangement is you don't need to have the reed switch permanently energised by a magnet - just press and release the switch for 1 second to turn on/off and quickly press and release to dim. The practical upshot is instead of having a magnet stuck to the torch permanently, I have one attached to my harness (with another spare on the umbilical cable). Wave the magnet over the lamp head for 1 second and it fires up. Wave it over again and it switches off.
For £40 you get a bit of kit that does so much - well worth it. They were originally made for Pizel caving head torches so are rugged and very small
When ordering, you specify the nominal voltage of the battery pack – mine is 16x1.2V = 19.2V. Runs more like 21V when fully charged. The recommended warning voltage and cut-off voltage will be recommended by them - they are very knowledgeable about this sort of thing and are a great help. They have an example setup for a bicycle headlamp of 100W with a 24V lead acid pack or 19.2V NiCad.

Battery Charging:

External terminals removing the need to constantly open and close the battery housing just has to be a good idea - leave it sealed

sealing is not possible with SLA's as they gas when charged. NiCd and NiMH only gas when severely overcharged - this would require extreme neglect with the slow-charging system described below but might be a concern with a fast-charging system

Use the wet connector as the charging connection and have a small bolt with an O-ring penetrating the cannister to be loosened when charging to release any gas. Good idea - I'll probably do this if I upgrade to a fast-charger

For ideas on a self-sealing gas vent, look at some commercial lights such as the tiny UK 2L. It's rated to 500', but has a pinhole covered by an O-ring to allow outgassing. The venting O-ring is separate from the one that makes the case to bezel seal

Off the shelf chargers
NB. for an effective "fast charging" system, you will need a unit that can deliver a current(A) equivalent to, at least, the capacity(Ah) of your chosen battery pack. This is far beyond the capabilities of most domestic chargers

Homebrew slow charger I’ve read up on NiCd and NiMH charging - slow charging seems to be the sensible option for both types for several reasons. It’s simple, cheap and there’s no real problem with overcharging. For slow charging you need a bit more than the battery’s rated voltage and a current(A) of no more than 0.1 of the capacity(Ah). At this rate it takes around 15 hours to fully recharge a completely flat battery, a half-discharged battery would recharge in half the time

A mains adaptor, modified to provide constant current is probably the simplest, cheapest and safest option. A 15V regulated adaptor should have enough space and a bit of pcb to fit the constant current circuit inside – if you hacksaw the thing open

Even though it is ‘safe’ to overcharge at these low currents, a mains timer would be a wise precaution – see time notes with the circuit


IP68 spec. IP stands for Index of Protection. The rating IPX7 is for 15cm depth for temporary immersion. The rating IPX8 should be qualified with a depth or pressure. For example, there are some glands in RS Components rated at IP68, 5 bar. There are others in RS Components rated at IP68 15bar. Same standard, different qualifier. IPX8 without a qualifier is no better than IPX7

use a "Wetmate” connector . . .. any details ?

connectors for 2 miles depths !! NSW Technology in Aberdeen (01224 703595)- anyone got any details ?

Use a wet connector in the cable or on the cannister. This would allow quick change of lamp, even under water

Bulgin Buccaner Standard tested at 100m

Subconn connectors - very nice, and their UK agent


O-rings source from washing machine spares shops, bearing stockists etc

fit so they are compressed with pressure

good technical information on O-rings and their usage at

Glands RS Components IP68 glands confirmed ok to 70m – recommended to drill and tap endplate and fit gland directly

Compression fittings some reported successes with standard plumbing compression fittings, makes me nervous though

Umbilical cable HO-7RN three-core 1.5mm pond cable

I'm not sure that 'special' cable is necessary, I'll be using 4 or 5 core for flexibility and to allow for some future development, eg. fast charging, dimmer etc


Technical Information:

The Divelight Companion
Some u/w lighting chat
Lamps / corrosion
- some general lamp history and notes on disimilar metal corrosion risks
General lighting info
- loads of information on every aspect of lighting
Philips Masterline ES
Osram LV Halogens
GE technical catalogue
ge technical catalogue.pdf
HID info
HID Ballast

NiMH info - Ever Ready
NiCd info - Ever Ready
NiMH / NiCd info - Budget
Yuasa SLA batteries
O-ring information

DIY torch examples:

Component and materials suppliers:

general electrical / electronic

cpc batteries

- Philips Masterline ES (IRC) and Osram Decostar (IRC) available


engineering plastics - good website with prices for all plastics / sizes + free UK shipping - confirmed ok for small orders + good materials info on website - confirmed ok for small orders - confirmed ok for small orders


stainless (316) fixings Arkwell Fasteners 0115 9731181


connectors - from UK distributor

cheap Maglites


Apologies for the merciless summarising etc - if you think I've missed something or missed your point, please let me know

Thanks to all contributors

Please send comments / tips / ideas to the uk.rec.scuba newsgroup for discussion

Mike Pratt