Celebrating the independent kiwi spirit of invention.

Caving Headlamp – 9036-A

By Ian Mander 8-13 April 2012, updated 14 May 2012.


  • Aluminium lamp housing; 90 mm x 36 mm – hence the (provisional) name. IP rated.
  • Plastic battery housing. IP rated.
  • Two Cree XM-L T5 neutral white LEDs with TIR optics providing centre-weighted flood.
  • One Cree XP-G R4 neutral white LED with aspheric lens providing spot beam.
  • Battery either 4-12x AA NiMH or 1-3x Li-ion.
  • Three general modes spaced at roughly 3x current levels; medium powerful enough for easy navigation.
  • Momentary turbo mode as stroppy as possible.
  • Option: Single 5mm LED run at low current as a "battery installed" indicator.
  • Option: Battery status indicator on one of the switch positions.

Lamp housing, LEDs & optics

The lamp housing is a Gainta Industries G102 waterproof aluminium enclosure from Surplustronics. 90 mm wide x 36 mm high x 30 mm deep. IP65 rated.

For general caving two Cree XM-L T5 neutral white LEDs are mounted at the ends of the enclosure. These use wide angle/diffusing TIR optics to provide a centre-weighted flood. The LEDs will need to be mounted to an aluminium angle attached to the sides (and end) of the enclosure. The bumpy front on the optics may hold mud and be hard to clean – this will need some testing.

A spot beam is provided using an aspheric lens with a Cree XP-G R4 neutral white LED positioned in the middle of the enclosure. The depth of the enclosure means the LED should be at about the right distance from the lens when the LED is mounted on the back of the enclosure – good for heat sinking.

Battery & battery housing

The battery housing is a Naithawk waterproof plastic box from International Outdoor Store. Measured dimensions 132 mm wide x 82 mm high x 37 mm deep; internal 118 mm wide x 68 mm high x 31 mm deep. Claimed shipping weight 65 g. It includes egg crate foam. IP67 rated.

The housing is large enough for the following battery configurations.

  • 12x AA cells. If wanting that many, it would probably be most sensible to install them in three parallel 4x AA packs as it's very hard to tell when an individual cell out of 12 in series goes flat; reverse charging is bad.
  • 3x Li-ion cells, with or without 4x AA cells.

The battery housing supplies power to the lamp housing with a 4 conductor cable (Surplustronics, no longer available), which allows the conductors to be paralleled for lower resistance, or used individually for separate battery packs. For example, three separate 4x AA packs with a shared ground, or a 3x Li-ion battery completely separate from a 4x AA battery.

The basic battery configurations with some specs. Protected Li-ion cells will have to be used in all situations except a single cell.

Battery Options
Battery Nominal Voltage Voltage Range Approx. Capacity Approx. Energy Weight
Single Li-ion
(unprotected an option)
3.7 V 3.0 - 4.2 V 2.4 Ah 8.9 Wh 46 g
4x AA NiMH 4.8 V 3.6 - 5.6 V 2.45 Ah 11.8 Wh 108 g
(124 g shipping weight)
2x Li-ion, parallel 3.7 V 3.0 - 4.2 V 4.8 Ah 17.8 Wh 92 g
2x Li-ion, series 7.4 V 6.0 - 8.4 V 2.4 Ah 17.8 Wh 92 g
3x Li-ion, parallel 3.7 V 3.0 - 4.2 V 7.2 Ah 26.7 Wh 138 g
3x Li-ion, series 11.1 V 9.0 - 12.6 V 2.4 Ah 26.7 Wh 138 g

Different batteries are suitable for different drivers.

Battery Pros & Cons for Various Drivers
Battery Driver Advantages Disadvantages
1-3x Li-ion parallel
4x AA NiMH
  • Very easy to get multiple modes.
  • Switches do not need to carry high current.
  • Headlamp will not suddenly die when the battery goes flat because the Li-ion protection circuit activation point is set to less than the Vf of the LED - dimming should be noticed even on the lowest mode.
  • Can be hard (impossible) to configure exact currents.
  • Turbo mode will run out of volts as battery goes flat (although 3x Li-ion cells isn't too bad).
  • Paralleling several single cell holders is a little more expensive. (Perhaps a triple could be modified.)
4x AA NiMH
2-3x Li-ion series
  • Low current modes can be continuous, not PWM - a little more efficient.
  • Mode currents can be configured exactly.
  • Easy to get different modes by changing set resistor.
  • Headlamp will stop without warning if any Li-ion cell protection activates.
  • Only 2.5 A maximum current.
  • Enabling modes by changing the set resistor depends on switch resistance.
3x Li-ion series PT4115
  • Easy modes with exact desired current using dimming feature.
  • Mode currents can be configured exactly.
  • Headlamp will stop without warning if any Li-ion cell protection activates.
  • Only 1.2 A maximum current.
  • 8 V minimum voltage rules out 4x AA.

A battery with 2x Li-ion cells in series could be used with an AMC7135 driver but would have to drive two LEDs in series. It would rule out any other battery configuration, so it's not an option because being able to work with 4x AA is deemed essential thanks to the ubiquitous availability of AA batteries.

Using up to three Li-ion cells in parallel will give lots of capacity and resilience against battery voltage sag if needed, and with the option of 4x AA will provide the most versatile option.

Drivers & mode switching

Wide Beam

If the AX2002 is going to be used it will have to be used for all the modes because it's too tricky to switch everything required to mix drivers.

Wide Beam Modes Minimum Driver Voltage
Mode Single LED Current LED Vf AMC7135 Minimum Voltage
to Stay in Regulation
AX2002 Minimum Voltage
to Stay in Regulation
(with switch resistance)
High 525 mA 2.85 V 2.97 V 3.35 V (3.40 V )
Turbo 2.5 A 3.27 V N/A 3.77 V (4.02 V)
2.8 A 3.31 V 3.43 V N/A

3.77 V is too high for more than a few minutes runtime with a single Li-ion cell. It's even worse if the switch contact resistance is considered. Contact resistance of a typical micro switch (used as a momentary crossover switch for the turbo mode) is 0.05 Ω. At 5.0 A that will drop 0.25 V across it and produce a serious amount of heat. (Knew there was some reason turbo mode is momentary.) That takes the voltage the AX2002 requires to stay in regulation to over 4.0 V. The AX2002 is ruled out.

One significant advantage of the AMC7135 is that it can be switched with a very small current to the VDD pin with the LED permanently connected, thereby saving the 0.28 V drop a micro switch would have in turbo mode – very handy.

However, even having settled on AMC7135 drivers, choosing particular drivers is not so easy, as there are many available, and the AMC7135 can be switched so easily, including by MCU. With some clever switching (and maybe diodes) it might be possible to use just one driver for all modes.

The wide beam will have three general modes plus a momentary "turbo" mode. Medium will be the normal mode used while caving.

The two XM-Ls will be run at the same current and for most configurations are in parallel run by the same driver.

Wide Beam Possible Modes
Mode Produced By Total Current Each LED Current Each LED Lumens Total Lumens
Low 3*AMC7135 @ 5% PWM
(eg sku.127686)
53 mA 27 mA 10 lm 20 lm
3*AMC7135 @ 10% PWM
(eg sku.7612)
105 mA 53 mA 20 lm 40 lm
8*AMC7135 @ 5% PWM 140 mA 70 mA 26 lm 52 lm
Two resistors
each 12 Ω
160 mA 80 mA 30 lm 60 lm
Two 3*AMC7135 @ 10% PWM
(eg sku.7612)
210 mA 105 mA 40 lm 80 lm
Medium Two 8*AMC7135 @ 5% PWM 280 mA 140 mA 52 lm 104 lm
3*AMC7135 @ 30% PWM
(eg sku.127686)
315 mA 158 mA 59 lm 118 lm
(eg, sku.1885)
350 mA 175 mA 65 lm 130 lm
3*AMC7135 @ 35% PWM
(eg sku.7612)
368 mA 184 mA 68 lm 136 lm
High 8*AMC7135 @ 20% PWM 560 mA 280 mA 104 lm 208 lm
  Two 3*AMC7135 @ 35% PWM
(eg sku.7612)
735 mA 368 mA 137 lm 272 lm
  8*AMC7135 @ 30% PWM 840 mA 420 mA 156 lm 312 lm
(eg sku.127686)
(eg sku.7612)
(eg, sku.1885)
1050 mA 525 mA 195 lm 390 lm
  Two 3*AMC7135
(eg sku.127686)
(eg sku.7612)
(eg, sku.1885)
2100 mA 1050 mA 372 lm 744 lm
  Two 8*AMC7135 @ 20% PWM 1120 mA 560 mA 208 lm 416 lm
  Two 8*AMC7135 @ 30% PWM 1680 mA 840 mA 307 lm 614 lm
Two 8*AMC7135
5.6 A 2.8 A 806 lm 1612 lm

If using PWM a three mode switch would be wired off-on-off-on as per the spot beam. This would allow lots of "interesting" modes and provide switch redundancy. DX sku.7612 is the leading contender because 20 lm seems too low for low mode, and a jump from 5% to 30% is too great. I strongly prefer the modes to be spaced at roughly multiples of 3. However, 136 lm might be too high for medium. A driver with PWM modes of 10% and 30% would be slightly better.

Using continuous operation, the switch would be wired for the three separate modes to enable the resistor or the AMC7135 chips. This would provide just the three modes configured and no switch redundancy. The advantage is that the low mode could be set to anything desired and medium might be a little more efficient because it wouldn't be PWM.

To switch between the general modes and turbo, a micro switch is wired in a crossover arrangement; NC is the general modes, NO is turbo.

I'll assume DX sku.7612 is used. This greatly simplifies the driver situation. But what a lot of effort to get to this point!

Spot Beam

There is little point in having more than one mode for the spot beam, so the choice of driver just depends on how well it will work with the battery. The two options for the spot beam driver are a multi-mode 4x AMC7135 at 1.4 A or an AX2002 at 1.5 A (using a 1 Ω resistor added in parallel to the 0.2 Ω resistor that comes with it).

Having only one mode means the spot beam will be switched using a three position switch wired off-on-off-on to provide a little redundancy for switch contacts going bad. The switch can apparently handle 1.5A OK but the AMC7135 driver could be switched with less than 1 mA – good because there won't be any power lost in the switch resistance.

Spot Beam Minimum Driver Voltage
Current XP-G R4 Lumens LED Vf AMC7135 Minimum Voltage
to Stay in Regulation
AX2002 Minimum Voltage
to Stay in Regulation
1400 mA 413 lm 3.34 V 3.46 V 3.86 V

Because the AX2002 will need about 3.86V to stay in regulation it cannot be used with a single Li-ion cell. The AMC7135 driver it is – DX sku.127685 seems ideal.


Wide beam general modes: 3x AMC7315 driver (DX sku.7612) providing PWM modes to two LEDs in parallel. Two Li-ion cells looks pretty good, and for around the same weight as 4x AA NiMH cells.

Wide Beam General Modes Runtimes
Battery Capacity
(varies by load)
105 mA
368 mA
1050 mA
1x Li-ion 2200-2400 mAh 23 hours 6.5 hours 2 hr 5 min
4x AA NiMH 2450 mAh 23 hours 6.6 hours 2 hr 10 min
2x Li-ion parallel 4800-4900 mAh 47 hours 13 hours 4.5 hours
3x Li-ion parallel 7300-7400 mAh 70 hours 20 hours 7 hours

Wide beam turbo mode: Two 8x AMC7135 drivers providing a constant 2800 mA to each LED, 5.6 A total. The really low values for a single Li-ion cell serve as a warning not to use turbo with only one cell.

Wide Beam Turbo Mode Approximate Runtimes
Battery Capacity Turbo
5.6 A
Reduced Output
down to 2 A
1x Li-ion 50 mAh 1/2 minute 15 minutes
4x AA NiMH 2200 mAh 23 minutes -
2x Li-ion parallel 1700 mAh 18 minutes 40 minutes
3x Li-ion parallel 6150 mAh 1 hr 5 min 1 hr 10 min

Spot beam: 4x AMC7135 driver providing a constant 1400mA.

Spot Beam Runtimes
Battery Capacity Full, 1.4 A
1x Li-ion 2100 mAh 1.5 hours
4x AA NiMH 2350 mAh 1 hr 40 min
2x Li-ion parallel 4300 mAh 3 hr 5 min
3x Li-ion parallel 6750 mAh 4 hr 50 min


Total is about $83 not including consumables. (This may have been reduced by the simple driver setup.)

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