by Matthew Ford 17th May 2008
© Forward Computing and Control Pty. Ltd. NSW Australia
All rights reserved.
This is a prototype re-chargeable torch / table lamp design. This prototype is a 35W design more..
- 10 Cree XR-E leds, P4's ~1700 lumens
- Ultra clear lens
- Runtime as battery torch ~25mins minimum to >24hrs maximum
- Runtime as mains powered lamp unlimited.
- Built-in delta-T cut-off charger.
- Torch powered by a 6 x Eneloop AA soldered battery pack, electrically isolated while running as a mains powered lamp.
- Variable light levels in 12 logarithmic steps from 1.5% to 100% current, brightness approximately doubles each two steps.
- Momentary Full Brightness function.
- Lockout function.
- Low battery voltage cut-off.
- Zero Off Current (ZOC) micro-processor controller. Batteries are electrically isolated from the controller 20sec after the torch is turned off. This ensures the shelf life of charged torch is only limited by the low self-discharge of the Eneloop cells (approximately 85% charge remaining after 1 year).
- Internal heat pipe to transfer heat to the tail fins.
Both the mains powered lamp and the battery powered torch the operation in the same way.
Click, a short press and release. Less then 0.5sec.
Press, press and hold the switch down. (>0.5sec)
Release, release the switch.
To turn the torch/lamp on, Click the switch.
To turn on at full brightness, Press the hold the switch. Release the switch to return to normal brightness setting.
To turn the torch/lamp off, Click the switch.
To get full brightness when the torch/lamp is already on, Press and hold the switch. Release the switch to return to normal brightness setting.
To lock the torch/lamp from turning on. Start with the torch/lamp off and Click 4 times in quick succession, in <1.7secs. After a short time the torch/lamp will flash once to indicate it is locked.
When the torch/lamp is locked, a Press or Click will not turn but will flash once after 1.7 secs.
To unlock the torch/lamp, Click the switch and wait for the torch/lamp to flash once. Then Click 4 times in quick succession, in <1.7sec. After a short time the torch/lamp will be unlocked and turn on.
The torch/lamp has two brightness settings:-
i) a normal brightness when the torch/lamp in on and the switch is released and
ii) a momentary maximum brightness setting while the switch is held Pressed.
The normal brightness setting can be varied by starting with the torch/lamp on and Clicking off and then Pressing on quickly (in <0.5sec). Hold the Press for 2 secs after which the torch/lamp will flash once and then after a short pause start stepping the brightness level up towards maximum.
When it reaches maximum brightness the torch/lamp brightness will stop increasing. To change direction from increase to decrease (and vice versa), release the switch and press and hold it again.
Each new press will change the direction of the brightness step changes.
To exit is mode and lock in the last setting, either Click the torch/lamp off or just leave the switch alone for 10sec.
To run as a torch just remove the torch from its base, or turn off the mains power. In either case the torch will now run on its internal batteries.
Returning the torch to its base with the mains power applied and the power supply switch ON (down) will allow the torch/lamp to run as a mains powered lamp. With the power supply switch is down the torch/lamp is supplied with 7.5V to run the 10 leds at 5Amps. The lamp, with it diffuser fitted, provides a soft area light from the ceiling bounce and the nylon tube diffuser.
When running as a mains powered lamp the torch batteries are completely isolated to prevent them from discharging. Since the batteries are low self-discharge Eneloop batteries, after running as a lamp for a year the batteries will still have about 85% of their charge to run as a torch.
To recharge the torch batteries, turn the torch off, insert the torch in the lamp base and switch the power supply switch OFF (up). This supplies the torch with 12V to charge the batteries via the internal battery charger.
A red led will start flashing in the torch head. When the flashing stops the charge cycle has finished. Note: Sometimes the charge cycle stops prematurely. A full charge of flat batteries should take about 70mins. If the charging stops early (i.e. in about 10mins), leave the torch rest for 15mins and restart the charge cycle by removing the torch from the base and then re-inserting it in the base.
Since the charger uses a delta-T cut off you can safely charge the torch any time, even if it is already fully charged.
The Torch has low voltage turn off protection to prevent the batteries being over-discharged. However after the torch turns off you can still turn it on and it will stay on for at least 1.5mins before turning off again on low voltage. Only do this in an emergency as over discharging the batteries will damage them.
(photos to follow next time I take the torch apart)
The Torch/lamp is based on a 2D M*g torch. The head has been turned down to give two flat cylinders onto which the fins were pressed.
The 10 Cree leds where clipped on the corners to isolate the base from the Led connections. Then connection wires soldered to each led before gluing them all to a copper heat sink with thermal epoxy. The copper heat sink consists of a disk of copper silver soldered to a square block of copper. The disk fits inside the torch head and the heat pipe is glued with thermal epoxy into a hole drilled in the block.
The lens are a glued stack of 6 degree lens.
Two sides of the copper block is machined out to mount two power Fets. One Fet for the torch controller and one Fet for the battery charger. The circuit boards mount off the Fets.
The 6 Eneloop batteries are soldered together in three groups of 2 end to end. The batteries fit around the heat pipe and the isolating switch (another 2 fets) is a floating circuit board on the other side of the heat pipe. A plug and socket connects the batteries to the circuit.
At the end of the heat pipe a rod of aluminium is clamped to the heat pipe to transfer the heat to the rear fins. The tail fins are press fitted on a tube with has a disk press fitted in it to bolt to the end face of the aluminium rod. The remaining space in the tail tube is used to house the circuit board the detects the input voltage, 7.5V to run as a lamp and 12V to recharge the batteries.
Finally the power plug is mounted in the end of the tail piece.
The power plug connects to the socket in the base to proved the power to the lamp.
The power supply consists of a 12V 5A supply which is supplied directly to the base to charge the torch when the switch is up. Inside the die-cast box is a 12V to 7.5V 5A switching regulator, the output of which is supplied to run at torch as a lamp when the switch is down.
Black matt paint was used on the fins. As you can see it does not wear well.
(more to follow)
While the heat pipe did transfer a measurable amount of heat to the rear fins, the effect (about 5 degs C) does not warrant the complexity the heat pipe entails. So the next prototype will dispense with the heat pipe and instead add extra fining to the head.
Also this prototype become too hot to hold after 15mins at full power so as well as adding extra fins the next prototype will include an insulating connection piece between the head and the barrel.
The next prototype will use 12 x R1 or R2 Cree leds and a 12 x AA Eneloop battery pack.
The leds will be mounted upside down on a pcb and then surface soldered to a copper disk. The pcb will provide the electrical connections. The whole package will then be bolted to aluminium plug pressed into the head tube. The 4 current pcbs will be replaced with one and the led controller and battery charger integrated into the same uC.
The fins will be anodized
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