TrustFire TF26650 5000mAh 3.7V: testing, a decent result, and a little DIY.

, and it arrived quickly. The battery and power supply were inside, in separate bags. It was shipped by Singapore Post.

1. One Hour Discharge: Fail: Low capacity; Capacity=3.322 Ah (66.4% rated).
2. Lithium-ion Charge: Capacity=4.721 Ah (94.4% rated).
3. One Hour Discharge: Pass; Capacity=4.601 Ah (92.0% rated).
4. Li-ion 50% Charge: Capacity=2.500 Ah (50.0% rated).
__________________

One Hour Discharge
Duration (h:m:s): 01:06:24
Load current: 3.002 A
Cut-off voltage: 3.000 V
Battery discharged capacity: 3.322 Ah
Exit condition: Battery cut-off voltage reached.
Lithium-ion Prequalify
Duration (h:m:s): 00:00:03
Charge current: 496.8 mA
Exit condition: MaxV
Lithium-ion Charge
Duration (h:m:s): 03:59:43
Charge current: 2.000 A
Charge voltage: 4.200 V
Battery charged capacity: 4.721 Ah
Exit condition: Final charge current reached.
Discharge/ Charge Cycle
Branching 1st time.
One Hour Discharge
Duration (h:m:s): 01:31:58
Load current: 3.002 A
Cut-off voltage: 3.000 V
Battery discharged capacity: 4.601 Ah
Exit condition: Battery cut-off voltage reached.
Li-ion Prequalify
Duration (h:m:s): 00:00:03
Charge current: 498.2 mA
Exit condition: MaxV
Li-ion 50% Charge
Duration (h:m:s): 01:41:10
Charge current: 2.000 A
Charge voltage: 4.200 V
Battery charged capacity: 2.500 Ah
Exit condition: Maximum charge reached.
Discharge/ Charge Cycle
Exit condition: Ran 2 iterations.

And I chose this rather rare flashlight for the conversion.


The flashlight is absolutely new; it even comes with its manual. It was manufactured in 1993.


Besides the manual, it even comes with a spare bulb :).


I'm going to modify the flashlight not only to use a new battery, but also to fit a new light source.


For this modification, I bought a Cree LED from the XTE series. I bought it locally; it cost about $1.7.


I routed a simple little circuit board.


And here's the complete kit.


I used a charger based on LTC4054 and an LED current regulator, AMC7135, from my reviews.




I couldn't resist taking a photo, so to speak, at the meeting point of two generations.


In the comments on my review of a lithium battery charger IC, several people asked me to check how the chip responds to a battery connected with reversed polarity. I didn’t have time to test it then, so I said I’d do it another time.
I said it, I did it :)
The chip didn’t take kindly to reverse polarity. I tested it with a bench power supply rather than a battery—I didn’t want to kill another battery, too. My hunch was right.
When I reversed the polarity, the power supply switched to current limiting, and the chip heated up instantly. I didn’t think to measure the temperature right away, and only took a reading half a minute later.
So, the chip went to the great hunting ground in the sky, but kept its magic smoke to itself.


I replaced the chip and moved on to the more demanding work: put down the soldering iron, picked up a vise and a hacksaw.
I had various heatsinks from power supplies lying around, so I picked one that looked right and sawed off the excess. You'll see what I had in mind next.


The bulb in the flashlight screws into a socket that's an integral part of the body.
That really didn't work for me, so I needed to cut it down to size.
I picked out a milling bit that was the right size.


Then I unscrewed the contacts (not all of them, just the side one, so I wouldn't blunt the milling bit) and cut away the excess.


To avoid doing the job twice, I used the same bit to make more room for the battery. The standard 373 cell, also known as size D, is a little longer than a 26650 battery.
I bent the positive contact into its new shape.
Everything fit perfectly.


I mounted the LED on a heatsink. Of course, it's far too large for this power level.
But I built in some headroom in case I decide to increase the current.
In my setup, the LED runs at 350 mA, but it also works fine at three times that current, albeit with lower efficiency.


Everything fit perfectly. I secured the heatsink inside the flashlight with a self-tapping screw, using the hole left by the screw that held the bulb's side contact.
Just like a construction kit. :)


I glued the board to the top of the body.


The main assembly is complete. You can see the self-tapping screw that holds the LED heatsink in place. The wire that went to this contact has been disconnected.
To preserve the flashlight's original character, I didn't replace the flashing bulb at the back with an LED; I left it as it was.
I like that warm incandescent glow, so I decided to keep it somewhere, at least. :)


The reflector took a bit of work, though. I had to trim it down and cut notches for the wires.
Since the original bulb sat higher, installing the LED just didn't work. It even reminded me of people trying to replace halogen bulbs with LEDs in car headlights, as some car enthusiasts do.
A bulb is different from an LED, and I couldn't get a decent beam pattern. After some experimenting, I found the best position, which matched the height of the LED on the heatsink, but I had to make the reflector smaller.
In the end, I got a broad, even light with no sharply defined beam, which was exactly what I wanted.


The flashlight works perfectly, and the switch on top still does its job: forward turns on the flashlight, backward turns on the flashing rear light, and the middle position is off.
There are now two holes, though: one for the charger and one for the charging indicator LED.


The flashlight is finished, but it also needs a charger. I didn't want to build one into the flashlight (though it would be easy enough), so I decided to make an external one.
While I was at it, I decided to compare the one that arrived with a couple of similar ones.
From left to right: the one I bought with the battery
The one that came with the electronic cigarette.
The one that came with the charger in the review of the charger IC (I used its connector and cable here)


While I was at it, I noticed something pretty funny. The photo shows the charging board for the electronic cigarette (the middle one in the previous photo).
In their quest to make the device cheaper, the Chinese engineers managed to outdo themselves.
The optocoupler soldered to the board is highlighted in red. To cut costs, the designers decided not to include feedback, but they still soldered in an optocoupler.


I needed a charger (or, more accurately, a power supply) with a cable, so I desoldered the USB socket from the board (it might come in handy), and to keep the cable from dangling through the hole, I used the case from a burnt-out 18650 battery charger.
That way, I killed several birds with one stone: a charger with decent internals, a plug with proper contacts, and a cable that doesn't dangle but sits neatly in the case's original opening. :))




Everything works great, the connector fits (they're a matching pair), charging works, and the LED lights up (though I got a rather dim one).


That's it, the conversion is done: a flashlight with a 4.6 Ah lithium battery, a Cree LED, and a charger.


I didn't actually need the flashlight, and the case wasn't mine either, but I think its owner (or rather, its owner) will be pleased.