These flashlights were designed to run on alkaline batteries, not rechargeable batteries. Rechargeable batteries are capable of a much higher current output than alkaline batteries. The switch in the end of the flashlight does not limit the current to below the 3 A maximum limit on the Cree XM-L datasheet.
The flashlight I'm about to disassemble was the victim of such careless behavior as to actually use rechargeable batteries in a Duracell branded flashlight. One click of the button and that was it. The LED was burned out. This feature made for some very unsatisfied customers. Now, for the disassembly.
Update 14 April 2018: I checked out the new Duracell 1000 lumen flashlights at Costco and they now say they work with rechargeable batteries.
First, I'll remove the lens with two strap wrenches.
Next, I'll unscrew the LED module.
Next, I'll pop the plastic off that surrounds the LED. This is the part that secures the LED and heat sink (MCPCB assembly). There is heat sink compound between the MCPCB and the aluminum housing. But this plastic piece doesn't seem to be a very secure or reliable method to make sure the MCPCB doesn't come off the base if the flashlight is dropped.
After un-soldering the two wires, the MCPCB can pop out.
The original MCPCB was part number RB-AL03, made by RAYBEN. It's rated at 0.5 - 0.9 C/W, with maximum operating temperature 110 C.
I looked up a similar LED on mouser.com and found an XML LED for $6.93 each, or $3.24 each for 2000 at a time. I didn't find the same MCPCB available online, but another one for an XML that sells for $1.01 each, or $0.44 each for 10,000 at a time. So it's not surprising that you can find XML MCPCB assemblies on ebay for less than $10 each.
But is it worth it to fix an $18 flashlight? Probably not. Your labor per hour, ordering the parts, and paying for shipping makes it impractical. However, if you could pop in a higher power MCPCB, then maybe it would be worth it to make a custom flashlight. Or, how about a UV LED for spotting fluorescent dye? Or how about a red, green, or blue flashlight?
And, of course, what teardown would be complete without a look at the power button assembly? I used a 17 mm socket and a hammer to push the button out. Then I rotated it counter-clockwise when the ground tabs got up to the threads so that they wouldn't get caught.
Here it is, the power switch board. This is the assembly that cost Duracell so much in product returns. (I have no idea how much.) They must not have realized that you should use a current source to drive LEDs, not a voltage source. Notice that there are no inductors on the board. That means they aren't using a DC-DC converter such as a buck converter. Now, was it worth it to have all those product returns to save a buck, leaving out an inductor? I think not.
Well, there you have it. The power button actually still worked (on my other flashlight) after I re-assembled it.
So the question is... How much current can this tail cap switch handle before melting? I have a mind to make a battery pack with two 18650s and a buck converter for this flashlight. I just need the tail cap to switch the power on the battery side of the buck converter. I measure 2.35 amps draw on the input side of the converter when powering this flashlight with two 18650s. Output voltage set at 5 volts with 2.2 amps.
ReplyDeleteI toasted the flashlight by putting 5000mAH C batteries. It does not have amp protection. I am pretty sure it will not handle 18650.
DeleteCool! My tailcap switch failed in a manner that it would just flash once when pressed. No other switch actions available. So I dismantled it per your instructions, and replaced it with the tailcap assembly, the whole thing!, from a cheap Harbor Freight 9 LED light. Now it works. Turns on bright all the time. The tailcap is no longer water resistant, but hey, I have a working flashlight. It was well beyond any Costco warranty so I had nothing to lose. Thanks!!!
ReplyDeleteAll I did was take out the switch clean off two tabs sticking in up in black part plastic and put a nickel in the button place. All I do is remove a battery to turn it off. And it works great, other than the time it takes to remove one battery.
ReplyDeletehow is it you got the switch apart. I don't see and release mechanism??
DeleteI was having problems with the light only momentarily turning on after a battery change. I simply pulled up on the cap spring, screwed it back on and all functions returned to normal operation. Hows that for luck?
ReplyDeleteIf you wanted to modify the light so that it does take rechargeable...anyone know how how one would go about doing that?
ReplyDeleteNo, it will not take rechargeable. Will fry.
DeleteAll you'd need is a resistor in series with the battery. The problem is without knowing the specification; you can't quite figure out the ohms. See this post:
Deletehttps://www.candlepowerforums.com/threads/how-to-stop-a-converted-unregulated-9-led-flashlight-using-3-x-aaa-to-18650-from-burning-out.479664/#post-5494162
Impressive and powerful suggestion by the author of this blog are really helpful to reduce our hack-tic life. My own views are matching with author and I have experienced such.t8 led
ReplyDeleteLet us know the contact detail of service centre in bengaluru
ReplyDeleteOn a 700 l installed three new c’s and experienced the momentary on then off problem. I tapped the switch numerous times and the on/off kept reoccuring. It reminded me of a curcuit breaker overload issue so l let the flashlight sit overnight, assuming peak start up voltage might drop a couple of tenths and fall under the breaker overload . The following morning the flashlight functioned as normal. In the future will short the batts for a few seconds before installing.
ReplyDeleteWhere can i buy those kind of led?
ReplyDeleteI fried mine too, using rechargable batteries
ReplyDeleteWow!!! Really
ReplyDeleteWhat size o-ring goes between the Lens Cap and the LED module? And where can i buy one? My o-ring broke.
ReplyDelete