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I have an old flashlight that says "15W Police Waterproof" on the handle, the battery compartment is normally for 3 type C batteries, unfortunately the bottom battery leaked and is stuck in there. Would it be possible to power this up from a 5V USB powerbank?

I don't want to burn the LED, is the driver more voltage-tolerant than the LED and will accept the higher voltage?

What has got my attention mostly is the note "AAA*3/AAA*4". - does it mean it can operate between 4.5-6 Volts?

PS: If you were going through the circuit, it might be helpful to know that the flashlight has 3 modes that cycle with power button - bright-dimm-strobe.
PS2: The whole powerbank (image below) fits in the compartment.
Note: I don't trust the 15W label as I have not found a single 15W LED on the internet.

pcb led flashlight powerbank

Click an image for high-res.

Search tags: HT-4.5S/1 , B17332A

/edit

So I have tried to power it:

  • The cheap powerbank immediately shuts down (and needs a reset by connecting a charger) as the output is too high. Such a shame. I guess I can't have nice things.
  • It draws 5.06V @ 0.23A (1.2W) at low mode
  • It draws 5.26V @ 1.94A (10.2W) at high (my source is limited to 2A per port)
    I will try it with a Y cable.
  • See compared High mode with 5W source and 10W source:

5W charger 10W charger pcb_back

Also included is the back side of PCB, the power switch is inserted between the central piece and positive source. Negative source is connected to the casing.

The flashlight is indeed around 10 years old.

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    \$\begingroup\$ 15W divided by 5V gives you 3A and no driver is 100% efficient, so it would probably wise to find a 5V 3A or 3.5A power supply if you intend to use it in high mode. Also note that many flashlights are not designed to run continuously in high power mode, so you may need to improve its heatsinking capabilities, especially if you will not be reconnecting the aluminum casing section you've removed. If your flashlight has current limiting or a time limit on the high power mode it will help. \$\endgroup\$
    – K H
    Commented Nov 22, 2018 at 23:49
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    \$\begingroup\$ It should be certainly possible, depending on your "a 5V USB powerbank". You have the flashlight, why don't you try and see the result? And +1 for photo quality. \$\endgroup\$ Commented Nov 23, 2018 at 0:00
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    \$\begingroup\$ Yes, I would take 3/4AAA to mean 4.5-6 Volts. I think it is safe to say it will work fine with a 5V power bank. That is to power the circuit board, not the LED directly. Trust the 15W. There are plenty of 3V white LEDs that can handle 5+ amp. This looks like a very high power LED. It appears the die is mounted on bronze for maximal thermal management. Not an inexpensive LED. \$\endgroup\$ Commented Nov 23, 2018 at 14:03
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    \$\begingroup\$ @Misunderstood, as usual, I tend to disagree with you :-(. If it is "15W LED", the current should be about 3-4A. The regulator looks like a simple linear one, there is no inductor in sight. The SOIC8 can't dissipate 3W. The aluminum substrate, even if thermally coupled with aluminum body, is also weak for 7W dissipation (assuming 50% LED efficiency). The triple switching mode (Full, Low, Blinking) also suggests a cheap Chinese mainstream knock-off controller found in $3 flashlights powered from 3xAAA cheap cells. I bet it is an ordinary 1W LED flashlight, bootleg edition. \$\endgroup\$ Commented Nov 23, 2018 at 18:59
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    \$\begingroup\$ Using two cheap powerbanks in parallel is not a good idea (current won't be equally drawn from both independent banks unless special balancing is involved). You better get a more powerful bank, with two 2.1A ports, and use Y-cable to split the load on connectors. \$\endgroup\$ Commented Nov 30, 2018 at 23:09

1 Answer 1

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The allowable input voltage is 2.5V to 6V. The question is, what is the forward voltage of the LED? And how does the input voltage affect the voltage applied to the LED?

Here is a similar schematic. Yours uses two 2A power FETs rather than the PNP transistor used in this schematic so the resistor values are also different. I did confirm the pinout of the pictured PCB and this schematic match.

enter image description here



The LED is huge and is mounted to a metal base.

The two 3W LEDs pictured below are much smaller than the LED used in this flash light.
NOTE: A dime is 17 mm (0.7") in diameter.

enter image description here

Considering the size of the LED and the aggressive thermal management of the metal base this could be an LED array like what is used in a CoB. The thing about CoBs is they generally have a higher Vf


The LED in this flashlight is about the same size as the 16.5 W max Luxeon M which comes in 3 voltages:
3V 5500 mA
6V 2750 mA
12V 1200 mA

Its dimensions are 7 mm x 7mm (0.276")
The light emitting surface is 3.5 mm x 3.5 mm.

enter image description here


The problem I found is this PCB is used in many flashlights in varying price ranges. One was driving a 90°, 100 lumen, 4W Cree XR-E Q4.

This controller must be a step down which would be what is needed for alkaline batteries and their large discharge voltage range. Three alkaline cells will start out at 4.5V but will discharge down to 2.4V before they are considered fully discharged. That is likely why this controller has a 2.5V minimum input. Problem is it does not appear to have boost step up capabilities. But if the Vf of the LED is around 3V then most of the battery capacity is used. At 2.5V it can still power a IR, red, orange, or yellow LED.


I like this LED. I've never seen one like it. My guess is it's thermal conductivity is superior to the typical ceramic substrate.

enter image description here

It certainly is NOT a cheap 1W LED.
I think it is an expensive 15W LED.
The Luxeon M is a $10 LED.
This flashlight is about 10 years old when LEDs like this were more expensive.

I do not see where the switch is connected to this PCB or the controller IC. That's a little puzzling.


Bottom Line

It is very likely safe to use 5V to power this LED. If it can be powered by three C cells the power bank should have plenty of capacity to power this. Highly unlikely the LED is being driven at its max current. Three type C alkaline cannot push but 4-5 watts.

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  • \$\begingroup\$ Nice find. Here is mine, not much, from hc360.com: "HC Network Manufacturers Shenzhen Nanbeixing Technology Development Co., Ltd. ..... You can contact the manufacturer directly to obtain the specific information of 2TC86 charging IC" It would be really useful if you can provide the link to application diagram. \$\endgroup\$ Commented Dec 1, 2018 at 18:24
  • \$\begingroup\$ I updated my question to provide more information. \$\endgroup\$
    – Qwerty
    Commented Dec 3, 2018 at 13:23

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