I recently got hold of 2 broken LED torchlights and I had the idea of putting the LED heads together (after I cut them off) in series to make 2 lights for a camping powerbox that I want to make (LEDs are fine, torch body was unusable.)

I am asking for your help, because I am totally new to electronics and just lost in all the calculations involved.

Tried to get forward voltage and LEDs lit up, but nothing registered on my multimeter except the 1 sign (used the diode setting, am I doing something wrong.)

Anyway, here are the specifications. I had and I hope someone can help with some good advice.

  • I will power from my 12v battery.
  • The LEDs are a cluster of 9 at 0.07w, 4.5v (there are 2 of these.)

Good Guess Souradeep with the cheapo yellow Chinese made multimeter.. Anyway, I am added some new info that you wanted

This the reading I get from attempted forward voltage reading,as you can see the LEDs light up dimly but they are super bright when connected to the batteries

voltage reading

Here is the Specifications.


Thanks in advance... (sorry for the incorrect grammar, or its too long of a post)

  • \$\begingroup\$ start by assuming 3.0v drop per actual white LED, put 3 in series, play with resistors until bright/cool enough. I would be willing to bet that the modules you speak of have a s/p config that needs to be accounted for. use a bench supply with a low current limit to find the arrangement, or decode the traces. \$\endgroup\$
    – dandavis
    Feb 25, 2020 at 18:58
  • \$\begingroup\$ 0,07W for a led ? Where did you get that ? Today's white led provide about 100lumen/W. A standard Chinese Torchlight is about 200-300lm meaning a power of 2-3W. I doubt that your specs are the good ones. Can you measure the current of each individual led ? \$\endgroup\$
    – Mathieu G.
    Feb 25, 2020 at 19:36
  • \$\begingroup\$ If these are the flashlights that have 3 AAA cells that power the LED array, the LEDs don't really drop 4.5V, it'll be 3-3.2V or so, and the rest of the drop is across the internal resistance of the battery, plus whatever limiting resistor is in series. 70mW would be about right for a single LED in those arrays. \$\endgroup\$
    – Phil G
    Feb 25, 2020 at 19:40
  • \$\begingroup\$ I will reply a few days later. Sorry, but i havve some imp stufff going on right now. \$\endgroup\$ Feb 28, 2020 at 17:26

2 Answers 2


I guess you are using that classic yellow chinese multimeter. The diode setting is used for testing circuit continuity, i.e., to check whether there are any breaks in the circuit. They are also used to test whether leds are working or not and display the resistance of the closed circuit. This is all. But I need you to edit your question and post pictures of your flashlight, pics of the circuit, pics of the circuit conection with the battery and pics of the leds. Then I am going to design the required circuit for you. Also tell me what kind of batteries did the torchlights use (what was the voltage rating?)


You have two in such cylinders of these type of led clusters? Just measure with your multimeter how much current your 12v power supply provides. If the current exceeds 1 Ampere, then you might want to use a resitor. If the current provided by the power source is less than or equal to 1 A, then you can simply connect the power source to the led blocks in series with a switch. This is the diagram : enter image description here

After connecting the leds you should check whether the leds are heating up too quickly or not. If they are heating up too quickly, then tell me in the comments.

  • \$\begingroup\$ So far, so good...LEDs are getting hot, but not too quick...I will probably put some sort of Heatsink for that....thanks for all your help! \$\endgroup\$ Mar 3, 2020 at 17:00

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