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I bought 10 red laser diodes from ebay for cheap and I wanted to create some art sculptures.

The diodes work fine. I connected 2 lasers together in parallel with 2xAA batteries, and it worked alright.

When I connected another 2 lasers, the wires started to overheat (and I smelled something burning.)

I couldn't explain this to myself with my "basic" knowledge of electrical circuitry.

I would expect the lasers not to light up, or the battery to overheat, but how come the individual wires heated up? How could it be that when an individual laser diode is connected it is somehow different when others are connected in parallel. The voltage on each diode is the same, as is the current in the wires.

What am I missing here?

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  • \$\begingroup\$ Did they all work? If you connect such a product backwards (or if it is defective) it can short out the battery and 2 fresh AA cells are definitely capable of burning light gauge copper wire. \$\endgroup\$ – Spehro Pefhany Feb 12 at 21:30
  • \$\begingroup\$ Yep. All of them light up. \$\endgroup\$ – Marakoss Feb 12 at 21:33
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    \$\begingroup\$ "The voltage on each diode is the same, as is the current in the wires." - did you measure the current in each wire? \$\endgroup\$ – Bruce Abbott Feb 13 at 0:29
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Since you have not mentioned any resistors, the current is mainly limited by the internal resistance of the AA cells. Such large currents can overheat wires, and can start a fire.

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  • \$\begingroup\$ Yeah that would be the solution. It didn't came to my mind, that I shouldn't treat those diodes as "lighbulbs" that use resistive materials to light up and are built to dissipate heat. So answer is to apply some current limiting element. Am I right? \$\endgroup\$ – Marakoss Feb 12 at 21:57
  • \$\begingroup\$ Lasers may come with drivers. \$\endgroup\$ – user263983 Feb 12 at 22:49

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