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9V battery, powering 10 LEDs, is overheating, what am I doing wrong? Answered

I've nearly completed the proto-type for my holiday project, but I've run into a snag with the power supply. I have 10 LEDs wired in pairs, with a resistor on each pair (I used the LED wizard... yay!). I have a simple push-button SPST switch for added convenience. When testing the wired up LEDs along the way, I used the battery, and even held the leads on the battery's contacts for a minute, and the battery did not change temperature. Gazing upon my 'success', I decided it was time to finish up the wiring, add the switch, the battery connector and battery, and bask in the glory of having finished the prototype. Not so much. Before I could even push the button to turn on the lights, the battery was already heating up (in less than 15 seconds). I pushed the button to see if the lights would go on, and they did. I immediately disconnected the battery and scratched my head. I changed the leads on the switch, although not a likely cause, it had to be ruled out. Same result. Can anyone offer some suggestions? Corrections? **trying not to weep openly but is glad she got an early start on her holiday project**


It's all fixed! Works great! Thanks all, for the hints and positive reinforcement.

xmas prototype.jpg

Nice ! If a little early in the year :-) Congrats on your first electrical project. Steve

I've gathered enough courage... and I'm headed back into the 'workshop'. I'm going to use a different switch, take my time with the soldering, and hope to solve the problem.

For those of you who've asked about my wiring diagram, I've included the plan I used, from http://led.linear1.org/led.wiz

Ok, well... I don't think my little .jpg uploaded. boo. I used these numbers to figure out the wiring: 9V >> 3.0 >> 20mA >> 10 leds I chose 'solution 1' - the 5 pairs with 1 resistor per pair.

I really need to see a wiring diagram, and some pictures. It sounds like you have a short circuit somewhere,which is shunting a lot of current. Now, LEDs don't need a lot of current, so they'll run on leftovers and glow which is what you are seeing. Look hard for a short. Something "obvious" is wrong ! Steve

Thank you for the reply! In my continuing search for the 'answer', I ran across another posting about an overheating iPhone battery and a short, due to messy soldering. Your reply is reinforcement to the potential problem. I'm so new to electronics, I think my soldering may have caused the problem. I think I will try a different kind of switch, that has leads attached, giving me less reason to make a mess of things. If all works out, the first -live- version of the project will become an Instructable! Thanks again! (hmm... I seem to up rather late... o.O)

Soldering the switch wrong will put the lamps on all the time, so I doubt its there. Sanity check: Wired like this drawing ? Steve


should look exactly like that diagram - my thought is if its a dpst switch and they are switching both positive and negative leads...and the switch is faulty :S

steveastrouk is right. His last sentence says it all. You have a short somewhere. If the 9v battery heated up that fast it has to be a dead short. Fix that and it will probably be fixed. It's easy to put a wire on the wrong terminal or get confuse and connect to the battery conn. twice with the same wire. Fixing the problems is just a part of the learning experience. Now when it works you can be doubly proud because you built it and then when it didn't work you fixed it. Good luck.

You have a short circuit. That's the only thing that would cause the battery to heat so quickly. Since the leds still work, makes me think its in the switch (wiring).


8 years ago