How Does LED Brightness Vary With Current: Getting Burned

[avatar_dac]

Every time I set up my experiment, I touch my battery holder, and I always get burned. Why?

[kgudger]

Hello and Welcome to the Forum!

I looked at the experiment write up, and have some questions for you. If you're getting burned, it would suggest that too much current is getting drawn from the battery. Could you describe what the circuit(s) are connected to your battery? Is the battery output 3V, 4.5V, or ??? Please tell us. What is the resistor in series with the LED? Also, is the light-to-voltage converter hooked up to the battery? Is the light-to-voltage converter working? If not, is there a chance that it's hooked up backwards? All of these things are good places to start looking for the excessive current draw. Please let us know! Thanks.

Keith

[avatar_dac]

Well, I haven't built any of the circuits that are needed for the experiment. I basically just followed the instructions on the Breadboard information page of the website. Its normally 0 or -0.01. I used a 10K Ohm resistor. I'm now sure, there hasn't been any sign of it working, though the first one kind of got burned (well at least the inside). I also used the jumper wires that came with the breadboard. I placed them behind in the same column as where the battery holder wires are placed. Thanks!

[amyC]

Hi Everyone - I'm posting a link back to the Project Idea on the Science Buddies site for convenience:

https://www.sciencebuddies.org/science- ... p037.shtml

Also, here is the link to the Breadboard info:

https://www.sciencebuddies.org/science- ... oard.shtml

Amy
Science Buddies

[deleted-71588]

Any electrical project for someone who has no electrical trouble shooting skills is going to require somebody who has those skills actually looking at the faulty circuit. Is there a teacher or neighbor that has some skills in this area? In my opinion, this is going to be the best way to determine what is wrong.

If you want to try it on your own, then disconnect your power source. The light sensing integrated circuit (or any other integrated circuit) can be destroyed if you get the polarity of the power source reversed. Some integrated circuits are protected against reverse polarity; however, they can draw an awful lot of current and get really hot.

1) Use a volt meter to measure the voltage of the power source. See https://www.sciencebuddies.org/science- ... sure.shtml for possible help and be sure to read the instruction manual for your meter. Is the voltage close to what is expected?
2) Use an ohm meter to measure the resistance between the two breadboard power connections. What does it read? If it is less than 1 Kohms (1000 ohms), something is wrong with your hookup. Make sure to reverse the leads to determine if there is a difference in resistance if hooked up in the opposite polarity. If one direction has a reasonable resistance and the other is too low, check to see if you have the positive and negative power source connections such that they will have the high resistance.
3) If you have unexplained low resistance, then you are going to have to start taking the circuit apart and measuring each individual component to figure it out. You may have "cooked" one and caused it to fail "shorted".
4) When you measure the resistance of each component, you need to also look for ones that measure too high a resistance. You may have "cooked" one and caused it to fail "open".
5) Use the ohm meter to determine the pattern of which holes on the bread board are connected to each other. Your short may simply be caused by putting a component in parallel with a breadboard internal connection that shorts it out so it looks like a short circuited component to the rest of your circuit.

You probably need to acquire a 1000 ohm resistor and some clip leads so that you can place the 1000 ohm resistor in series with the power source positive terminal before it connects to the breadboard. This way, you can avoid "cooking" additional parts until you have it figured out.

Lots of luck. Electrical projects that are badly misbehaving are not things that anybody can trouble shoot remotely. Even with a highly trained technician on site, it can be very confusing communicating by phone to get an adequate description of what happened along the way in order to figure it out if the person on site can't figure it out mostly on their own.