I may not be as smart as my 5th grader but we ran into an issue with our electrical circuit project. The purpose of the project was to test the effect of different batteries on the brightness of a light bulb.

The project is mounted on a board and we have a single light bulb. We wired a the circuit and soldered in momentary switches (normally closed) to 5 different battery configurations 2 AAA, 1 AA, 1 D, 1 9V & 1 6V.

The problem is that the the batteries are getting hot. He can't leave this at school! What could we have done wrong?

 

The problem is that the switches are normally closed, so the batteries are in circuit unless someone holds them open. Without knowing your circuit arragement, it's only a guess, but it sounds like you have a situation where the higher voltage batteries are trying to charge the lower voltage ones. Not quite a short circuit, but the batteries will get hot.

 

Thank you,

We started with normally open switches and we had the same issue. We concluded the circuit would be broken by the normally closed switch and it would not affect the batteries.

 

You may have mixed up your battery connections, too.

Have a look at the attached schematic. I suggest that you connect all of the battery - terminals together except for the two AAA batteries in series, the top battery negative is connected to the bottom battery's positive.

Use battery holders. Please do not try to solder wires to batteries, as this is very likely to cause them to explode.

As has been already suggested, you do need to use Normally Open pushbutton switches. You may have purchased a switch assortment that contains both NC and NO switches. I suggest that you test each switch, using a single battery and a lightbulb. The bulb should be OFF unless the button is pressed. For the test circuit, you can use the attached schematic, but with only S5, BA6 and L1 connected.

If more than one button is pushed down, it will cause different voltage batteries to try to charge/discharge each other, which will cause them to overheat and possibly explode.

Click on the attachment to view full size.

 

Thank you SgtWookie. After review of your diagram I found my problem. I created a fault with my wiring of the switches.