Thursday, January 7, 2010

Chapter 1 - Exercise 2

Alright... time for some fun.

The author provides a LOT of warnings in this chapter, and although most of them are common sense stuff, it's still worthwhile to read over them. You hear an occasional story throughout the year about someone having a really bad day with electricity. Like power tools and judges, we're supposed to show some respect...

I hated to destroy a perfectly good battery, but I've told myself I'm going to follow Mr. Platt's instructions and perform these exercises. So... that means shorting a single 1.5v battery. (I hope he doesn't tell me to jump off a bridge in Chapter 5...)

Was there an explosion? No.
Was I drenched in battery acid? No.
Did the battery and wires get hot. Oh, yeah...

(Be sure to wear your safety goggles as the instructions tell you - why take chances with your eyes, right?)

So, we're learning in this exercise about amperage - the flow of electricity, or current. Be sure to read carefully over the Background info on page 10. Some simple things to remember.

Finally, we get to play with a fuse. There's a definite S-shape wired in there (you can see this in my comparison photo - blown fuse on top, good fuse on bottom). After connecting up the 1.5v battery and sticking a fuse in the circuit, I'm serious when I say I heard a slight "click" - that would be the fuse melting quickly. You can see two small black burn marks on the blown fuse in the photo.

Since the fuse can only handle up to 3 amps, this little exercise tells me that a 1.5v battery shorted is definitely producing more than 3 amps.

And be sure and read over the Fundamentals section on AC and DC current on page 12 - this is just a basic introduction, and lets you know that it's DC power that we'll be dealing with for most of the book.

So, with Experiment 2 completed, what do you need to take from it? Well, here are some thoughts and suggestions:

* Understand why the wires and battery heat up when shorted
* Know how voltage and current are measured - volts and amperes, respectively
* Realize that a 3 amp fuse is all it takes to save a single 1.5v battery that's shorted
* Burn out a fuse - just so you can say you did it
* Prepare and give a 2 minute speech on Alessandro Volta - 2 points off for every "uh" and "um"
* Label and take the dead battery to Radio Shack or any place that will recycle it (when you have time)
* Feel free to throw the blown fuse away... or tape it in your log book. It makes a nice discussion piece.


  1. When I tried this, and I've tried it a twice now. I haven't blown the fuse. I've ended up shorting the battery. I'm using the same fuse the book said to get.

  2. Hmm... not sure. Mine was instant. Even heard a little pop.

  3. I suspect it had to do with the battery. I just tried it again, 3rd time with brand new batteries. Less than 3 seconds before it went.

    The other batteries had been kicking around for about a year. The new one had 1.62 volts the others were between 1.3 and 1.5.

    I'm really glad Make: had your blog listed, and you're doing this. It's nice to have someone else to compare my results to. Co-worker is interested but not enough to do get the book and play along.

  4. Chris,

    Not a problem... and please feel free to send me your results or posts comments... I'm sure others will appreciate more data, more feedback, more opinions... thanks for yours.

  5. I couldn't find the automotive style fuses during my first Radio Shack visit, so I just bought the glass tube version with the same Amp limit. They're just a little trickier to grab with the alligator clips, but totally doable.

    My second Radio Shack trip (to a different one) got me some automotive fuses, so I did the experiment again :-)

  6. i'm having the same problem as chris. my fuses haven;t blown and i've gone through 3 fresh batteries. weird.

  7. That is odd... I wouldn't worry about it, though. You understand the theory and what is supposed to happen, so I'd just move forward.

  8. ok. thanks for putting up this website. i'm glad to see your progress & will be using it as a reference :)

  9. I tried two of the AA's that came with the Components pack 1 and neither would blow the fuse. I then went to the box in the refrigerator and got a new duracell AA and it blew the fuse in a jiffy.

  10. Given the comments, the 3A fuse was probably a bad choice for the test (or it least the exercise should note that weaker batteries might not blow this size fuse).

    If you do not blow the 3A fuse, check that your batteries are getting warm (if not, there is no connection).

    Give it 30 seconds - some fuses burn slow.

    If nothing, and the batteries seem "good", replace the 3A fuse with a 2A or 2.5A fuse.

    A battery with high internal resistance or low voltage will probably not put out enough juice.

    General comment:
    A fuse will be pretty important insurance if you wire up a few batteries in a pack, for powering something. It is always remotely possible that 1 battery will internally short, which can pull dangerous amounts of power from the other batteries (possibly fire, leak, etc.).

    To illustrate the NEED for a fuse on multi-battery applications, I kind of wish this book had an exercise for creating your own 9V battery pack from just AA's. But I am getting off topic here. :-)

  11. I'm also having trouble getting my 3A fuse to blow. I wonder if it has to do with the type of fuse. I noticed in the book it says to get the type ATM fuse, and I'm using the ATC type instead. Maybe it's just slower to burn through or something.