DIYbanter - View Single Post

wrote:

snipped

Some of these ideas can be demonstrated by experimenting with bulbs in
series, which is effectively a single filament divided into segments.
Say you have a car battery (12V) and 5 to 10 identical automotive bulbs
in series. When you complete the circuit, you'll see that one gets
initially brighter than the others, then it may even get dimmer as the
others "catch up" to finally achieve uniform brightness. That's because
even though they are "identical," there are slight differences in the
bulbs and the one with the highest initial resistance and/or the
quickest heating filament will absorb most of the power till the others
heat up. I noticed this effect when I was about 6 years old, though I
had no idea what was causing it; I just knew I could rearrange the
order of the bulbs in series till they lit up from left to right and it
was pretty cool.

I've never noticed that effect, but it seems possible.

I'm guessing it was holiday lighting (Xmas tree strings) you were
experimenting with when you were around age 6, right?

I'm having a hard time visualizing what ten 12 volt bulbs across a 12
volt battery would end up doing. Wouldn't seem like there'd be enough
voltage available to produce anything other than infrared "uniform
brightness" with just 1.2 volts across each bulb, or did you misspeak
about the battery's voltage?

Oh, and my face is red for geting lured into agreeing that triacs
"switch on" at zero crossings. I know better, but it's been so long
since I built anything with triacs that I forgot that they "latch on"
once triggered and have to wait for a current zero crossing to drop out.

Jeff
--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

"As long as there are final exams, there will be prayer in public
schools"