why did it break

[randomname]

i took a 12v 300ma transformer (meant for a little submersible pump)
and cut the wire and stripped it. then i used it as a power supply for
a simply 555 circuit with about 10 LEDs strobing... for some reason
they were strobing a lot faster than with the 6v batteries id been
using, so i start switching resistor values.

eventually, the transformer just died.

why did this happen? whats different from a transformer and a battery?

-sam

 

[Puckdropper]

i took a 12v 300ma transformer (meant for a little submersible pump)
and cut the wire and stripped it. then i used it as a power supply for
a simply 555 circuit with about 10 LEDs strobing... for some reason
they were strobing a lot faster than with the 6v batteries id been
using, so i start switching resistor values.

eventually, the transformer just died.

why did this happen? whats different from a transformer and a battery?

-sam

Age and heat immediately come to mind. You need to make sure you're not
overheating it.

Puckropper

 

[Tim Williams]

Presumably, you have a rectifier on there. Eh well this is SEB, one can
never be too sure..

Tim

 

[Chris]

i took a 12v 300ma transformer (meant for a little submersible pump)
and cut the wire and stripped it. then i used it as a power supply for
a simply 555 circuit with about 10 LEDs strobing... for some reason
they were strobing a lot faster than with the 6v batteries id been
using, so i start switching resistor values.

eventually, the transformer just died.

why did this happen? whats different from a transformer and a battery?

-sam

Hi, Sam. Assuming you've got a 12VDC wall wart (you can check on the
label), it's made to open up (no power) when it's drawing too much
current.

If you're drawing more than 300mA, it's supposed to croak, and that
would be my first guess. You might want to check your wiring, and get
another wall wart.

Actually, it might be a good idea to make yourself a little power
supply that has overcurrent protection, and use the wall wart after
it's debugged and ready to go.

Sorry -- hope you can iron it out.

Good luck
Chris

 

[Eeyore]

i took a 12v 300ma transformer (meant for a little submersible pump)
and cut the wire and stripped it. then i used it as a power supply for
a simply 555 circuit with about 10 LEDs strobing... for some reason
they were strobing a lot faster than with the 6v batteries id been
using, so i start switching resistor values.

eventually, the transformer just died.

why did this happen? whats different from a transformer and a battery?

Well......... A battery is DC and a transformer is AC. But do you actually mean
a 'transformer' or some 'wall wart' type device ?

Graham

 

[randomname]

Well......... A battery is DC and a transformer is AC. But do you actually mean
a 'transformer' or some 'wall wart' type device ?

Graham

it was 12v AC 300ma.

i guess i just tried to pull too much current from it. it was really
hot when it died. i miss it.

thanks,
-sam

 

[Eeyore]

it was 12v AC 300ma.

Not DC ?

i guess i just tried to pull too much current from it. it was really
hot when it died.

Watch out for that. It's the heat that kills them.

i miss it.

You may find a similar one thrown out with rubbish. There's a depot near me where
they keep aside things like that if they get a chance.

Graham

 

[David Harmon]

On 30 Aug 2006 21:41:22 -0700 in sci.electronics.basics,

it was 12v AC 300ma.

What did you use to convert the AC to DC to match the requirements
of your 555 circuit?

 

[jasen]

it was 12v AC 300ma.

(aside) them 555's are robust devices.

i guess i just tried to pull too much current from it. it was really
hot when it died. i miss it.

yup, the reason being that the 555 was seeing backwards voltage some of the
time... the 555 wants DC, you'd need a rectifier and a big capacitor to
smooth out the humps to get that from 12V DC. this setup will typically
produce about 16V...


Bye.
Jasen

 

[Chris]

it was 12v AC 300ma.

i guess i just tried to pull too much current from it. it was really
hot when it died. i miss it.

thanks,
-sam

Hi, Sam. So, your wall wart was 12VAC, not DC. I'm kind of shocked it
worked at all. Of course, you were using the wall wart for a small
pump motor -- that would have been AC. My bad, I should have caught
that. And when the AC was reverse-biased, you probably had really high
current through your circuit. ICs aren't made to be powered up
bass-ackwards.

If you want to drive your 555 circuit with an AC wall wart, you'll have
to do something like this (view in fixed font or M$ Notepad):

|
| 12VAC .----. +
| o------. ,--o~ +o-----o---o
|120VAC in)|( | | |
| )|( | | +|
| o------' '--o~ -o-. --- 15VDC out
| '----' | ---
| BR1 | |470uF
| | |25V
| '---o---o
| -
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

If you get a bridge rectifier and a largish cap from Radio Shack, you
can have this working well quickly.

And by the way, don't feel bad for the wall wart. Most of them just
get thrown out in the trash when their gadget dies or the owner gets
tired of it. Yours not only did its job, but it died to serve you.
That's how they're designed. Just give it an honorable burial.

Cheers
Chris