Author Topic: shotcicut protection  (Read 1715 times)

0 Members and 1 Guest are viewing this topic.

Offline 07Pepa

  • Contributor
  • Posts: 6
shotcicut protection
« on: July 10, 2015, 03:26:10 pm »
Hi I am preaty much biginer. there is my case:  i want filter the output of diode brige with capacitor. i know right walue for that but, i want to protect it from cap failtiure i read somewhere i can do it by just resistor in serie. but i need a value ( it will be +/- 12V dc at maximaly 50W (and i can proof the walue are corect i am using cheep chinese ac to ac trafo wich is hopefuly strong enougt to power 12v dc 30W led strip.

THX for help
 

Offline PSR B1257

  • Regular Contributor
  • *
  • Posts: 243
  • Country: de
Re: shotcicut protection
« Reply #1 on: July 10, 2015, 03:42:00 pm »
There is noting to protect for any cap-failure.
Your LED-strip by the way, will work fine also without a filter cap.
In theory, there is no difference between theory and practice. But, in practice, there is.
 

Offline 07Pepa

  • Contributor
  • Posts: 6
Re: shotcicut protection
« Reply #2 on: July 10, 2015, 04:44:23 pm »
PSR B1257 you are right but just knd of. I can see a 50hz flicker (in peripheral viev)
 

Online Zero999

  • Super Contributor
  • ***
  • Posts: 14068
  • Country: gb
  • 0999
Re: shotcicut protection
« Reply #3 on: July 10, 2015, 04:49:51 pm »
A fuse will provide short circuit protection but it needs to be slow blow type, in order to avoid it blowing when the circuit is turned on and the capacitor charges.
 

Offline PSR B1257

  • Regular Contributor
  • *
  • Posts: 243
  • Country: de
Re: shotcicut protection
« Reply #4 on: July 10, 2015, 06:20:21 pm »
Quote
I can see a 50hz flicker
No you don't, since
Quote
output of diode brige

I just tried it myself and can't see any flicker whatsoever.

But if I just connect a single rectifying diode the flicker is pretty terrible.

Therefore either you're diode bridge is damaged or you have hooked it up wrong.

P.S.: A filter cap is in this case rather problematic since it raises the voltage by the factor of sqrt(2), like every bridge rectifier with an filter cap. The LED-stripe is designed for a nominal voltage of 12V - about 15V might be too high for the LED-stripe (long term seen).
The so called Average rectified value of a sinusoidal voltage however is 0.9URMS. Meaning it is no problem to hook up 12VAC bridge rectified directly to a 12VDC load.
« Last Edit: July 10, 2015, 06:32:46 pm by PSR B1257 »
In theory, there is no difference between theory and practice. But, in practice, there is.
 

Offline IanB

  • Super Contributor
  • ***
  • Posts: 9681
  • Country: us
Re: shotcicut protection
« Reply #5 on: July 10, 2015, 06:24:57 pm »
It is certainly possible to see a 100 Hz flicker from a full wave rectifier in your peripheral vision if you have good eyesight. Why the disbelief?
I'm not an EE--what am I doing here?
 

Offline PSR B1257

  • Regular Contributor
  • *
  • Posts: 243
  • Country: de
Re: shotcicut protection
« Reply #6 on: July 10, 2015, 06:43:18 pm »
Quote
Why the disbelief?
Just because I can't see any sign of flicker (independent of viewing angle and distance) - that's all  :)

I only can see it with an oscilloscope (who would have thought :D ) and through a camera...
In theory, there is no difference between theory and practice. But, in practice, there is.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf