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Author Topic: shotcicut protection  (Read 2237 times)

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Offline 07PepaTopic starter

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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
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Offline PSR B1257

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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.
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In theory, there is no difference between theory and practice. But, in practice, there is.
 

Offline 07PepaTopic starter

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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)
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Offline Zero999

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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.
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Offline PSR B1257

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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 »
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In theory, there is no difference between theory and practice. But, in practice, there is.
 

Online IanB

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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?
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Offline PSR B1257

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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...
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