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Will this work- 220 VDC 4A power supply - Help Reqd. Answered

I need to generate 220V DC rectified from mains with suitable capacitor. I need to load my four micro switches in parallel with 4A load (with each node 1A). Can anybody help me choosing the values of capacitor and the diode for 4A. I've already blown off the Diodes BY127+330mfd which i used to connect earlier with 1A load.

This is for testing the contact resistance of a given micro switches.I need to run these tests for a full day.

I'd appreciate some immediate help... thanx in advance guys...

5 Replies

chuppandi (author)2011-06-12

Thanks a ton for the reply guyz

@ Steve

Yes i knew higher current rating would b required for diodes. Can u suggest me some 4\5A diodes or rectifiers with 220 VDC for this application. Also i've added the resistors\loads with a typical value of around 220 Ohms. Do u feel that it would still fry my diodes or capacitors...

@ Grenadier

Yeah i was accounting only for the RMS voltage. As u rightly said with my initial setup carrying BY127 diodes it fried up like in seconds.

So guyz i still am searching for the answers and too much googling had left me stranded. All I need is this

- Some standard diode \ Rectifier (Pl. Suggest some values for even 5A)
- Equivalent capacitor for 220VDC with 5A (Again some values)
- Equivalent load \ resistance value for sharing 1A each amongst the four nodes (so that i can load my four micro switches)

Thanks again guyz for the great help

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steveastrouk (author)chuppandi2011-06-12

Big bridge rectifiers should be pretty easy to find, as will power diodes of a suitable rating - more is better, and not much more expensive than one that is "just" the right size.

You need, as I said, ABOUT 75 Ohms per channel.


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grenadier (author)2011-06-11

Well full wave rectified 220V from the wall will supply you with 220/.707 = 311 volts, not 220.

Your diodes are probably exploding due to a large inrush current when charging up the capacitor. IIRC the BY127 is only a 1 amp diode, so even if you charged up the capacitor you'd still explode the diodes when drawing 4A.

Solution: Bigger diodes. Also, don't put smaller ones in //.

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chuppandi (author)grenadier2011-06-12

I forgot to mention i am planning to use a variac in case to reduce the voltage to my desired levels (220 VDC) hope that helps.

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steveastrouk (author)2011-06-11

Yes, MUCH bigger diodes would be needed, if you really DID want to do this the way you have shown. Peak currents will be pretty astronomical - take a typical contact resistance of 10mOhm, peak current = 311/0.01 = 31,000 Amps....

Surely, you want a maximum current of 4A, in which case you MUST have limiting resistors of roughly 311/4 or roughly 75 ohms.


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