power ratings of resistors - Page 2 - diyAudio
Go Back   Home > Forums > Design & Build > Parts

Parts Where to get, and how to make the best bits. PCB's, caps, transformers, etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 4th August 2004, 05:24 PM   #11
dhaen is offline dhaen  Europe
diyAudio Moderator Emeritus
 
dhaen's Avatar
 
Join Date: Jun 2002
Location: U.K.
Wink Nice schematic

Caps go bang when the leakage current through them is too high. That will happen if the polarity is reversed, or if their voltage rating is exceeded.
Don't forget that the DC across those caps will be nearly 1.5 x the AC into the rectifier. Also the AC voltage may be 20% higher than specified with no load current being taken.

I'll pray for your caps...
  Reply With Quote
Old 4th August 2004, 05:53 PM   #12
6SN7GT is offline 6SN7GT  United Kingdom
diyAudio Member
 
6SN7GT's Avatar
 
Join Date: Jun 2004
Location: Sarf Koast
dhaen,

You beat me to it .. I couldn't get at diyAudio .. it just timed out

The caps almost certainly were connected reverse polarity.
The sequence of events, time line, and the consequence says this is most likely.

I can hear the bubbles forming

That is one of the best circuit diagrams ever, alecwek !

Assuming it's to scale, I calculate the BANG to be 108.43dB spl at 1 metre
  Reply With Quote
Old 4th August 2004, 06:10 PM   #13
Netlist is offline Netlist  Belgium
diyAudio Moderator Emeritus
 
Netlist's Avatar
 
Join Date: Jan 2003
Quote:
Originally posted by 6SN7GT

Assuming it's to scale, I calculate the BANG to be 108.43dB spl at 1 metre
Ohm's law?

Love the drawing, be careful though!

/Hugo
  Reply With Quote
Old 4th August 2004, 06:27 PM   #14
diyAudio Member
 
jackinnj's Avatar
 
Join Date: Apr 2002
Location: Llanddewi Brefi, NJ
A 50Kohm/20 Watt Vitreous Dale resistor is about 1.5 inches long, .6 inches in diameter, the sand cast power resistors are a little smaller.

Bleeders -- you should figure that the value of the bleeder resistor will reduce the voltage on the capacitors by about 90% in the time it takes you to remove the amplifier cover -- 30 seconds -- the equation is: V(f) = V(i) * e^(-t/RC).

where Vi is the initial voltage and Vf the final voltage --

let's say you are using 470uF of filtration on 400 VDC -- a 27K ohm resistor will bleed the caps by 90% in 30 seconds or thereabouts.

the current drawn by the bleeder is 400V / 27000 Ohms = 14.8 ma. The power is thus (.0148^2) * 27000 = 6 watts. A 10 Watt resistor will accomodate a big swing in the supply voltage. this is a lot of power to burn, however.
  Reply With Quote
Old 4th August 2004, 08:14 PM   #15
alecwek is offline alecwek  Denmark
diyAudio Member
 
Join Date: Jul 2004
Location: dk
ok... now that u mention it...the caps were connected in revers.....man!!!its cause when i kept flipping the breadboard round ...up down....alittle to the left!!!...i guess i must have gotten the rails the wrong way round........i drew schematics on the non copper side before soldering so i had to keep flipping to solder.....man i gotta learn how to make pcb.....also u should see how crap my finished peices look...hmm...ah well.....
what is the best looking.....quickest.....(cheapest )way of making curcuits....pcb look a bit expensive and complicated....plus how on earth do you sheild pcb lines..........
  Reply With Quote
Old 4th August 2004, 08:16 PM   #16
alecwek is offline alecwek  Denmark
diyAudio Member
 
Join Date: Jul 2004
Location: dk
oh and thanks for all the help so far
  Reply With Quote
Old 4th August 2004, 08:38 PM   #17
6SN7GT is offline 6SN7GT  United Kingdom
diyAudio Member
 
6SN7GT's Avatar
 
Join Date: Jun 2004
Location: Sarf Koast
Ah ha!, I think we got to the bottom of the exploding caps problem OK.
So that's good.

I agree, you have to be careful with breadboard designs and remember which side you are working from.

Why do you want to shield PCB lines ?
Because the interconnect wiring is effectively 2D, crosstalk (interference) can be managed reasonably well.
You have something in mind I guess ? Do tell.
  Reply With Quote
Old 4th August 2004, 09:54 PM   #18
alecwek is offline alecwek  Denmark
diyAudio Member
 
Join Date: Jul 2004
Location: dk
well its just cause i heard,....from one of the thousands sources (that are found in great abundance in electronics)
that high voltage lines should be sheilded ...and also high voltage points...caps..etc...i guess cause of noise, also i could imagine it being ......ummm.....healthier, to keep power rails and high voltage ,current lines sheilded...less chances of accident...but man, electronics is polluted with so much good advice its hard to get a grip on it all....
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Hammond PT power ratings dsavitsk Tubes / Valves 4 23rd August 2009 08:23 PM
Power supply resistors power ratings Nihilist Tubes / Valves 13 31st July 2009 01:47 AM
Tube power ratings Brian Donaldson Tubes / Valves 19 20th November 2005 02:59 PM
Power Ratings BAM Multi-Way 1 13th October 2001 11:05 PM


New To Site? Need Help?

All times are GMT. The time now is 09:52 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2