Tweakers' Asylum

Unfortunately, no.

71.141.230.162

Al Sekela

In Reply to: RE: I leave the ground alone. posted by Awe-d-o-file on December 23, 2007 at 09:25:03

Visualize a capacitor in series with a resistor. The other end of the capacitor is connected to the AC hot. The other end of the resistor is connected to the AC neutral. There are three of these R-C pairs in parallel, each with a different value of C and the same value of R.

I have one friend who prefers 91 ohms instead of 120 ohms for R, so some experimenting would be useful.

Follow Ups:

RE: Unfortunately, no. - Awe-d-o-file 20:41:10 12/25/07 (5)
OK thats easy. What is the value of the cap and working voltage? Polarized paper electrolytic? Something better? And the resistor needs to be what wattage? Why did the other friend prefer 91 ohms? Was it brighter, warmer etc. Lots of questions-sorry. Thanks in advance.

ET
- Important to use X- and Y-rated caps. - Al Sekela 13:23:50 12/26/07 (2)
  These are capacitors built to withstand surges on the AC line without forming resistive leakage paths. Other types of capacitors may survive a surge, but develop a leak. After enough surges, the leak becomes a heater and sets your device or house on fire.
  
  You can identify such caps by a marking such as "X2" and an AC voltage rating such as "275 ~."
  
  "X" rated caps are for line to neutral and come in a variety of sizes. They may fail to a short and set the resistor on fire unless it is a flame-proof type. I put mine (not flame-proof) inside short pieces of Teflon tubing, which will withstand the flame. The flame is about as big and long-lasting as a kitchen match.
  
  "Y" rated caps are for line and neutral to ground. They are designed to only fail to an open-circuit, as a ground leak would be dangerous. They only come in small sizes to avoid significant 60 Hz ground current. Since they are more rugged than X caps, it is OK to use them in a line-neutral application.
  
  The maximum AC power in a 120-ohm resistor with a 1 microfarad capacitor is 0.25 watts at 60 Hz. Half-watt resistors are fine for 120-volt applications.
  
  My friend has done experiments to convince himself that 91 ohms is optimum. I calculated the 120 ohm value from my crude measurements of inductance and capacitance of a sample of house wire plastic cable. The measurements could be in error, and different cable types would have different characteristic impedances, so it is a good idea to experiment and see what value of resistance works best in your application.
  - RE: Important to use X- and Y-rated caps. - Awe-d-o-file 14:47:08 12/26/07 (1)
    Thanks for the extra info. Time to gather parts and ready them for a winter weekend project.
    
    ET
    - One more item... - Al Sekela 16:47:28 12/27/07 (0)
      If you can browse the parts bins, take a magnet and look for capacitors that are not attracted to the magnet. Some are and some are not.
- I'm using a different setup - bartc 21:05:43 12/25/07 (1)
  Using X-caps of .47, then downward two more levels each a factor of .1 of the previous value. I'm using flameproof NITE resistors, 1/2 Watt 120 Ohms 1% value. One R for each value of C, all nicely separated by electrical tape and all surrounded with microsorb as a unit and then with Ti-Shield which is grounded with 12 AWG wire. Works like a real charm. Best I've found with Al's basic formula. I use this for AC parellel filtering on its own and installed where I join a snipped captive power cord with a DIY power cord of better quality. Works in both applications well.
  
  Since this formula work so very well in several AC applications for me I haven't experimented with any others.
  
  Have experimented with different values of silver mica caps on both ends of speaker cables in R-Cs. Al calculated the best values related to the characteristics of my particular cable, but a 10 or 20 Ohm resistor works with a 3 cap descending array from 10,000 pf downward in those applications. IN my case I'm using his recommended Halco non-ferrous Rs at 15 Ohms for my cable in particular. But the other values work reasonably well.
  - RE: I'm using a different setup - Awe-d-o-file 07:26:44 12/26/07 (0)
    Thanks for that imformative post. Seems a good project for a cold winter weekend!
    
    ET

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