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Joseph Hebert
12/27/05 09:47
Read: 1691 times
Okemah, Ok
United States


 
#106023 - Current Limiting Capacitor
Responding to: Suresh R's previous message
Hi Suresh,

The capacitor produces infinite resistance (R, at zero hertz) plus a capacitive reactance (-j(X_c)) inversely proportional to any frequency higher than zero hertz. The sum of these two components is the impedance (Z; Z = R j X | X = X_l - X_c).

In this example the writer states that the capacitor will limit the current to approximately 20 mA. The voltage is 120 V_rms at 60 Hz. The capacitor is 0.47 F. Therefore Z = R -j X_c = 0 - [2*@PI*60*0.47E-6]^(-1) = 5644 OHMS. Thus, by Ohm's Law i = 120/5644 = 0.021 amps.

Now that all of that is said, for the sake of intellectual curiosity, go back and read Kai and Erik's posts again. And then when you've read them again, read them even yet again. This is a good example of a circuit that should not be built by anyone who doesn't already know the answers to the questions you've posed.

As a researcher I frequently kluge things together in ways that are not intended to be safe, usually because I need a certain circumstance just long enough to test whatever I am really working on at the time. A perfect example of this is a suicide cord (a power cord with a two prong plug on one end and alligator clips on the other). I might use it to temporarilly get power to something I am testing, but I would never give one to someone else to use.

Yet another real world example happened several years ago. I was working on an rf supply for a system I was working on. In order to test it I kluged together a class B (push pull) amp with some pretty high current transistors. By the time I finished my measurements, my bench was scorched with the imprints of the transistors and a couple of the bias resistors.

Good luck, and be careful.

List of 56 messages in thread
TopicAuthorDate
Circuit Analysis      Suresh R      12/27/05 00:40      
   Analysis      Farshid Jafari Harandi      12/27/05 04:15      
   Dangerous!      Kai Klaas      12/27/05 07:09      
      bungling amateurs "bragging" on the web      Erik Malund      12/27/05 08:55      
         Not electronic, but an amusing example      Joseph Hebert      12/27/05 09:58      
            OLD idea ?      Steve M. Taylor      12/27/05 12:09      
               New and improved      Joseph Hebert      12/27/05 17:11      
                  Safety first      Steve M. Taylor      12/28/05 06:43      
         I think you meant...      Kalpak Dabir      12/27/05 10:01      
         deja vu all over again!      Andy Neil      12/27/05 18:23      
      resistor replaced by capacitor      Suresh R      12/28/05 01:11      
         Phase shift      Kai Klaas      12/28/05 06:30      
         dissapation      Terry Lingle      12/28/05 06:38      
            Dissipation      Steve M. Taylor      12/28/05 06:48      
               It's a real world after all      Terry Lingle      12/28/05 07:11      
                  What ? Make mistakes ?      Steve M. Taylor      12/28/05 07:33      
                     are you sure      Erik Malund      12/28/05 09:05      
                     or ..      Andy Curda      12/29/05 13:21      
            Non ideal cap performance      Kai Klaas      12/28/05 06:58      
   Diodes!      Andy Neil      12/27/05 07:14      
   Current Limiting Capacitor      Joseph Hebert      12/27/05 09:47      
      Capacitor Filters      Suresh R      01/12/06 01:15      
         Some basic theory needed      Kalpak Dabir      01/12/06 01:25      
         12 */~2 ~ 17 so I doubt you see 19V      Erik Malund      01/12/06 06:31      
         Output voltage      Kai Klaas      01/12/06 07:54      
            Regulation      Steve M. Taylor      01/12/06 11:20      
            current flow      Suresh R      01/13/06 00:43      
               What current?      Kai Klaas      01/13/06 06:10      
                  What iam trying to know is      Suresh R      01/15/06 21:29      
                     inrush current      Terry Lingle      01/15/06 23:20      
                     Naiive analysis      Steve M. Taylor      01/16/06 06:33      
                        Laplace Transformation      Kai Klaas      01/16/06 07:19      
                           Could be worse....      Steve M. Taylor      01/16/06 11:39      
                              Me too!      Kai Klaas      01/16/06 11:58      
                                 Minds are failing      Steve M. Taylor      01/16/06 12:28      
                     DC component      Kai Klaas      01/16/06 12:03      
                        Suresh, have as look      Erik Malund      01/16/06 12:18      
                           analog and digital ground      Suresh R      01/17/06 00:24      
                              discussed ad nauseam do a search      Erik Malund      01/17/06 06:56      
                              Use a splitted ground plane      Kai Klaas      01/17/06 07:32      
                                 did i got it right      Suresh R      01/18/06 00:49      
                                    Also datasheet of ADUC can help you      Kai Klaas      01/18/06 06:44      
                                       Placing Vias      Suresh R      01/24/06 00:18      
                                          Maybe..      Kai Klaas      01/24/06 06:08      
                                             Copper fills      Terry Lingle      01/24/06 08:25      
                                          I do not know about 2 layers      Erik Malund      01/24/06 09:09      
                                        Auto route      Suresh R      01/25/06 00:00      
                                          Solid ground plane has to be solid!      Kai Klaas      01/25/06 08:37      
                                             Thank you Kai      Suresh R      01/26/06 21:12      
                                                circuit for a despensing unit      Suresh R      01/28/06 02:58      
                                                   ICM7555 + 2M2 + 68      Kai Klaas      01/28/06 10:14      
                                                      why a totally unrelated post in the midd      Erik Malund      01/30/06 08:07      
                              Separate signal traces.      Joseph Hebert      01/17/06 10:01      
                                 What has God to do with this??      Kai Klaas      01/17/06 19:20      
               DC DC      Steve M. Taylor      01/13/06 06:19      
               DC DC      Steve M. Taylor      01/13/06 06:19      

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