Figuring out Output current.
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 19th September 2004, 05:16 PM #1 mjarve   diyAudio Member     Join Date: Apr 2004 Location: Northeastern Minnesota Figuring out Output current. I was playing around with a new amp this morning and I noticed on the back, near the speaker binding posts a label that said: "4(ohms) 400Watts" then below: "40 volts RMS" Now this is stating the output per channel (400Watts @ 4(ohms)), of course, but I got to thinking what the output current would be (I'm funny this way)? So if I know the Voltage, the Impedance, and the ultimate Power Output for a given load, how do I determine output Current? I seem to remember some formula that went along the lines of: P=(Ei)/R, but using this, the current turns out to be a rather incredible 40-amps, and I know that cannot be correct. Thank you for helping me with my little brain fart. __________________ /Mike
 19th September 2004, 05:40 PM #2 lubbie   diyAudio Member   Join Date: Mar 2003 Location: Dawson Creek, British Columbia According to a little excel sheet i designed.. With the info you supplied the current would be 14 amps.. Output Voltage(RMS)/Speaker Resistance. <- down and dirty. __________________ Ralph Electronics Tech.
 19th September 2004, 07:32 PM #3 mjarve   diyAudio Member     Join Date: Apr 2004 Location: Northeastern Minnesota Thanks. 14 amps seems much more reasonable than 40, and much closer to the mark too (judging from the power transformer and output array). __________________ /Mike
 19th September 2004, 09:25 PM #4 cunningham   diyAudio Member   Join Date: Jun 2004 Location: Knoxville Actually..... I=sqrt(400W/4Ohms)=10A. 10A X 40V=400W This would be 10A RMS. Which peak current is 10A X sqrt of 2 or ~14.1A. 14.1A X 4Ohms is 56.6V peak.
 19th September 2004, 10:29 PM #5 lubbie   diyAudio Member   Join Date: Mar 2003 Location: Dawson Creek, British Columbia You are correct.. That is peak output current through the transistors. I used peak to determin output transistor requirements. __________________ Ralph Electronics Tech.

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