T&T: 12 volt Charging options

[Peter Bennett]

Tuesday, May 29, 2007, 5:43:15 PM, Gil wrote:

GJ> Peter, right you are on RMS.  So, with the exception of an
GJ> o'scope how would you read the actual p-p voltage?

doesn't everyone have a 'scope?  :-)

Cheap meters may actually read peak voltage, but be calibrated to read
RMS, assuming they're measuring a sine wave.  Better meters are
described as "True RMS Reading" and will display the actual RMS
voltage, regardless of the waveform.

GJ> Gil

GJ> ----- Original Message ----
GJ> From: Peter Bennett <peterbb4@interchange.ubc.ca>
GJ> To: Gil Johnson <dogtrawler@yahoo.com>;
GJ> trawlers-and-trawlering@lists.samurai.com
GJ> Sent: Tuesday, May 29, 2007 8:36:54 PM
GJ> Subject: Re: T&T: 12 volt Charging options


GJ> Tuesday, May 29, 2007, 3:52:28 PM, Gil wrote:

GJ>> Jeff, I'm confused.  110VAC is 110-120VAC, meaning that it's
GJ>> peak to peak voltage is 110.  Use any AC voltmeter and you'll
GJ>> likely read something between 110 and 125 VAC.  If they are
GJ>> suggesting a different method of measuring the voltage, it would
GJ>> be helpful to understand.  Not having that point of reference
GJ>> would make it impossible to troubleshoot a suspected voltage
GJ>> problem.

GJ> No.  AC voltage is normally specified as the RMS (Root mean square)
GJ> value.  AC of a given RMS voltage will produce the same power as DC of
GJ> the same voltage.

GJ> The peak voltage of a sine wave is 1.4 times the RMS value - hence
GJ> 120VAC RMS has a peak voltage of 168 volts.  Peak-to-peak voltage is
GJ> 2.8 times the RMS value.

GJ> From some previous comments (Arilds?), apparently some generators
GJ> produce a distorted waveform, with flattened (and therefore lower
GJ> voltage) peaks.

GJ>> "In order to meet its ratings, 164 peak volts are required. A
GJ>> battery charger uses only the top portion of the input sinewave.
GJ>> Therefore, small variations in peak voltage results in large
GJ>> variations in the amount of the waveform that the charger has to
GJ>> work with. Standard public power of 117V has a peak voltage of
GJ>> 164V."

GJ>> Gil





-- 
Peter Bennett, VE7CEI    Vancouver, B.C., Canada
Lien Hwa 28 (AKA Polaris 30) "Sea Spray"
GPS and NMEA info: http://vancouver-webpages.com/peter 
Vancouver Power Squadron: http://vancouver.powersquadron.ca