[Shop-talk] 130v/260v?

[Mark Watson]

OK, the former electronics teacher has to speak up here.  A nominal line 
voltage of 120V RMS = 120* sqrt(2) V Peak = 170 V Peak = 2* 170 V Peak = 340 
V P-P (approx.).  The conversion from Peak to RMS is V Peak * 1 / sqrt(2) = 
0.707 * V Peak for a sinusoidal waveform.  For any other waveform you have 
to square the wave, find its mean, then take the square root of that result. 
Of course it's called RMS = ROOT MEAN SQUARE which is the required 
operations in reverse order just to confuse everyone.  Most cheap DMM's 
don't actually do the RMS function but display the RMS value based on 
measuring the peak voltage.  So if the power at the David's house is a 
highly distorted sine wave that might explain the voltage difference though 
I'd be inclined not to think that that's the problem.

In case anyone wants to rail against using RMS instead of peak or 
peak-to-peak (usually my students would immediately start this about the 
time they heard the first lecture about RMS and perceived the difficulties 
of dealing with it) basically the industry uses it because it allows direct 
"comparison" to DC measurements.  That is the power dissipated by a resistor 
(P = V * I) calculated for a DC voltage impressed on a resistor is exactly 
the same as the power dissipated by the same resistor with the same RMS AC 
voltage impressed on it.  And since power dissipation is basically just heat 
that's what's important to consider.

And don't get me started on audio amplifier power ratings that are given 
based on peak to peak values instead of RMS - pure marketing HYPE!

Hope this helps,

Mark Watson
-----Original Message----- 
From: Ronald.Griffing at comcast.net
Sent: Wednesday, March 30, 2011 4:47 PM
To: David Hillman
Cc: shop-talk at autox.team.net
Subject: Re: [Shop-talk] 130v/260v?

If your meter is measuring peak to peak, that's about right.  The given 
voltage is in Root Mean Square, or RMS which will be lower than the 
peak-to-peak.


----- Original Message -----
From: "David Hillman" <hillman at planet-torque.com>
To: shop-talk at Autox.Team.Net
Sent: Wednesday, March 30, 2011 10:47:28 AM
Subject: [Shop-talk] 130v/260v?

    I have been curious about this for a while, but unable to find an
answer online.  My house has standard residential AC electrical service,
100a at a nominal 120v.  Whenever I put a meter on a circuit, though, I
always measure about 130v.  Similarly, on the double-pole breaker circuit
I just installed for my welder (nominally 240v) I measure ~264v.  I have
used at least three different (cheap) meters, all with similar results.

    Is this highly unusual?  For a given resistance, 264v is going to
provide about 10% more current than the nominal standard on the
double-pole circuit.  Is this risky or problematic?  The single-pole
circuits have been in-place for years, with no apparent problems, but I
obviously don't want to blow up my Syncrowave.

    Thanks.

--
  David Hillman
_______________________________________________

Shop-talk at autox.team.net
Donate: http://www.team.net/donate.html
Suggested annual donation  $12.96
Archive: http://www.team.net/archive
Forums: http://www.team.net/forums
Unsubscribe/Manage: 
http://autox.team.net/mailman/options/shop-talk/ronald.griffing@comcast.net
_______________________________________________

Shop-talk at autox.team.net
Donate: http://www.team.net/donate.html
Suggested annual donation  $12.96
Archive: http://www.team.net/archive
Forums: http://www.team.net/forums
Unsubscribe/Manage: 
http://autox.team.net/mailman/options/shop-talk/watsonm05@comcast.net