REFLECTOR:A (re)volting problem

Chuck Jensen reflector@tvbf.org
Fri, 3 Oct 2003 11:42:20 -0400


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Al,
 
Thanks for the straight info on power vs. current.  I was thinking about the
power relationship between voltages but it's actually current that is
pertinent to this situation.
 
I never got the exact straight story from the original owner.  He said he
thought the heating element was maybe damaged during the plating process,
then, on second thought, surmised that maybe the popping circuit breaker was
associated with the higher rated voltage requirement.  His make-good was a
new 12v pitot but its of the standard design and painted, so I was hoping to
be able to salvage the installed one.
 
Since it popped a 10a breaker, your suggestion about looking for a partial
short is certainly a good one.  Perhaps its a partial short caused by the
plating process during which the heating elements weren't/couldn't be
removed.  Are the elements in a pitot typically replaceable or is the whole
assembly tossed?
 
Next time I move, instead of looking at prices and neighborhoods, I think
I'll pitch a tent on an empty lot that has a EE living on one side and an ME
on the other.  Life would be simpler.

Chuck Jensen  

 -----Original Message-----
From: reflector-admin@tvbf.org [mailto:reflector-admin@tvbf.org]On Behalf Of
Al Gietzen
Sent: Friday, October 03, 2003 9:32 AM
To: reflector@tvbf.org
Subject: RE: REFLECTOR:A (re)volting problem



 

The plot thickens.  Yesterday evening, I went out to get my night landings

in for currency and tested the pitot.  I pushed in the circuit breaker and

turned on the pitot switch.  After 5-10 seconds, the "10" (amp, I assume)

breaker popped.  I cycled it again, same results.  I checked and the voltage

dropped from 12.8v to about 11.0v, then the breaker would pop after a few

seconds.

 

Based on my passing understanding of electricity (I once passed by the

Electrical Engineering building), when you go up in volts, you go down in

amps.  I assume the converse holds true; when the voltage is cut in half,

the amps double?  So, an instrument rated for 10a at 24v is going to need a

20a circuit at 12v (actual draw is approximately 80%, or 16a)?

 

Chuck:

 

Current = voltage/resistance.  As others pointed out a couple of days ago,
for the same resistance cutting the voltage in half cuts the current in half
as well.  Look for another problem, like a partial short somewhere, or
something faulty about the PT.

 

As I also mentioned, heated pitot tubes generally are self-regulating, i.e.;
as the temp goes up the resistance goes up in order to limit current and
overheating.  Your case may vary, but the heated PT that I have with 12v
draws about 3.5 amps initially, dropping to 2 amps after a couple of
minutes.  It is recommended to use a 7 amp breaker with 24V, so a 5 amp
ought to do it for 12v.

 

If you are making power, like in an electric motor, making the same power
will take twice as much current with half as much voltage.  Power = volts x
amps.

 

Al


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<DIV><SPAN class=046105214-03102003><FONT face=Arial color=#0000ff 
size=2>Al,</FONT></SPAN></DIV>
<DIV><SPAN class=046105214-03102003><FONT face=Arial color=#0000ff 
size=2></FONT></SPAN>&nbsp;</DIV>
<DIV><SPAN class=046105214-03102003><FONT face=Arial color=#0000ff size=2>Thanks 
for the&nbsp;straight info on power vs. current.&nbsp; I was thinking about the 
power relationship between voltages but it's actually current that is pertinent 
to this situation.</FONT></SPAN></DIV>
<DIV><SPAN class=046105214-03102003><FONT face=Arial color=#0000ff 
size=2></FONT></SPAN>&nbsp;</DIV>
<DIV><SPAN class=046105214-03102003><FONT face=Arial color=#0000ff size=2>I 
never got the exact straight story from the&nbsp;original owner.&nbsp; He said 
he thought the heating element was maybe&nbsp;damaged during the plating 
process, then, on second thought, surmised that maybe&nbsp;the popping circuit 
breaker was associated with the higher rated voltage requirement.&nbsp; His 
make-good was a new 12v pitot but its of the standard design and painted, so I 
was hoping to be able to&nbsp;salvage the installed one.</FONT></SPAN></DIV>
<DIV><SPAN class=046105214-03102003><FONT face=Arial color=#0000ff 
size=2></FONT></SPAN>&nbsp;</DIV>
<DIV><SPAN class=046105214-03102003><FONT face=Arial color=#0000ff size=2>Since 
it popped a 10a breaker, your suggestion about looking for a partial short is 
certainly a good one.&nbsp; Perhaps its a partial short caused by the plating 
process during which the heating elements weren't/couldn't be removed.&nbsp; Are 
the elements in a pitot typically replaceable or is the whole assembly 
tossed?</FONT></SPAN></DIV>
<DIV><SPAN class=046105214-03102003><FONT face=Arial color=#0000ff 
size=2></FONT></SPAN>&nbsp;</DIV>
<DIV><SPAN class=046105214-03102003><FONT face=Arial color=#0000ff size=2>Next 
time I move, instead of looking at&nbsp;prices and neighborhoods, I think I'll 
pitch a tent on an empty lot that has a EE living on one side and an ME on the 
other.&nbsp; Life would be simpler.</FONT></SPAN></DIV>
<P><FONT face=Arial size=2>Ch</FONT><FONT face=Arial size=2>uck</FONT><FONT 
face=Arial size=2> Jensen</FONT>&nbsp;<SPAN class=046105214-03102003><FONT 
face=Arial color=#0000ff size=2>&nbsp;</FONT></SPAN></P>
<P><SPAN class=046105214-03102003>&nbsp;</SPAN><FONT face=Tahoma 
size=2>-----Original Message-----<BR><B>From:</B> reflector-admin@tvbf.org 
[mailto:reflector-admin@tvbf.org]<B>On Behalf Of </B>Al Gietzen<BR><B>Sent:</B> 
Friday, October 03, 2003 9:32 AM<BR><B>To:</B> 
reflector@tvbf.org<BR><B>Subject:</B> RE: REFLECTOR:A (re)volting 
problem<BR><BR></P></FONT>
<BLOCKQUOTE dir=ltr style="MARGIN-RIGHT: 0px">
  <DIV class=Section1>
  <P class=MsoPlainText><FONT face=Arial color=#0000ff size=2><SPAN 
  style="FONT-SIZE: 11pt"></SPAN></FONT>&nbsp;</P>
  <P class=MsoPlainText><FONT face=Nimrod size=2><SPAN 
  style="FONT-SIZE: 11pt">The plot thickens.&nbsp; Yesterday evening, I went out 
  to get my night landings</SPAN></FONT></P>
  <P class=MsoPlainText><FONT face=Nimrod size=2><SPAN 
  style="FONT-SIZE: 11pt">in for currency and tested the pitot.&nbsp; I pushed 
  in the circuit breaker and</SPAN></FONT></P>
  <P class=MsoPlainText><FONT face=Nimrod size=2><SPAN 
  style="FONT-SIZE: 11pt">turned on the pitot switch.&nbsp; After 5-10 seconds, 
  the "10" (amp, I assume)</SPAN></FONT></P>
  <P class=MsoPlainText><FONT face=Nimrod size=2><SPAN 
  style="FONT-SIZE: 11pt">breaker popped.&nbsp; I cycled it again, same 
  results.&nbsp; I checked and the voltage</SPAN></FONT></P>
  <P class=MsoPlainText><FONT face=Nimrod size=2><SPAN 
  style="FONT-SIZE: 11pt">dropped from 12.8v to about 11.0v, then the breaker 
  would pop after a few</SPAN></FONT></P>
  <P class=MsoPlainText><FONT face=Nimrod size=2><SPAN 
  style="FONT-SIZE: 11pt">seconds.</SPAN></FONT></P>
  <P class=MsoPlainText><FONT face=Arial color=#0000ff size=2><SPAN 
  style="FONT-SIZE: 11pt"></SPAN></FONT>&nbsp;</P>
  <P class=MsoPlainText><FONT face=Nimrod size=2><SPAN 
  style="FONT-SIZE: 11pt">Based on my passing understanding of electricity (I 
  once passed by the</SPAN></FONT></P>
  <P class=MsoPlainText><FONT face=Nimrod size=2><SPAN 
  style="FONT-SIZE: 11pt">Electrical Engineering building), when you go up in 
  volts, you go down in</SPAN></FONT></P>
  <P class=MsoPlainText><FONT face=Nimrod size=2><SPAN 
  style="FONT-SIZE: 11pt">amps.&nbsp; I assume the converse holds true; when the 
  voltage is cut in half,</SPAN></FONT></P>
  <P class=MsoPlainText><FONT face=Nimrod size=2><SPAN 
  style="FONT-SIZE: 11pt">the amps double?&nbsp; So, an instrument rated for 10a 
  at 24v is going to need a</SPAN></FONT></P>
  <P class=MsoPlainText><FONT face=Nimrod size=2><SPAN 
  style="FONT-SIZE: 11pt">20a circuit at 12v (actual draw is approximately 80%, 
  or 16a)?</SPAN></FONT></P>
  <P class=MsoPlainText><FONT face=Nimrod size=2><SPAN 
  style="FONT-SIZE: 11pt"></SPAN></FONT>&nbsp;</P>
  <P class=MsoPlainText><FONT face=Verdana size=2><SPAN 
  style="FONT-SIZE: 11pt; FONT-FAMILY: Verdana">Chuck:</SPAN></FONT></P>
  <P class=MsoPlainText><FONT face=Verdana color=black size=2><SPAN 
  style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Verdana"></SPAN></FONT>&nbsp;</P>
  <P class=MsoPlainText><FONT face=Verdana color=black size=2><SPAN 
  style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Verdana">Current = 
  voltage/resistance.&nbsp; As others pointed out a couple of days ago, for the 
  same resistance cutting the voltage in half cuts the current in half as 
  well.&nbsp; Look for another problem, like a partial short somewhere, or 
  something faulty about the PT.</SPAN></FONT></P>
  <P class=MsoPlainText><FONT face=Verdana color=black size=2><SPAN 
  style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Verdana"></SPAN></FONT>&nbsp;</P>
  <P class=MsoPlainText><FONT face=Verdana color=black size=2><SPAN 
  style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Verdana">As I also 
  mentioned, heated pitot tubes generally are self-regulating, i.e.; as the temp 
  goes up the resistance goes up in order to limit current and 
  overheating.&nbsp; Your case may vary, but the heated PT that I have with 12v 
  draws about 3.5 amps initially, dropping to 2 amps after a couple of minutes. 
  &nbsp;It is recommended to use a 7 amp breaker with 24V, so a 5 amp ought to 
  do it for 12v.</SPAN></FONT></P>
  <P class=MsoPlainText><FONT face=Verdana color=black size=2><SPAN 
  style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Verdana"></SPAN></FONT>&nbsp;</P>
  <P class=MsoPlainText><FONT face=Verdana color=black size=2><SPAN 
  style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Verdana">If you are making 
  power, like in an electric motor, making the same power will take twice as 
  much current with half as much voltage. &nbsp;Power = volts x 
  amps.</SPAN></FONT></P>
  <P class=MsoPlainText><FONT face=Verdana color=black size=2><SPAN 
  style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Verdana"></SPAN></FONT>&nbsp;</P>
  <P class=MsoPlainText><FONT face=Verdana color=black size=2><SPAN 
  style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Verdana">Al</SPAN></FONT></P></DIV></BLOCKQUOTE></BODY></HTML>

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