REFLECTOR:A (re)volting problem
Chuck Jensen
reflector@tvbf.org
Fri, 3 Oct 2003 11:42:20 -0400
This message is in MIME format. Since your mail reader does not understand
this format, some or all of this message may not be legible.
------_=_NextPart_001_01C389C4.EE986790
Content-Type: text/plain
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
------_=_NextPart_001_01C389C4.EE986790
Content-Type: text/html
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=us-ascii">
<META content="MSHTML 6.00.2800.1226" name=GENERATOR>
<STYLE>@font-face {
font-family: Verdana;
}
@font-face {
font-family: Nimrod;
}
@page Section1 {size: 8.5in 11.0in; margin: 1.0in 62.3pt 1.0in 62.3pt; }
P.MsoNormal {
FONT-SIZE: 12pt; MARGIN: 0in 0in 0pt; FONT-FAMILY: "Times New Roman"
}
LI.MsoNormal {
FONT-SIZE: 12pt; MARGIN: 0in 0in 0pt; FONT-FAMILY: "Times New Roman"
}
DIV.MsoNormal {
FONT-SIZE: 12pt; MARGIN: 0in 0in 0pt; FONT-FAMILY: "Times New Roman"
}
A:link {
COLOR: blue; TEXT-DECORATION: underline
}
SPAN.MsoHyperlink {
COLOR: blue; TEXT-DECORATION: underline
}
A:visited {
COLOR: purple; TEXT-DECORATION: underline
}
SPAN.MsoHyperlinkFollowed {
COLOR: purple; TEXT-DECORATION: underline
}
P.MsoPlainText {
FONT-SIZE: 11pt; MARGIN: 0in 0in 0pt; FONT-FAMILY: Nimrod
}
LI.MsoPlainText {
FONT-SIZE: 11pt; MARGIN: 0in 0in 0pt; FONT-FAMILY: Nimrod
}
DIV.MsoPlainText {
FONT-SIZE: 11pt; MARGIN: 0in 0in 0pt; FONT-FAMILY: Nimrod
}
DIV.Section1 {
page: Section1
}
</STYLE>
</HEAD>
<BODY lang=EN-US vLink=purple link=blue>
<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> </DIV>
<DIV><SPAN class=046105214-03102003><FONT face=Arial color=#0000ff size=2>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.</FONT></SPAN></DIV>
<DIV><SPAN class=046105214-03102003><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=046105214-03102003><FONT face=Arial color=#0000ff size=2>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.</FONT></SPAN></DIV>
<DIV><SPAN class=046105214-03102003><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </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. 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?</FONT></SPAN></DIV>
<DIV><SPAN class=046105214-03102003><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=046105214-03102003><FONT face=Arial color=#0000ff size=2>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.</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> <SPAN class=046105214-03102003><FONT
face=Arial color=#0000ff size=2> </FONT></SPAN></P>
<P><SPAN class=046105214-03102003> </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> </P>
<P class=MsoPlainText><FONT face=Nimrod size=2><SPAN
style="FONT-SIZE: 11pt">The plot thickens. 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. 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. 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. I cycled it again, same
results. 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> </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. 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? 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> </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> </P>
<P class=MsoPlainText><FONT face=Verdana color=black size=2><SPAN
style="FONT-SIZE: 11pt; COLOR: black; FONT-FAMILY: Verdana">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.</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> </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. 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.</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> </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. 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> </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>
------_=_NextPart_001_01C389C4.EE986790--