Hi Rick:
> If a product has a 4A rated input current (120V AC), how does one
> determine the rating of the in-line Fuse for safety/Fault testing?
There is no relationship between input rating and the fuse
rating.
The input rating is the maximum input under normal operating
conditions.
The fuse rating is less than the worst-case (not maximum) input
under fault conditions.
The first problem is to identify faults that can occur in the
primary circuit. The fault you are looking for is that fault
that creates the least current at which some component overheats
to the point of destroying insulation, e.g., change of color of
plastic or PWB material, or softening of EMI filter bobbin, or?
SMPS components that are candidates for overheating include the
EMI filter, the bridge rectifier, the snubber resistor, the
snubber diode, the switching transistor, the current-sampling
resistor, transient suppressors, the transformer, connectors,
etc. Most of these components overheat as a result of excessive
current through the device. These devices will couple the heat
to nearby various polymeric or organic materials. One big sign
of overheating is the color change of the PWB or plastic
materials.
One way of creating overheating events is to put a humungous
variable resistor (e.g., 0-10 ohms) in parallel with various
primary circuit components. Reduce the value of the resistor,
and watch for signs of heating of the other components. Monitor
the ac input current.
The worst-case input is the least fault current that causes
unacceptable overheating.
Once you have determined the least fault current, then you
select a fuse that is rated one-half of that fault current.
(Fuses do not operate at 100% rated current at normal temperatures;
fuses operate at 200% rated current in less than one minute.)
Typical fuse rating should be about twice rated current (or more).
(Of course you must balance the fuse value with the duration of
normal peak currents.)
Enjoy!
Rich
-------------------------------------------------------------
Richard Nute Product Safety Engineer
Hewlett-Packard Company Product Regulations Group
AiO Division Tel : +1 619 655 3329
Effective 6/12/99: +1 858 655 3329
16399 West Bernardo Drive FAX : +1 619 655 4979
Effective 6/12/99: +1 858 655 4979
San Diego, California 92127 e-mail: [email protected]
-------------------------------------------------------------
> From [email protected] Thu May 13 12:12:54 PDT 1999
> Received: from hpsdlo.sdd.hp.com (hpsdlo-sw.sdd.hp.com [15.26.112.11]) by
> hpsdlfsg.sdd.hp.com with ESMTP (8.7.6/8.7.3 TIS 5.0/sdd epg) id MAA17861 for
> <[email protected]>; Thu, 13 May 1999 12:12:53 -0700 (PDT)
> Received: from ruebert.ieee.org (ruebert.ieee.org [199.172.136.3])
> by hpsdlo.sdd.hp.com (8.8.6 (PHNE_14041)/8.8.5btis+epg) with ESMTP id
> MAA20003
> for <[email protected]>; Thu, 13 May 1999 12:12:50 -0700 (PDT)
> Received: by ruebert.ieee.org (8.8.8+Sun/8.8.8)
> id OAA23315; Thu, 13 May 1999 14:21:07 -0400 (EDT)
> Message-ID:
> <[email protected]>
> From: Rick Loiselle <[email protected]>
> To: "EMC-Safety (E-mail)" <[email protected]>
> Subject: Fuse rating
> Date: Thu, 13 May 1999 14:21:42 -0400
> MIME-Version: 1.0
> X-Mailer: Internet Mail Service (5.5.2232.9)
> Content-Type: multipart/alternative;
> boundary="----_=_NextPart_001_01BE9D6D.739BAE72"
> Sender: [email protected]
> Precedence: bulk
> Reply-To: Rick Loiselle <[email protected]>
> X-Resent-To: Multiple Recipients <[email protected]>
> X-Listname: emc-pstc
> X-Info: Help requests to [email protected]
> X-Info: [Un]Subscribe requests to [email protected]
> X-Moderator-Address: [email protected]
>
>
> 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_01BE9D6D.739BAE72
> Content-Type: text/plain;
> charset="iso-8859-1"
> Content-Transfer-Encoding: quoted-printable
>
> Greetings Group,
> =A0
> If a product has a 4A rated input current (120V AC), how does one
> determine the rating of the in-line Fuse for safety/Fault testing?
> =A0
> The Fuse will be used at the AC connector Inlet, inside the product =
> (not
> user accessible) on the Hot lead wire.=A0 I do know that it will be an =
> in-line
> type fuse
> holder, UL and CSA approved, 5X20.
> =A0
> We test to UL6500 and IEC 60065.
> =A0
> Best Regards,=20
> Rick=20
> =A0
>
> ------_=_NextPart_001_01BE9D6D.739BAE72
> Content-Type: text/html;
> charset="iso-8859-1"
>
> <!DOCTYPE HTML PUBLIC "-//W3C//DTD W3 HTML//EN">
> <HTML>
> <HEAD>
> <META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1">
>
>
> <TITLE>RE: Car Audio Amplifiers</TITLE>
> <META content='"MSHTML 4.72.3110.7"' name=GENERATOR>
> </HEAD>
> <BODY>
> <DIV><FONT size=2>
> <DIV><FONT color=#0000ff size=2></FONT><SPAN class=990194017-13051999><FONT
> color=#000000 face=Arial size=2>Greetings Group,</FONT></SPAN></DIV>
> <DIV><SPAN class=990194017-13051999><FONT color=#000000 face=Arial
> size=2></FONT></SPAN> </DIV>
> <DIV><FONT color=#0000ff size=2>If a product has a 4A rated input current
> (120V
> AC), how does one</FONT></DIV>
> <DIV><FONT color=#0000ff size=2>determine the rating of <SPAN
> class=990194017-13051999><FONT color=#0000ff face=Arial
> size=2>the</FONT></SPAN>
> in-line Fuse for safety<SPAN class=990194017-13051999><FONT color=#0000ff
> face=Arial size=2>/</FONT></SPAN><SPAN class=990194017-13051999><FONT
> color=#0000ff face=Arial size=2>Fault testing</FONT></SPAN>?</FONT></DIV>
> <DIV><FONT color=#0000ff size=2> </FONT></DIV>
> <DIV><FONT color=#0000ff size=2>The Fuse will be used at the AC connector
> Inlet,
> inside the product (not</FONT></DIV>
> <DIV><FONT color=#0000ff size=2>user accessible) on the Hot lead
> wire.
> <SPAN class=990194017-13051999><FONT color=#0000ff face=Arial size=2>I do
> know
> that i</FONT></SPAN>t will be an in-line type fuse</FONT></DIV>
> <DIV><FONT color=#0000ff size=2>holder<SPAN class=990194017-13051999><FONT
> color=#0000ff face=Arial size=2>, UL and CSA approved,
> 5X20</FONT></SPAN>.</FONT></DIV>
> <DIV><FONT color=#0000ff size=2></FONT> </DIV>
> <DIV><SPAN class=990194017-13051999><FONT color=#0000ff face=Arial
> size=2>We
> test to UL6500 and IEC 60065.</FONT></SPAN></DIV>
> <DIV><FONT color=#0000ff size=2></FONT></FONT><FONT color=#0000ff
> size=2></FONT> </DIV></DIV><FONT color=#0000ff size=2></FONT>
> <DIV><FONT color=#0000ff size=2>Best Regards, <BR>Rick </FONT></DIV>
> <DIV> </DIV></BODY></HTML>
>
> ------_=_NextPart_001_01BE9D6D.739BAE72--
>
> ---------
> This message is coming from the emc-pstc discussion list.
> To cancel your subscription, send mail to [email protected]
> with the single line: "unsubscribe emc-pstc" (without the
> quotes). For help, send mail to [email protected],
> [email protected], [email protected], or
> [email protected] (the list administrators).
>
>
>
---------
This message is coming from the emc-pstc discussion list.
To cancel your subscription, send mail to [email protected]
with the single line: "unsubscribe emc-pstc" (without the
quotes). For help, send mail to [email protected],
[email protected], [email protected], or
[email protected] (the list administrators).
