X-Virus-Scanned: clean according to Sophos on Logan.com X-SpamCatcher-Score: 1 [X] Return-Path: Received: from smtprh01.spirittelecom.com ([165.166.0.77] verified) by logan.com (CommuniGate Pro SMTP 5.1.6) with ESMTPS id 1846227 for flyrotary@lancaironline.net; Sun, 18 Feb 2007 23:28:39 -0500 Received-SPF: pass receiver=logan.com; client-ip=165.166.0.77; envelope-from=jewen@comporium.net X-Report-Abuse-To: abuse@spirittelecom.com X-DKIM: Sendmail DKIM Filter v0.5.2 smtprh01.spirittelecom.com l1J4Ror7003040 DKIM-Signature: a=rsa-sha1; c=relaxed/simple; d=comporium.net; s=spiritmail; t=1171859272; bh=bX+Wdn9vYVch0orEZWFOWEOvHtg=; h=Message-ID:From:To: References:Subject:Date:MIME-Version:Content-Type:X-Priority: X-MSMail-Priority:X-Mailer:X-MIMEOLE:X-Virus-Scanned: X-Virus-Status; b=WK4hpbWrEqyrLDAw6RewiV8TQpOE8ZCkxY8He4GGNV6xLquMA 5fUbIltEpbYuzUHB5IxNV+8usRIED09OYZWKg== Received: from Engineer1 (208-104-87-198.lnhe.2wcm.comporium.net [208.104.87.198] (may be forged)) by smtprh01.spirittelecom.com (8.13.6/8.13.1) with SMTP id l1J4Ror7003040 for ; Mon, 19 Feb 2007 04:27:52 GMT Message-ID: <00cf01c753de$4fa188e0$6805a8c0@cooleygroup.local> From: "Joe Ewen" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: CBs and fuses Date: Sun, 18 Feb 2007 23:27:48 -0500 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_00CC_01C753B4.66A55B40" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.3028 X-MIMEOLE: Produced By Microsoft MimeOLE V6.00.2900.3028 X-Virus-Scanned: ClamAV 0.88/2597/Sun Feb 18 20:30:28 2007 on smtprh01.spirittelecom.com X-Virus-Status: Clean This is a multi-part message in MIME format. ------=_NextPart_000_00CC_01C753B4.66A55B40 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable SNIP have an awfully high holding current; that is, the current to maintain = the device temp to hold it in the tripped state.=20 Per the manufacture's data sheet, they define "hold current: maximum = current device will sustain for 4 hours without tripping in 20C still = air. This is not the current to hold the device in the tripped state. The = current to hold the device in the tripped state can be calculated from = the manufactures value Pd (Power dissipated in tripped state). A 30R 5 = amp has a Pd of 3 W, which would yield about 1/4 amp flow to keep the = device in the tripped state. As far as I can see, PTCs do not have an interrupt rating like a circuit = breaker would. Since there are no mechanical contacts that could fuse = together before the device trips, I am not sure the interrupt rating in = the classic sense is appropriate. The max current the device can handle = is 40A (R30 series), after 40A the device blows all its smoke out and = stops conducting electricity (that is until the device is repacked with = smoke, available from Lucas.) To ensure the devices would work in my = application, I bought one and set up a test across a fully charged 12v = battery. 20+ direct shorts across the battery yielded positive tripping = and no warming of the 20 ga test leads. I feel comfortable that PTCs, properly applied in my application will = work well, but please keep in mind this is just one man's opinion and = anyone else's mileage may vary. Joe ----- Original Message -----=20 From: Wendell Voto=20 To: Rotary motors in aircraft=20 Sent: Sunday, February 18, 2007 10:26 PM Subject: [FlyRotary] Re: CBs and fuses > SNIP > >=20 > > I am curious what PTCs you are using. I used PTCs > > on some circuits. I used=20 > > a Buss ATC form breaker, removed the bimetallic and > > soldered a PTC to the=20 > > frame. Then plugged into a ATC fuseblock. This > > worked well, bit I am=20 > > curious if you found a packaged PTC. > >=20 > > Thanks, > > Joe > >=20 Concerning the PTC devices, I was interested in them and a friend also = building a Cozy wants to use the PTC devices but I am reluctant to say = to use them. If correct, many of the ones Mouser lists that allow high = current (1 - 18 amp) seem to have an awfully high holding current; that = is, the current to maintain the device temp to hold it in the tripped = state. Be careful of the device you choose, it's holding current could = be 50% of the trip value (Littel 30R series for instance). This would = not be good for protecting the wiring. Also, you need to know the max interrupt current. A battery can dump = a lot of current through a fuse before it goes and it must be able to = interrupt that current. A typical 5 amp fuse can flow over 75 amp in a = battery supply situation before it blows. Some fuses might actually weld = together and never interrupt the current when used in a battery powered = situation. I had to do some UL testing on some fuses many years ago and = it would surprise you how much current a small fuse will pass before = blowing. Will your wire take the current that a direct short can = deliver, of course different for each situation, something to think = about even when using breakers. This is why they need to rated for = battery supply use. Wendell ------=_NextPart_000_00CC_01C753B4.66A55B40 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
SNIP
have an awfully high holding current; that = is, the=20 current to maintain the device temp to hold it in the tripped=20 state. 
Per the manufacture's data sheet, they define "hold current: = maximum=20 current device will sustain for 4 hours without tripping in 20C still = air.
This is not the current to hold the = device in the=20 tripped state.  The current to hold the device in the tripped state = can be=20 calculated from the manufactures value Pd (Power dissipated in tripped=20 state).  A 30R 5 amp has a Pd  of 3 W, which would yield about = 1/4 amp=20 flow to keep the device in the tripped state.
 
As far as I can see, PTCs do not have = an interrupt=20 rating like a circuit breaker would.  Since there are no mechanical = contacts that could fuse together before the device trips, I am not sure = the=20 interrupt rating in the classic sense is appropriate.  The max = current the=20 device can handle is 40A (R30 series), after 40A the device blows all = its smoke=20 out and stops conducting electricity (that is until the device is = repacked with=20 smoke, available from Lucas.)  To ensure the devices would work in = my=20 application, I bought one and set up a test across a fully charged 12v=20 battery.  20+ direct shorts across the battery yielded positive = tripping=20 and no warming of the 20 ga test leads.
 
I feel comfortable that PTCs, properly = applied in=20 my application will work well, but please keep in mind this is just one = man's=20 opinion and anyone else's mileage may vary.
 
Joe
 
 
 
----- Original Message -----
From:=20 Wendell = Voto=20
Sent: Sunday, February 18, 2007 = 10:26=20 PM
Subject: [FlyRotary] Re: CBs = and=20 fuses


> SNIP
> >
> > I am curious what PTCs you = are=20 using.  I used PTCs
> > on some circuits. I used =
> > a=20 Buss ATC form breaker, removed the bimetallic and
> > = soldered a PTC=20 to the
> > frame.  Then plugged into a ATC = fuseblock. =20 This
> > worked well, bit I am
> > curious if you = found a=20 packaged PTC.
> >
> > Thanks,
> > = Joe
> >=20
Concerning the PTC devices, I was interested = in them=20 and a friend also building a Cozy wants to use the PTC devices but I = am=20 reluctant to say to use them.  If correct, many of the ones = Mouser lists=20 that allow high current (1 - 18 amp) seem to have an awfully high = holding=20 current; that is, the current to maintain the device temp to hold it = in the=20 tripped state.  Be careful of the device you choose, it's holding = current=20 could be 50% of the trip value (Littel 30R series for instance).  = This=20 would not be good for protecting the wiring.
 
Also, you need to know the max interrupt=20 current.  A battery can dump a lot of current through a fuse = before it=20 goes and it must be able to interrupt that current. A typical 5 amp = fuse=20 can flow over 75 amp in a battery supply situation before it = blows.=20 Some fuses might actually weld together and never interrupt the = current when=20 used in a battery powered situation. I had to do some UL = testing on=20 some fuses many years ago and it would surprise you how much current=20 a small fuse will pass before blowing. Will your wire = take the=20 current that a direct short can deliver, of course different for each=20 situation, something to think about even when using breakers. =20 This is why they need to rated for battery supply = use.
 
Wendell 
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