Return-Path: Received: from mtain-ma10.r1000.mx.aol.com (mtain-ma10.r1000.mx.aol.com [172.29.96.18]) by air-da04.mail.aol.com (v129.4) with ESMTP id MAILINDA043-863c4d2b27ab364; Mon, 10 Jan 2011 10:37:15 -0500 Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by mtain-ma10.r1000.mx.aol.com (Internet Inbound) with ESMTP id 3343A3800009A; Mon, 10 Jan 2011 10:37:12 -0500 (EST) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1PcJnO-0003Uj-5y for rs_out_1@blacksheep.org; Mon, 10 Jan 2011 15:36:34 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1PcJnN-0003UV-GA for rsgb_lf_group@blacksheep.org; Mon, 10 Jan 2011 15:36:33 +0000 Received: from cavuit02.kulnet.kuleuven.be ([134.58.240.44]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1PcJnL-0000mf-Pu for rsgb_lf_group@blacksheep.org; Mon, 10 Jan 2011 15:36:33 +0000 Received: from smtps02.kuleuven.be (smtpshost02.kulnet.kuleuven.be [134.58.240.75]) by cavuit02.kulnet.kuleuven.be (Postfix) with ESMTP id 2E7EE75A032 for ; Mon, 10 Jan 2011 16:36:19 +0100 (CET) Received: from ICTS-S-HUB-N1.luna.kuleuven.be (icts-s-hub-n1.luna.kuleuven.be [10.112.9.11]) by smtps02.kuleuven.be (Postfix) with ESMTP id 156F0F3862 for ; Mon, 10 Jan 2011 16:36:19 +0100 (CET) Received: from ICTS-S-EXC2-CA.luna.kuleuven.be ([10.112.11.13]) by ICTS-S-HUB-N1.luna.kuleuven.be ([10.112.9.11]) with mapi; Mon, 10 Jan 2011 16:36:19 +0100 X-Kuleuven: This mail passed the K.U.Leuven mailcluster From: Rik Strobbe To: "rsgb_lf_group@blacksheep.org" Date: Mon, 10 Jan 2011 16:32:29 +0100 Thread-Topic: Capacitor warning and First 500kHz Class E breadboard Thread-Index: Acuw0j0cFDF7akHhRUa9DVazaQQeNAACVpvZ Message-ID: References: In-Reply-To: Accept-Language: nl-NL, nl-BE Content-Language: nl-BE X-MS-Has-Attach: X-MS-TNEF-Correlator: acceptlanguage: nl-NL, nl-BE MIME-Version: 1.0 X-KULeuven-Information: Katholieke Universiteit Leuven X-KULeuven-Scanned: Found to be clean X-KULeuven-Envelope-From: rik.strobbe@fys.kuleuven.be X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001 Subject: LF: RE: Capacitor warning and First 500kHz Class E breadboard Content-Type: multipart/alternative; boundary="_000_BF4A524700075746A6467658DFC7102C88715AEA30ICTSSEXC2CAlu_" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.0 required=5.0 tests=HTML_MESSAGE, TO_ADDRESS_EQ_REAL autolearn=no version=2.63 X-SA-Exim-Scanned: Yes Sender: owner-rsgb_lf_group@blacksheep.org Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rs_out_1@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false x-aol-global-disposition: G x-aol-sid: 3039ac1d60124d2b27a8307a X-AOL-IP: 195.171.43.25 X-Mailer: Unknown (No Version) --_000_BF4A524700075746A6467658DFC7102C88715AEA30ICTSSEXC2CAlu_ Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Andy, I do use polypropylene capacitors for 137kHz and 500kHz. Farnell has them from 33pF up to several uF Ceramic caps are no good in resonant applications, as you found out. 73, Rik ON7YD ________________________________ Van: owner-rsgb_lf_group@blacksheep.org [owner-rsgb_lf_group@blacksheep.or= g] namens Andy Talbot [andy.g4jnt@gmail.com] Verzonden: maandag 10 januari 2011 15:22 Aan: rsgb_lf_group@blacksheep.org Onderwerp: LF: Capacitor warning and First 500kHz Class E breadboard A warning to anyone contemplating making power amps - especially class E= types. Don't even think about using the small high voltage ceramic caps availalbl= e at low cost from the suppliers - and sold as "suitable for SMPSUs etc"= in resonant circuits They are appalling, terrible, revolting things. You only have to breath= on them and they change their value.wildly These things http://www.g4jnt.com/Download/UselessCaps.jpg I've just made up a first version of a breadboard for a 500kHz Class E am= plifier, (target design 500W from 50 V supply), calculated the L/C values= as per Alan's spreadsheet, combined with an L matched output for 50 ohm.= For the capacitors I aimed to get within 5% of the calculated values usi= ng many of these small ceramic objects in parallel - lots in || should sha= re the current, shouldn't they, which would be good? So I soldered them up - used the G4HUP L/C meter to measure the values -= at which point I should have been a bit suspicious as the measured C was= sometimes a fair bit lower than it should have been. At the time I just= put it down to "finger trouble" - one does tend to ignore little things= like that sometimes. Anyway, made up the amp, used a 12V supply rail and monitored the switchin= g waveforms, expecting to see something vaguely approaching the half sine= on drains etc. Results, terrible, nowhere near what they should have been - clearly summa= t was very wrong I remeasured the || combination of the caps - after unso= ldering they were sometimes as much as half the value they should have bee= n - until they cooled right down and approached room temp. Occasionally= a cap value approaching correct would show up on the meter once in a whil= e - but that was was probably just coincidence :-) And yes, I did double, triple and quadruple check the meter against good= caps - it was OK every time. These little blue things appear to have a huge temperature coefficent - ar= e completely useless, designed to do nothing of value, and all have now go= ne into the waste bin. In fact, I was wondering if they were random-capacitors. I did have a just two trusted 22nF caps in the junk box that were within= 20 - 30% of the right values for the amp and an awful lot of 3.3nF 1700V= things of a more respectable heritage, so just put these into the circuit= , tested at 12V and got waveforms almost correct. Increased drive freq= to 515kHz (no real scope for changing cap values at this stage, so freq= change would be easier to try with) where the waveform looked best, and= increased supply volts. Got to 30V and it was delivering 150 Watts;= 40V and was getting around 350 Watts at which point I assumed it was goin= g to work, so switched off for a break. Wasn't going to tempt fate by go= ng to the full 50V having not even bothered to tune things up properly A picture of that breadboard can be seen at http://www.g4jnt.com/Downloa= d/ClassE_BrdBd01.jpg The yellow cap shunting the device was running quite warm - which is hardl= y surprising just a single poly[whatever] carrying all those amps - and th= e one in series with the tank was slightly warm. So, now need to browse= the Farnell catalogue (the cubic printed paper version is easier) for som= e caps that will do the job properly - like more of those yellow ones. Ac= tually, may have enough of the 3.3nF ones, but that would end up with lots= in parallel So, for anyone who is contemplating a class E amplifier design: Get close to the calculated component values and it will probably mostly-w= ork immediately. Play with the drive frequency while monitoring waveforms to see which way= tuning needs to go Don't use cheap high voltage ceramic capacitors Don't use cheap high voltage ceramic capacitors They would work well in a random number generator tho..... Andy www.g4jnt.com --_000_BF4A524700075746A6467658DFC7102C88715AEA30ICTSSEXC2CAlu_ Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Andy,
 
I do use polypropylene capacitors fo= r 137kHz and 500kHz.
Farnell has them from 33pF up to sev= eral uF
Ceramic caps are no good in resonant= applications, as you found out.
 
73, Rik  ON7YD
 
Van: owner-rsgb_= lf_group@blacksheep.org [owner-rsgb_lf_group@blacksheep.org] namens Andy= Talbot [andy.g4jnt@gmail.com]
Verzonden: maandag 10 januari 2011 15:22
Aan: rsgb_lf_group@blacksheep.org
Onderwerp: LF: Capacitor warning and First 500kHz Class E breadboar= d

A warning to anyone contemplating making power amps - especially clas= s E types.
Don't even think about using the small high voltage ceramic caps avai= lalble at low cost from the suppliers - and sold as "suitable for SMP= SUs etc"  in resonant circuits
They are appalling, terrible, revolting things.  You only have= to breath on them and they change their value.wildly
 
 
I've just  made up a first version of a breadboard for a 500kHz= Class E amplifier, (target design 500W from 50 V supply),  calc= ulated the L/C values as per Alan's spreadsheet, combined with an L= matched output for 50 ohm.  For the capacitors I aimed to get within 5% of the calculated values using many of these small ceramic= objects in parallel - lots in || should share the current, shouldn't= they, which would be good?  
 
So I soldered them up - used the G4HUP L/C meter to measure the value= s - at which point I should have been a bit suspicious as the me= asured C was sometimes a fair bit lower than it should have been.  At= the time I just put it down to "finger trouble" - one does tend to ignore little things like that sometimes.  &nb= sp;
Anyway, made up the amp, used a 12V supply rail and monitored the swi= tching waveforms, expecting to see something vaguely approaching the half= sine on drains etc.
 
Results, terrible, nowhere near what they should have been - clearly= summat was very wrong  I remeasured the || combination of the caps= - after unsoldering they were sometimes as much as half the value th= ey should have been  - until they cooled right down and approached room temp. Occasionally a cap value approaching correct wo= uld show up on the meter once in a while - but that was was= probably just coincidence :-) 
And yes, I did double, triple and quadruple check the meter against= good caps - it was OK every time.
 
These little blue things appear to have a huge temperature coefficent= - are completely useless, designed to do nothing of value, and all have= now gone into the waste bin.
In fact, I was wondering if they were random-capacitors.  <= /div>
 
I did have a just two trusted 22nF caps in the junk box tha= t were within 20 - 30% of the right values for the amp and an awful lot of= 3.3nF 1700V things of a more respectable heritage, so just put these into= the circuit, tested at 12V and got waveforms almost correct.   Increased drive freq to 515kHz (no real scope= for changing cap values at this stage, so freq change would be easier to= try with) where the waveform looked best, and increased supply volts= .      Got to 30V and it was delivering 150 Watts= ; 40V and was getting around 350 Watts at which point I assumed= it was going to work, so switched off for a break.   = Wasn't going to tempt fate by gong to the full 50V having not even bothere= d to tune things up properly
A picture of that breadboard can be seen at   http://www.g4jnt.com/Download/ClassE_BrdBd01.jpg 
 
The yellow cap shunting the device was running quite warm - whic= h is hardly surprising just a single poly[whatever] carrying all those amp= s - and the one in series with the tank was slightly warm.  &nbs= p; So, now need to browse the Farnell catalogue (the cubic printed paper version is easier) for some caps that will do the job= properly - like more of those yellow ones.  Actually, may have enoug= h of the 3.3nF ones, but that would end up with lots in parallel
 
So, for anyone who is contemplating a class E amplifier design:
 
Get close to the calculated component values and it will probably mos= tly-work immediately.
Play with the drive frequency while monitoring waveforms  to see= which way tuning needs to go
Don't use cheap high voltage ceramic capacitors
Don't use cheap high voltage ceramic capacitors
 
They would work well in a random number generator tho.....
 
Andy
 
 
 
--_000_BF4A524700075746A6467658DFC7102C88715AEA30ICTSSEXC2CAlu_--