RE: [AMRadio] High Voltage Power Supplies
Hi Eddy, The first thing I would do is get rid of those resistors and capacitors across the diodes! They can cause more problems than they cure. Especially if the resistors are carbon type. They change values tremendously. But if you want to still use old vintage diodes you should have resistors and capacitors across them. But use film resistors rather than carbon. I would put in all new diodes like 1n4007 or 1n5408, s. With modern diodes you should not put any resistors or capacitors across them. They can upset the reverse current balance in the diode string and actually cause failure. If you can use a bridge instead of a full wave circuit you will also have fewer problems with transients. With a bridge circuit there can be no reverse transients across the diodes as the large filter capacitors are always across the diodes. 73 Gary K4FMX > -Original Message- > From: [EMAIL PROTECTED] [mailto:amradio- > [EMAIL PROTECTED] On Behalf Of Ed Swynar > Sent: Sunday, October 30, 2005 10:07 AM > To: Discussion of AM Radio > Subject: Re: [AMRadio] High Voltage Power Supplies > > Hi Jim, > > Many thanks for all the info! > > Well, mine is the "classic" late 70's era string of 7 diodes per leg, each > paralleled with a resistor / disk capacitor combo. The transformer is, > indeed, centre-tapped, & the design is full-wave rectification, the output > of which goes directly to a series of "parallel resistor-equalized" > high-voltage electrolytics. > > The transformer itself is a classic --- an old Fred Hammond job, with a > cast > iron(!) frame! The thing weighs-in at a "mere" 90 pounds! I got it surplus > NOS from an old surplus house in Montreal some 30 years ago now... > > I took a suggestion of Bry's, Jiim, & placed an RCA plug-in type surge / > transient suppressor that I happened to have available between the p.s. & > the AC outlet --- that is one thing that I'd never done before. If / when > the supply fails again in future, I'll most likely "upgrade" the silicone > string with some of the newer, more robust chunks of silicone that were > simply unavailable 30-odd years ago... > > ~73!~ Eddy VE3CUI - VE3XZ > > > > > ----- Original Message - > From: "Jim Candela" <[EMAIL PROTECTED]> > To: "Discussion of AM Radio" ; > <[EMAIL PROTECTED]> > Sent: Sunday, October 30, 2005 9:42 AM > Subject: Re: [AMRadio] High Voltage Power Supplies > > > > Eddy, > > > > It might be helpful if you describe that power > > supply topology. Is it full wave with transformer > > center tap, full wave bridge, and is the filter a pi > > type, choke input filter, etc. If this is an option > > for you, make a sketch, and scan it into a JPEG file, > > and upload it to the net soemwhere. I have net space > > if you email it to me. This way we can all look at > > your schematic, and comment better without guessing. > > > >In general diodes fail from two transient factors. > > The first is current surge, and the second is > > avalanche reverse voltage breakdown. Since you added a > > step/start circuit already, the current surge issue > > should be contained. That leaves reverse breakdown. As > > Brian mentioned, a transformer primary varistor (like > > V130LA10A, for 115 volts, or V250LA10A, for 220 volts) > > might help from power line transients. > > > > If you look at the Bill Orr handbooks around 1970, > > Bill goes into detail describing diode failure modes, > > and ways to protect them. This includes a custom > > series R-C across the transformer secondary, and > > across the filter choke (if choke input). Today's > > diodes are tougher, and this precaution is often > > unnecessary so long as good diodes are used, and the > > diode PIV rating is at least 2X what the formulas > > state you need. However diodes like the 1N4007 (1A 100 > > PIV) need protection, whereas diodes like the 1N5408 > > (3A 100 PIV) are a lot more rugged. In researching > > diodes, look for the term "controlled avalanche". > > These are the best because they can take repetitive > > PIV spikes beyond rating without turning into a piece > > of wire. The 1N4001 to 1N4007 series are not in this > > catagory. Unfortunately the data sheets sometimes omit > > the "controlled avalanche" term. > > > > Regards, > > Jim Candela > > WD5JKO > > > > --- Ed Swynar <[EMAIL PROTECTED]> wrote: > > > > > 'Morning All, > > > > > > I'm curious as to why I have to replace the silicon > >
Re: [AMRadio] High Voltage Power Supplies - varistors
Brian, Littlefuse has a whole line of varistors. Go to www.mouser.com, and enter the following part numbers: v130LA10a v130LA20a v250LA20a The 10, or 20 in the p/n specifies the diameter in mm for the part. The 130 or 250 is for the rated RMS voltage the varistor is designed to protect. The larger diameter has higher Joule capability. Look at the data sheets relating clamping voltage versus current through the device. These items offer some protection for your equipment, BUT these are only one component towards protecting your equipment from power line transients. They are intended to suppress the once in a while transient, and are not intended to be working repetively since they will warm up, and eventually be another toasted charcoal brick. Other things to consider are ferrite beads, common mode transformers, feed through capacitors, bypass capacitors, etc. Most if not all of these items are used on computer power supplies where the input 120 vac is converted to DC. Sometimes you can "saws-all" the filter off a computer power supply, and use that for protecting ham gear of similar power ratings (< 250 watts). Jim --- [EMAIL PROTECTED] wrote: > Noit sure Don - a fellow ham traded these to me. > They are black disks and look pretty much like a > large > ceramic capacitor, if you can imagine... > > They are marked: > STM and CL-30 > > I think the resistance at rest is about 3 to 5 ohms. > > On 30 Oct 2005 at 9:24, Rev. Don Sanders wrote: > > > OK Bry, You got my interest. What is the part > number and are they from > > Mouser? I know I need several for my boatanchors > and my 2 Astrons(20 and 35 > > amp). > > > > Healthfully yours, > > DON W4BWS > > - Original Message - > > From: <[EMAIL PROTECTED]> > > To: "Discussion of AM Radio" > > > Sent: Sunday, October 30, 2005 7:27 AM > > Subject: Re: [AMRadio] High Voltage Power Supplies > > > > > > > On 30 Oct 2005 at 9:08, Ed Swynar wrote: > > > > > > > Is this the reult of transients / voltage > spikes somehow "overwhelming" > > > > the diodes...? > > > > > > Probably - why not try one of those transient > suppressors (varistor I > > think) > > > on the primary side of your power tranny? > > > I just put one in my Astron 35M and it > eliminated the "THUNK!" > > > at power-on. > > > > > > A number of guys have put them into Johnson > xmtrs with similar > > improvement. > > > Maybe it could save your diode strings. > > > > > > Do you have a capacitor-input filter on the > p.s.u.? > > > Choke input filters tend to be a bit kinder to > the rectifiers. > > > > > > 73 de AF4K, Bry > > > > > > > __ > > > AMRadio mailing list > > > Home: > http://mailman.qth.net/mailman/listinfo/amradio > > > Help: http://mailman.qth.net/mmfaq.html > > > Post: mailto:AMRadio@mailman.qth.net > > > AMfone Website: http://www.amfone.net > > > AM List Admin: Brian Sherrod/w5ami > > > > > > > > > > __ > > AMRadio mailing list > > Home: > http://mailman.qth.net/mailman/listinfo/amradio > > Help: http://mailman.qth.net/mmfaq.html > > Post: mailto:AMRadio@mailman.qth.net > > AMfone Website: http://www.amfone.net > > AM List Admin: Brian Sherrod/w5ami > > > __ > AMRadio mailing list > Home: > http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net > AMfone Website: http://www.amfone.net > AM List Admin: Brian Sherrod/w5ami >
Re: [AMRadio] High Voltage Power Supplies
They tell me that with some of the newer diodes you don't need all of those equalizer resistors and caps. Back in the 1970s I regularly ran a pair of 4-400As at about 2.8 to 3.2 KV. The diode strings consisted of eight per leg, rated for 1000V p.i.v. at 2.5 A - and I think they blew out about every three months or so! I guess the other gentleman was probably about right with his suggestion of a 10 KV rating for the string! On 30 Oct 2005 at 11:07, Ed Swynar wrote: > Hi Jim, > > Many thanks for all the info! > > Well, mine is the "classic" late 70's era string of 7 diodes per leg, each > paralleled with a resistor / disk capacitor combo. The transformer is, > indeed, centre-tapped, & the design is full-wave rectification, the output > of which goes directly to a series of "parallel resistor-equalized" > high-voltage electrolytics. > > The transformer itself is a classic --- an old Fred Hammond job, with a cast > iron(!) frame! The thing weighs-in at a "mere" 90 pounds! I got it surplus > NOS from an old surplus house in Montreal some 30 years ago now... > > I took a suggestion of Bry's, Jiim, & placed an RCA plug-in type surge / > transient suppressor that I happened to have available between the p.s. & > the AC outlet --- that is one thing that I'd never done before. If / when > the supply fails again in future, I'll most likely "upgrade" the silicone > string with some of the newer, more robust chunks of silicone that were > simply unavailable 30-odd years ago... > > ~73!~ Eddy VE3CUI - VE3XZ > > > > > - Original Message ----- > From: "Jim Candela" <[EMAIL PROTECTED]> > To: "Discussion of AM Radio" ; > <[EMAIL PROTECTED]> > Sent: Sunday, October 30, 2005 9:42 AM > Subject: Re: [AMRadio] High Voltage Power Supplies > > > > Eddy, > > > > It might be helpful if you describe that power > > supply topology. Is it full wave with transformer > > center tap, full wave bridge, and is the filter a pi > > type, choke input filter, etc. If this is an option > > for you, make a sketch, and scan it into a JPEG file, > > and upload it to the net soemwhere. I have net space > > if you email it to me. This way we can all look at > > your schematic, and comment better without guessing. > > > >In general diodes fail from two transient factors. > > The first is current surge, and the second is > > avalanche reverse voltage breakdown. Since you added a > > step/start circuit already, the current surge issue > > should be contained. That leaves reverse breakdown. As > > Brian mentioned, a transformer primary varistor (like > > V130LA10A, for 115 volts, or V250LA10A, for 220 volts) > > might help from power line transients. > > > > If you look at the Bill Orr handbooks around 1970, > > Bill goes into detail describing diode failure modes, > > and ways to protect them. This includes a custom > > series R-C across the transformer secondary, and > > across the filter choke (if choke input). Today's > > diodes are tougher, and this precaution is often > > unnecessary so long as good diodes are used, and the > > diode PIV rating is at least 2X what the formulas > > state you need. However diodes like the 1N4007 (1A 100 > > PIV) need protection, whereas diodes like the 1N5408 > > (3A 100 PIV) are a lot more rugged. In researching > > diodes, look for the term "controlled avalanche". > > These are the best because they can take repetitive > > PIV spikes beyond rating without turning into a piece > > of wire. The 1N4001 to 1N4007 series are not in this > > catagory. Unfortunately the data sheets sometimes omit > > the "controlled avalanche" term. > > > > Regards, > > Jim Candela > > WD5JKO > > > > --- Ed Swynar <[EMAIL PROTECTED]> wrote: > > > > > 'Morning All, > > > > > > I'm curious as to why I have to replace the silicon > > > diode strings in my 2500 VDC power supply about > > > every 8-10 years, or so...I just went through the > > > exercise again early this morning --- turned on the > > > B+ to my 2 x 813 linear, & got nothing back for my > > > trouble but smoke from inside the enclosed p.s. > > > unit... > > > > > > Opened it up, & the resistor across the relay in my > > > time delay circuit --- transformer primary side --- > > > was fried. I checked the conductivity of both legs > > > of my diode string (it's a full-wave set-up), & sure
Re: [AMRadio] High Voltage Power Supplies
Noit sure Don - a fellow ham traded these to me. They are black disks and look pretty much like a large ceramic capacitor, if you can imagine... They are marked: STM and CL-30 I think the resistance at rest is about 3 to 5 ohms. On 30 Oct 2005 at 9:24, Rev. Don Sanders wrote: > OK Bry, You got my interest. What is the part number and are they from > Mouser? I know I need several for my boatanchors and my 2 Astrons(20 and 35 > amp). > > Healthfully yours, > DON W4BWS > - Original Message - > From: <[EMAIL PROTECTED]> > To: "Discussion of AM Radio" > Sent: Sunday, October 30, 2005 7:27 AM > Subject: Re: [AMRadio] High Voltage Power Supplies > > > > On 30 Oct 2005 at 9:08, Ed Swynar wrote: > > > > > Is this the reult of transients / voltage spikes somehow "overwhelming" > > > the diodes...? > > > > Probably - why not try one of those transient suppressors (varistor I > think) > > on the primary side of your power tranny? > > I just put one in my Astron 35M and it eliminated the "THUNK!" > > at power-on. > > > > A number of guys have put them into Johnson xmtrs with similar > improvement. > > Maybe it could save your diode strings. > > > > Do you have a capacitor-input filter on the p.s.u.? > > Choke input filters tend to be a bit kinder to the rectifiers. > > > > 73 de AF4K, Bry > > > > __ > > AMRadio mailing list > > Home: http://mailman.qth.net/mailman/listinfo/amradio > > Help: http://mailman.qth.net/mmfaq.html > > Post: mailto:AMRadio@mailman.qth.net > > AMfone Website: http://www.amfone.net > > AM List Admin: Brian Sherrod/w5ami > > > > > __ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net > AMfone Website: http://www.amfone.net > AM List Admin: Brian Sherrod/w5ami
Re: [AMRadio] High Voltage Power Supplies
Maybe you need a higher PIV rating for your diodes. Should be at least 10 kv. 73, Ed Richards, K6UUZ Simi Valley, California, 93065 Home of Air Force 1 Pavilion On Sun, 30 Oct 2005 09:08:11 -0500 "Ed Swynar" <[EMAIL PROTECTED]> writes: > 'Morning All, > > I'm curious as to why I have to replace the silicon diode strings in > my 2500 VDC power supply about every 8-10 years, or so...I just went > through the exercise again early this morning --- turned on the B+ > to my 2 x 813 linear, & got nothing back for my trouble but smoke > from inside the enclosed p.s. unit... > > Opened it up, & the resistor across the relay in my time delay > circuit --- transformer primary side --- was fried. I checked the > conductivity of both legs of my diode string (it's a full-wave > set-up), & sure enough, one leg was A-OK, but the other displayed > conductivity on BOTH sides of each diode...not good. > > Is this the reult of transients / voltage spikes somehow > "overwhelming" the diodes...? > > It used to be more frequent prior to the incorporation of the delay > circuitry --- but, despite its presence, this HAS to be at least the > second time that a re-build was in order. > > Any thoughts re. a dose(s) of possible "preventative maintenance" > for the future...? I'm at a loss as to anything else here that I > might try... > > Thanks in advance... > > ~73!~ Eddy VE3CUI - VE3XZ > > __ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net > AMfone Website: http://www.amfone.net > AM List Admin: Brian Sherrod/w5ami > >
Re: [AMRadio] High Voltage Power Supplies
Typo, Those diodes I mentioned are both 1000 volts PIV. I incorrectly stated 100 volts. 1N5408 Data sheets: http://www.datasheetcatalog.com/datasheets_pdf/1/N/5/4/1N5408.shtml 1N4007 data Sheets: http://www.datasheetcatalog.com/datasheets_pdf/1/N/4/0/1N4007.shtml Article about reverse breakdown voltage in a diode: http://www.voltagemultipliers.com/html/bvr.html excerpt from above: " In the past, the term controlled avalanche diodes referred to those diodes that had "sharp" breakdown characteristics and which would survive over-voltage with controlled reverse current. The term non-controlled avalanche diodes typically referred to those diodes that had very high reverse currents at considerably lower voltages than the breakdown voltages. This high reverse current leads to overheating and very round breakdown curves. Rectifiers are generally subjected to a peak inverse voltage (PIV) test to identify their breakdown characteristics. This test is performed by applying 60-hertz half-wave reverse voltage of sufficient amplitude to initiate breakdown. During the test, the reverse current is usually limited to 50µA. The resulting waveform is observed on an oscilloscope to determine the sharpness of the "knee" at the point of breakdown. Both planar and deep-diffusion processes yield controlled avalanches under PIV test conditions." --- Jim Candela <[EMAIL PROTECTED]> wrote: > Eddy, > > It might be helpful if you describe that power > supply topology. Is it full wave with transformer > center tap, full wave bridge, and is the filter a pi > type, choke input filter, etc. If this is an option > for you, make a sketch, and scan it into a JPEG > file, > and upload it to the net soemwhere. I have net space > if you email it to me. This way we can all look at > your schematic, and comment better without guessing. > >In general diodes fail from two transient > factors. > The first is current surge, and the second is > avalanche reverse voltage breakdown. Since you added > a > step/start circuit already, the current surge issue > should be contained. That leaves reverse breakdown. > As > Brian mentioned, a transformer primary varistor > (like > V130LA10A, for 115 volts, or V250LA10A, for 220 > volts) > might help from power line transients. > > If you look at the Bill Orr handbooks around > 1970, > Bill goes into detail describing diode failure > modes, > and ways to protect them. This includes a custom > series R-C across the transformer secondary, and > across the filter choke (if choke input). Today's > diodes are tougher, and this precaution is often > unnecessary so long as good diodes are used, and the > diode PIV rating is at least 2X what the formulas > state you need. However diodes like the 1N4007 (1A > 100 > PIV) need protection, whereas diodes like the 1N5408 > (3A 100 PIV) are a lot more rugged. In researching > diodes, look for the term "controlled avalanche". > These are the best because they can take repetitive > PIV spikes beyond rating without turning into a > piece > of wire. The 1N4001 to 1N4007 series are not in this > catagory. Unfortunately the data sheets sometimes > omit > the "controlled avalanche" term. > > Regards, > Jim Candela > WD5JKO > > --- Ed Swynar <[EMAIL PROTECTED]> wrote: > > > 'Morning All, > > > > I'm curious as to why I have to replace the > silicon > > diode strings in my 2500 VDC power supply about > > every 8-10 years, or so...I just went through the > > exercise again early this morning --- turned on > the > > B+ to my 2 x 813 linear, & got nothing back for my > > trouble but smoke from inside the enclosed p.s. > > unit... > > > > Opened it up, & the resistor across the relay in > my > > time delay circuit --- transformer primary side > --- > > was fried. I checked the conductivity of both legs > > of my diode string (it's a full-wave set-up), & > sure > > enough, one leg was A-OK, but the other displayed > > conductivity on BOTH sides of each diode...not > good. > > > > Is this the reult of transients / voltage spikes > > somehow "overwhelming" the diodes...? > > > > It used to be more frequent prior to the > > incorporation of the delay circuitry --- but, > > despite its presence, this HAS to be at least the > > second time that a re-build was in order. > > > > Any thoughts re. a dose(s) of possible > "preventative > > maintenance" for the future...? I'm at a loss as > to > > anything else here that I might try... > > > > Thanks in advance... > > > > ~73!~ Eddy VE3CUI - VE3XZ > > > > > __ > > AMRadio mailing list > > Home: > > http://mailman.qth.net/mailman/listinfo/amradio > > Help: http://mailman.qth.net/mmfaq.html > > Post: mailto:AMRadio@mailman.qth.net > > AMfone Website: http://www.amfone.net > > AM List Admin: Brian Sherrod/w5ami > > > > __ > AMRadio mailing list > Home: > http://mailman.qth.net/mailman/listinfo/amr
Re: [AMRadio] High Voltage Power Supplies
OK Bry, You got my interest. What is the part number and are they from Mouser? I know I need several for my boatanchors and my 2 Astrons(20 and 35 amp). Healthfully yours, DON W4BWS - Original Message - From: <[EMAIL PROTECTED]> To: "Discussion of AM Radio" Sent: Sunday, October 30, 2005 7:27 AM Subject: Re: [AMRadio] High Voltage Power Supplies > On 30 Oct 2005 at 9:08, Ed Swynar wrote: > > > Is this the reult of transients / voltage spikes somehow "overwhelming" > > the diodes...? > > Probably - why not try one of those transient suppressors (varistor I think) > on the primary side of your power tranny? > I just put one in my Astron 35M and it eliminated the "THUNK!" > at power-on. > > A number of guys have put them into Johnson xmtrs with similar improvement. > Maybe it could save your diode strings. > > Do you have a capacitor-input filter on the p.s.u.? > Choke input filters tend to be a bit kinder to the rectifiers. > > 73 de AF4K, Bry > > __ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net > AMfone Website: http://www.amfone.net > AM List Admin: Brian Sherrod/w5ami >
Re: [AMRadio] High Voltage Power Supplies
Ed Swynar wrote: Hi Jim, Many thanks for all the info! Well, mine is the "classic" late 70's era string of 7 diodes per leg, each paralleled with a resistor / disk capacitor combo. The transformer is, indeed, centre-tapped, & the design is full-wave rectification, the output of which goes directly to a series of "parallel resistor-equalized" high-voltage electrolytics. The transformer itself is a classic --- an old Fred Hammond job, with a cast iron(!) frame! The thing weighs-in at a "mere" 90 pounds! I got it surplus NOS from an old surplus house in Montreal some 30 years ago now... I took a suggestion of Bry's, Jiim, & placed an RCA plug-in type surge / transient suppressor that I happened to have available between the p.s. & the AC outlet --- that is one thing that I'd never done before. If / when the supply fails again in future, I'll most likely "upgrade" the silicone string with some of the newer, more robust chunks of silicone that were simply unavailable 30-odd years ago... Simply because I like tubes, I'll make this suggestion... 3B28's are -much- more forgiving as far as transients. 866's are too, but they tend to generate some noise in the reciever. I've never noticed it, but then again I mostly operate 40 and 75m and any background noise would cover up the little noise that might be generated by the mercury vapor rectifiers. I'm fixing to start on a choke input power supply here, that will incorporate a pair of 872A's, a 3.2kV (@ 2.5kVA) plate transformer, a couple of 4henry chokes @ 500mA and some 18uf of capacitance, @ 4kVDC. I'll control the primary voltage of that transformer with a vari-ac. --- 73 = Best Regards, -Geoff/W5OMR
Re: [AMRadio] High Voltage Power Supplies
Hi Jim, Many thanks for all the info! Well, mine is the "classic" late 70's era string of 7 diodes per leg, each paralleled with a resistor / disk capacitor combo. The transformer is, indeed, centre-tapped, & the design is full-wave rectification, the output of which goes directly to a series of "parallel resistor-equalized" high-voltage electrolytics. The transformer itself is a classic --- an old Fred Hammond job, with a cast iron(!) frame! The thing weighs-in at a "mere" 90 pounds! I got it surplus NOS from an old surplus house in Montreal some 30 years ago now... I took a suggestion of Bry's, Jiim, & placed an RCA plug-in type surge / transient suppressor that I happened to have available between the p.s. & the AC outlet --- that is one thing that I'd never done before. If / when the supply fails again in future, I'll most likely "upgrade" the silicone string with some of the newer, more robust chunks of silicone that were simply unavailable 30-odd years ago... ~73!~ Eddy VE3CUI - VE3XZ - Original Message - From: "Jim Candela" <[EMAIL PROTECTED]> To: "Discussion of AM Radio" ; <[EMAIL PROTECTED]> Sent: Sunday, October 30, 2005 9:42 AM Subject: Re: [AMRadio] High Voltage Power Supplies > Eddy, > > It might be helpful if you describe that power > supply topology. Is it full wave with transformer > center tap, full wave bridge, and is the filter a pi > type, choke input filter, etc. If this is an option > for you, make a sketch, and scan it into a JPEG file, > and upload it to the net soemwhere. I have net space > if you email it to me. This way we can all look at > your schematic, and comment better without guessing. > >In general diodes fail from two transient factors. > The first is current surge, and the second is > avalanche reverse voltage breakdown. Since you added a > step/start circuit already, the current surge issue > should be contained. That leaves reverse breakdown. As > Brian mentioned, a transformer primary varistor (like > V130LA10A, for 115 volts, or V250LA10A, for 220 volts) > might help from power line transients. > > If you look at the Bill Orr handbooks around 1970, > Bill goes into detail describing diode failure modes, > and ways to protect them. This includes a custom > series R-C across the transformer secondary, and > across the filter choke (if choke input). Today's > diodes are tougher, and this precaution is often > unnecessary so long as good diodes are used, and the > diode PIV rating is at least 2X what the formulas > state you need. However diodes like the 1N4007 (1A 100 > PIV) need protection, whereas diodes like the 1N5408 > (3A 100 PIV) are a lot more rugged. In researching > diodes, look for the term "controlled avalanche". > These are the best because they can take repetitive > PIV spikes beyond rating without turning into a piece > of wire. The 1N4001 to 1N4007 series are not in this > catagory. Unfortunately the data sheets sometimes omit > the "controlled avalanche" term. > > Regards, > Jim Candela > WD5JKO > > --- Ed Swynar <[EMAIL PROTECTED]> wrote: > > > 'Morning All, > > > > I'm curious as to why I have to replace the silicon > > diode strings in my 2500 VDC power supply about > > every 8-10 years, or so...I just went through the > > exercise again early this morning --- turned on the > > B+ to my 2 x 813 linear, & got nothing back for my > > trouble but smoke from inside the enclosed p.s. > > unit... > > > > Opened it up, & the resistor across the relay in my > > time delay circuit --- transformer primary side --- > > was fried. I checked the conductivity of both legs > > of my diode string (it's a full-wave set-up), & sure > > enough, one leg was A-OK, but the other displayed > > conductivity on BOTH sides of each diode...not good. > > > > Is this the reult of transients / voltage spikes > > somehow "overwhelming" the diodes...? > > > > It used to be more frequent prior to the > > incorporation of the delay circuitry --- but, > > despite its presence, this HAS to be at least the > > second time that a re-build was in order. > > > > Any thoughts re. a dose(s) of possible "preventative > > maintenance" for the future...? I'm at a loss as to > > anything else here that I might try... > > > > Thanks in advance... > > > > ~73!~ Eddy VE3CUI - VE3XZ > > > > > __ > > AMRadio mailing list > > Home: > > http://mailman.qth.net/mailman/listinfo/amradio > > Help: http://mailman.qth.net/mmfaq.html > > Post: mailto:AMRadio@mailman.qth.net > > AMfone Website: http://www.amfone.net > > AM List Admin: Brian Sherrod/w5ami > > > > __ > AMRadio mailing list > Home: http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net > AMfone Website: http://www.amfone.net > AM List Admin: Brian Sherrod/w5ami >
Re: [AMRadio] High Voltage Power Supplies
Eddy, It might be helpful if you describe that power supply topology. Is it full wave with transformer center tap, full wave bridge, and is the filter a pi type, choke input filter, etc. If this is an option for you, make a sketch, and scan it into a JPEG file, and upload it to the net soemwhere. I have net space if you email it to me. This way we can all look at your schematic, and comment better without guessing. In general diodes fail from two transient factors. The first is current surge, and the second is avalanche reverse voltage breakdown. Since you added a step/start circuit already, the current surge issue should be contained. That leaves reverse breakdown. As Brian mentioned, a transformer primary varistor (like V130LA10A, for 115 volts, or V250LA10A, for 220 volts) might help from power line transients. If you look at the Bill Orr handbooks around 1970, Bill goes into detail describing diode failure modes, and ways to protect them. This includes a custom series R-C across the transformer secondary, and across the filter choke (if choke input). Today's diodes are tougher, and this precaution is often unnecessary so long as good diodes are used, and the diode PIV rating is at least 2X what the formulas state you need. However diodes like the 1N4007 (1A 100 PIV) need protection, whereas diodes like the 1N5408 (3A 100 PIV) are a lot more rugged. In researching diodes, look for the term "controlled avalanche". These are the best because they can take repetitive PIV spikes beyond rating without turning into a piece of wire. The 1N4001 to 1N4007 series are not in this catagory. Unfortunately the data sheets sometimes omit the "controlled avalanche" term. Regards, Jim Candela WD5JKO --- Ed Swynar <[EMAIL PROTECTED]> wrote: > 'Morning All, > > I'm curious as to why I have to replace the silicon > diode strings in my 2500 VDC power supply about > every 8-10 years, or so...I just went through the > exercise again early this morning --- turned on the > B+ to my 2 x 813 linear, & got nothing back for my > trouble but smoke from inside the enclosed p.s. > unit... > > Opened it up, & the resistor across the relay in my > time delay circuit --- transformer primary side --- > was fried. I checked the conductivity of both legs > of my diode string (it's a full-wave set-up), & sure > enough, one leg was A-OK, but the other displayed > conductivity on BOTH sides of each diode...not good. > > Is this the reult of transients / voltage spikes > somehow "overwhelming" the diodes...? > > It used to be more frequent prior to the > incorporation of the delay circuitry --- but, > despite its presence, this HAS to be at least the > second time that a re-build was in order. > > Any thoughts re. a dose(s) of possible "preventative > maintenance" for the future...? I'm at a loss as to > anything else here that I might try... > > Thanks in advance... > > ~73!~ Eddy VE3CUI - VE3XZ > > __ > AMRadio mailing list > Home: > http://mailman.qth.net/mailman/listinfo/amradio > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net > AMfone Website: http://www.amfone.net > AM List Admin: Brian Sherrod/w5ami >
Re: [AMRadio] High Voltage Power Supplies
On 30 Oct 2005 at 9:08, Ed Swynar wrote: > Is this the reult of transients / voltage spikes somehow "overwhelming" > the diodes...? Probably - why not try one of those transient suppressors (varistor I think) on the primary side of your power tranny? I just put one in my Astron 35M and it eliminated the "THUNK!" at power-on. A number of guys have put them into Johnson xmtrs with similar improvement. Maybe it could save your diode strings. Do you have a capacitor-input filter on the p.s.u.? Choke input filters tend to be a bit kinder to the rectifiers. 73 de AF4K, Bry
