John and others,
You have to remember though that a potted transformer will run hotter
internally than one which is of standard construction. It works the same as
adding insulation around the oven in you kitchen to keep it from loosing heat,
or around the refrigerator to keep the cold in. There's no way for the heat to
escape in a potted transformer, so you have to use insulation on the wire with
a higher temp. ability than standard wire like Formvar, etc. There is tricks to
dunking the transformer in varnish, one is leaving it in the tank for a good 8
hours allowing it to soak. The next is adding a small vibrator to the tank
which will help expell the air bubbles. The last and best is to vacuum
impregnate the coil with varnish, not potting compound. Then comes a bake
unless your using air dry varnish which they do make especially for
transformer/motor use. The major problem for the Ham is expense. A new potted
transformer will cost at least X2 what a standard construction transformer will
co
st due to the wire type and the vacuum potting process. The only way around it
would be buy a surplus one like the Harris in mention. You have to keep in mind
that the potting is only used to keep out any moisture. To me, a good varnish
dipped transformer is better for amateur use providing it's dipped correctly.
First, it runs cooler, gaining life expectancy, and is cheaper to buy new. If
one is done right, it will last for years. Look at the original transformers
still plugging along in a lot of old equipment. It's all in the design, and the
designer wheather a transformer is any good or not.
You can calculate the temp. rise as you mentioned with a transformer which has
already been built. I forgot about that one. The formula earlier I refered to
was for transformers under design. The other way was to use a thermometer
placing it's wire down in the center of the inner-most winding. Then, while
under load, monitor the temp. rise. After your done, simply slip the wire out
or cut it off if its varnished in place. They'll generally slide out though.
This is only done on the first one out of a run or design. Most of the time
though, it is calculated at design time and comes out pretty close to what it
is. These new point and aim, non-contact thermometers will give a good idea of
what the external temp. is. This can be used to roughly figure what the
internal temp. is by extrapolation.
Best,
Will
To: amps@contesting.com
Subject: [Amps] HV transformer test tspa
Date: Wed, 15 Jun 2005 09:03:54 -0600
>
> I agree with Harold about it being coated. Although I have bought
> plenty of HV transformers (single and three phase) which had only a
> sinple varnish overcoat that are in commercial transmitters
> (numbering in the hundreds of units in field since 1982). I say
> simple, well, probably they had numerous coats, but they were not
> potted solid like would be if they were done in a tank under vacuum.
> Another trick would be to just place the iron into a large polymer or
> steel tank, full of good oil.
>
> I remember a trick from a now retired transformer designer from SNC
> (Oshkosh, WI), which was to measure the copper primary resistance
> cold (use a four wire milliohmeter) then power test it and measure it
> hot. You should be able to calculate the average temperature rise in
> the winding from the delta R of the copper.
>
> The most potted HV transformer I have seen is the plate tranny from a
> Harris RF102 that I got. It looks like a blob of epoxy, with the
> edges of the lams exposed and flying leads coming out of the gunk.
>
> Depending on the insulation, class B, class F, class H, etc, the
> transformer can run very hot without damage. If it is only class B
> for instance, it must be wound with heavier guage wire and use more
> iron to keep the temp rise down. You can read about these ratings in
> any of the big thick Electronics Handbooks, like the one by IEEE.
>
> 73
> John
> K5PRO
>
>
>
>
>
> > Send Amps mailing list submissions to
> > amps@contesting.com
> >
> > To subscribe or unsubscribe via the World Wide Web, visit
> > http://lists.contesting.com/mailman/listinfo/amps
> > or, via email, send a message with subject or body 'help' to
> > amps-request@contesting.com
> >
> > You can reach the person managing the list at
> > amps-owner@contesting.com
> >
> > When replying, please edit your Subject line so it is more specific
> > than "Re: Contents of Amps digest..."
> >
> >
> > Today's Topics:
> >
> > 1. SBE SB1-LA Power out meter (Randy K4QO)
> > 2. questions on my tranformer test (kenw2dtc)
> > 3. Re: questions on my tranformer test (Dr. William J. Schmidt, II)
> > 4. Fw: TRANSFORMER-TEST (Harold B. Mandel)
> > 5. Re: TRANSFORMER-TEST-webpage (kenw2dtc)
> > 6. Re: questions on my tranformer test (kenw2dtc)
> > 7. GS35 QUESTION (ON4IQ)
> > 8. Re: questions on my tranformer test (Steve Thompson)
> > 9. Re: GS35 QUESTION (Ian White GM3SEK)
> >
> >
> > ----------------------------------------------------------------------
> >
> > Message: 1
> > Date: Sun, 12 Jun 2005 12:29:41 -0400
> > From: "Randy K4QO" <k4qo@earthlink.net>
> > Subject: [Amps] SBE SB1-LA Power out meter
> > To: <Amps@contesting.com>
> > Message-ID: <018201c56f6b$ef492820$6401a8c0@randyyf6hns82y>
> > Content-Type: text/plain; charset="iso-8859-1"
> >
> > Anyone out there in Amps-land know of a defunct SBE (SideBand Engineers)
> > model SB1LA linear that might have a working RF Output meter I can obtain
> > from it? (or perhaps the whole thing...)
> >
> > I have a restored SB1-LA in need of the stock meter. I have a generic meter
> > in there now and while its not totally ugly (and it works) it would be nice
> > to put the stock meter in there.
> >
> > Thanks and 73,
> > Randy
> > K4QO
> >
> >
> >
> >
> > ------------------------------
> >
> > Message: 2
> > Date: Sun, 12 Jun 2005 14:39:52 -0400
> > From: "kenw2dtc" <kenw2dtc@comcast.net>
> > Subject: [Amps] questions on my tranformer test
> > To: <amps@contesting.com>
> > Message-ID: <000301c56f7e$1f12dee0$67612744@ken>
> > Content-Type: text/plain; format=flowed; charset="iso-8859-1";
> > reply-type=original
> >
> > Hi,
> > I'm trying to figure out the current rating of a plate transformer. This is
> > my test setup:
> >
> > http://w2dtc.com/2005-0610-transformer-test-page.htm
> >
> > Questions:
> > 1. Is this a valid way to find the secondary current capability?
> > 2. Is the internal temperature of 180 degrees F too high for a transformer
> > under load for 5 hours?
> > 3. Is there a problem running this center tapped beast in a full wave
> > capacitive input configuration?
> >
> > Thanks and 73,
> > Ken W2DTC
> >
> >
> >
> >
> >
> >
> > ------------------------------
> >
> > Message: 3
> > Date: Sun, 12 Jun 2005 14:11:50 -0500
> > From: "Dr. William J. Schmidt, II" <bill@wjschmidt.com>
> > Subject: Re: [Amps] questions on my tranformer test
> > To: "kenw2dtc" <kenw2dtc@comcast.net>, <amps@contesting.com>
> > Message-ID: <00dd01c56f82$a7209850$1600000a@SchmidtNet.local>
> > Content-Type: text/plain; format=flowed; charset="iso-8859-1";
> > reply-type=original
> >
> > I would think that the best way to tell is measure the wire size of the
> > secondary winding. The second best way is measure he cross-sectional area
> > of the transformer, as theoretically it is related to the power capabilities
> > of the steel.... which you can back into current (after accounting for
> > reasonable efficiencies). 180F seems a little warm for a CCS transformer...
> > maybe Will can weigh in here...
> >
> > Sincerely,
> >
> > Dr. William J. Schmidt, II K9HZ
> > Trustee of the North American QRO - Central Division Club - K9ZC
> >
> > Email: bill@wjschmidt.com
> > WebPage: www.wjschmidt.com
> >
> > "If computers get too powerful, we can organize them into a committee; that
> > will do them in." -- Bradley's Bromide
> >
> >
> > ----- Original Message -----
> > From: "kenw2dtc" <kenw2dtc@comcast.net>
> > To: <amps@contesting.com>
> > Sent: Sunday, June 12, 2005 1:39 PM
> > Subject: [Amps] questions on my tranformer test
> >
> >
> >> Hi,
> >> I'm trying to figure out the current rating of a plate transformer. This
> >> is
> >> my test setup:
> >>
> >> http://w2dtc.com/2005-0610-transformer-test-page.htm
> >>
> >> Questions:
> >> 1. Is this a valid way to find the secondary current capability?
> >> 2. Is the internal temperature of 180 degrees F too high for a
> >> transformer
> >> under load for 5 hours?
> >> 3. Is there a problem running this center tapped beast in a full wave
> >> capacitive input configuration?
> >>
> >> Thanks and 73,
> >> Ken W2DTC
> >>
> >>
> >>
> >>
> >> _______________________________________________
> >> Amps mailing list
> >> Amps@contesting.com
> >> http://lists.contesting.com/mailman/listinfo/amps
> >>
> >
> >
> >
> > ------------------------------
> >
> > Message: 4
> > Date: Sun, 12 Jun 2005 15:23:23 -0400
> > From: "Harold B. Mandel" <ka1xo@juno.com>
> > Subject: [Amps] Fw: TRANSFORMER-TEST
> > To: amps@contesting.com
> > Message-ID: <20050612.152329.2444.4.ka1xo@juno.com>
> > Content-Type: text/plain; charset=us-ascii
> >
> >
> > Dear Ken,
> >
> > You did a great job in investigating the transformer!
> >
> > Let's see: My PWD monster that took three tries to get right
> > from Peter is 12" high by 11" wide by 10 inches across, and weighs
> > 167 pounds. It is a "hypersil" object rated at 0 - 1800 - 3000 volts,
> > at 3 amperes CCS.
> >
> > Peter had to do it over and over because he didn't wind a 3 ampere
> > CCS piece and I caught it when it arrived.
> >
> > Since I build monster power supplies I have learned the hard way
> > about component ratings, (almost electrocuting myself last Fall.)
> >
> > The one feature I see on your iron is that the windings are not
> > potted. This means the unit, as it heats and cools, absorbs moisture
> > from the air around it, said moisture settling in the paper laminations
> > and
> > in the wiring. To forestall disaster, I myself pot HV stuff, especially
> > transformers, chokes and coils.
> >
> > I found that the best stuff isn't too expensive: Dolph's Synthite AC-41.
> >
> > It's about 25 dollars a gallon and is made for HV insulation potting, and
> > has
> > the consistency of plain old varnish, but with much better breakdown
> > characteristics. There are several distributors and the stuff is made in
> > Monmouth Junction, New Jersey (732) 329 - 2333. For my 10KV
> > plants I use about 10 layers, either brushing or dipping.
> >
> > The test jig you set up is perfect for doing a preliminary examination.
> > Once you place the transformer into service I would suggest using
> > a mighty fan such as a Tarzan 320CFM, 230vac to move air around
> > the structure.
> >
> >> From your temperature observations I would concur that this is a 2 ampere
> > CCS
> > transformer.
> >
> > However, the acid test will be to actually construct a load bank. Your
> > calculation
> > of 6719.33 vac, after filtering, would yield 6047.40 VDC. (Applying the
> > 0.9 factor).
> >
> > Since the power factor comes out to 12KW using around 3K of resistance, I
> > don't
> > know if you want to invest in a bunch o' resistors to do the test, but
> > let's figure
> > this transformer was made for broadcast use.
> >
> > Two 4-1000A's would need 2 amps at 6KV.
> >
> > You'll not probably melt the transformer down at 2 amps CCS, but if you
> > jump to
> > three amps and run AM 'Phone or RTTY it will get plenty hot.
> >
> > Just choose your rectifier bank carefully, Ken. Build it for 18KV,
> > minimum, at four
> > amps, minimum. Cool the diodes with that Tarzan fan, and then, let's
> > talk about
> > capacitors. Please don't tell me you're going to use photoflash
> > oil-filled caps
> > unless you see their voltage rating at 30% of what's written on the cans.
> > One screw-up
> > and the blown cap takes out your diode string and the transformer. I had
> > a huge argument
> > with my capacitor supplier about this and ended up backing up my argument
> > with
> > written evidence. The end result was that for the same money I was
> > shipped three times
> > the actual units to make up a 100 percent Working Voltage Direct Current
> > filter
> > instead of a Peak Voltage Direct Current filter. Your filter better be
> > rated at 12KV
> > also.
> >
> > Work Safely!
> >
> > Regards,
> >
> > Hal Mandel
> > W4HBM
> >
> >
> > ------------------------------
> >
> > Message: 5
> > Date: Sun, 12 Jun 2005 15:53:03 -0400
> > From: "kenw2dtc" <kenw2dtc@comcast.net>
> > Subject: Re: [Amps] TRANSFORMER-TEST-webpage
> > To: "Harold B. Mandel" <ka1xo@juno.com>
> > Cc: amps@contesting.com
> > Message-ID: <002a01c56f88$58515dd0$67612744@ken>
> > Content-Type: text/plain; format=flowed; charset="iso-8859-1";
> > reply-type=original
> >
> > Hal said:
> >
> > "The one feature I see on your iron is that the windings are not potted.
> > This means the unit, as it heats and cools, absorbs moisture from the air
> > around it, said moisture settling in the paper laminations and in the
> > wiring. To forestall disaster, I myself pot HV stuff, especially
> > transformers, chokes and coils. I found that the best stuff isn't too
> > expensive: Dolph's Synthite AC-41. It's about 25 dollars a gallon and is
> > made for HV insulation potting, and has the consistency of plain old
> > varnish, but with much better breakdown characteristics"
> >
> > Sounds good Hal. I can't lift this transformer so painting would be best.
> > I guess I would apply a gererous amount on the top and let it drain into the
> > windings and paint the bottom and sides. You mentioned 10 layers. Does
> > this mean you paint it, let it dry and paint it again etc., if so how long
> > is the drying period between applications?
> >
> > 73,
> > Ken W2DTC
> >
> >
> >
> > ------------------------------
> >
> > Message: 6
> > Date: Sun, 12 Jun 2005 16:07:20 -0400
> > From: "kenw2dtc" <kenw2dtc@comcast.net>
> > Subject: Re: [Amps] questions on my tranformer test
> > To: "Dr. William J. Schmidt, II" <bill@wjschmidt.com>,
> > <amps@contesting.com>
> > Message-ID: <004101c56f8a$574ad860$67612744@ken>
> > Content-Type: text/plain; format=flowed; charset="iso-8859-1";
> > reply-type=response
> >
> > Dr,
> > I agree with you on measuring the wire size; however, upon investigation the
> > secondary terminals are fed with , thick flat copper bus which has much more
> > area then the actual secondary wires, so I'm not going to tear open the
> > beast to find the wires. A couple of other gentlemen suggested that maybe
> > the transformer has a 2 amp rating, so for the heck of it I will run the
> > test for another 5 or 6 hours at 2 amps and check the temperature again.
> >
> > 73,
> > Ken W2DTC
> >
> > ------------------------
> >
> > ----- Original Message -----
> > From: "Dr. William J. Schmidt, II" <bill@wjschmidt.com>
> > To: "kenw2dtc" <kenw2dtc@comcast.net>; <amps@contesting.com>
> > Sent: Sunday, June 12, 2005 3:11 PM
> > Subject: Re: [Amps] questions on my tranformer test
> >
> >
> >> I would think that the best way to tell is measure the wire size of the
> >> secondary winding. The second best way is measure he cross-sectional area
> >> of the transformer, as theoretically it is related to the power
> >> capabilities of the steel.... which you can back into current (after
> >> accounting for reasonable efficiencies). 180F seems a little warm for a
> >> CCS transformer... maybe Will can weigh in here...
> >>
> >> Sincerely,
> >>
> >> Dr. William J. Schmidt, II K9HZ
> >> Trustee of the North American QRO - Central Division Club - K9ZC
> >>
> >> Email: bill@wjschmidt.com
> >> WebPage: www.wjschmidt.com
> >>
> >> "If computers get too powerful, we can organize them into a committee;
> >> that will do them in." -- Bradley's Bromide
> >>
> >>
> >> ----- Original Message -----
> >> From: "kenw2dtc" <kenw2dtc@comcast.net>
> >> To: <amps@contesting.com>
> > > Sent: Sunday, June 12, 2005 1:39 PM
> >> Subject: [Amps] questions on my tranformer test
> >>
> >>
> >>> Hi,
> >>> I'm trying to figure out the current rating of a plate transformer. This
> >>> is
> >>> my test setup:
> >>>
> >>> http://w2dtc.com/2005-0610-transformer-test-page.htm
> >>>
> >>> Questions:
> >>> 1. Is this a valid way to find the secondary current capability?
> >>> 2. Is the internal temperature of 180 degrees F too high for a
> >>> transformer
> >>> under load for 5 hours?
> >>> 3. Is there a problem running this center tapped beast in a full wave
> >>> capacitive input configuration?
> >>>
> >>> Thanks and 73,
> >>> Ken W2DTC
> >>>
> >>>
> >>>
> >>>
> >>> _______________________________________________
> >>> Amps mailing list
> >>> Amps@contesting.com
> >>> http://lists.contesting.com/mailman/listinfo/amps
> >>>
> >>
> >
> >
> >
> > ------------------------------
> >
> > Message: 7
> > Date: Sun, 12 Jun 2005 22:09:00 +0200
> > From: "ON4IQ" <on4iq@telenet.be>
> > Subject: [Amps] GS35 QUESTION
> > To: <amps@contesting.com>
> > Message-ID: <001201c56f8a$9297a970$e8b9a451@PIV3000>
> > Content-Type: text/plain; charset="iso-8859-1"
> >
> > I have a 2m amp running a gs35 tube and a G3SEK triode board in it.
> > While runnning the anode at 3.2kv , i get good bias control and all is well.
> >
> > Raising the voltage to 4.2kv off load gives met correct Ia when
> > in ptt, but once
> > the tube goes in cut off , the Ia drops to zero ( thats good) but
> > grid current goes
> > completely negative. After changing tubes with brand new one
> > still have the same problem.
> >
> >
> > I suspect there is something wrong in circuits or power supply.
> > I've checked power supply and find no leakage to ground.
> >
> > Would you have any idea where this negative grid current comes
> > from when tube is in cuttoff.
> >
> > Its abt 50ma.
> >
> > Best regards
> >
> >
> > Johan
> >
> > ------------------------------
> >
> > Message: 8
> > Date: Sun, 12 Jun 2005 21:14:21 +0100
> > From: Steve Thompson <g8gsq@ic24.net>
> > Subject: Re: [Amps] questions on my tranformer test
> > To: amps@contesting.com
> > Message-ID: <42AC979D.1090406@ic24.net>
> > Content-Type: text/plain; charset=ISO-8859-1; format=flowed
> >
> > kenw2dtc wrote:
> >> Hi,
> >> I'm trying to figure out the current rating of a plate
> >> transformer. This is
> >> my test setup:
> >>
> >> http://w2dtc.com/2005-0610-transformer-test-page.htm
> >>
> >> Questions:
> >> 1. Is this a valid way to find the secondary current capability?
> > I think so. Remember that what you have measured is the rms secondary
> > current - which defines the heating effect. The dc current you can end
> > up with depends on several factors but is likely to be 30-50% of the rms
> > value. Best check is with the Duncan Amps PSU designer which will tell
> > you the rms current in the winding for different configurations,
> > capacitor values and load resistances, but you will have to edit the
> > rectifiers file to create a diode with enough PIV.
> >
> > It's also worth checking how much it heats up with full primary volts
> > and o/c secondary, and derate the secondary current if necessary. I have
> > transformers that run cold like that, and others with noticeable iron loss.
> >
> >> 2. Is the internal temperature of 180 degrees F too high for a
> >> transformer
> >> under load for 5 hours?
> >
> > I'll pass on that one - if you run it at 2.9A rms but, say, 50% duty
> > cycle then the temperature rise will be much lower.
> >> 3. Is there a problem running this center tapped beast in a full wave
> >> capacitive input configuration?
> > Depends on the insulation between the centre tap and the frame. If the
> > designer assumed the ct was going to be ground, it might not be rated
> > for it. I've lost a transformer that way.
> >
> > Steve
> >
> >
> > ------------------------------
> >
> > Message: 9
> > Date: Sun, 12 Jun 2005 22:42:59 +0100
> > From: Ian White GM3SEK <g3sek@ifwtech.co.uk>
> > Subject: Re: [Amps] GS35 QUESTION
> > To: amps@contesting.com
> > Message-ID: <ffNtqvkjxKrCFAYo@ifwtech.co.uk>
> > Content-Type: text/plain;charset=us-ascii;format=flowed
> >
> > ON4IQ wrote:
> >> I have a 2m amp running a gs35 tube and a G3SEK triode board in it.
> >> While runnning the anode at 3.2kv , i get good bias control and all is
> >> well.
> >>
> >> Raising the voltage to 4.2kv off load gives met correct Ia when in ptt,
> >> but once
> >> the tube goes in cut off , the Ia drops to zero ( thats good) but grid
> >> current goes
> >> completely negative. After changing tubes with brand new one still have
> > >the same problem.
> >>
> >>
> >> I suspect there is something wrong in circuits or power supply.
> >> I've checked power supply and find no leakage to ground.
> >>
> >> Would you have any idea where this negative grid current comes from
> >> when tube is in cuttoff.
> >>
> >> Its abt 50ma.
> >
> >
> > What's happening is that with the higher B+, the tube needs a higher
> > bias voltage to cut it off. This voltage may be greater than the turn-on
> > voltage of the VDRs, so some current will flow through the VDRs.
> >
> > If you trace the current path back to B-minus, you will find that it
> > flows in the reverse direction through the grid current monitoring
> > resistor - that is why you see the apparent reverse grid current. You
> > will also probably find that the VDRs get slightly warm on standby
> > (careful!).
> >
> > If you know what is happening, this is actually not a big problem. I
> > suggest that you do not increase the VDR voltage, because the VDRs are
> > protecting the bias circuit from excess voltage.
> >
> >
> >
> > --
> > 73 from Ian GM3SEK
> >
> >
> > ------------------------------
> >
> > _______________________________________________
> > Amps mailing list
> > Amps@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
> >
> >
> > End of Amps Digest, Vol 30, Issue 15
> > ************************************
>
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
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