[Amps] Control transformers

[Jim Hargrave]

Gerald,
Comments embedded below:

73, Jim - w5ifp at gvtc.com


>> -----Original Message-----
>> From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of
>> Gerald Williamson via Amps
>> Sent: Saturday, April 9, 2016 7:17 AM
>> To: kd4lyh at yahoo.com; amps at contesting.com
>> Subject: Re: [Amps] Control transformers
>> 
>> Jeff, I have not done that but conceptually it should work well.
If
>> you use  two of the 3kva transformers, one would expect to
>> generate enough d.c. to supply  a 6 KW load.
>> 
>> The voltage doubler will charge the filter C to 2.8 times the rms
>> voltage so two of the 600v units would have a no load voltage of
>> 3394v and full load  maybe 3100v or so.At 6 KW, the current could
>> be upwards of 1.7 amps.
>> 
>> There are other considerations such as the much higher peak
>> currents caused  by a C only filter that would tend to reduce the
>> current capability somewhat to  prevent over heating the
>> transformers. Fortunately the copper losses are related  to
current
>> squared so a modest reduction in current equates to a large
>> reduction  in heating.
>> 
>> You would wise to find a way to test the insulation break down
>> between windings and the core. Perhaps you could build or borrow
>> a break down tester.
>> They are very easy to build based on an old microwave oven
>> transformer.
>> 
>> For a very rough test, you could connect a 100w incandescent
light
>> bulb in series with the 120 or 240v primary and connect the 600v
>> windings in series. One  end of the 1200v can be connected to the
>> core and that would subject the other  end of the 1200v winding
to
>> about 1700v peak. If the 120v windings were  connected in
parallel
>> and 240v applied, the secondary voltage would then be  about
>> 3400v peak.

[W5IFP] Did you really mean "connected in parallel" ?

 You can't run it this way but fine for a brief test. The
>> light  bulb will limit the current flow in case there is a
breakdown. It
>> will also give  a relative indication of the amount of leakage in
the
>> transformer. One would  expect only a dim glow if all is well.
Also, it
>> would be a good idea to connect  the two transformer cores
>> together and to ground (or neutral) for the brief  test. Be
careful as
>> bad stuff can happen!
>> 
>> 73,
>> Gerald K5GW
>> 
>> 
>> 
>> 
>> In a message dated 4/8/2016 11:16:07 P.M. Central Daylight Time,
>> amps at contesting.com writes:
>> 
>> Good day,
>> I have learned alot from  this list over the years. What I
propose to
>> try may work or it wont. Im  thinking it wont work but it dont
hurt to
>> ask. From time to time I come across  1kva,2kva,3kva control
>> transformers. 0 -120v on one side and 0  -240,480,575,600 volts
on
>> the other. If I was to series two of the 600 volt  windings then
feed
>> a fullwave doubler, would this work or not? I would also  like to
>> series the 120v side feed it 240v. For there intended purpose I
think
>> with control transformers, the higher voltage winding serves as
the
>> primary  and the secondary is the 120v winding. Not sure how
>> robust machine control  transformers are.or if there is enough
>> insulation between primary and  secondary. Im sure current
>> capacity would drop if I step up the  voltage.
>> 
>> Jeff
>> 
>> KD4LYH
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