[Amps] Control transformers

[Paul Kraemer]

A very good approximation of transformer current is that the transformer 
current will be three times the dc load current for full wave doubler. 
Exactly how much more or less depends on the capacitor size
Paul K0UYA

-----Original Message----- 
From: Gerald Williamson via Amps
Sent: Saturday, April 09, 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. 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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