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@yahoo.com ; amps@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@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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