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2.5KVA transformer on square wave 1000hz mains



 
 
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  #1  
Old April 22nd 12, 12:06 AM posted to rec.radio.amateur.homebrew
raypsi
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Posts: 242
Default 2.5KVA transformer on square wave 1000hz mains

I just bought a 50/60 hz transformer rated 575VAC
pri to 230VAC sec
rated at 2.5KVA on ebay. I remember reading some time ago that
transformer companies rated their transformers to 1000 hz.

I'm needing like a 3KVDC at about 1.5KVA semi regulated supply but
don't like to use lots of mfd's of filtering at higher voltages to get
there. For a 4X1 PA ima building.

So I figure getting there by using a tl494 and bridge switching 4
IGBT's at 1000hz
square wave on a 130VDC supply to the 230VAC winding on the
transformer. AT square wave I figure 325 VAC output, from the 575VAC
side.

Running a 10 step ladder multiplier, that would be 5 steps negative
and 5 step positive I should get around 3250VDC. On a half wave
multiplier I figure the last step being hit by 200 hz pulses at each
end of the ladder.

So Am I just spinning my Wheels? and stick with 60hz and lots of mfd's
with a autoformer configuration getting more VDC per step and going
with 6 steps, 3 up and 3 down at 60hz? And no easy way of regulation?

73
de N8ZU somewhere in 8 land
  #2  
Old April 28th 12, 05:21 PM posted to rec.radio.amateur.homebrew
Leland C. Scott
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Posts: 43
Default 2.5KVA transformer on square wave 1000hz mains

Raypasi,

Running the transformer at 1KHz will likely cook the core. The laminations
will be much too thick at that frequency to keep the eddy current heating to
an acceptable level. Generally the higher the frequency the thinner the
laminations have to be. At some point the core material is changed to
something else, like ferrite, to keep the heating down.

73's

Leland C. Scott
KC8LDO


"raypsi" wrote in message
...
I just bought a 50/60 hz transformer rated 575VAC
pri to 230VAC sec
rated at 2.5KVA on ebay. I remember reading some time ago that
transformer companies rated their transformers to 1000 hz.

I'm needing like a 3KVDC at about 1.5KVA semi regulated supply but
don't like to use lots of mfd's of filtering at higher voltages to get
there. For a 4X1 PA ima building.

So I figure getting there by using a tl494 and bridge switching 4
IGBT's at 1000hz
square wave on a 130VDC supply to the 230VAC winding on the
transformer. AT square wave I figure 325 VAC output, from the 575VAC
side.

Running a 10 step ladder multiplier, that would be 5 steps negative
and 5 step positive I should get around 3250VDC. On a half wave
multiplier I figure the last step being hit by 200 hz pulses at each
end of the ladder.

So Am I just spinning my Wheels? and stick with 60hz and lots of mfd's
with a autoformer configuration getting more VDC per step and going
with 6 steps, 3 up and 3 down at 60hz? And no easy way of regulation?

73
de N8ZU somewhere in 8 land



  #3  
Old May 1st 12, 04:15 AM posted to rec.radio.amateur.homebrew
raypsi
external usenet poster
 
Posts: 242
Default 2.5KVA transformer on square wave 1000hz mains

On Apr 28, 12:21*pm, "Leland C. Scott" wrote:
raypsi,

Running the transformer at 1KHz will likely cook the core. The laminations
will be much too thick at that frequency to keep the eddy current heating to
an acceptable level. Generally the higher the frequency the thinner the
laminations have to be. At some point the core material is changed to
something else, like ferrite, to keep the heating down.

73's

Leland C. Scott
KC8LDO

Hey OM:

I've seen 400 Hz transformers from old air force airplanes it's true
the lamination's are thinner but the physical size per unit power is
1/6 that of a 60 hz transformer. To wit a 2.5 k VA transformer made
for 400 Hz would weigh in at about 6 pounds compared to my Hammond
Canadian made performer at 40 pounds.

Looks like I'm going to be switching 230 v Dc from 2 separate 115 vac
lines on the same side of the main 230 vac line. I'll keep the switch
speed down to 120 Hz Since I found a stacked doubler that gives a
quadruple output. Thus the output capacitor charges twice as fast over
a ladder style multiplier.

Though one fellow ham told me to just buy a 1.5 k VA isolation
transformer to convert 115 to 230 vac. He is a Canadian ham also since
I have a Canadian Transformer.

Thanks for the advise

73 OT
de N8ZU
 




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