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Transformer an rectifier ?




 
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Donnie SWL
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« on: May 19, 2019, 06:21:12 PM »

Ok here it goes my stupid question. I have a transformer that has 2 separate windings 2000 volt at 220 ma ea.Now i know if i tie the two winding in parallel i would have 2000 at 440 mils an i could run this to a full wave bridge rectifier....So what if i done a full wave ct ground configuration with the windings in series what kind of amperage would i have...Would i have just the 220 ma or would it come closer to the 440 i get when the windings are parallel ?


Anyway im having brain fart on this...

Thanks Don
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PA0NVD
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« Reply #1 on: May 19, 2019, 08:07:58 PM »

Will be the same, also 440 mA Whatever configuration, the power you get will not change. In CT FW configuration every winding has to supply 440 mA but only 50% of the time. So 2000V at 440 mA or 4000V at 220 mA
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WZ1M
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« Reply #2 on: May 20, 2019, 01:45:29 AM »

I would be very careful about drawing more than 1/4 amp with a series center tap winding. In series, the wire is still the same size and from my 30 years of past experience, the HV wire size is pretty small and mite not handel more than 1/4 amp.
Regards,
Gary
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KK4YY
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Your best isn't as good as you can be.


« Reply #3 on: May 20, 2019, 04:36:09 AM »

Not a stupid question. Each one of us, at one point, have asked it.

Please be careful at those voltages!

They may not give you a second chance.


Don
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WD8BIL
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« Reply #4 on: May 21, 2019, 10:16:28 AM »

Current in a series circuit is constant. 220ma in series... 440ma in parallel.
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WZ1M
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« Reply #5 on: May 22, 2019, 03:27:08 AM »

Because you have dubbled the wire size but now have half the voltage.
Regards,
Gary
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WD5JKO
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WD5JKO


« Reply #6 on: May 22, 2019, 09:32:08 AM »

Was never stated what kind of transformer this is. What if it is a Toroidal transformer? Toroidal transformers usually bifiliar wind the secondaries. Putting them in series and phased for FW CT rectification will put a lot of HV stress one winding to the other. If they are rated for this, OK, but if not?

Jim
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Donnie SWL
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« Reply #7 on: May 22, 2019, 01:08:36 PM »

Thanks for all the replies..If you have ever seen a big 3 phase transformer with the 3 big coils on them this looks like one of those but only 2 coils an miniature ...It came out of an old home brew transmitter i think it had 2 805's in the modulator an this tranny was the supply for them an still has the wires connected to it...looks like they were using it as full wave ct ground...an the tranny tag said 220 ma per coil witch made me scratch my bald head because the 2 805's would pull 400 mils as the data sheets say.....
 
thanks again Don
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WD5JKO
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WD5JKO


« Reply #8 on: May 22, 2019, 01:34:11 PM »



  Don,

   Those 805's will pull 400ma as you say, but that is with sine wave drive. With speech it will be roughly half of that...

As said earlier by others, in FW CT, each side is conducting only 50% of the time, and it was common in the day to pull 2X the current 50% of the time. The winding DC resistance, and core leakage inductance make this practice less than ideal.

Look at the Mercury vapor tubes used back then. An 866 rated for 250 ma was used in a FW CT supply to deliver 500ma. Same with 816's rated at 125ma where used in supplies pulling 250ma.

BTW, the 805 is seriously underrated. I once ran a pair in class C plate modulated service, 2500v X 400ma = 1KW DC input. Output was almost 800 watts! Ran the same pair for many years.

Jim
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