[Amps] Big transformer request TSPA

[TexasRF at aol.com]

Hi All, just based on the dc voltages produced, not accounting for IR  
losses, core losses,etc:
 
3000vdc .5A is 1500 watts delivered to the load. A choke  filter typically 
delivers .9 times rms secondary voltage. Turning this  around, the transformer 
would then have about 3000/.9 volts or 3333v rms. A  Capacitor type filter is 
expected to deliver 1.414 times rms or 4713vdc (no  load). Assuming a voltage 
drop of 500v, this leaves 4213vdc. Back to the same  1500w, this means a 
current of 1500/4213 = .315 A. This is a ratio of 1.59 which  is pretty close to the 
stated derate factor.
 
There will be some extra heating due to higher IR losses in the copper wire  
caused by the much higher peak currents in the filter C. After the microwave  
oven discussion yesterday, it seems there might be some core heating (losses) 
as  well due to these same high peak currents.
 
Just another way to look at the question.
 
73/k5gw
 
 
In a message dated 3/21/2006 6:54:25 P.M. Central Standard Time,  
craxd1 at verizon.net writes:

John,

It's according to what type of rectifier circuit you'd use  with the 
capacitor. For a full wave bridge and capacitor input, the secondary  current is from 
1.6 to 1.8 times the DC current. That variance I don't know  for sure where 
both came from as some formulas I've seen use either. It has a  lot to do with 
the size of capacitor of course. Hammond has a downloadable pdf  with these 
formulas in it, and I'm pretty sure they use 1.6. Ohter transformer  
manufacturers though I've seen use 1.8.

The one you found, didn't the  primary have it where you could change the 
voltage? Most always had this  because there are some places using 220/240  VAC.

Best,

Will

*********** REPLY SEPARATOR   ***********

On 3/21/06 at 5:39 PM John T. M. Lyles  wrote:

>Before I start searching for 3 KVA pole pigs I will ask  here. I have 
>a UTC LS-184, a beautiful transformer from the 1950s,  weighs 102 lbs. 
>It is 7 kV RMS CT. With a choke input, it would do a 3  kV DC 500 mA 
>supply all day long, according to UTC. I need ~ 4 kV at  0.6 - 0.8 
>Amps. If I ran it into a capacitor only, and it charged up  to near 
>peak, it should do the voltage fine. However, I am not certain  how 
>much current derating it would need for running into a Capacitive  
>load.
>
>Does anyone have a single phase plate  transformer, which has 220/240 
>primary and good for ~4 kV DC @ 0.6-0.8  Amps? I would prefer to us a 
>full wave bridge but two diodes and a  center tapped pig would work 
>too. I just found a 4.1 kV @ 2 Amp today  at a junk yard in town, but 
>it has 480 VAC primary, and is LARGE. I  have several pieces for 3 kV 
>DC supplies, but nothing for a higher  voltage tube. Numerous 
>broadcast transmitters and RF industrial  generators used such power 
>in the good old days.
>
>There  were some very nice 3 kVA 4160VAC/220 dry distribution 
>transformers  made by Westinghouse years back, before ABB bought them, 
>and they  outsourced to China. Into a choke, they would be fine. I am 
>not  planning on using this for SSB.
>
>Thank  you.
>73
>John
>K5PRO
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