[Amps] Resistor before the capacitor REDUX

[Gary Schafer]

Hi Jim,

I just ran a bunch of numbers on PSU designer and got quite different
numbers than yours. I suspect it is because of the way measurements are
being made. That is if I am doing things right here!

I used a 30V RMS transformer with 1 ohm winding resistance. 
I did the load with 2200 ohms and 15K ohms to simulate full load and ZSAC
during idle.
I also did it with 10 MFD and 100 MFD filter cap.
It is also done with and without the 22 ohm series resistor. The filter
capacitor had a 2 ohm series resistance.  
Interesting results.
You can multiply all the voltage and current numbers to get to the
equivalent of a 3000 volt transformer rather than a 30 volt.

1 ohm 30 VRMS transformer. 22 ohm series resistor.

				Load		Vs peak	Vs RMS	Vo RMS(DC)
Vo p-p	Io RMS

10 MFD filter	2200		2.2048	787.48m	36.236		10.111
16.471ma
10 MFD filter	15K		1.0966	203.23m	40.111		1.9580
2.6741ma

100Mfd filter	2200		2.7393	954.81m	39.241		1.3082
17.837ma
100MFD filter	15K		1.661	234.72m	40.734		247.19m
2.7156ma

---------------------------------------------------------------------
No series resistor.

10 MFD filter	2200						36.337
10.118	16.516ma
10 MFD filter	15K						40.110
1.9614	 2.674ma

100MFD filter 	2200						40.218
1.4851	18.280ma
100MFD filter	15K						40.811
272.64m	2.7207ma

Notice that with the 10 MFd filter and 22 ohm series resistor the Vo drops
387 (multiplied by 100) volts from 267 ma load to 1.64 amp load.
With a 100 MFD capacitor that voltage drop is only 149 volts.

With no series resistor and a 10 MFD filter the voltage swing is 377 volts.
Only 10 volts better than with the 22 ohm resistor.

But with the 100 MFD filter the voltage swing from 272 ma to 1.82 amps is
only 59 volts without the 22 ohm resistor. This is about 100 volts better
regulation than with the 22 ohm resistor.


Should we not worry so much about low resistance windings on our
transformers?

Hope all the columns line up.

73
Gary  K4FMX




> -----Original Message-----
> From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com]
> On Behalf Of Jim Garland
> Sent: Monday, February 08, 2010 7:05 PM
> To: amps at contesting.com
> Subject: Re: [Amps] Resistor before the capacitor REDUX
> C= 10uF, and C=100uF. I also looked at the waveforms on a Tek 2465B
> oscilloscope. The results are quite interesting and here they are:
> (Actually, I've multiplied all the results below by 100, since I used a
> 30V
> supply to simulate an HV supply with a no-load output of 3000V.) In the
> table below, Vs(peak) is the instantaneous peak voltage drop across the
> 22
> ohm series resistor. Vs(DC) is the DC voltage drop across the 22 ohm
> resistor. Vo(DC) is the DC output voltage of the power supply with the
> 2200
> ohm load, Vo(p-p) is the peak-to-peak ripple voltage across the 2200 ohm
> load, and Io(DC) is the DC current through the load.
> 
> C                  Vs(peak)     Vs(DC)       Vo(DC)       Vo(p-p)
> Io(DC)
> 0 uF             31V p-p       18.2V           1820V          2920V
> 0.87A
> 10 uF           165V p-p     25.8V           2580V          660V
> 1.17A
> 100 uf          156v P-P     27.5v           2750v          78v
> 1.25a
>