I just looked at PSUD with a 25 ohm transformer, 2500 VAC and 25uf with 8
ohm esr filter cap. No resistor before filter.
The surge current on the first half cycle is around 26 amps. Then peak
current settles down to around 4.5 amps with around 1 amp rms on the load.
With a 25 ohm resistor added before the filter the surge current at startup
is around 22 amps and peak current settles to around 4 amps.
It doesn't look like the resistor does much good as far as startup. Only 4
amps different on peak current on the first half cycle.
It seems to me that a primary step start is a much better way to go, if one
is even needed. As long as the breaker don't trip and the diodes can handle
the peak current.
73
Gary k4FMX
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]
> On Behalf Of TexasRF@aol.com
> Sent: Thursday, February 11, 2010 11:23 AM
> To: Jim.thom@telus.net; amps@contesting.com
> Subject: Re: [Amps] Results from new PSUD... resistor b4 the B+ filter
> caps !
>
> One last question: Does the resistor in the secondary provide any
> benefits
> over a proper value resistor located in the primary circuit?
>
> 73,
> Gerald K5GW
>
>
>
>
> In a message dated 2/11/2010 8:55:31 A.M. Central Standard Time,
> Jim.thom@telus.net writes:
>
> OK, Now that I have the latest version of psud... it just reafirms
> my
> real life test, done on a 3100 vdc real supply,
> using a 46 lb dahl xfmr.... and a 25 uf cap....... and a 22 ohm
> resistor BEFORE the 25 uf cap.
>
> I used the 2000 vac tap on the 46 lb dahl [ it has taps for
> 1500/2000/2500/2750]
>
> Pri is DUAL 110 vac windings.. with windings in series. [220 vac] ..
> and
> 240 vac stuffed into it. [ sec ends up a little , at 2181 vac]
>
> 220 vac pri = .16 ohm dc resistance
> 2181 vac sec = 25.5 ohms dc resistance
> Input Z of xfmr is = 38.72 ohms
>
> 25 uf filter.... [ 8 ohms esr, old style 200 uf caps were 1 ohm esr
> each... 8 x caps in series]
>
> Load is 900 ma cxr.
>
>
> Results WITH 22 ohm resistor inserted B4 the 25 uf cap.
>
> vdc across load = 2752 vdc [UNDER A 900 Ma LOAD]
>
> V drop across 22 ohm resistor = 101 v MAX on peaks.... or 40 vrms
>
> Current through the 22 ohm resistor = 4.68A MAX.... or 1.82A RMS
>
> Current flowing into 25 uf cap = 3.7 A max..... 1.58A RMS
>
> ........................................................................
> ....
> ........................................................................
> ....
> ........................................................................
> ....
> ........................................................................
> ....
> ........................................................................
> ....
> ...........
>
> OK.... now with 22 ohm resistor REMOVED !!!
>
> Vdc across load = 2820 vdc [ UNDER THE SAME 900 Ma LOAD] An
> INCREASE of just 68 vdc ..... not a helluva big difference.
>
> Current into 25 uf cap = 4.31 a MAX..... or 1.71 A RMS.
>
> ........................................................................
> ....
> ........................................................................
> ....
> ................................................................
> OK.. here we increase the load to 2 A .... and NO resistor
>
>
> 2624 vdc under load of 2 A
>
> ........................................................................
> ....
> .................................
>
> Now with the 22 ohm resistor.. and a 2A load.
>
> 2514 vdc under load of 2A A 110 vdc DROP.. with 22 ohm
> resistor in the circuit. More of a difference here.
>
> ........................................................................
> ....
> ........................................................................
> ....
> ...........
>
> OK.... now lets IN-crease the filter cap..from 25 uf..... up to 312
> uf
> + .136 ohm TOTAL ESR [ ,017 ohm per cap, 8 x caps in series,
> caps
> are CD 400 series... 2" diam x 4" long]
>
> 2581 vdc under load of 2A and 22 ohm resistor IN the circuit.
>
> ........................................................................
> ....
> ................................................
>
> OK... 312 uf filter cap and a load of 2A.... and NO 22 ohm
> resistor.
>
> 2710 vdc under load of 2 A.... and the 22 ohm R is OUT of the
> circuit.
> This is a 129 vdc improvement with the 22 ohm resistor
> REMOVED.
>
> BTW.... conduction time of pulses INTO the 312 uf cap is 2 msecs
> with
> 22 ohm resistor In the circuit... and 1.8 msecs with 22 ohm resistor
> OUT of the circuit.
>
> ........................................................................
> ....
> ........................................................................
> ....
> ........................................................................
> ....
> ...............................................
>
> ### So with a run of the mill 3 kv supply......and sucking 900
> ma... adding a 22 ohm resistor B4 the filter cap cost you aprx 68
> vdc
> drop. And it MIGHT be able to be used for step start.... since
> it takes
> 70 msecs to ramp up to max vdc.... on initial turn on. [ NO load..
> except for the 800K eq resistor /bleeder [ 100k per cap] Dunno
> if it's
> really worse the hassle of shorting out the 22 ohm resistor.. with a
> vac
> relay... for a lousy 68 vdc increase.
>
> Sri for the diatribe, it appears Mr. Garland, W8ZR is correct on all
> accounts.
>
> later......... Jim VE7RF
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