[Amps] HV lytic max V ratings..some notes.

[Carl]

----- Original Message ----- 
From: "Jim Thomson" <Jim.thom at telus.net>
To: <amps at contesting.com>
Sent: Friday, April 09, 2010 8:13 AM
Subject: [Amps] HV lytic max V ratings..some notes.


> Somebody was asking abt how high you can safely operate a typ 450 v lytic.
> Per Cornel dublier's  eng notes, buried pretty good,  they say..[ and I 
> don't know
> if this pertains to new ...'wonder caps'  that pack a lot of uf into a 
> small can,
> or the older types].. for  commercial / military applications, don't run 
> em over
> 75%  of their V ratings.   And for aerospace applications, don't run em 
> over 50%
> of their ratings.
>
> That's 75%  of the  working vdc.. NOT the ...'surge rating'.    Typ surge 
> V rating is
> 525 vdc.      That surge rating is typ 3-8 seconds MAX.
>
> They also  depicted  a graph of leakage current in micro amps VS  voltage, 
> from 90-110%
> of a 450 vdc  cap.   The leakage current dropped like a rock, when the cap 
> was run at  90%
> of it's rating  VS  100% .   They  don't  show leakage current < 90%... 
> but it drops even more.
>
> I notice the stock  200 uf  @  450 vdc caps  in my 4 x old 1977 era  Drake 
> L4B's  seem too last
> forever. B+ on em is 2650 vdc  NO load on RX.   2650/3600 = 73.6%    A 
> heath SB-220 and similar
> amps  with the same  8 x 450 vdc caps, run at 3300-3600 vd.... don't fare 
> as well after yrs of use.
>


** The Drake secondary is 780/1065 VAC. The Heath is 860/1171 VAC.  Where do 
you get your numbers from?

** Most of the SB-220 series I get thru here have good original caps. Get 
rid of the 30K heaters and go with 100K MOX and verify that the voltage 
deltas arent excessive. I use the standard Mouser 5% Xicon, no need for 1%.

** Amazingly Im still getting mid 60's NCL-2000's in with original caps. 
National used a custom built 80uF  450V rated for high ripple current, about 
an inch longer than a comparable Sprague Atom.

Carl
KM1H




> The L4PS  uses  100 k  2 watt  carbon comp resistors's and even those 
> things didn't drift anywhere
> near as bad as I thought they would.   [ I replaced both the caps and the 
> 100 k resistors  with bigger
> caps  and 3 watt, 1%  tol resistor's]
>
> Regardless of hv cap value, [from 200 uf  up to 4800 uf],  a 100K 3 watt 
> MOF  works  very well.
> The total bleeder current more than swamps out the leakage current of the 
> caps... by a ratio of
> 10-15 : 1
>
> The absolute ideal eq resistor is the  VISHAY  100k  3 watt  MOF   1%  Tol 
> units.   I bought 300
> of em [100 per box]  and all  300 of em are exactly  200 ohms  on the low 
> side of 100 K. [.02% low]
> The kicker is.. there is no more than a few ohms difference  between all 
> 300 of em... and this is
> 3 x different lot #'s.       NO more  playing..'matchup'.   Just grab as 
> many as you  need for a
> given project.
>
> Mouser  cat part #     CFP-31003FB14
> Cust PN  71-CPF3-F-100K-T2
> Vishay PN CPF3100K00FHB14
>
> These are only  [I think] 50 ppm  temp coefficient too.  W4ZE, Tony King 
> [sk]  put me onto
> these Vishay / Mouser resistors a few yrs ago.  Tony was fed up with 
> playing matchup all the time.
>
> On these HB  HV supply's  I have been building, using surplus  HV lytic's, 
> I don't run the  caps  at
> more than 68-75%  of their  working vdc ratings.
>
> The  resulting leakage current is through the floor.   Also, if any 
> spikes, transients, surges,etc
> gets past  the  250/277/120 vac MOV protection, the HV caps  will just 
> absorb the spikes + transients.
>
> These  surplus caps I have been using have bucket loads of uf anyway.. so 
> it's not like I'm short
> of total C.   As  far  as  surplus  lytics.. I have seen  everything from 
> 1600 uf, 2000 uf ,  2300 uf
> 2500 uf, 3900 uf, 4800 uf and now  10,000 uf.    There are also some good 
> deals  on 350 vdc rated
> caps.. you just require more of them.   A buddy used a string of 30 x 5200 
> uf caps on a 7700 vdc
> supply, with great success.   Every config tried always had the  100 K  3 
> watt  mof  across it... and
> also a RVS connected  6A10  safety diode.   The  resulting V drop  across 
> each cap is virtually
> identical... within a few volts.   I put the Vishay  resistors in the 4 x 
> drake amps as well.
>
> later... Jim  VE7RF
>
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