On Oct 22, 2006, at 11:51 PM, pentalab wrote:
--- In ham_amplifiers@..., R L Measures <r@...> wrote:
On Oct 22, 2006, at 7:39 AM, pentalab wrote:
...
[If u ran the lytics at the prescribed 75%
max V rating the manufacturer's recomend, they will NOT blow
up, if
the bleeder EQ resistor's open up.]
I'll bet a medium pizza with 5 toppings that I can show an
example where a 75% safety factor would cause a serious problem if
a bleeder- R opened.
### U may well be correct
There goes the pizza.
IF the caps were badly mismatched in
UF to start with.
Not even with 1% matched.
### why is that??? Why wouldn't the V drop be proportional to
UF [One eq resistor open up... the rest intact}
Example: In a series string of 4 electrolytic filter caps, with an
open bleeder on one cap, the potential on the other 3 caps would
slowly bleed down to zero volts, and the voltage on the cap with the
open bleeder would rise 4x to the full potential coming from the
rectifiers. For example, a TL-922: It uses 4, 200uF, 500V caps in
each half of a FWD. Normally there is c. 380v on each filter cap.
If one bleeder/equalizer R opened, the potential across the cap with
the open bleeder would rise to 4x normal or 1520v - but of course a
500v electrolytic would probably fail before the potential rose to
600v.
.
### also.. My idea of adding a 2nd 100K resistor across each
cap is flawed.
Agreed. We have sold over 12k Matsushita, 3W, 100k-ohm MOF
resistors, so far there have been zero reported failures, and ther
is typically <0.3% variation in measured R in the same 1000-unit
box. .
### Excellent.... what is the max DC voltage rating on them ???
500V at 70?C.
I'm guessing 450-500 V ?? Put 8 of em on an AL-1500, and u got
450 V per resistor right there.
...
With 8 caps, opening one equalizer -R would eventually increase
the voltage at the open R's cap by 8x.
### why is that ??
Explained above.
With just one R per cap... and any one R
opened up... there should be NO current flowing in the remaining
7 x intact R's. With 2 x R's per cap...
I was talking about 1 resistor per capacitor.
...
IMO.. 1 x resistor per
cap... that's it. THEN, if any resistor let go... V would
divide according to each caps UF... with the caps with the
highest UF getting the most V.
Eventually there would be 0v on all the caps with intact
equalizer/ bleeder resistors and 100% of the voltage on the cap
with the open R.
### say what ?? Why would the cap with the open resistor
take 100% of the plate V ?? [1 x resistor per cap]
Because direct current does not flow through a capacitor.
Of course the potential would never get there since electrolytics
tend to go BANG with not much of a surge in voltage.
correct
### I'll bite. When one cap goes BANG.... does it blow open...
or short out?
In the only case I witnessed, the guts blew apart, the can shot up,
and hit the 25' ceiling in the cal lab. It sounded like a 12ga shotgun.
If it went open... no HV on remaining caps... if it
shorted out... then it's just plate V / remaining caps. in the
case of a L4B.. with 8 x 450 v caps.... even with 7 x
remaining... it's STILL only 378 V per cap.
not when one disappears
...
### Is Riley H gonna use his 922 for an IPA ??
He didn't say.
...
R L Measures, AG6K, 805.386.3734
r@..., , rlm@..., www.somis.org
