The best way to use elctrolytic condensers is the swedish- danish way:
I have in my shack a number of swedish toroids with a 1kVA core and abt 2000
VDC output that have 6 windings of around 250 VAC each. Each winding has its
own diode bridge rectifier and electrolytic capacitor and all sections are
in series.
The caps can never get any severe overload voltage and I can use one or two
sections for my screen voltage. The caps and diodes are mounted in a
separate module together with relays and electronics for automatic mains
voltage compensation.
Now for my question: the caps seem to be around 15 years old and there is no
way to see what kind of caps they are dry or wet as the text on them is
hidden behind other components?. Can I use them after so many years? They
have never been in service.
Talking about flash condensers: why do you not use one of those high voltage
metal-paper condensers from copying machines one can find as junk? Made by
BOSCH or ITT. They can be rated at 2500 volts 40 uF and are selfhealing. I
have tried to test them with very high voltage and at around 5000 VDC there
was a flash-over and the cap was kaputt for ever. BOSCH once told me the
caps were basically the same as the ones used in transmitters but the edge
isolation was not as good. If they do not flash over in rael service they
may take it they said. Also they have been used in the past with success in
linear amps.
There are also Russian caps on the surplus market in wooden crates rated
40uF 5kV. Is there anybody from over there who can say if this 5 kV is test
or working voltage? Who sells them and at what price?
Prosit de Hans SM5KI
----------
>Från: "Phil T. (VA3UX)" <phil@vaxxine.com>
>Till: amps@contesting.com
>Ämne: [AMPS] Cap leakage
>Datum: tis 18 jan 2000 14.55
>
>
>Jim, you can't go wrong if you follow Rich's suggestion of replacing
>anything with more than 250 ua leakage, but you may end up replacing
>certain caps prematurely with that rule-of-thumb.
>
>My review of the Mallory catalogs shows that a leakage current formula is
>given for each series of capacitor. So satisfactory leakage current for a
>Mallory type CG won't necessarily be the same as you'd find on a type CGS.
>Here's an example :
>
>For Mallory type CG, dc leakage current = (6 x C x V)/ 10^6, after 30
>minutes at full rated voltage, maximum not to exceed 4.0 ma. C is uf and
>V is max. rated working voltage.
>
>For Mallory type CGHand CGS, dc leakage current = 0.006 x sq.root(C x V),
>after 5 minutes at full rated voltage, not to exceed 6.0 ma.
>
>Mallory don't give a leakage formula for the FP series. The FP's were
>originally designed for non-critical radio/TV service . Ripple current
>rating for these things would only be perhaps 100 - 200 ma.
>
>The CD multisection caps appear to be a down and dirty quick fix.
>
>The 0.5 ma may or may not be OK - again depends on the original spec. My
>experience with reforming caps (using a machine similar to yours) is that
>almost any good cap ends up with a fairly low leakage current, almost
>regardless of the spec. For low, I would have to agree with Rich's 250 ua
>number in general. I have several 300 uf/450V caps with leakages well
>below 100 ua.
>
> Suspect units show leakage that tends to bounce around, and don't approach
>the low end. They're still probably useable, but for how long ?
>
>
>At 09:08 PM 1/17/2000 -0600, you wrote:
>>
>>I have am going thru the process of reforming the PS caps in a ML-2500 amp.
>>I am using a Eico 950B resistance capacitance comparator bridge for a
>>variable PS and am measuring the ma by monitoring the voltage across a 20K
>>resistor in series with the cap. The general technique is to rise the
>>supply voltage until I see about 1 ma of current (20 volts across the 20K
>>resistor. . I let the voltage set until the indicated current quits
>>dropping and then rise the voltage until I see about 1 ma of current again
>>and then repeat the cycle.
>>
>>This schematic on this amp shows 6 FP electrolytics 150 mf a @450 Vdc. The
>>amp has 3 spragues that match the skematic and 3 CD caps that are mutli
>>section that are hooked in parallel. So far I have reformed the 3 spragues
>>which had a leakage of about .5 ma at 450 Vdc. I will have to see how the
>>CDs look.
>>
>>This subject has be covered before, but what is a good leakage limit guide
>>line for reuse or replace in this application and if replacement is
>>warranted, what is a good source for replacement caps?
>>
>>The amp uses a 100K ohm carbon comp resistor across each cap. I plan to
>>replace these 3 watt MOF resistors.
>>
>>73,
>>
>>Jim Zellmer, KA0VSL
>>
>>
>>--
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>>
>>
>>
>
>
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>
>
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