Well Below Rated Working Voltage

7/21/2010 2:24:16 AMLou

Gentlemen:

I am restoring a Silvertone radio and I happen to have on hand the proper electrolytic capacitor value for one of the cap replacements. It is rated around 450 VDC.

The problem is that the ORIGINAL capacitor has the same value but is rated at only 275 VDC ( which is still proper for this design, by the way ).

Is there any downside to using the 450 volt cap at 275 volts of rating? I have heard that the cap may not form correctly when used at a voltage much lower than its' "working voltage" rating.

Thanks
Lou

7/21/2010 4:00:38 AMWalter

The cap will have an easy life.
I see 1600 WVDC caps in audio tone/crossover control circuits. Not that the voltages would ever reach that high, but that the highest quality components are desireble in such a circuit.

7/21/2010 8:56:42 PMAlan Douglas

That's right. The myth of electrolytics reforming at lower voltages is still being perpetuated on some websites, but has not been true since the 1930s. I've measured unused capacitors from the late 1940s, which show no change in capacitance from their marked values. If the oxide layer thinned out in response to storage at zero volts, you would expect the capacitance to increase.

7/26/2010 12:09:45 PMJ. Jackson

I've heard 2 views on the high voltage caps used in some radio circuits - one, as Walter notes, for the quality / low-leakage aspect .... but others claim it is to simply to handle spikes that can be produced in those circuits at higher volumes. What's the rub???

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: The cap will have an easy life.
: I see 1600 WVDC caps in audio tone/crossover control circuits. Not that the voltages would ever reach that high, but that the highest quality components are desireble in such a circuit.
:

7/26/2010 12:10:16 PMJ. Jackson

I've heard 2 views on the high voltage caps used in some radio circuits - one, as Walter notes, for the quality / low-leakage aspect .... but others claim it is to simply to handle spikes that can be produced in those circuits at higher volumes. What's the rub???

--------

: The cap will have an easy life.
: I see 1600 WVDC caps in audio tone/crossover control circuits. Not that the voltages would ever reach that high, but that the highest quality components are desireble in such a circuit.
:

7/26/2010 6:22:17 PMAlan Douglas

Capacitors in the plate circuit of audio-output stages can see fairly high voltages, generated by the leakage inductance of the output transformer. If the plate current is suddenly cut off, by a static crash for instance, the inductance will try to keep the current flowing and will generate whatever voltage it takes to do so. It's possible to calculate mathematically the energy stored in the leakage inductance (1/2 L x I^2) and the voltage across the capacitor can likewise be calculated assuming all the energy is transferred to it (1/2 C x V^2). Kilovolts are possible. Without any cap, the socket or the transformer itself can arc over.

7/22/2010 9:28:15 AMTerry Decker

:Gentlemen:
:
:I am restoring a Silvertone radio and I happen to have on hand the proper electrolytic capacitor value for one of the cap replacements. It is rated around 450 VDC.
:
:The problem is that the ORIGINAL capacitor has the same value but is rated at only 275 VDC ( which is still proper for this design, by the way ).
:
:Is there any downside to using the 450 volt cap at 275 volts of rating? I have heard that the cap may not form correctly when used at a voltage much lower than its' "working voltage" rating.
:
:Thanks
:Lou
:
Terry

7/24/2010 12:28:35 AMLou

Thanks all for your inputs.

I was still working under the illusion that you needed to be near the WVDC to allow the cap to work properly.

Well, my Silvertone will be happy ( and so will my wallet since I don't have to stock so many values).

Thanks
Lou

::Gentlemen:
::
::I am restoring a Silvertone radio and I happen to have on hand the proper electrolytic capacitor value for one of the cap replacements. It is rated around 450 VDC.
::
::The problem is that the ORIGINAL capacitor has the same value but is rated at only 275 VDC ( which is still proper for this design, by the way ).
::
::Is there any downside to using the 450 volt cap at 275 volts of rating? I have heard that the cap may not form correctly when used at a voltage much lower than its' "working voltage" rating.
::
::Thanks
::Lou
::
:
:You can ALWAYS use a higher voltage rating. The cap is not offering the circuit a resistance or inductance, therefore current is not an issue.
:Terry
:

7/24/2010 6:46:30 PMEdd

Sir Lou . . . . . .

. . .
WHAM ! . . .and another fallacy bit the dust . . . .another fallacy bit the dust . . .

The ONLIEST bugaboo that I am finding in that respect is with lower capacitance values along with that much HIGHER voltage rating, is if being in modern SS electonics circuitry, in the shifting up too high in voltage rating and with that accompanied internally thicker formed oxide barrier.

That caps ESR is greater and can result in poorer decoupling /filtering action.

Now, if I just HAVE to work with that being the only capacitor available, I just scope
across the capacitor for its waveform in operation and then either shunting a tandem .01 or .1 ufd ceramic ( all in accordance to the frequencies being involved) across that electrolytic will solve the problem.

73's de Edd

Thanks all for your inputs.

I was still working under the illusion that you needed to be near the WVDC to allow the cap to work properly.

Well, my Silvertone will be happy ( and so will my wallet since I don't have to stock so many values).

Thanks
Lou

Gentlemen:

I am restoring a Silvertone radio and I happen to have on hand the proper electrolytic capacitor value for one of the cap replacements. It is rated around 450 VDC.

The problem is that the ORIGINAL capacitor has the same value but is rated at only 275 VDC ( which is still proper for this design, by the way ).

Is there any downside to using the 450 volt cap at 275 volts of rating? I have heard that the cap may not form correctly when used at a voltage much lower than its' "working voltage" rating.

Thanks

You can ALWAYS use a higher voltage rating. The cap is not offering the circuit a resistance or inductance, therefore current is not an issue.

7/27/2010 10:06:20 AMCodefox

Agree with all. You can also safely use, say a modern 22 mf 450 volt to replace a 16 mf 250 volt cap, and expect the filtering/decoupling the same. Tolerences on ancient electrolytics were quite large, so the matter is somewhat moot for all but the most sensitive applications. Just be careful with the first smoothing capacitor after the rectifier; I wouldn't go much higher than the value regardless of the working voltage of the replacement.

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:Sir Lou . . . . . .
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:WHAM ! . . .and another fallacy bit the dust . . . .another fallacy bit the dust . . .
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:The ONLIEST bugaboo that I am finding in that respect is with lower capacitance values along with that much HIGHER voltage rating, is if being in modern SS electonics circuitry, in the shifting up too high in voltage rating and with that accompanied internally thicker formed oxide barrier.
:
:
:That caps ESR is greater and can result in poorer decoupling /filtering action.
:
:
:Now, if I just HAVE to work with that being the only capacitor available, I just scope
:across the capacitor for its waveform in operation and then either shunting a tandem .01 or .1 ufd ceramic ( all in accordance to the frequencies being involved) across that electrolytic will solve the problem.
:
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:73's de Edd
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:Thanks all for your inputs.
:
:I was still working under the illusion that you needed to be near the WVDC to allow the cap to work properly.
:
:Well, my Silvertone will be happy ( and so will my wallet since I don't have to stock so many values).
:
:Thanks
:Lou
:
:
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:
:Gentlemen:
:
:I am restoring a Silvertone radio and I happen to have on hand the proper electrolytic capacitor value for one of the cap replacements. It is rated around 450 VDC.
:
:The problem is that the ORIGINAL capacitor has the same value but is rated at only 275 VDC ( which is still proper for this design, by the way ).
:
:Is there any downside to using the 450 volt cap at 275 volts of rating? I have heard that the cap may not form correctly when used at a voltage much lower than its' "working voltage" rating.
:
:Thanks
:Lou
:
:
:
:
:
:You can ALWAYS use a higher voltage rating. The cap is not offering the circuit a resistance or inductance, therefore current is not an issue.
:Terry
:
:
:

7/28/2010 12:00:56 PMTerry Decker

:Gentlemen:
:
:I am restoring a Silvertone radio and I happen to have on hand the proper electrolytic capacitor value for one of the cap replacements. It is rated around 450 VDC.
:
:The problem is that the ORIGINAL capacitor has the same value but is rated at only 275 VDC ( which is still proper for this design, by the way ).
:
:Is there any downside to using the 450 volt cap at 275 volts of rating? I have heard that the cap may not form correctly when used at a voltage much lower than its' "working voltage" rating.
:
:Thanks
:Lou
:
There is one exception to the higher rated rule: That concerns the mica caps around the RF and IF circuits. The values of these caps are much more critical. It's true that the voltage can be increased, but the value must be within 10% of the marked value. Drastically changing these values could throw off the oscillator or make alignment difficult. Fortunately these caps VERY SELDOM go bad and need replacing. One exception would be repairing the dreaded "silver mica disease".
Like I said, this just FYI.
Terry