| nina |
Hi,
Just wonder if there are any recommendation on how to select voltage rating for capcitor, esp. filter cap? How many percent of extra volatge rating required?
Is that safe to use 56Vdc (from 40-0-40 tranformer) with a cap 63V?
Thanks, |
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| anatech |
Hi nina,
Yes, you are perfectly safe.
-Chris |
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| pinkmouse |
| Well, the caps may be safe, but the chip amp would likely blow up, 56 V rails are way over spec for all the ones I can think of. |
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| AndrewT |
Hi,
40Vac will take the 63Vdc cap right to the limit if the regulation of the transformer is about 5%.
If the transformer regulation is more than 5% then you should use 75Vdc or 80Vdc caps.
But Pink is right. You probably need a 25Vac or 30Vac transformer. |
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| anatech |
I guess the question now is, what chip amp? What is the N.L. DC voltage? Some STK chips will run this high.
Andrew is correct in that an unloaded transformer will output a much higher voltage than it's rated at. Your AC mains could very well take this over the cap rating.
It is okay to use a 63V cap when the measured DC is around 56V. I have seen worse in mass market units.
-Chris |
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| poobah |
Did Nina say chip amp? Who said chip amp?
Caps these days are generally given 2 ratings: "WORKING VOLTAGE" & SURGE.
Caps perform at their peak when run as close to, but NOT over their WVDC (Working Volts DC) rating.
So... 40 times 1.414 times 110% = 63 Volts... PERFECT!!!!!!!!!!
Pull up to the second window...
;) |
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| pinkmouse |
| quote: | Originally posted by poobah
Did Nina say chip amp? Who said chip amp? |
We are in the chip amp forum! ;) |
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| poobah |
uh... uh... uh...
:smash:
:( |
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| anatech |
Yup,
Poobah, some times it's all about location, location, location. :D
-Chris |
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| poobah |
| Jeeze guys... I'm working with 2 brains cells here... one wants a drink and the other has a hangover....... |
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| djk |
All parts last longer if you de-rate them from their maximum, caps included.
How much?
For caps I like to see 10%, unless the transformer is smaller than 300VA, then 15%, smaller than 100VA, then 20%. If you live in an area with poor line regulation you may need more de-rating than this.
The 'surge' voltage rating is for 1/2 of the 50/60 hz line cycle and is for choke input filters (tube stuff) only. |
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| poobah |
| quote: | | All parts last longer if you de-rate them from their maximum, caps included. |
Very GOOD point... that is true for nearly all parts because of temperature which applies to electrolytic caps as well... the life of most devices tends to halve with every 10-11 C in operating temperature. Electrolytics have one quirk though... they need voltage to maintain their insulating layer.
Maximum life for an electrolytic is derived from:
1) Best practice when mounting, wiring, and cleaning... i.e. do not damage the elastomeric seals (this is often the a big culprit). Keep them away from ozone, UV, and chlorine in all its forms.
2) Maintain the lowest ambient temp (we are not talking cryo here).
3) Reduce the RMS currents as budget will allow (more capacitance per unit of RMS current).
4) Run as close to, but do not exceed, the WVDC rating. NEVER exceed the surge rating (this means proper consideration of line/circuit variations as "dkj" said above.
:D
PS... don't hook them up backwards (dramatically shorter working life). |
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