maximum voltage for capacitor

[Mamak]

if i have 10000uf/100V capacitor,what maximum voltage for this cap work very well?

[geraldfryjr]

100v! ????

[wintermute]

Hi Mamak, the two things you need to take into consideration are (assuming this is for use as a smoothing cap in a powersupply) the transformer regulation, and the mains voltage fluctuations. in a worst case scenario you need to add 20% for mains Plus the transformer regulation.

Say you have a transformer with regulation of 6%. When it is running with no load the voltage output will be 6% higher than the nominal rated voltage. If the mains is also at its maximum variation of +20% you need to increase that by a further 6% or around 27% in total.

Based on this a nominal voltage of around 78V (at full load with standard mains voltage) should be safe with 100V caps.

Tony.

[wintermute]

sorry I think that figure of 20% for mains variation is wrong (too high when I actually did the calculation for 240V)... I'll have to check

a quick google search resulted in Australian standards being 230V +10% -6%

so substituting 10% instead of 20% above we would get approx 85V for the safe post rectification no load at nominal mains voltage. Obviously the power specs in your area should be used as a guide

Tony.

[jfitz57]

Originally Posted by Mamak

if i have 10000uf/100V capacitor,what maximum voltage for this cap work very well?

The voltage on the capacitor is the "working voltage". If your transformer puts out 70 volts or less then it will work well.

[Shelby]

take care. transformer should not deliver more than 60Vac. Vdc ~ 1,41 times higher!!!