Power Calculation

[penno64]

Hi All,

Can someone help with a formula or some ideas on how to calculate -

how long a 230v-25W Incandescent buld should stay lit from a preloaded
3300uf(200v) Capacitor at 190v.


Thanks in advance, Penno

I should have added my calcs -

The energy stored in a capacitor can be expressed as

W = 1/2 C V2 (1)

where

W = energy stored (Joules)

C = capacitance (Farad)

V = potential difference (Voltage)


Since power is energy dissipated in a time - the potential power generated by a capacitor can be expressed as

P = W / t (2)

where

P = potential power (Watts)

t = dissipation time (s)


so my calcs -

p= 0.5 x 0.0033 x 190 x 190
= 59.56 joules

so for 25watt bulb

25 = 59.56 / t

t = 0.419 seconds

[wonju]

Penno,

That is not an easy calculation! The problem is that the resistance of the filament is not constant. For example, if you measure the resistance of a 120vac 100W incandescent light bulb you will find that is less than five ohms. When your turn it on, the heat raises the resistance. In other words, there is a current in-rush when the incandescent light bulb is turn on, initially the current is high but the heat up increases the resistance of the filament making the current to fall quickly. The current inrush is the reason why incandescent light bulbs fail when turning on.

Wonju

[penno64]

Thanks Wonju,

I guess what I am looking for is -

how long I should expect the cap to keep the lamp "REASONABLY" lit?

Thanks.