jwong852

原帖由 Motti_sir 於 2009-9-12 23:40 發表
超sad~ 學校無學過true power = Prms x P.F.
最多只係計Prms 同埋P.F.
最後想問多少少野.....
true power =/= Vrms x Irms
係咪因為V同I 唔同phase?

係咪因為V同I 唔同phase?   ------------- 係
就算同phase, 唔同波型, power factor 都唔係=1.

Power 只有continuous power, peak power, 無 rms power !

[ 本帖最後由 jwong852 於 2009-9-13 11:11 編輯 ]

Offer

原帖由 jackli 於 2009-9-13 09:35 發表
間唔中都會有唔少人出post...
唔理power factor

因為佢地多數在50V DC以下玩,AC計算Power不是那麼簡單

Motti_sir

原帖由 jwong852 於 2009-9-13 11:09 發表


係咪因為V同I 唔同phase?   ------------- 係
就算同phase, 唔同波型, power factor 都唔係=1.

Power 只有continuous power, peak power, 無 rms power !

有道理!!
rms power 係無意思~
要求教科書講多少少
唔該晒各位ching
又學到野

ciel

原帖由 stephenwong 於 2009-9-10 11:17 發表
AC 220V from your socket is NOT 220V peak-to-peak ah!

220V is an rms value, which equals to 220 x 1.414 = 325V peak and 650V peak-to-peak.

That's my understanding.

Stephen Wong @ Hong Kong

Typo, I guess.

220 V x 1.414 = 311 V
230 V x 1.414 = 325 V

From Wiki:
In Europe, agreement was reached to change the various national voltages, which ranged at the time from 220 V to 240 V, to a common European standard of 230 V.
So in UK (originally 240 V), as an interim measure, electricity suppliers can work with an asymmetric voltage tolerance of 230 V+10%-6% (216.2-253 V).
France, Germany, Greece, Hungary, Ireland, Italy, Netherland etc. all changed from 220 V to a nominal 230 V value.

Will Hong Kong change also to 230 V?

There was precedent that Hong Kong had changed the AC voltage value. In fact many years ago the Hong Kong AC voltage was 200 V.
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原帖由 jwong852 於 2009-9-13 11:09 發表
Power 只有continuous power, peak power, 無 rms power !

It is interesting. The term 'rms power' seems originating from the HI FI industry.

Why there is no such thing as 'RMS watts' or 'watts RMS' and never has been
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[For the engineer: You have read that there is no such thing as "RMS power." Technically, you are right. However, over the years the term, regarding audio gear, has come to be applied to the measurement technique outlined above, so we use that language here, rather than terminology with which the customer is unfamiliar. Yes, the computation is mathematically an integral of the instantaneous power.]

An Explanation of RMS Power Measurement
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Power is simply the product of RMS Volts and RMS Amps, and the resulting figure is 'power'. Not 'RMS Power' - or any of the insane derivatives described above - just 'power'.

http://sound.westhost.com/power.htm

[ 本帖最後由 ciel 於 2009-9-13 17:00 編輯 ]