Now, how about the next example. RMS of a sine wave using only 4 samples
but this time use 170 volts peak value and 144 ohms (100 watt light bulb).
I have rounded the following to the nearest tenth to make it easier to read
but if you wish to carry it out to all digits it works perfectly.
phase V V Squared Power into 50 ohms
0 0 0 0
90 170 28900 200.7
180 0 0 0
270 -170 28900 200.7
Total 0 57800 401.4
Average 0 14450 100.3
Sq.root 0 120.2
Power = Vrms Squared/R= 14448/144 = 100.3
How about that. only 4 samples.
By the way that is how most power inverters produce a "modified Sine Wave".
The important point is that the RMS and PEAK values are correct. Electronic
devices with capacitive input filters are happy and so are other things
like light bulbs, motors ,etc.
They use a high frequency inverter (switcher) to get the 170
volts DC and then use a pair of H-Bridge power MOSFETs to put the proper
voltages on each of the 120 volt output connectors. One thing, the cheaper
ones do not have a "hot and return" they have two hot terminals that are
180 degrees out of phase. This is bad news if you are using a hot chassis
AC/DC set. You are going to have 60 Volts RMS on the chassis no matter
which way you insert the plug.
73
Bill wa4lav
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|