calculating wattaqe using a ssr

[mako86]

I've reading somewhere that you can't using voltage or amperage readings to determine wattage using a phase angle controller because of the way the controller changes the sine wave. Is this true with a ssr controller, if so how do I figure out the wattage? I know at full power it is correct.

[Maritimer]

Hi mako,

You need a meter that reads true RMS. Measure the voltage across the element and then measure the current. Multiply them together to get the wattage.

The resistance of the element will change a little when it's hot, but maybe not enough to matter. You could measure the resistance of the element, then calculate the wattage using the formula P=V2/R. See if this agrees with the voltage X current. If it's OK, then you can just make a table or graph of V2/R and use it to convert the voltage reading to power.

M

[rad14701]

I wrote and posted a Power Controller Wattage Chart Calculator a while back which calculates a chart based on Voltage and element Wattage rating... It can be downloaded and run in your browser...

[mako86]

Using the ampmeter on my controller and checking the voltage at the element I am getting flooding at 2.9kw with my VM still with 42" of spp. Using p = V squared/R I come up with only 2kw. That makes me think that W=AxV is closer to the truth using the ssr. Although I still think it's incorrect. I would think flooding would occur at much higher power input. Just over 19 amps is wide open with my 4500 watt element. At 17 amps it's showing only 165 volts at the element, which is 2.8kw. A fraction more on the dial and I have 4.5kw. I wil have to try to find where I seen about the sine wave being manipulated in a way that a meter won't give you correct wattage.

[sambedded]

regular Voltmeters / Ammeters shows lower measured value for non sinus waves than TrueRMS meters.
And worse of all same reading on regular volt/ammeter can be on different power depending initial voltage at your mains.
Let say you have set 40% of power by dial. and your mains voltage is 240V and you have a 5500Watt element

Voltmeter's reading
Regular - 108.1V True-RMS - 158.7

Power on your element is ~ 2405Watt

Then imagine your mains voltage fluctuated (by standard +/5% is OK) and now it's 228V.

You adjust your dial to keep previous 108.1V reading but TrueRMS voltage will be 155.8V
Now your element gives you only 2318 Watt

So i'ts almost 100Watt difference while you a thinking that power is the same.

If you want know real power - use True RMS voltmeter or ammeter.