well the RMS calculations didn't work out. my base reading from the sensor with no current is 1/2 vcc which gets translated to roughly 507. Hooking up the heater I get up to 570 on high which the kill a watt reports to be 1300 watts. The RMS calculation climbed to 509 maybe 510 doing the math in a spreadsheet using the current sensor datasheets estimate of approximately .023 mV/amp The peak readings was off by about 15% adjusting the math to 0.026 mV/amp I get within 2% for all of my readings done above 500 watts. The values below 500 watts are 12, 17,26,53 and they are off by 47%,75%,47%,18%.
At this point I'm going to go with this method and just the higher adjusted value. The water heater is closer to 5000 watts then 50 watts so hopefully things stay close up there. I'd love to get a real instantaneous reading to know how close I am on the tank but I don't have the equipment to do it.
Another concern I have is the watt meter tells me I have 119 V, when I kick the heater on full the voltage drops to 114 V. I'm assuming the same will happen with the hotwater heater however it won't be running on a close to overloaded circuit like the portable heater was. I'll probably just guess at the voltage on the line as being 230 and live with that. Now that I think about it I suppose I could read it directly using the multimeter one day when the heater is running.
|