electric meter rotor rpm vs power
electric meter rotor rpm vs power
Does anybody know how to take the rpm of the rotor on an electric meter and convert it to kilowatts? I have found general info on the net that says the meters are calibrated with a strobe, but nothing specific that says how you know many RPMs = 1kW (or how many rotations = 1 kWH).
Re: electric meter rotor rpm vs power
Hi.
I would say every power meter manufacturer can do it their ways.
Try counting how many disc turns takes to change the least significant digit one count; if that digit is tenths of a KWH, multiply by 10 to get the number of revolutions per KWH.
Miguel
I would say every power meter manufacturer can do it their ways.
Try counting how many disc turns takes to change the least significant digit one count; if that digit is tenths of a KWH, multiply by 10 to get the number of revolutions per KWH.
Miguel
- Abolish the deciBel ! -
Re: electric meter rotor rpm vs power
I asked my friend, who worked for the power company, how many turns of the wheel for 1 KWH. He said there is a number on the front, something like KH=xxxx, which is the number of turns for 1/1000 of a KWH. I checked my meter which has Kh7.2. I counted 50 turns and there was very little motion of the first digit, so 7200 turns/KWH may be right.
Re: electric meter rotor rpm vs power
Thanks; I'll check it out and see if I get something reasonable on mine.
Re: electric meter rotor rpm vs power
I think you have to know what your load is and go from there or go from what you know your motor is drawing.<p>You might have a 1 HP motor (that's about 746 Watts), but you can't know whether the motor is suppling full load. The rpms ought to be about the same whether turning a full load or spinning freely (no-load), the difference is how much current is drawn. So you need to know the current your drawing, the voltage is given. If you've never taken a current reading, be safe. Make sure you know what to do and get a sanity check from someone.<p>Useful conversions for you.
1 Horsepower equals about 746 Watts.
Power = Voltage(rms)*Current (not true for three phase, I rember that 3phase was confusing for me).
Energy = Power*time<p>If you knew you had a 1HP motor and that the motor liked to rotate at 1000 rpm and that when you had the load connected you drew 5 Amps at about 115 VAC(rms), you would know that
5*115 = 575 Watts and that if that same load were continually supplied with power that in one hour you would have used 575 Watt*hours and if you knew that your loaded rpm was 950 you would know that at 575 Watt*hours your motor rotates at 950 rpm. You could experiment and come up with a correlation between load and rpm but I honestly don't remember if it's a terribly linear thing (I think so though). I seem to remember that there is motor statistic that gives the fall off in rpm from no load to full load that would make your life a lot easier. I think it comes as a percentage, not sure. Not much help, huh?
-Rick
1 Horsepower equals about 746 Watts.
Power = Voltage(rms)*Current (not true for three phase, I rember that 3phase was confusing for me).
Energy = Power*time<p>If you knew you had a 1HP motor and that the motor liked to rotate at 1000 rpm and that when you had the load connected you drew 5 Amps at about 115 VAC(rms), you would know that
5*115 = 575 Watts and that if that same load were continually supplied with power that in one hour you would have used 575 Watt*hours and if you knew that your loaded rpm was 950 you would know that at 575 Watt*hours your motor rotates at 950 rpm. You could experiment and come up with a correlation between load and rpm but I honestly don't remember if it's a terribly linear thing (I think so though). I seem to remember that there is motor statistic that gives the fall off in rpm from no load to full load that would make your life a lot easier. I think it comes as a percentage, not sure. Not much help, huh?
-Rick
Re: electric meter rotor rpm vs power
Sorry about that, I just realized that had nothing to do with your question. :-\
Rick
Rick
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