Author Topic: Periodic / predictible power factor issue?  (Read 2530 times)

dduffey

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Periodic / predictible power factor issue?
« on: October 07, 2015, 04:53:37 PM »
Now that the AC is not running as often I noticed a strange reading, it may have been this way for awhile but not sure I can get the history to see how long this has been happening.  I'm pretty sure this is a recent development, but not 100% sure.

The last two days I noticed that my Downstairs AC CT was using 350watts periodically between 3am-8am.  Normally this pulls about 3kw when ON and 0 when not running.  Between 8am-2am everything looks normal (0kw when OFF, 3kw when ON).  Then almost on the done, around 3am the CT starts reading 350 watts (the mains still show less than 350 watts, so I don't think it is actually pulling any load).  I thought it might be when the fridge compressor is OFF, or when the underground sprinkler turns ON, but it doesn't seem to perfectly correlate... so I am not sure exactly what could be happening at that time that could cause the AC CT to read funky.

I'm using and ecobee thermostate so I can see that nothing should be happening at that time (system is not kicking on)... any ideas about what might be causing this weird PF reading on what I think should be a dedicated circuit only between these times?

I'de like to fix it, because I'm still focusing on where to put my efforts and the anomaly causes the downstairs AC appear to be consuming a larger % of the electricity than it actually is.

RussellH

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Re: Periodic / predictible power factor issue?
« Reply #1 on: October 07, 2015, 09:48:43 PM »
the CT starts reading 350 watts (the mains still show less than 350 watts, so I don't think it is actually pulling any load).
Is there any change in the current reported by the main MTU?


dduffey

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Re: Periodic / predictible power factor issue?
« Reply #2 on: October 08, 2015, 09:00:04 PM »
the CT starts reading 350 watts (the mains still show less than 350 watts, so I don't think it is actually pulling any load).
Is there any change in the current reported by the main MTU?



Yes, but not an increase.  For example, MAINs were reading .325 when AC was reading .350, and then when AC was reading 0 MAINs were reading .450 ... at the time it looked like the AC was reading .350 when the fridge turned off.  When the fridge turned on (different circuit) the AC read 0.  But now I think that could just be by chance ... and I suspect it might actually be the underground sprinkler that it may be affecting the AC reading ... but the times for that don't match perfectly either (off by 2 hours).

Although I noticed this Tues/Wed morning, today Thursday the AC read 0 all night (and also the sprinkler didn't kick on).

So I'll keep an eye out and next time I see it I'll export the data and look for correlations with other circuits and the sprinkler system.

RussellH

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Re: Periodic / predictible power factor issue?
« Reply #3 on: October 08, 2015, 09:48:13 PM »
You might want to make sure all the clamps are completely closed.  And try to keep the CT wires away from others - or at least run at right angles.  Since sensing is via magnetic fields, stray stuff could be causing problems.

And make sure you're sensing the "hot" wire.  If you're sensing the neutral or white wire, you may be getting a reading affected by another circuit.

tlveik

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Re: Periodic / predictible power factor issue?
« Reply #4 on: October 09, 2015, 04:39:27 AM »
Some of your results seem backward so another thing you might check is if one of your current clamps is attached backward.  That can give some pretty strange results.

I can't imagine a sprinkler system using much power, unless you're pumping water, so I wouldn't spend much time looking at that.  The fridge on the other hand is worth looking at.

Russell's comment about making sure the current clamps are completely closed is a good one.

Tom