I have a big 3-phase AC motor and I want to measure the total power consumption over a single day.
No need for fancy measurements, just the total KWh over a single day. Is there a cheap instrument for that?
Sort of a specialized tool, not like a Kill-aWatt meter for ordinary appliances.
I wonder if you could rent the device you need from a tool shop or an electrical contractor?
What exactly are you calling cheap? Your typical 3 phase power logger will cost you several thousand dollars (and has a lot of fancy features you don’t need related to power quality). You can usually rent one for maybe $50 to $100 per day though. Would that be cheap enough?
Does the motor have a constant load? If so a simple amp prob and some math can give you the answer. If the load varies go with the engineer.
Can you use a clamp ammeter on one of the wires?
Thanks for the replies.
It is an air compressor motor and starts and stops at irregular times.
I could measure the current while turned on with a clamp meter and find the wattage drawn.
Then I could connect an hour meter like this.
I can check the hour meter reading after a week or a month and from this I can calculate the average KWh per day.
Several points
A $2.00 mechanical clock which works with a 1.5 V battery works well as an hour meter up to 12 hours. As long as it gets power it advances and when it does not get power it stops without losing the accumulated time. You can rig this in a few minutes but if the device runs often then you would need to check the meter daily. This is the system I used on the bilge pump on my boat which would only total a few minutes a day.
The bad news is that you cannot assume the motor’s electrical power consumption is constant as long as it is running. Far from it. The electrical consumption will vary with mechanical load and that will vary a lot. It is that way with motors running compressors, A/C, refrigerators, etc. Rated or nominal consumption is ideal under certain ideal, theoretical conditions. In reality it can vary by 50% or more.
Also, measuring current is not much help as you also need to measure cos(phi) which also varies with load. Of course, it all depends on how precise a measurement you need.
A better approximation is to measure the power consumption in one phase and if the voltage is the same on all three phases it can be extrapolated by multiplying by three. This is a much better approximation.
An old electro-mechanical single phase meter can be used to measure the power on one phase. Of course, if you have three then you can use one on each phase and add all three.
You can probably find an old power meter for little or nothing. If not you can get one of those killawatt or whatever.
Not sure if any of these integrate real power over time, but they’re worth checking out:
E-Mon 3-phase submeters (look on eBay)