Kwh

[western mainer]

I will be getting a 1 1/2 Hp motor and would like to know how much power it would use in one hour (KWH) so I would have an idea how much my power bill would be per day.
Thanks Brian

[TheMapleMoose]

Take the amps the motor draws, multiply by its voltage to get watts. Divide the watts by 1000 to convert to kilowatts.
Ex. If its 15a 220v: 15(220)=3,300watts. 3300/1000=3.3kw. Multiply the kw by the hours it will run. 3.3(5hrs)=16.5kwh. 16.5kwh @ .17/kwh is $2.80 per day.

[western mainer]

Thanks for the info.
Brian

[maple flats]

I don't think so. A 1.5 HP motor uses .746 KW/hr X 1.5= 1.119 KWH x the run time in hours. Then you must add the surge figure and add it. At start up there is a surge that must be measured to be exact, but it will likely add less that 1 KWH to the run time. Now multiply X your rate. Here our rate is $.17/kwh taxes delivery, line charge and all included. If you run it 12 hrs you use maybe 14 KWH, roughly double that for 24 hr use.

[TheMapleMoose]

I just used some numbers fir example but Yeah, you're right. Hp is output power so that's what you use to find its kw usage. It's hard to get an exact cost of operation without knowing the efficiency or load but it should give you an idea.

[lpakiz]

It has nothing to do with the HP of the motor. You are paying for how many times the meter revolves when you turn the motor on. Volts times amps equals watts. You are paying for watts (kilowatts) times the hours you use them. For one hour, it is the volts times amps thing, divided by 1000 to convert to kilowatts. Works for water heaters, light bulbs, motors, everything. Use a voltmeter and a clamp on ammeter and get your numbers. Yes, the startup surge is there, for a few seconds per day. Essentially nothing in the whole days running. The amperage may vary depending on how heavily the motor is loaded. That's why you need to measure these things while running at the load the motor is pulling.

[wiam]

If you are trying to estimate next year it has everything to do with hp/amps on the plate on the motor

[PerryW]

yes, a 1.5 HP motor's power consumption will vary widely, depending on load.

In theory, a 1.5 HP (under constant full load) will use 1.12 KW-HR's every hour (0.746 X 1.5), or about 16 cents per hour at a rate of $0.15 per KW-HR.

[maple flats]

Look it up from the manufacturer of the motor, they should have a guideline on usage on that motor.
For example, I just looked up info on the motor I am putting on my RO to replace a 4 HP Honda. The motor is 2 HP, by Leeson. When I look in the Leeson info they have a chart at the end, showing amps at various loads. It is a 230 V motor. With a 25% load it will draw 4.54 A, 50% load= 5.68A, 75% load = 7.19A, 100% load = 8.95 A. You can see how the amps rise as the load increases. Testing load % is harder, but testing the amps when running the load gives a good idea for calculation purposes.
If you use the FLA rating to calculate it will only be correct if you are using the whole rated HP since FLA means full load amps.

[maple flats]

Another way is to turn everything else off and run the motor. Watch your meter with nothing else on line. Time a measured interval and record the reading change during that time. Then do some math. For this to be close the motor must be running at the same load as it will during the season.

[lpakiz]

Now we are right on! Also, if you measure amps and find you are well under the FLA, you might want to find a smaller motor, which will probably run cheaper, provided you are still within its HP range, again, measured at the motor, not off the data tag of the motor.
Also, you may be able to to go the big-box home improvement store and buy a device which plugs into the wall and you plug your load into this device. I will display the amp draw. I believe some even allow you to enter your electric rate and they will display what it is actually costing you to operate any given load.

[wiam]

Now we are right on! Also, if you measure amps and find you are well under the FLA, you might want to find a smaller motor, which will probably run cheaper, provided you are still within its HP range, again, measured at the motor, not off the data tag of the motor.
Also, you may be able to to go the big-box home improvement store and buy a device which plugs into the wall and you plug your load into this device. I will display the amp draw. I believe some even allow you to enter your electric rate and they will display what it is actually costing you to operate any given load.

I have one for 110 but have not seen one for 220

[maple flats]

If you have an ammeter that clamps around a single lead that is all you need. Then in your formula to calculate the watts the amps are the same but the volts is double. Also, don't go by a std 110V, 220, 230, 240, but rather read the voltage in use on that line. Read it several times through the day. Voltage is often not constant. It fluxuates within a usually small window. Peak use times for the grid often see lower voltages and vise versa. Time of day also give different voltages for this reason. What ever you get in your voltage readings, average them using 10 or maybe even 20 different readings taken at different times of day and even days of the week. Remember if you are only reading 1 leg you double the voltage it says. Use the average, multiply times the average amps you got and that is your watts used. Now multiply the answer by the number of hours you expect to run the motor and devide that by 1000 to get KWH. Now multiple that by your rate/KWH. For this use a recent bill and get the total KWH used and the total charge with taxes etc. Divide to get a real life answer. Make sure you use the total, many suppliers charge for usage and delivery separate, if your's does add them for a total.

[western mainer]

Thanks for all the info here.
Brian

[PerryW]

Yes, they are called Kill-a-Watt meters but they only do 115 volts. They will keep track of the actually KW-HR's used over a period of up to 30 days. They also wll display AMPS Kv-A's, watts, and line voltage.

http://www.smarthome.com/9034/P3-International-P4400-Kill-A-Watt-Energy-Meter/p.aspx