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  1. #1
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    Default Calculating the cost of running a three phase motor?

    Could someone with the right skillset please work out the running costs of this one for me -

    • 415V three phase
    • 19.7 amps
    • 11.0kW
    • 25.6 cents kWh


    If any more info is needed please let me know?

    Help would be appreciated!

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  3. #2
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    What is it running?

    Those specs (11.0kW) will be under some sort of nominal full load but might only drawing 1/4 of that under a light load.
    If its full load is 11kW x 25.6c kW/hr or $2.82 per hour.

    If its a dust extractor if will depend mainly on the amount of restriction - the greater the restriction the less air is moved the lower the load.
    For example the supposed 4HP (3kW) motor on my DC uses 2.3 kW when all the gate valves are fully open, But <1kW with just a 4" port open.

  4. #3
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    Quote Originally Posted by BobL View Post
    What is it running?

    Those specs (11.0kW) will be under some sort of nominal full load but might only drawing 1/4 of that under a light load.
    If its full load is 11kW x 25.6c kW/hr or $2.82 per hour.

    If its a dust extractor if will depend mainly on the amount of restriction - the greater the restriction the less air is moved the lower the load.
    For example the supposed 4HP (3kW) motor on my DC uses 2.3 kW when all the gate valves are fully open, But <1kW with just a 4" port open.
    Running a Hydrovane rotary vane compressor - Hydrovane Compressors | Rotary Vane Compressor Solutions
    Compressor.JPG

  5. #4
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    Compressor running costs depend on actual running load, use pattern, pressure cycle time and pressure range.

    Starting from atmosphere they don't draw full load but will draw close to full load when they get past about half way through their pressure range.
    Then they usually draw close to full power while recharging.

    Unless you draw more than at the compressor output, cost then mainly depends on time in hours to recharge x number of recharges per hour (which will depend on use) x motor rating.

    Lets say it takes 2 minutes to recharge, and recharges 3 times an hour then its 2*3/60* 11 x 25.6 = ~ 26 c per hour.

    Whats the planned use.

    An 11 kW will required a dedicated 32A 3P line and breaker.

  6. #5
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    Hydrovane compressors are different from the normal piston ones in that they run continuosly and have no reservoir to recharge. They run at constant pressure and vary the volume of air delivered as required. They are very efficient at deliveries of air close to their design capability but become very inefficient at lower rates.

    An 11kw unit will deliver up to approx ~60 cfm at 120psi but if you are not using any air will still draw about 4kw.

    Smaller air usage will result in a continuous consumption of between 11 and 4kw.

    Good for an industrial application where there are multiple users drawing air continuosly but a real money pit for the single user.

  7. #6
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    Quote Originally Posted by BobL View Post
    Compressor running costs depend on actual running load, use pattern, pressure cycle time and pressure range.

    Starting from atmosphere they don't draw full load but will draw close to full load when they get past about half way through their pressure range.
    Then they usually draw close to full power while recharging.

    Unless you draw more than at the compressor output, cost then mainly depends on time in hours to recharge x number of recharges per hour (which will depend on use) x motor rating.

    Lets say it takes 2 minutes to recharge, and recharges 3 times an hour then its 2*3/60* 11 x 25.6 = ~ 26 c per hour.

    Whats the planned use.

    An 11 kW will required a dedicated 32A 3P line and breaker.
    The rotary vane compressors are designed for 100% constant flow use rather than recharging, this one is going to supply constant flow breathing air to our laboratory at the rate of 450 lpm per person where we are going to be experimenting with some ethyl methyl nasty shortly, and it will also supply breathing air to my woodworking shop instead of using a PAPR. I was just wondering how much it was going to add to our electricity bill to make sure that I wasn't going to receive a massive bill shock!

  8. #7
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    Quote Originally Posted by Bohdan View Post
    Hydrovane compressors are different from the normal piston ones in that they run continuosly and have no reservoir to recharge. They run at constant pressure and vary the volume of air delivered as required. They are very efficient at deliveries of air close to their design capability but become very inefficient at lower rates.

    An 11kw unit will deliver up to approx ~60 cfm at 120psi but if you are not using any air will still draw about 4kw.

    Smaller air usage will result in a continuous consumption of between 11 and 4kw.

    Good for an industrial application where there are multiple users drawing air continuosly but a real money pit for the single user.
    Many thanks for that info Bohdan - that helps fill in the gaps a bit for me. So effectively these run a bit like a VSD - vary their load/output to meet the need?

    It sounds like it will cost about $1 per hour for low usage, and close to $3 for full usage.

  9. #8
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    Quote Originally Posted by RSD View Post
    The rotary vane compressors are designed for 100% constant flow use rather than recharging, this one is going to supply constant flow breathing air to our laboratory at the rate of 450 lpm per person where we are going to be experimenting with some ethyl methyl nasty shortly, and it will also supply breathing air to my woodworking shop instead of using a PAPR. I was just wondering how much it was going to add to our electricity bill to make sure that I wasn't going to receive a massive bill shock!
    That's exactly what they are designed to do. It will cost you somewhere between $1 to $2.82 for every hour that it is switched on at 120psi.

    The delivery pressure is the variable here and my figures are based on 120psi where you will get ~1800lpm.

    What pressure do the breathers run at?

    At lower pressures the power consumption will be much less even though the air quantity delivered will not change.

  10. #9
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    Quote Originally Posted by Bohdan View Post
    That's exactly what they are designed to do. It will cost you somewhere between $1 to $2.82 for every hour that it is switched on at 120psi.

    The delivery pressure is the variable here and my figures are based on 120psi where you will get ~1800lpm.

    What pressure do the breathers run at?

    At lower pressures the power consumption will be much less even though the air quantity delivered will not change.
    The filters have an OPV set at 95psi and the PPE runs at 75psi I think. I'm not sure how the output pressure is adjusted at the compressor though - I haven't gotten that far into the project yet.

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