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Thread: Power usage calculation

  1. #1
    Wine_of_the_Bean
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    Power usage calculation

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    If a piece of equipment is rated at 3300W, how would one convert that into power usage/time? Is it 3300W/second?

  2. #2
    Senior Member flynnaus's Avatar
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    Re: Power usage calculation

    Its usually usage (or energy) = power (kilowatts) x time (hours) so in 1 hour, energy used by a 3300W device would be 3.3 kWh (ie 3.3kilowatt hours).

    Do you need to work out the cost of running? Check your bill for electricity rates at bthe time of usage.

  3. #3
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    Re: Power usage calculation

    3300W is 3.3KW so if run for an hour that would be 3.3KwH......

    At say 14c per Kwh (Perth prices) that will cost you 46.20c per hour...or $11.09 per day..... or $332.64 per month if on 24/7!!!

    But that assumes it is using 3300W permanently..... If a coffee machine they normally run at about 10% duty cycle..... so that is $32 per month.....

    Mine is a 4200W on 24/7....... at about 10%..... so work out what it costs me!

  4. #4
    Wine_of_the_Bean
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    Re: Power usage calculation

    Thats what I thought. I just needed the power consumption/hour.

    If the thing is used for say 28.75 mins, it will be approx 1.58kWh

  5. #5
    Senior Member redzone121's Avatar
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    Re: Power usage calculation

    JavaB, any idea of cost to run a VBM 1800w 24/7. I guess there is no duty cycle for a non commercial machine, if so thats 1800w x 24hrs?

    Cheers

    CB

  6. #6
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    Re: Power usage calculation

    CB,

    The duty cycle does vary from machine to machine...... and that is "steady state" - when actually being used it increases to replace the lost heat..... but generally they run somewhere between about 10% and 20% duty cycle whilst idle.

    So you could probably guess at 15%..... which would be .27Kw x 24hrs ...... about 6.5 KwH per day.

    If you want to be more accurate - time how long the heater light is on/off (if you have one).... or listen for the clicks from the pressurestat..... one click, another say 7 seconds later..... then one 60 seconds after that.... means the duty cycle is 7 divided by 7+60...... 7/67 or 10%

  7. #7
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    Re: Power usage calculation

    By the way for those who are scared when they see how much a machine consumes when left on 24/7.....

    During the warm up from cold the heater is on pretty much 100%...... so no duty cycle.....

    My warm up consumes about the same amount of power as the machine does in 8 hours if left on..... so switch it on and off twice a day = running non stop for 16 hours..... 3 times a day.... and you might as well leave it on! And no temperature stability problems or waiting for heat up either.

    However is your machine doesnt have a reasonably heavy duty thermostat or pressurestat..... leaving it on could cause premature failure as it will be cycling constantly.

    But turning a machine off to save power..... probably wont make a lot of difference - unless you are a one coffee a day person...... and who does that ::) ;D

  8. #8
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    Re: Power usage calculation

    Quote Originally Posted by redzone link=1219471403/0#4 date=1219476464
    JavaB, any idea of cost to run a VBM 1800w 24/7. I guess there is no duty cycle for a non commercial machine, if so thats 1800w x 24hrs?
    Sure there is a duty cycle for every machine. In standby mode, the thermostat will from time to time switch the electric heating elements on, in order to maintain a constant temperature. If the machine has a boiler or two, it will aim at maintaining water temperature constant. In the case of a thermoblock machine, the aim is to keep block temperature constant.

    How often the heater(s) are switched on during standby, and for how long, is what determines the power usage in standby mode. Every machine is different in this regard, but I would not expect any to exceed a power usage of more than 5-10% of the maximum wattage on the rating plate whilst in standby mode. In your case that is around 90 to 180 Watt-hours. Or in other words, about what one or two old fashioned incandescent globes would use if left permanently on.

    How often the heater(s) are switched on during standby, and for how long, depends on many factors, most notably:
    - ambient temperature, the colder the room the more often and longer will electric energy be consumed.
    - how well is the boiler or block insulated. The better the insulation, the less energy will be consumed. But many coffee machines are on purpose built with a poor insulation or no insulation at all, the heat losses being used to preheat the cups on top of the machine. In summer that can cost energy two times, once to heat the cups and once to aircondition the room.... in winter it may save a few firewood logs ;).

    Of coure power consumtion will rise with usage of the machine, since more water will need to be heated. However, in a non commercial environment this is only a tiny small portion of the overall energy use if left on 24h/7days.

    Me personally, I switch off the machine after use, unless I feel another cup may be required in under say half an hour time. I would recommend to at least turn it off overnight. It also depends a bit on how long a given machine takes from turning on until reaching an even and stabilised temperature. Domestic machines are usually designed to be quite fast in this regard, since the vast majority of home users only turn it on when they actually want to have a coffee.

    Chris

  9. #9
    Senior Member redzone121's Avatar
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    Re: Power usage calculation

    Thanks JavaB and Chris.

    Ill now turn mine on in the morning and offf again at night.

    CB



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