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Good day, I am wondering if it's possible to estimate the continuous current consumption of a DC motor vs startup or rated current.

I am trying to put together a solar powered aquaponics system. The system would have one water pump that is rated at 24V/250W and two air pumps rated at 12V/80A. Obviously head height comes into play for a specific estimate but I would be happy with a general rule of thumb or a rough estimate of what my continuous power consumption would likely be.

I suspect these ratings are maximum or startup and the continuous wattage would be considerably lower?

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  • \$\begingroup\$ The air pumps seem to be the biggest load at 1kW while the water pump may start at 800% and lower to <=250W depending on differential pressure. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Aug 1 '18 at 22:35
  • \$\begingroup\$ Tony, thank you, that gives me a much better idea of what to expect. \$\endgroup\$ – Tim Christensen Aug 3 '18 at 0:08
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For general purpose motors, the rated current, input power and mechanical power are the levels at which the motor cam be operated continuously without reducing the life of the motor below the expected life. For motors sold as part of a product, the ratings are the expected maximum current for normal use. For products that are not normally used continuously for long periods of time, the current or power marked on the product may be higher than would be advisable for continuous use.

For a pump, the product input power rating would be based on the design head and flow that should be part of the pump specifications. If the pump will be operated at a different operating point you would need to calculate the input power based of the actual head, flow and efficiency. Normally the pump and motor efficiency are highest at the design head and flow.

You could estimate based on estimating what percent of head and flow you expect as a percentage of the capacity of the pump.

The situation for the air pump is probably somewhat similar, but you would need to determine what type of machine it is to know the effect of operating conditions.

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  • \$\begingroup\$ Charles, Thank you most kindly. That's the kind of clarification I was looking for. \$\endgroup\$ – Tim Christensen Aug 3 '18 at 0:04

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