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# Calculation of the engine power

> > Engine power

### Which motor (kW) do I need?

Following formula is used to calculate the required drive power : > > > Formula (1)

P = Engine Power [kW]
p = Pump Pressure [bar]
Q = Flow rate [l/min]
510 = 600*Efficiency 0,85

The Flow Rate of the pump can be calculated the following way: > > > Formel (2)

Q = Flow rate [l/min]
Vg= geometric flow rate of the pump [cm³/U]
n = Speed of the drive motor [R/min]

To drive gear pumps with electric motors only engines with 1000, 1500 oder 3000R/min are possible. The optimal speed is 1500R/min!

It is important to note that E-motors can be overloaded by 1.4-times temporarily. Petrol or Diesel motors are not able to do this.
Example wood splitter: A small E-motor will do, because the required force is needed only temporarily, almost no force is needed during no-load and return stroke which gives the motor time to cool down.

Example:
A power unit for a wood splitter.
A pressure of 200bar and a flow rate of 20l/min are needed.

Formula (1) can calculate the required E-motor power:

P = 200bar * 20l/min / 510 = 7,84kW

In this case the nominal three-phase motor with 7,5kW and 1500R/min would be chosen.

The next step is to calculate the flow rate of the pump by changing Formula (2) to Vg:

Vg = Q * 1000 / n > > > Formula (3)

Vg = 20l/min * 1000 / 1500R/min = 13,3cm³/U

In this case a gear pump with 14cm³/U.

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