Difference between electric and hydraulic motors 1

[Abdzaidy]

Hello every one
in advance I'd like to thank everybody here
I need a comparison between electric and hydraulic motors..
and I need to know how to calculate mechanical, volumetric and total efficiencies. if it is possibles with examples... thank youuuuu

 

[BrianPetersen]

For what purpose?

Electric motors generally like spinning fast. Hydraulic motors generally don't. They're used in totally different applications. An electric servo motor and a gearbox can substitute for a hydraulic motor for a low-speed application. A hydraulic motor in a high-speed application just doesn't work very well.

And there's many types of electric motors, and many types of hydraulic motors, each suitable for different application.

More information = better answers.

 

[IRstuff]

Is this for school? You seem to be asking a bunch of homework-style questions.

Student posting is forbidden

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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[PNachtwey]

Hydraulic motors were used to lift the sections of the New Bay Bridge. These sections weighed up to 860 tons. Hydraulic motors provide high torque without a gear box. They are also good for holding a load. Electric motors are not good for holding a load because a lot of current is required to generate the required torque just to hold the load. Hydraulic motors may leak a bit when holding a load bit it is easy to compensate for the leakage.

Hydraulic motors will stop as soon as the oil supply is shut off. Electric motors will not stop unless the is power to generate a braking torque or there are mechanical brakes the will stop the electric motor when power is gone. This is a safety issue. Hydraulic motors will stop when power is removed. Electric motors will coast when power is removed. I do not like controlling electric motors in a linear application because of this. Too many times the customer has not thought about braking with no power. When the motion controller detects a fault it sets the control output to 0 but that alone does not stop an electric motor. Our controller does have a fault output to go to the drive but this assumes the customer wired the fault output do do something. Sometimes the motor can be setup to act a generator and dissipate energy through a bank of resistors.

BTW, it was my experience with hydraulic and electric motors that convinced me that inertia matching isn't really necessary. Electric motor guys always talk about inertia matching but hydraulic motors almost always very large inertia mismatch yet the hydraulic motors still work.


Peter Nachtwey
Delta Computer Systems

http://www.deltamotion.com

http://forum.deltamotion.com/

 

[akkamaan]

Pump efficiency can't just be calculated with measuring key inputs.
Vołumetric efficiency is actual output flow divided with the measured physical displacement. The difference is due to internal leakage (under pressure). In a pump with no "casing" like a common gear pump, the internal leakage goes back to the inlet side. In a pump with casing like a piston pump, we have internal leakage both back to the inlet side and into the casing and led back to tank in a drain line. Measuring flow in this drain line is a useful part in getting input for the volumetric efficiency calculation but it won't tell the "full story". O e have tu use a flow meter to know the real output flow from a pump to be able to calculate volumetric efficiency.
The mechanical friction efficiency is hard ant not to say impossible to measure since it has to be done together with pressure and flow. But the total efficiency can be estimated by measuring the electric input power ie voltage and amperage to the prime mover. But the motor also has it's own internal losses. Electric motor and hydraulic pump manufacturers do provide efficiency diagrams that "should be" more relied on than our own calculations.
But for a maintenance purpose we often have to measure a pumps actual output flow to determine if it is practically and economically efficient.

 

[TimSchrader2]

Hello

Good points.
With a Hydrl motor once the max load is reached the hydrl motor will stall unless more pressure and flow is delivered. With a elec motor its stall torque is usually about 1.5 to 2 times its rated torque. So it can work in a pinch before the overload relays trip. So, you generally need to be more conservative with required torques from hydrl motors.
One elect motor and HPU can drive several much much smaller Hydrl motors. So if space is a concern there is no contest between Hydrl motors and electric motors.