5 replies to this topic

[satya23]

hello
in our organisation we r using hydraulic pump with 3 hp and 4.54 rated amps motor for rotating a tool which cleans a propellent in a bowl.This Pump of10LPM can develop 150bar but maximum pressure we used is 120 bar because motor is taking current of 5.2 amps against rated.Even at 120 bar the pump torgue is just sufficient to rotate the tool or could not rotate the tool in case if material viscosity raises a little bit. for trail purpose we have Another pump with 7.5 hp motor avilable in the same unit for rotating the same tool for cleaning the propellent of same viscosity.we could rotate the tool almost at same speed at 120 bar. but this is drawing current of 12 amps against rated of 10 amps.
my doubt is how this 7 hp motor is drawing more current than 3 hp motor for the same duty.And now the designer is going for 5 hp motor in place of 3 hp for the duty.

[Qalander (Chem)]

Dear satya23 Hello,

May I suggest you to Re-view,Re-Study the text of your query and the title.

I understand that this is nothing but obvious logically for a higher hp Electric prime mover to draw more current, then a lower hp machine.

Then what is the problem?
Best regards
Qalander

[satya23]

dear che jedi,
my question is that generally as i know 40-50 % of rated current of any motor is used for no load running remaining whatever the motor is drawing will be utilised for load.if we see like that 3 hp motor of rated 4.5 amps ,2.3 amps approx. is for no load running and above that remainng 3 amps (as motor is drawing a current of 5.3 amps in load condition) is using for tool rotation.
but for 7 hp motor(rated 10amps )is taking 12 amps so arround 7 amps is taking for same load.
so my doubt is that 7.5 hp requires higher power than 3hp motor for the same work?.
and now we r going to install 5 hp motor for the same duty will it be sufficient for the work ?or it also takes higher than rated ?.
please make me understand.

[Qalander (Chem)]

dear che jedi,
my question is that generally as i know 40-50 % of rated current of any motor is used for no load running remaining whatever the motor is drawing will be utilised for load.if we see like that 3 hp motor of rated 4.5 amps ,2.3 amps approx. is for no load running and above that remainng 3 amps (as motor is drawing a current of 5.3 amps in load condition) is using for tool rotation.
but for 7 hp motor(rated 10amps )is taking 12 amps so arround 7 amps is taking for same load.
so my doubt is that 7.5 hp requires higher power than 3hp motor for the same work?.
and now we r going to install 5 hp motor for the same duty will it be sufficient for the work ?or it also takes higher than rated ?.
please make me understand.

Dear Friend,
Although It is not still clear from your second post what is your exact query.I will request you to remove vagueness.
However note that
Your OP never indicated

1.'load' or 'no load' issue

2.It descibes usage of 3HP motor drive and 7HP motpr drive in similar duties

3.You enquired drawing of more current by higher HP motor and went on to discuss use of a 5HP motor case

5.Obviously and most logically may draw current in between 3HP& 7HP motor Subject to that all the under discussion motors are identical w.r.t. Phase(Single or Three phase and Base Voltage)

Hope this helps
Regards
Qalander

[satya23]

dear friend,
my question is why 7.5 hp motor requires more power than 3 hp motor for doing the same work.

[Qalander (Chem)]

dear friend,
my question is why 7.5 hp motor requires more power than 3 hp motor for doing the same work.

I don't know why are you confused
P=VXI whereas

P i.e Power is a multiplicative product of

V i.e Voltage and

I i.e wheras I is the Current flowing through circuit.

Also by definition V=IXR(wheras I is the Current flowing through circuit,R is that Circuit's Resistance)
Or P=IXIXR
Since resistance of a particular machine(is usually constant) power is directly propotional to square of Current's value
Hope everything gets clarified
regards
Qalander