No Load Consumption of Motor

Uncouple it and test it, or ask the motor manufacturer. Normally you will not have anything like the required information to even begin calculating it.

For medium sized motors (3 phase 3000 rpm) it will be around 25 to 40% of rated current. More for smaller and slower motors.

thank u.

if the motor full load current is 40A and the no load consumption will be around(40*.35*415=5810W) considering 35% will be no load consumption and supply voltage as 415V ac.

Correct me if i m wrong

The no-load current 20 - 40% FLC is higher than you might expect, but that doesn't mean the power drawn is 20 - 40%. At no-load the power factor is much lower than at full-load, at a guess 0.2 - 0.25, so input power is lower.

Codey

pls suggest me how to calculate the no load consumption of the motor.

i will be happy if u explain it with an example

Assuming it's a 3-phase system, as is likely from 40 amp in your #2, electrical input power (watt) = √3*volts*amps*power factor.

Volts is phase-phase voltage (looks like 415 in your case). Amps is current in each phase.

Codey

Just use a Tong Tester (Current Tester) and measure the motor current running at no load condition and use the current recorded in to this formula and you will get the power consumption of the motor

√3*volts*amps*power factor. -- For 3 phase System

A motor that is running idle, does not take much power from the grid.

Only the fan on the back side of the friction in the bearings are the biggest losses.

Aditional you have the warming up of the motor as losses.

I would guess +/- 8 % losses when driving idle

8% of what?

+/- 8% of the nominal output power of the motor

Sounds about right. If the current and power factor are both down by factor ~ 3, power is down by ~ 10.

Cheers..........Codey

I want to buy your motors - there is no way that a motor running under no load will only use 8% of full load current.

It doesn't use 8% of full load current. No-load current is 25-40% of full load current - see earlier posts.

It uses 8-10% of full load power, due to low power factor.

Cheers.........Codey

My apologies - did not read the 8% of what answer and assumed wrongly that you guys were talking about 8% of full load current. The Prof with his 25 to 40% seems to be about correct, which you confirm.

@Codemaster, I agree totally with you cheers

No Load Current is not calculated ...........

It is a measured parameter to calculate the few types of losses

I don't understand why the manufacturers do not stamp it on the nameplate of all motors.

Why should they? It's of little interest, you buy a motor to drive a load, not to run it on no-load for any length of time. Switch it off when it's not needed, but the power drawn is practically negligible compared with full load.

I have mentioned already in another thread the importance of no load current. First when you rewind a motor and test on no-load it will confirm whether the no-load current and pf have changed during the rewinding process. Secondly it will be useful to calculate the size of capacitor required for pfc. Thirdly it will be useful to calculate the size of capacitor required for shunt-capacitor type starting.

No-Load Power consumption is

Sq.Root of 3 x V x I x Cosphi = watts, where V is voltage and I is No-Load Current and cos phi is Power Factor at no-load.

You have to have a phase angle measure meter for current to know the angle by which the current is lagging at no-load. value of cosphi.

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