# Motor Current calculation

Dear all,

I have small doubt in calculation & selection of proper motor

I have two application

1. Solar tracker : where i used below actuator which is rated 24v , 4A,500 rpm used to caary 800Kg load.

power =244=96w
torque=(0.096
9550)/500=1.833N-m
Here is motor will stop every 5 min

1. In another project., Air condition blower application with continuous operation, motor designed to carry 48v . 5A rated ,axial load and radial load can carry upto 10kg.
The power: P=5A48V=240W
The torque: 0.24KW
9550/1550RPM=1.528Nm (PS: the torque you required before: 0.59 Nm) this is desired
But we want to run it for 2400 rpm
1.528NM*2400RPM/9550=0.384KW

because of change in wattage our stator got damage. bearing got disturb etc.

My question over here .
In first application we running motor almost 500 rpm carrying 800kg of load
where in second case we running motor 2400 rpm @48v and carry load of 900gm
I would like to why huge amount of current draw in above case??
what are points are doing in selection of motor???

in above case if we increase wattage of motor we can run motor.

Linear actuator.pdf (172 KB)

That actuator is rated at 8000N and 2.8mm/s, so it does 22.4W of mechanical

You cannot scale up power linearly with speed in a fan blower, air resistance goes
up as the square of velocity and thus work done as the cube of velocity.
Thus going from 1550rpm to 2400rpm will cause a nearly 4-fold increase in
load to 890W, which explains the motor burning out.

The load of a blower depends on the speed/torque characteristics of the fan,
the axial/radial loads are purely the strength of the bearings to support the
weight of the fan (which is clearly not an issue here).

Balancing the load gets more important with speed too (imbalance forces
go up as square of speed).

Without knowing anything more about the blower motor its hard to say more.

here i am attaching fan image. this wieghs 450gms. These are rested on either side of shaft.
shaft dia is 0.5 inch.

1)How can i balance load here??
2) motor should run 48v,5A,2500rpm, application air condition blowers

mysetup is like this. I am using fan
http://www.searspartsdirect.com/partsdirect/part-model/whirlpool-parts/air-conditioner-parts/Model-ACM062XH0/1198/0904032/o2028376/00001

Its already been balanced, there's a clip-on weight visible on one of the fan blades.

If its a plastic fan blade then it may change shape with age and become less balanced.

If its designed for 1550rpm then it may not be rated for 2400rpm (forces are 2.4
times as large, both centrifugal and air load forces).

To spin that fan at 2400rpm will take a certain amount of power, and the motor
has to be rated to provide that amount. Finding out what that power is isn't
trivial without a measuring rig. You can't tell what electrical power is needed
without knowing the load power and motor efficiency.

Fan loads depend roughly on the cube of the rotation speed and the reciprocal
of the square of the thermdynamic temperature (because air density changes with
temperature). A datasheet for the fan would provide some answers. The back pressure
of the ducting system its installed in will also affect load. Fans also have a maximum
back-pressure rating, above this the airflow stalls over the blades and they stop
working properly.

Can you share relevant equations for calculating torque, power, heat disspiation. Motor shaft length if uniformly distributed load.
relevant fan picture and dimension attached in above link.

If you can share some link to determine calculation it will be better,

AMPS-N:
Can you share relevant equations for calculating torque, power, heat disspiation. Motor shaft length if uniformly distributed load.
relevant fan picture and dimension attached in above link.

If you can share some link to determine calculation it will be better,

Consult a physics tutorial? Google and wikipedia are always good starting points for the curious.