[SOLVED] Can we calculate the horsepower by only AC current flow in windings in AC motor?

[Alper özel]

I saw this AC motor parameter calculator online: https://www.engineeringtoolbox.com/electrical-motor-calculator-d_832.html

It says for 100 Horse power, in 90% efficiency, 0.9 Power Factor and 220 V AC supply, 300A current is needed. But when I calculate like:

220V AC * 300 A AC * 0.707 (sine root mean sq) / 745.7 W (1 Horse power) = 56 HP

I get. Is my logic wrong?

Also, for a special purpose, I need to calculate the horsepower based on current flow in windings. In these windings below:



Because I only know my inductance(L) value, radius(R), turns(N) and RMS current which is going to flow through these winding coils. I know these below;

L = 60 mH
R = 5 cm
d(wire diameter) = 0.4 mm
N = 210
And RMS current for each phase (current flow on armature windings) is 12 A (peak to peak)

how can I calculate the horse power by only these parameters? Can I be sure that this parameters are whether enough or not enough to drive a car? Thanks.

 

[KlausST]

Hi,

your picture shows no rotor. The will influence the inductance.

And the rotation causes back emf, wich additionally drops the current.

I doubt that it is possible to calculate the motor HP just from the windings.

****
Actual drawn motor power = 3 x RMS_voltage (to star point) x RMS_current x cos(phi) (If I remember right)
For sure it varies with load. The higher the mechanical load (torque) the higher the power.

But it won´t tell you how much continous power the motor can withstand.

Klaus

 

[Warpspeed]

Klauss is right. True total in phase power is what really matters here, but then you have to estimate the efficiency to come up with developed mechanical power.

That is difficult, but you might be able to make a VERY rough estimate of mechanical efficiency by measuring the slip speed as a percentage, and doubling that.

Check out the rating plate data.
There should be an operating RPM which when the number of poles and excitation frequency are taken into account, will tell you the percentage slip. Typically for example you might find 6% slip for an 88% efficient motor. (100-(2x6%)=88%
That's not always true, but it should get you close as a rule of thumb.

Full load amps will be in VA not Watts, and sometimes there is a power factor quoted, it all gets a bit tricky using that.

Only way to know for sure is with a tachometer, torque sensor, and true power meter.

 

[srizbf]

Your assumption of VxIx0.707 for calculating power is not valid.

From the data given it looks like a 3phase BLDC motor.
(my assumption may not be correct .).
In that case , your calculation HP is different.

Even otherwise , calculating HP based on the minimal set of data(given by you) is not possible.

 

[schmitt trigger]

Your power calculations have a couple of errors.

First and as mentioned earlier, the 0.707 factor is already implicit in RMS values.
Second, you are not taking into account power factor
Third, you calculated single phase power