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Question about the inductor and inducted with a DC motor ?

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The inductor and inducted with a 120V DC motor ?

Hello folks

I'd like to precede the explanations of my lab of yesterday which are gonna be next monday.

The thing is that I had to mount a little circuit for a DC motor (1/4hp 120VDC - 2.8A), with a by-passable 50 ohms resistor.

To cut short, I had to measure the current in the inductor (stator) and inducted (rotor) when:

1) 'current with empty load at the start' inductor = 415mA inducted = 5A
2) 'nominal current with empty load at the start' inductor = 415mA inducted = 130mA
3) 'current with full load at the start' inductor = 415mA inducted = 700mA
4) 'nominal current with full load at the start' inductor = 415mA inducted = 120mA

* Do you say empty load or just no load, in english ? (I study in french.. ) *

So my question is, why is the inducted so differant than the inductor ? The inducted kicks the **** out of the 5A display at the start to come back to 130mA, but the inductor is roughly the same in the 4 cases, around 415mA.

When I measure the current in the inductor at the start without load, it seems that there's a little hesitation around 120mA before going to 415mA but it probably lasts around 100ms so it's hard to tell and it appears linear (just not as linear as when measuring the inductor with full load at the start.

Asked the teacher, he said that he would not give any explanation before monday or tuesday.
I don't want to wait.

All he said is " V = RI "
Well thank you for the deep explanation teacher.. should I reply E = mc2 ? Everything is V=RI, could you be less vague (...)

Thanks for your time and if anyone could spare some knowledge, it'd be very appreciated.
 
The excitation current on the stator will be reasonably stable.... The 5 A seen on the rotor at startup also appears normal (startup current, can always be higher)

Full load... I would expect to see more than 700mA on a 2.8 amp motor at full load....

As for nominal current..... where did this come from!!!! Nominal current at full load is 2.8A

Nominal current is the manufactures figures usually printed on the motor.
 
When you said "Full load" I assumed you had some sort of braking system attached that allowed the motor achieve full torque...

If you mean just spinning freely....Then the rotors will take very little current atall.
 
The load is my 50 ohm resistor.

I will have a mod to do to my circuit tho, to use 3 phase AC. I'll post the details this week-end.
 
The load is my 50 ohm resistor.
Isn't the 50 Ohm a by-pass resistor (post #1)? By motor load we mean a mechanical load trying to slow it down.
 
I don't know exactly ? Yes it's meant to slow it down but I have a switch and I can bypass it.
I'll post the diagram when I come back from work
 
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