dc motor full load current and no load

[CataM]

Even for a DC motor, the inside is AC because the commutators convert the external DC into an internal AC.

I think it is the other way around. You feed DC and rotor moves in a motor. In a generator, you get AC which is converted to DC by commutator.

 

[mshh]

Any help.?

 

[c_mitra]

I think it is the other way around. You feed DC and rotor moves in a motor. In a generator, you get AC which is converted to DC by commutator.

I find this rather strange. Please try to think this way (not wrong, any way):

You feed DC to the rotor via slip rings and it will refuse to rotate. If you feed AC, the same motor will merrily turn. You use commutators instead of the slip rings, and DC becomes AC, on both ways. In fact, when the rotor turns slowly, the internal AC frequency is low and the back-emf produced is low and the current at const voltage is higher thereby maintaining a good torque.

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From the mass of the motor, it could easily deliver 100-200W of power. Is it written 92W on the boiler plate?

 

[FvM]

Any help.?

Help for what? The only unclear point is the meaning of the 11 A specification. All other data are plausible so far. What's your exact problem?

 

[mshh]

Help for what? The only unclear point is the meaning of the 11 A specification. All other data are plausible so far. What's your exact problem?

I mentioned my problem in the beginning of this thread. the current on the plate is 11 A and 4 A in datasheet. i am afraid to use the motor it with a driver 10 A which is lower than its current then it blow up.
it's written 92 W on its plate.

 

[c_mitra]

it's written 92 W on its plate.

It is better to be conservative and not wise to push too far. Perhaps 11A is the absolute maximum limit. Use 4A as a typical value and 8A as the operating maximum. It will not blow up or meltdown at 8A.

 

[mshh]

but if it is rated was 11 A the maximum will be around 20 A and that will blow the driver.

 

[c_mitra]

It may draw 20A only when it is stalled. That will correspond to 480W which appears very high for the size and weight of the motor. The manufacturer may list the absolute max rating on the face plate. I do not think that motor can deliver 480W of power. The no-load current is 1A and the maximum current cannot be more than 10 times this value for normal motors.

 

[FvM]

The motor is rated for 96W and 24V, so it can't be rated for 11 A at the same time.

It's quite easy to determine the maximum stall and inrush current, just measure the motor DC resistance, turning the shaft a bit back and forth to get the absolute minimum resistance.

 

[mshh]

The motor is rated for 96W and 24V, so it can't be rated for 11 A at the same time.

did you mean 96/24= 4 A ? not 11 A
and if this assumption is correct it would conflict with datasheet which mentioned that nominal power is 31 W

 

[c_mitra]

Frankly speaking, I do not understand the real question. DC motors are voltage run and you apply the right voltage and it will take whatever current it deems fit. You may change the voltage by +/-20% to change the speed but the speed in most cases is best changed by gears. It is possible to have DC motors that have a very wide range of speed and that is controlled by voltage applied on the the motor.

If the power is 31W, then perhaps it is possible to stop the rotor by hand; I am not sure about gear motors though.

 

[CataM]

did you mean 96/24= 4 A ? not 11 A
and if this assumption is correct it would conflict with datasheet which mentioned that nominal power is 31 W

(147.692*2*pi/60)*2=30.9 W Nominal power which is different from electrical power !
There are looses on your motor meaning that some of the electrical power will get lost and only 30.9 W will be mechanical power ! Meaning that there is (30.9/96)*100≈32% efficiency as FvM said in post #15.

 

[mshh]

(147.692*2*pi/60)*2=30.9 W Nominal power which is different from electrical power !
There are looses on your motor meaning that some of the electrical power will get lost and only 30.9 W will be mechanical power ! Meaning that there is (30.9/96)*100≈32% efficiency as FvM said in post #15.

so What is the difference between 96 W and 30.9 W?
both of them were named nominal power.

 

[CataM]

so What is the difference between 96 W and 30.9 W?
both of them were named nominal power.

On your datasheet it is specified nominal power, nominal speed, nominal torque, nominal voltage, nominal current.

Nominal voltage*Nominal current (96 W) gives you the electrical power you need to feed to your motor to give nominal power (mechanical power, 30.9 W) which means, power that is useful to use.

 

[mshh]

so this proves my point, mominal current 4A *nominal voltage 24=96 W , and that mean 4A is the rated current not 11A. and 11 A is the maximum

 

[chuckey]

As 24V is the maximum voltage (draws 4A). 11A is the maximum current (at 3V or .8 V locked rotor ?)
Frank

 

[c_mitra]

As 24V is the maximum voltage (draws 4A). 11A is the maximum current (at 3V or .8 V locked rotor ?)

When the motor stalls, there is no AC (back emf) and the max current will be decided by the resistance alone. If the motor is series wound, I doubt it will take 11A. On the other hand, if it is parallel or shunt mode, then perhaps it can draw 11A (possible but depends only on the equivalent resistance). At 3V, it may take even less than 1A. Small motors are often shunt wound for better characteristics (whatever that may mean) under load. The motor, with 96W input power, may be having an effective resistance of 2-5 ohms (if measured by a multimeter).

 

[mshh]

please give me a summary for my question.

 

[c_mitra]

please give me a summary for my question.

I do believe that the 11A current rating is not accurate and you should ignore that value.

 

[schmitt trigger]

Small motors are often shunt wound for better characteristics (whatever that may mean) under load.

Shunt wound or permanent magnet motors speed vs. load characteristics are essentially flat (minus the rotor's IR drop). Whereas on a series wound the speed varies inversely with the load.
As a fact an unloaded series wound motor can actually reach dangerous speeds, destroying itself with centrifugal forces and probably sending high speed metal fragments flying everywhere.