# DC Motor failed to run on load

## Main Question or Discussion Point

Hello,

Im using DC motor to run the conveyor but suddenly the armature shows high current 130 A for 30 V power and the speed cant increase anymore. The motor power stated in the name plate is 93.8 KW, Armature voltage is 453 V and Armature ampere is 225 A. The motor can run free load after disconnected from the load but fail to run on load. We have checked the field coil, armature coil and the brushes . The are no insulation damaged since it can be run free load.

What are the possible causes to the motor that fail to run on load? Is it because not strong magnetism or another mechanical failure?

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jim hardy
Gold Member
2019 Award
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sounds to me like the electrical supply is not stout enough to maintain voltage when it's loaded to as little as 30 amps.
130 volts at 30 amps is how many watts?
How many watts does the conveyor require?
Can the motor deliver more watts out of its shaft than it receives in the wires from its supply?

What do you have powering this motor?

old jim

It is 30 V 130 A.... The actual armature voltage is 453 V. But when the voltage reaching only 30 V the armature current already 130 A. The the armature stop to rotate.

NascentOxygen
Staff Emeritus
Im using DC motor to run the conveyor but suddenly the armature shows high current 130 A for 30 V power and the speed cant increase anymore.
This is a motor that has been operating satisfactorily in this task for a long time? Then suddenly it has stopped turning under load, and you have made no changes in the motor's controller nor the conveyor?

How did you check the field coil? I'm thinking that a short in the field would still show continuity, yet give a major reduction in torque. How to reveal this? Maybe if you could give it rated field current, and as it warms up use an infra-red camera to monitor the temperature of the outside casing, you might find an ominously cool area indicating no heating underneath.

The rated armature current is 225A. Why are you stopping at 130A (at 30V)?? Keep increasing the voltage until you get 225A, if that don't give you enough speed (or any speed at all) then we can say something is wrong.
Its normal for DC motor to consume large current when stalled or during starting. It is also normal for it to consume rather large* current when applied with rather small voltage than rated, because this results in not enough power being developed and motor either refuse to starts or rotates very slowly.
*large in the sense of ratio of Applied Voltage/Current.

dlgoff
Gold Member

Just sayin'

jim hardy
Gold Member
2019 Award
Dearly Missed
an open field results in high armature current and virtually no torque.

is it series or shunt field?

The voltage stopped at 30 V only and can not increase anymore. And the current showed 130 A at that time.. The motor is in series field.

uart