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mohammed ismail
Active Contributor

Join Date: Oct 2016
Posts: 19

DC Motor Not Running At Load

02/26/2018 6:18 AM

Dear all users,

hope you are good,

i need suggestion on the DC motor rectification,

i have a very old DC motor For travelling long Rail on a automatic welding machine system,

the problem is before 1 week it stopped while travelling on the rail,

the motor is coupled with gear so i checked the motor by means physical and technical by physical i found bearing and some power control problem on the wiring control panel so i rectified the problem by replacing bearings and faulty control cable,

after that i found the dc power is not delivering the motor so i checked the power at PCB board nil showing so i arranged the 48 VDC rectifier to run the motor, the problem is when motor start running at no load it will run but if apply load motor is not even moving checked the continuity of the motor found OK and also checked the ampere of the dc motor its showing 0.371ADC at both states.

please suggest me what to do next
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PWSlack
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#1

Re: DC Motor not running at load

02/26/2018 6:33 AM

Dismantle the motor carefully. Observe the slots in the commutator. If these are blocked with carbon, remove same with a wooden toothpick or similar. Check the tension in the brush springs and the condition and wear of the brushes; if these are "tired" or "worn out", replace with like-for-like new parts, preferably from the original equipment manufacturer's recommendations. Polish the surface of the commutator with a glassfibre brush or similar. Lubricate motor bearings. Reassemble motor, and test. If the commutator sparks and the motor runs poorly, then a winding may be open-circuit, in which case either have the motor rewound or replace it with a new motor, depending on economics and availability. Return to this thread once the above has been completed, and report, please.

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mohammed ismail
Active Contributor

Join Date: Oct 2016
Posts: 19
#2
In reply to #1

Re: DC Motor not running at load

02/26/2018 11:14 AM

Dear sir,

Thank you for your quick suggestion

As you had mention i removed motor and dismantle the motor and checked the armature commutator found carbon dust in the slots so cleaned all the slots,

Then replace the bearings also because it's hasn't maintenance done

The carbons are same in physical way

After the inspection of all above i reassembled the motor and checked the motor it's acting same,

As per your suggestion

May be the motor become weak so i will send this motor to rewinding centre.

Once it will get i will write you

Thank you
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PWSlack
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United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

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#4
In reply to #2

Re: DC Motor not running at load

02/26/2018 2:24 PM

Personal communication might deny the forum the benefit of this thread as it develops. It would be preferable to simply post the findings to this thread. <Unsubscribes>

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Rixter
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#3

Re: DC Motor Not Running At Load

02/26/2018 11:27 AM

0.371 A DC is not much current. Motor torque is proportional to current, so that is why it is not running under load. Somewhere in the circuit is excessive resistance.

Measure voltage directly across the motor. If there is 48 volts there when the motor is stalled, the problem is internal to the motor. (I would guess that brushes would be the most likely problem.)

If the voltage across the motor is significantly less than 48 volts, the problem is external to the motor. The sum of the voltage drop around the circuit is 48 volts. Use a voltmeter to find out where the drop occurs and that's where your problem is.
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GW
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Join Date: Oct 2006
Location: Surrey BC Canada
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#5

Re: DC Motor Not Running At Load

02/26/2018 11:06 PM

It would be helpful if you gave us the nameplate data on the motor. I can't tell if you have a 10 watt or 1000 watt machine.

Try checking the motor terminal volts and amps - if you have 48 volts at the motor and no current you may have a bad motor.

For a DC machine be sure you are measuring DC volts and DC amps. If your meter thinks it is AC you will get bad readings.
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nvirciglio
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#6

Re: DC Motor Not Running At Load

02/26/2018 11:35 PM

Sounds like the series field is open.

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dkwarner
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#7

Re: DC Motor Not Running At Load

02/26/2018 11:58 PM

You didn't say what kind of DC motor it is. If it is a PM (Permanent Magnet) motor, it is possible for the magnets to be weakened or completely de-magnetized. Weak field magnets (permanent or electro-) means very little torque.

As always, the more information you give, the more likely you are to receive appropriate advice.

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kumarpradeep
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Join Date: Mar 2017
Posts: 41
#8

Re: DC Motor Not Running At Load

02/28/2018 12:44 AM

Such a very nice blog.. I really like this post..

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dkwarner (1); GW (1); kumarpradeep (1); mohammed ismail (1); nvirciglio (1); PWSlack (2); Rixter (1)

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