DC Motor Won't Run Under Load

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afritech Participant Join Date: Jan 2010 Posts: 4	DC Motor Won't Run Under Load 03/09/2010 1:32 PM
	direct current motor and generator. if a dc motor refuses to run under load...possible causes could be,, field coils too weak or polarity is not right..if im not mistaken but off load the motor runs.and full voltage is given by the generator..under load the voltage will drop on the generator, the motor runs a gearbox...could the gearbox be a problem, and why does the voltage drop on the generator..the genny does not arc or anything of the sort.... any information and instruction will be extremely appreciated!
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dvmdsc Guru Join Date: Mar 2010 Location: In the pool because it is too hot. Posts: 3054 Good Answers: 141	#1 Re: dc motor does not run under load 03/09/2010 2:39 PM
	Besides possible malfunctions of generator the drop can be generated by too much load on the motor. __________________ Plenty of room here
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techno Guru Join Date: Jan 2007 Location: Canada Posts: 1024 Good Answers: 40	#2 Re: DC Motor Won't Run Under Load 03/09/2010 9:35 PM
	Could be the gearbox or whatever the gearbox is driving. Also look into the bearings, and alignment of the shafts. The voltage drop is definitely caused by the large load. The motor is trying very hard to drive the gearbox and drawing allot of current. The generator is having a hard time supplying the large amount of current, which results in the voltage drop. Do not run too long in this condition or it will burn out the motor. __________________ Perfection is a subjective and abstract concept.
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msamad Guru Join Date: Feb 2009 Location: Houston, USA Posts: 946 Good Answers: 244	#3 In reply to #2 Re: DC Motor Won't Run Under Load 03/09/2010 9:47 PM
	The motor is generating the starting torque that is not enough for start with the load but enough for start with only the gearbox. The required starting torque with load is higher than that with only the gearbox. You didn't mention the motor size and generator capacity. Most probably the generator capacity is not adequate for the motor size to start. To start a motor from generator, a higher size generator is required. Like induction motor, the starting current of DC motor is also high (due to no back emf with no speed or low speed) and because of the high starting current, the voltage drop is large at starting. This cause lower voltage applied to the motor terminal and the motor is not able to develop enough starting torque. The torque developed by the motor is proportional to the voltage. DC series (armature and fields are in series) motor can develop higher starting torque than DC shunt motor. I am guessing you have DC shunt motor. A useful link for DC motors: http://www.tpub.com/content/doe/h1011v2/css/h1011v2_116.htm - MS __________________ "All my technical advices in this forum must be consulted with and approved by a local registered professional engineer before implementation" - Mohammed Samad (Linkedin Profile: http://www.linkedin.com/in/msamad)
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Tim Hawley Master Mech Commentator Join Date: Jan 2010 Posts: 83 Good Answers: 1	#4 Re: DC Motor Won't Run Under Load 03/10/2010 7:05 AM
	Disconnect the drive or gear box and start the motor. Check the line voltage and current draw before and are start. This should isolate the problem,wheather it's the motor or drive. Check drive rotation is it free or binding. Re-attach drive and check again. Check for motor end play and see if it will free spin with power and brake off. Only some thoughts. Tim
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afritech Participant Join Date: Jan 2010 Posts: 4	#5 Re: DC Motor Won't Run Under Load 03/11/2010 1:21 AM
	thanks guys, will let yourll know if i resolve the problem.
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