How to control a DC Motor

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DrMogbl Active Contributor Join Date: Sep 2008 Location: Saudi Arabia, Jeddah Posts: 17	How to control a DC Motor 12/28/2008 2:04 AM
	Hi Every One, & Happy New Year. I have a DC motor 220 V. I want to control its speed throw controlling its FIELD & Armature Voltage. If we connected the field & armature both directly to 220 V DC, the maximum speed will be around 490/RPM. I need to make a circuit to control the motor : - first 5 seconds with normal speed - then I need to increase the speed to be around RPM * 2 as every one know, if we connect the armature directly to 220 V DC but decreased the field voltage (100 V DC as example ) the RPM will Increases. I tried this situation manually several times & it works very will. Also for both direction (Right & left). The reading was : Arm. Voltage, Field Voltage, Load, RPM 200 V, 200 V, 0.8 A., 430 200 V, 100 V, 1.2 A., 830 When I made my circuit (with AVR Microcontroller), it work 1 or 2 times only, then the relay –some time the bridge also- get damage. I used 15 Amp relay & 1000 V, 50 A Bridge. I tried several solution, but it not solve the problem.
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Anonymous Poster	#1 Re: How to control a DC Motor 12/28/2008 11:12 PM
	Dear: The DC machine (and in general inductive loads) has a lot of other issues to be considered than only control DC voltage in armature and field, for example the thyristor bridge should have a snubber protection circuit for overvoltage protection. other issue is the reduction of the field current, they only can be reduced to a specific value (this value is a characteristic of the motor), if you reduce more than this value, the motor move to a critical operation zone, in this zone the curren increase a lot and it's a destructive zone. You need to know the parameters of the motors before to try a design the DC controller. I can send you technical information (Theory) of the commercial DC Motors and information about the motors and DC Drives (if you send a email to jesus.balarezo@pucp.edu.pe). Regards.
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Delmar Power-User Join Date: Sep 2006 Location: Houston Texas Posts: 282 Good Answers: 16	#2 Re: How to control a DC Motor 12/28/2008 11:35 PM
	Why reinvent the wheel? There are many good and inexpensive variable-speed SCR and PWM drives on the market. The one I recommend is the model KBCC drive from KB Electronics. You can control them from the included potentiometer, or via a 0-10 volt signal from your PLC. Click for datasheet http://www.kbelectronics.com/data_sheets/kbcc240d.pdf Regards, Delmar Schmidt Melfi Technologies Houston www.melfitechnologies.com __________________ Specializing in Dynamic Weighing Systems for Powder and Bulk Solids Handling
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Wavebourn Active Contributor Join Date: Dec 2008 Location: EB, SF Bay Area Posts: 10	#3 Re: How to control a DC Motor 12/29/2008 1:44 PM
	1. When you switch it off huge voltage is generated, as by any inductance abruptly disconnected. Think of it as a device that saves current. Capacitor saves voltage, so when you short it it tries to keep the voltage the same generating very high level of current. Similarly, a coil disconnected tries to keep current the same generating huge voltage. 2. Also, the better way to control DC motors is a device with negative dynamic resistance. Neither stable regulated voltage, or current, may help you to stabilize speed; you need a device with negative dynamic resistance, for example modified voltage regulator.
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Anonymous Poster	#4 Re: How to control a DC Motor 12/29/2008 6:08 PM
	I have similar proyect, but I dont have right now the motor, but a think that this adress can help you, I think about a controller and throtle. try it. http://www.electricvehiclesusa.com/product_p/ki-lem-170-he.htm
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Anonymous Poster (2); Delmar (1); Wavebourn (1)

You might be interested in: DC Motors, DC-DC Converter Chips, AC-DC Adapters

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