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Electronics => Electronics => Topic started by: macbook on October 10, 2011, 03:06:28 AM

Title: Value of damping capacitor for DC motors
Post by: macbook on October 10, 2011, 03:06:28 AM

Hi,

I am making a bot with 35 kgcm dc motors. We put damping capacitors across the motors to take care of high frequency spikes or back emf spikes. What should be the optimum value of these capacitors for 35 kgcm dc motors?

Thank you

Title: Re: Value of damping capacitor for DC motors
Post by: newInRobotics on October 10, 2011, 06:56:38 AM

It's not torque that is required for bypass cap calculations - it's max current draw, voltage, etc.

Bypass Capacitor Selection for High-Speed Designs (http://download.micron.com/pdf/technotes/TN0006.pdf) might help You, also have a look at Filtering Techniques: Isolating Analog and Digital Power Supplies in TI’s PLL-Based CDC Devices (http://www.ti.com/lit/an/scaa048/scaa048.pdf).

Title: Re: Value of damping capacitor for DC motors
Post by: Soeren on October 11, 2011, 05:22:29 PM

Hi,

Quote from: macbook on October 10, 2011, 03:06:28 AM

I am making a bot with 35 kgcm dc motors. We put damping capacitors across the motors to take care of high frequency spikes or back emf spikes. What should be the optimum value of these capacitors for 35 kgcm dc motors?

Caps are used for dampening HF noise by quenching sparks in the commutator, they must be mounted directly at the motor terminals and must be as low ESR as possible - ceramic caps of 100nF will be excellent.
Mount one across the terminals and one from each terminal to the motor housing (which should have a low impedance connection to ground if possible.

For surviving inductive kickback, either use a MOV, a Tranzorb/Transil or an LC filter and remember fast reverse mounted diodes over your power transistors.