Author Topic: removing capacitors in Mabuchi SF-266 motor  (Read 41 times)

faithie999

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removing capacitors in Mabuchi SF-266 motor
« on: April 12, 2021, 08:28:46 AM »
the Mabuchi SF-266 is one of the current popular choices on the Repower and Regear forum, as they run well and are only $2 on ebay.

one member disassembled a motor to drill mounting holes and discovered two capacitors.  he claimed that the performance on DCC was better without the caps.

would it be necessary to disable/remove the caps on railpro?  here is the discussion.

https://groups.io/g/RepowerAndRegear/topic/28727856#19306

thanks

ken


G8B4Life

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Re: removing capacitors in Mabuchi SF-266 motor
« Reply #1 on: April 12, 2021, 09:27:58 AM »
Possibly related reading: https://rpug.pdc.ca/index.php/topic,295.msg2103.html#msg2103.

I'm certainly no expert on this but in our model train world a capacitor across a motor is part of a filtering circuit and filtering circuits can cause havoc with DCC and RailPro because the motor is driven with high frequency PWM. We usually see inductors as well as the capacitor in our application so I'm not entirely sure what effect just the capacitors will have. Easiest way to find out would be to try one I guess.

I do recall from discussions past that there was a version with and a version without the capacitors. I might be thinking on another motor that was discussed as well.

- Tim

Alan

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Re: removing capacitors in Mabuchi SF-266 motor
« Reply #2 on: April 12, 2021, 09:42:41 AM »
The capacitors are there to suppress the electrical noise caused by brushes. On a DC system the caps prevent the "noise" from propagating down the supply line (wires, wheels, track) which then acts as an antenna. Brush "noise" occurs at a broad range of frequency so any number of radio devices may pick it up. For example, without the capacitors your favorite FM channel may get staticy when your DC train passes certain areas of the layout.

With DCC and RP systems there is no antenna effect because the motor is driven by a PWM module in close proximity. There is no wide spectrum noise emission and thus no need for capacitors. On a PWM system the capacitors may have a small effect on the square wave being fed to the motor. They may round off the edges so to speak. Whether that is noticeable or not depends on myriad factors.

Personally, I would leave them in place for a DC layout. Remove them for a DCC or RP layout.

Alan

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When I was a kid... no wait, I still do that. HO, 28x32, double deck, 1969, RailPro

faithie999

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Re: removing capacitors in Mabuchi SF-266 motor
« Reply #3 on: April 12, 2021, 10:06:32 AM »
thanks to both of your for your quick replies!

Ken