MRC power pack creates (audible) buzz

[emkay_777]

Hello Group,

 

I just noticed that on a couple of old MRC Tech II power packs, my (N scale) Kato locos make a buzzing sound when applying low voltage and then diminishes as the loco speeds up.  This does not happen with the Kato power pack.  I'm assuming that this is related to the pulsing voltage supplied by the MRC pack.  Is this harmful to the motors?  Thanks,

 

Evan

[HantuBlauLOL]

that controller uses PWM method for the speed controller.

PWM signal on 20-20kHz frequency does create a buzzing sound. (fix me if i'm wrong please)

 

it won't harm brushed and brushless DC motors, but pretty dangerous for coreless motors. also its safe for DC analog light boards.

 

tomix CL controllers use PWM too for the constant lighting feature, but it operates on 21kHz, so you can't hear your trains buzzing.

Edited January 29, 2016 by HantuBlauLOL

[kvp]

I would like to add PWM is only dangerous for low voltage coreless motors, so anything that is designed to withstand the full throttle voltage should be ok. The PWM sound can be heard if the frequency is in the audible range.

 

The MRC however seems to use simple unfiltered DC, meaning you hear the 50 or 60 Hz buzz from the rectifier bridge and then this smooths out as you add more power. It's called pulsed power and it's less advanced as PWM control, but at least it won't damage anything if you don't turn the throttle up too much as the packs seem to be H0 rated. (the Kato pack has the H0 range at the top in the red bar area)

[HantuBlauLOL]

so the original AC power didn't get fully rectified?

[kvp]

It gets rectified, but rectified AC is a bumpy DC power with double the frequency of the original waveform. A smoothing capacitor is needed to filter this out into a flat DC voltage. For slow speed, it's possible to add a bit of a bumpy wave that gets larger with the turn of the knob and at the same time add the filtering effect too, so at full power you get a smooth and flat DC wave, with small bumpy pulses at low speeds. This helps a bit, but not as effective as a PWM drive which gives maximum torque even at its lowest settings.

[velotrain]

When I first saw the subject I thought you meant buzz in terms of lots of conversation.

 

My initial thought was - What?  I can't imagine MDC doing anything innovative or buzz-worthy.

[inobu]

When I first saw the subject I thought you meant buzz in terms of lots of conversation.

 

My initial thought was - What?  I can't imagine MDC doing anything innovative or buzz-worthy.

LOL,

 

It's so true Headline wording. It lacked "a new" which gives it "a new" meaning.

 

Inobu

Edited January 29, 2016 by inobu

[cteno4]

ok now no more befuddled charles.

 

jeff

[velotrain]

late and low