I want to add an inexpensive DC digital panel meter to my MRC 2400 to measure track voltage and current. I attempted to power the meter using the fixed DC output of the power pack. The panel meter flickered a lot. So I tested the panel meter powered from a 9V battery and it worked just fine. My conclusion is that the fixed DC output from the power pack is noisy, unfiltered, PWM or something strange. Has any looked at the signal with a scope. It sure doesn't seem to be clean DC.
I suspect that it is not completely unfiltered, but very noisy. I do have a scope but have not haad it out in a few years, if I get a chance I may get it out and take a look.
davefrMy conclusion is that the fixed DC output from the power pack is noisy, unfiltered, PWM or something strange.
The Tech 2 model 2400 might have been one of the first Pulse Width Modulated power packs on the market. I know the 2500 was PWM.
If your panel meter uses RMS calculations for the display, it should work fine with PWM.
-Kevin
Living the dream.
I don’t have a 2400 but a 1KΩ resistor with a 100ų cap should filter it pretty good. Mel Modeling the early to mid 1950s SP in HO scale since 1951My Model Railroad http://melvineperry.blogspot.com/ Bakersfield, California Aging is not for wimps.
Thanks guys. I did add a 100 uF cap to fixed DC to power the meter and it works fine. It appears the panel meter needs clean DC as its power source but will read "dirty" DC.
Anyone know why MRC used PWM or whatever oddball waveform as DC. Did they just want to save the cost of a filter cap? Is there any advantage to PWM vs. clean filtered DC for running analog locomotives? My locomotives seem to run just as good after I filtered the DC. Just curious?
davefrAnyone know why MRC used PWM or whatever oddball waveform as DC.
PWM is something of a gold standard for voltage-controlled motors, although the kind you have from MRC is probably gated chopping of the sine-wave output via a Darlington (in this equipment) followed by output filtering to give a more consistent DC voltage.
I have read discussions that claim MRC intentionally used some 'dirty' waveforms to get better effect from relatively primitive motors -- a little asymmetric ripple for example giving a little 'shot' to a balky motor many times a second.
I’m sorry Dave, I do have a 2400. I didn’t recognize it until I saw your picture, really like the way you installed the meter. I took a look at the fixed DC output with my cheapo scope and there is a small amount of ripple so Overmod is probably correct about a cap giving up.Slick install, might give that a shot too. I don’t even have to order a meter, got one I bought for a project that I didn’t get around to. Mel Modeling the early to mid 1950s SP in HO scale since 1951My Model Railroad http://melvineperry.blogspot.com/ Bakersfield, California Aging is not for wimps.