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imageI’m considering buying a Piko engine for my Garden Railroad that info on says can run on analog as long as it’s a “pure” DC signal or something to that effect. How do I know what my two transformers are putting out. I know that one of the transformers I’m not using indicated that it had “pulse” of which the disclaimer said not to use. Thanx for any help.

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There are several ways that DC can be dirty (not "pure").

The first and most obvious is DCC.  It imparts a significant distortion on the pure DC that comes out of most DC power packs.  This "distortion" is what carries the command information to the DCC decoder in the engine which then unleashes all the fancy bells and whistles.  Makes sure that DCC is off or not connected to keep your DC pure.

The second is Pulse Power.  This is designed to give better performance as the loco starts to move.  Make sure that it's off.  You may want to use it until the engine is rolling, but it needs to go off very soon afterwards.

The third is poor filtering of the power coming out of the rectifier inside the power pack.  This rectifier changes AC coming in (from the wall outlet, and stepped down by a transformer) to the DC going out.  Poor filtering means less purity.  This is one very important place where you get what you pay for.  Buy a good one.  You won't regret it.

The MRC unit on the left in your picture looks to be a basic DC power pack with some of these advanced features that dirty up the DC coming out, like pulse power.  Keep them shut off.

The other one may not even produce DC, although I could be wrong.  It may be AC output; adequate for 3-Rail only.

The best way to tell what's coming out is with a tool that most of us don't have, an oscilloscope, which allows one to look at the quality of the output.  Is is nice and flat, a straight line?  Or does it have ripples?  Are they tiny or huge?

Second choice would be a voltmeter, digital or old fashioned analog, either will work but you'll only really be able to tell whether you have AC or DC coming out and not how pure the DC is, if it's putting out DC.

Mike

Last edited by Mellow Hudson Mike

And the third is a telephone butt set, (an old analog desk telephone set will work) combined with a well-trained human ear.

Arthur, you made my day.

I sat here for the past two hours trying to think of number 3 and came up short.

Listening to detect the quality (purity) of the DC output?  Excellent idea!

Buzz, pops and clicks, and several other things would indeed be detectible this way, everything but slow changes in voltage or artifacts too high in frequency to hear.

Thanks.

Mike

@obxtrainman posted:

Ok, I appreciate everyone’s input. But no one actually answered my question. What tells us as a laymen which transformer/power  source is providing pure DC?  I provided a pic. I don’t care about what does what. Are the two transformers in the pic adequate for my purpose?  

In researching Piko requirement I found this link and title blurb.

https://www.piko-america.com/p...38231-prr-mogul-loco

* Analog DC operation requires well-filtered "pure" DC power supply/control.  Poorly filtered DC, pulsed power or PWC will cause problems.

From a sideways picture, I was able to guess that the left transformer is a MRC 6200. To figure out the guts of that since the manual was not telling me much other than voltage and power of what it could do rating wise, I found this page. http://www.trainelectronics.com/MRC_6200/

Bottom line, I didn't see any bulk DC capacitors for filtering in that transformer and so while it appears to be passbank using 2 large BJT transistors, again, my bet is, the DC output is not filtered. So I'm guessing no, this transformer failed to meet the requirements.

So then searching for the left transformer where I believe it also has the MRC logo and style, I had to google MRC DC throttle pack, look at pictures, and guess which model it is. I came up with MRC Power AG990 https://www.modelrectifier.com...ower%20G%20AG990.pdf

That explains some of the transformer construction

FEATURES

• 10 continuous Amps for massive power
• Large pilot light and overload LEDs
• Heavy-duty reverse switch
• Rugged cabinetry with slide transformer for smooth linear control • Large throttle handle looks and feels like the real thing

• Fixed 22 VDC output terminals for accessories
• Heavy-duty wire attachment lugs. No tools needed.

ELECTRICAL SPECIFICATIONS Input: 120 VAC, 60 Hz

Output: 0 ~ 22 VDC variable for track, 22 VDC for accessories 10 Amps sustained power output

To me this sounds like the typical MRC transformer with a mechanical slider or tab arm, and then just a bg honking DC rectifier and switches. On mylargescale, I found a user said this "I have heard horror stories that 10 amp units can be hard on a sound system."

Another user confirmed the construction details: "the mrc AG 990 is a very old school power pack as it has no electronics .......... it is just a variable transformer and a full wave bridge"

Bottom line, between those 2 statements, I would say not just no, but heck no don't use that with an expensive Piko that demands pure DC.

Further, I just looked at starter sets to see what they were using https://www.piko-america.com/c...assenger-starter-set

  • Analog/DC track power set with R/C pocket remote controller
      -  controller includes Fixed DC Accessory Power
      -  R/C system has over 80' range
      -  8 Easily selectable channels




So again, no, I would not recommend using either of those units. to power these new PIKO analog DC capable trains as they seem to have a pretty strict requirement and straying from that could cause damage.

In fact, being honest, I had a little trouble reading up what even PIKO recommends. Obviously they have a solution for the starter sets with the remote control, and I found this pre-order pure DC rated unit a forum sponsor Trainworld https://www.trainworld.com/sho...ure-dc-w-remote.html

Last edited by Vernon Barry

My guess is that PIKO just wants you to use a full-wave bridge rectified DC power supply. A half-wave or modulated output (PWM etc.) would probably confuse the DCC decoder. A little bit of ripple will probably be OK, and probably won't damage it. If it did, it would be a pretty useless decoder because way worse stuff happens during derailments and traversing blocks and dirty track.

One option would be to use batteries to supply power, that's about as "pure DC" as it gets.

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