# Dirty Meter



## CliffyJ (Apr 29, 2009)

I was delinquent in following certain advice to get a proper DCC meter, but I need some sort of readout for electrical work tomorrow. 

This isn't the way one is supposed to handle it, but here goes. I'm basically going to make an adapter for my meter that has a built-in bridge rectifier, only that.

Sorry for the crappy pics. Two dual banana jacks, chopped with a dremel tool while plugged together, resulting in this:










After fishing out the bits, I soldered the flared thingies onto their posts (left hand jack), and began to work the diodes in:










The fourth diode is on the other side. These are rectifier diodes, BTW.

I secured the set screws as I went, trimmed and soldered the ends. At least it fit onto the meter OK:










Now, out to see if it works...










Yes!

Then some quick mummification...










And I think I'm better prepared for at least comparative voltage checks tomorrow.

Should get the real meter though. But just so I understand, what should I be cautious of with this approach?

Thanks, 

===>Cliffy


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## Greg Elmassian (Jan 3, 2008)

Need a filter capacitor and a noise capacitor to get best reading, but other than that, good job! 

Greg


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## Curmudgeon (Jan 11, 2008)

Hmmm....I put one of those across my rails and I got nothing. 
Do I have to wait for the flux capacitor to charge fully? 
I do have a sign somewhere that says "Danger High Impedance" that would help calm folks down when the meter reads zero......


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## Greg Elmassian (Jan 3, 2008)

Yep, you have a defective flux capacitor, they are normally only found on the ends of Bachmann motors ha ha. 

Seriously, the filter cap and noise cap are on the output side, not across the rails. 

Otherwise you would be running AC into an electrolytic cap... sort of like running an analog loco on DCC with no decoder.... the buzzing noise will eventually go away though as the noise caps melt down. 

(for those of you who might not get all the gags, this is all in fun) 

Greg


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## Dan Pierce (Jan 2, 2008)

I have a large DANGER 1 MEG OHM in red on a sign above my work bench. Gets lots of attention as people back up and ask what it means. 
It does keep many from reaching out and touching things.


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## CliffyJ (Apr 29, 2009)

... the filter cap and noise cap are on the output side, not across the rails. 

So, both are wired across the + and - output of the bridge, at the top of the "adapter," correct? Could you recommend some specs for these?

Thanks Greg,

Cliff


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## CliffyJ (Apr 29, 2009)

Here's the mobile version:










Made it easy to bump along, and see readings along the way.


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## Greg Elmassian (Jan 3, 2008)

.1 mfd disc capacitor, 50 volts or higher.... these are non polarized. http://www.radioshack.com/product/index.jsp?productId=12579931 

maybe a 220 microfarad electrolytic capacitor, at least 35 volts... and this is indeed polarized, do not hook up backwards, it has plus and minus symbols. http://www.radioshack.com/product/index.jsp?productId=12460841 

none of the values are critical, and they may not make significant changes in the readings. 

Greg


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## CliffyJ (Apr 29, 2009)

Thanks Greg, I really appreciate your looking those up. 

Cliff 

PS, When I said, "So, both are wired across the + and - output of the bridge, at the top of the "adapter," correct?", I should have said "bottom," at the meter end.


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## JackM (Jul 29, 2008)

At the risk of showing my lack of knowledge in this area, what did you build? Or, what is it for? 

I'm pretty sure that my five dollar Harbor Freight meter isn't a whole lot better than your meter, but mine seems to read my AC track voltage without your gizmo. It looks like a good project for a rainy afternoon like Right Now, but I'm not sure why I would need it. 

JackM


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## JackM (Jul 29, 2008)

I especially like the mobile version!


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## CliffyJ (Apr 29, 2009)

Posted By JackM on 02 Sep 2013 02:37 PM 
At the risk of showing my lack of knowledge in this area, what did you build? Or, what is it for? 

I'm pretty sure that my five dollar Harbor Freight meter isn't a whole lot better than your meter, but mine seems to read my AC track voltage without your gizmo. It looks like a good project for a rainy afternoon like Right Now, but I'm not sure why I would need it. 

JackM Jack, you scared me, maybe I never did switch over to AC to get a reading. I'm sure I've done that many times, and read zero. But maybe it was all my imagination? So I just went out and checked, and yep, AC setting on my meter reads zero. 

We're talking DCC, right?

It's been coming in handy for me, to see discontinuities in track voltage around the layout. At first, there were a lot. But they were mainly "fixed" with some cleaning. I'm expecting it to be useful in trouble-shooting any problem areas of track, such as those suffering from a bad joiner. However, I've not yet discovered that kind of thing in the last couple days, only dirt. 

Glad you liked it though! Maybe you'll have better / related ideas. 
===>Cliffy


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## JackM (Jul 29, 2008)

Cliffy -

You definitely did scare me, so I went out to the garage and put my cheapo HF meter to the track and, uh, sorry but.... 












Standard NCE DCC system. Maybe this'll make up for that lousy set of box wrenches I bought there a few years ago. 
JackM


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## CliffyJ (Apr 29, 2009)

Photoshopped!


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## CliffyJ (Apr 29, 2009)

Huh, mine doesn't do that. 
So... why doesn't yours read 20-ish volts? 

Grey-aaayg...


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## CliffyJ (Apr 29, 2009)

HF has great c-clamps, I got a nice selection, weighed about 50 lbs, and they still honored the flat shipping rate...


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## toddalin (Jan 4, 2008)

Posted By CliffyJ on 02 Sep 2013 04:24 PM 
Huh, mine doesn't do that. 
So... why doesn't yours read 20-ish volts? 

Grey-aaayg...










His scale is on ac and yours is on dc.


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## JackM (Jul 29, 2008)

Someday I'll increase the volts. Simple enough to get to 18 of course. But I think I'll wait til the granddaughters are older. 16 VAC is good enough for my big stuff for now, and not so much that Thomas goes flying into the pacysandra.


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## Greg Elmassian (Jan 3, 2008)

Jeez guys..... dcc is square wave ac.... your hf meter will only read 60 cycle per second sinusoidal ac accurately 

To read square wave ac of varying frequency you need a true rms ac voltmeter... or you can rectify the dcc signal and read the resultant dc voltage. 

If anyone is giving advice here and does not already know and understand what I have written you would best serve your fellow hobbyists by learning or understanding first... 

Greg


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## CliffyJ (Apr 29, 2009)

His scale is on ac and yours is on dc. No, my meter, on AC, reads 0 across the rails; his reads 15-plus. 

Don't mean to belabor it, or give faulty advice.


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## Greg Elmassian (Jan 3, 2008)

Not you cliff, was pointed elsewhere.. 

Suffice it to say that meters use assumptions in their design.. and the assumptions used may be different.... so they both work on 60hz sine wave ac... didn't I say to read dcc ACCURATELY you need a different meter? 

The reality is that nether meter here is accurate, and they are inaccurate in different ways... 

Greg


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## CliffyJ (Apr 29, 2009)

Posted By Greg Elmassian on 02 Sep 2013 06:31 PM 
didn't I say to read dcc ACCURATELY you need a different meter? 
GregYeah, you did. But, didn't I open with:

I was delinquent in following certain advice to get a proper DCC meter... 


I think my foresight (of the consequences of my own lethargy) just trumped your knowledge!









More seriously, thanks Greg, you confirm how neither meter is designed to measure DCC volts; and Jack and I have just exhibited, perhaps, a vivid object lesson. 

===>Cliffy


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## Dan Pierce (Jan 2, 2008)

Just borrow an oscilloscope and you can not only see the voltage peaks, but verify if the square waves have rounded edges.


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## SLemcke (Jun 3, 2008)

I would think if all you are doing is comparative testing, your meter set up will work just fine. All you are looking for is a change, don't need an accurate reading for that purpose. 
However if you want accuracy then you need the proper meter. 
Steve


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## Greg Elmassian (Jan 3, 2008)

That is true Steve, and I've recommended this before for people looking for voltage losses, on this forum in fact.. 

In this case, it does show that the two meters have different methods of sampling the signal. 

Regards, Greg


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## SLemcke (Jun 3, 2008)

Greg, 
A little OT, but my Massoth system has a voltage and amperage reading on the handheld and base station. Does the NCE system do this also. I use mine for this sort of trouble shooting while running and engine around the track. 
Steve


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## Greg Elmassian (Jan 3, 2008)

No, the NCE does not have those things, it's nice to have, although you do pay for it, the Massoth system is approximately double the price, so I have a RampMeter in line, and can remove it for spot checking. 

While, of course, the main output voltage and total current is what I normally monitor, it's really not very helpful for troubleshooting "weak" rail joints or feeder delivery problems, thus the use of a portable meter. 

I also added a nice portable 8 amp load that I can clip on anywhere... that really makes the troubleshooting simple. 

Greg


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## CliffyJ (Apr 29, 2009)

Thanks for the further conversation guys. And now my head is spinning. 

Has someone already written up, or does someone have a link to, a procedure to (I'm struggling for the proper terms here) check DCC voltage issues across a layout? 

I don't know if I'm overcomplicating, or oversimplifying, but from my perspective of wanting to finish with debugging track & electrical (and move on to deck refinishing, ugh...), here goes with a "straw man" check list:

For each far point (farthest from center feeds), in my case three farthest loop points, 

1. Attach an 8 amp load (light bulbs?), and switch on the DCC
2. Working from center, take voltage readings and note them on a track plan 
3. For any abrupt change, track down the offending joiner or switch connection or whatever, and fix it
4. Keep going to the furthest points

Hypotheses:

A. For debugging purposes like this, this procedure should work with my "dirty meter"; though greater accuracy would be achieved perhaps by 1) adding the capacitors Greg suggested, or 2) getting a proper DCC meter 

B. To get the best read of track connectivity, maybe I should disconnect all feeds except the center ones, and let the voltage go thru rails only, and drop to whatever point it wants to. 

C. For my three furthest points, the distance from center feeds is about the same, so I should expect roughly the same V-drop at each of those far points, and the same degradation trend towards them.

Comments / corrections?

===>Cliffy


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## Greg Elmassian (Jan 3, 2008)

Yep, but you can measure the voltage drop at the 3 most distant points... if there is no appreciable drop with a heavy load, everything is perfect. 

If you have a significant drop, then try going halfway between the 2 spots... this way you can quickly see where the "bad spot" is, normally one place.... if it's several bad spots then you do have to proceed in a linear fashion. 

Your meter should give you a pretty darn accurate reading, and yes expect roughly the same drop at all locations. 

It may take some work to come up with an 8 amp load though, this is mine:


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## CliffyJ (Apr 29, 2009)

Holy... 
Wow, battery jumper cables even... 
Are those honkin' big capacitors?


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## CliffyJ (Apr 29, 2009)

You've got me thinking Greg, 
But my thinking is limited to components I somewhat understand.

For the sake of learning, how about 8 or 9 of these?

http://www.1000bulbs.com/search/?fi...29%5D=24.0

25w / 24v rating (x 21/24 for track voltage reduction)

So, 8 bulbs x (25/24) x (21/24) = 7.3A

I'm not sure if the equation can be set up that way though, because hooking up a regular 100 watt bulb on the track couldn't be:
(100/120) x (120/21) = .15A (requiring 55 bulbs!!)
Or could it?

===>Cliffy


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## CliffyJ (Apr 29, 2009)

Posted By CliffyJ on 04 Sep 2013 02:43 PM 
Holy... 
Wow, battery jumper cables even... 
Are those honkin' big capacitors? Oops, meant to say resistors...


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## CliffyJ (Apr 29, 2009)

Greg,

Here's a higher-wattage bulb,

http://www.amazon.com/Industrial-Pe...amp;sr=1-7 

Here's my estimate:

Bulb Full Volts 24 Bulb Watts @ Full V 100 Bulb Amps @ Full V 4.2 Track Volts 20.5 Voltage Reduction 0.85 Amps Actually Drawn 3.6 Qty of Bulbs 2 Total Amps Drawn 7.1 
Does this appear correct? If so, I'll jury-rig something temporary for my final testing. 

Thanks again, 
Cliff


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## Greg Elmassian (Jan 3, 2008)

Not really, the current vs. the voltage is nonlinear... get one, run at 20 volts and measure the current. 

But you are in the ballpark... get them and hook it up. 

Greg


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## CliffyJ (Apr 29, 2009)

Cool, thanks Greg. Bulbs are on order, and I'll post when I get 'em hooked up.


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## CliffyJ (Apr 29, 2009)

Here's the load car:










Seemed to work pretty well. I described the setup and findings in the main ("Laying Track on the V&T") build thread.


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## Greg Elmassian (Jan 3, 2008)

Now, your "DCC voltmeter" and see the voltage with and without the load. 

Greg


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## CliffyJ (Apr 29, 2009)

Yes, quite dramatic. At the main feed in the center, 18.4 with, 20.5 without. 

Here's some specific readings, on one of the 3 main legs of the layout. Main feed on the right, readings taken toward the load on the left, with 2 aux feeds toward the left. Cable = 10AWG.









Seems like there might be an issue with one of the top center switches, where voltage drops suddenly from 18.3 to 17.6.

Other than that, maybe a 1.3 volt reduction over ~50 feet is normal(?)

Cliff


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## Greg Elmassian (Jan 3, 2008)

yep, not too bad. 

You need to jumper around your switches, usually the feeds underneath are garbage. 

I use 2 jumpers at the "frog end" of the turnout, to jumper "past" the turnout... 

Greg


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## CliffyJ (Apr 29, 2009)

Thanks Greg, that's great confirmation. So far, 3 of my switch or crossing jumpers have had cold-soldered joints that had separated. To fix these, I think it's easier to do what you describe than fixing the factory jumpers. 

Once more, I've started two threads that I initially thought were separate, but now are converging. So I'll post my latest measurements on the "track testing car" thread. For anyone who's following this, sorry for the confusion. 

===>Cliffy


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