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Author Previous Topic: Decoder  Attaching Topic Next Topic: Atlas switches that short out on DCC  

jerbear

Posted - 2009 December 06 :  10:25:08 AM  Show Profile
What should the voltage be on the track with a meter? I have n-scale and I want to check the power all the way around the track.
Thanks,
Jerbear

Country: | Posts: 17

Hugh

Posted - 2009 December 06 :  2:07:43 PM  Show Profile
DCC? or what. It makes a difference.

Chessie System on the Pere Marquette

Country: USA | Posts: 668 Go to Top of Page

Selector

Posted - 2009 December 06 :  2:41:34 PM  Show Profile
True. Your typical home meter won't read the DCC voltage accurately...close, but not nearly as well as it will measure DC current.

I would guess that your meter should read DCC power in N scale near 12-13 volts. HO should read near 14-16 volts.

-Crandell



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mmyers

Posted - 2009 December 07 :  04:27:38 AM  Show Profile
If it's DCC, which DCC system are you using? Measure the voltage at the terminals first. A load should be applied to get an accurate measurement. We used a 3 amp load and a 5 amp system to measure NTRAK layouts for the RP.

Martin Myers



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DJCONWAY

Posted - 2009 December 07 :  08:34:00 AM  Show Profile
Martin has the right idea, your not so much interested in the empirical voltage as in looking for any significant drops.
Put the system under load, measure at the output terminals of the booster, then at verious points around the rr. Where there is a drop additional feeders need to be added.


Do your part buy stuff!

Country: USA | Posts: 2536 Go to Top of Page

seanm

Posted - 2009 December 07 :  4:09:57 PM  Show Profile  Visit seanm's Homepage
If you want a "retail" solution, check out something called a RAMP Meter from Tony's Trains. They just lowered the price on them. Handy device. I have one and like it very much.

Sean B. McCaskey
"No man is a failure
who has friends" ---Clarence

Country: USA | Posts: 627 Go to Top of Page

steve turner

Posted - 2009 December 07 :  10:03:18 PM  Show Profile
This works good http://www.digitrax.com/appnote_trvolt.php


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alsilverstein

Posted - 2009 December 08 :  12:16:17 PM  Show Profile
Here I go again folks.

There is more here than just the measuring of the voltage and loading of the output where voltage to the rails is concerned.

The rail power bus wire plays a part in what voltage actually reaches the decoder. The smaller the size of the wire the higher the resistance per foot and the lower the voltage as the distances between the command/booster and the decoder increases.

The meter that you use to measure the voltage will have an effect on the accuracy of the measurement. It is simple folks some meters are better than others. Probably the most accurate meter for the measuring of voltage and current demands of a DCC controlled layout at this time is the RRamp Meter. I am currently using a digital meter manufactured by Idea (model 61-312) that I purchased at Lowe's for general measurements of voltage and the RRamp Meter for total current demands.

The voltage at the rails of a DCC controlled layout is very different than the voltage at the rails of a DC controlled layout and the top voltage of both are not equivalent in structure. On a DCC controlled layout the maximum output is always applied to the rails and the voltage output to the motor is controlled by the decoder as directed by the engineers throttle. On a DC controlled layout the output varies from zero to maximum output and is controlled by the engineers throttle.

The DCC signal/voltage at the rails does not go directly to the motor or the lights. The voltage goes through the decoder and because of the circuitry the maximum voltage output to the motor drops by about 2 volts. Thus a 14v DCC signal really only generates a 12vdc maximum output to a motor. The voltage output of the decoder to the functions is dependent on the type of output the decoder is designed to control. The actual voltage drop varies from decoder to decoder I have yet to notice an substantial variation that is great enought to effect the overal engine operation.

Another point to remember is that prior to DCC most N scale layouts were controlled by the same power packs as most HO scale layouts where the voltage range was from 0 to 12 volts DC. Thus it is safe to assume that a N scale engine can handle 12 vdc the same as a HO scale engine thus any DCC system that powers a HO scale layout can also power a N scale layout.

Then there is the reality that not all DCC command stations have variable DCC outputs. Many of the DCC command systems like the MRC Prodigy, NCE Power Cab, and Digitrax Zephyr have only one output voltage setting that are generally non adjustable.

One last thing I would like to point out and that is unless your layout requires multiple boosters there really isn't any need to worry about the output voltage for any HO or N scale layout unless you are worried about voltage drop do to the using of smaller than recommended rail bus wiring. The only time there needs to be a concern is for voltage matching between rail booster sections or where large scale models are concerned.

Always remember that the NMRA determined that all decoders to be in conformance with the NMRA Standards must be able to handle input voltages of at least 20 volts from the rails. Thus all decoders are safe to use with N scale if the decoder will fit inside a N scale engine.

Al





Country: USA | Posts: 201 Go to Top of Page

Hugh

Posted - 2009 December 08 :  4:50:48 PM  Show Profile
jerbear, we have not heard back from you are you using DCC or DC. & it really does matter what type of meter you are using on DCC. But, then again that depends on how accurate you want the readings to be.

Chessie System on the Pere Marquette

Country: USA | Posts: 668 Go to Top of Page

High Ball

Posted - 2009 December 09 :  11:30:09 AM  Show Profile
Hello;

Very interesting.

Now I'm confused more then ever.

Please explain why a home meter will work with DC but not DCC.

As I understand it a DC system controls the track. O volts up to, what, 14 volts maximum. 0 volts nothing is moving. 14 volts, she's a really rippin boys.

The DCC system controls the locomotive. That with DCC the voltage is high and constant. What exactly high is I don't know. I just can't understand why a home meter won't work. I know you are right but just wonder why.

thanks.


nicholas

Country: USA | Posts: 688 Go to Top of Page

Selector

Posted - 2009 December 09 :  12:06:29 PM  Show Profile
A home meter is perfectly fine for an indication of the sustained voltage passed through to the rails on a DCC system...it just won't be completely accurate. You would get an B+ grade on your answer if "close" counted.

The characteristics of the square wave make it a problem for the meters that you can buy for $15, analog or digital. So, say your system was really putting out a steady 16.2V AC on the rails. Your digital meter might say it is fluctuating between 14.7 and 15.4...and that is precisely what my digital meter does...it never indicates a constant voltage. But it will indicate whether or not you are getting the HO scale voltage or the O scale voltage, as it did when I found my own tracks getting an "indicated" 19 volts once when I had the toggle in the wrong position. As soon as I corrected the toggle, the voltage fell to the range I indicated above.

So, you want a ball-park figure showing you are getting decent voltage for your scale. If you want an A grade on your measurements, you will need something like an oscilloscope or a Ramp meter.



Edited by - Selector on 2009 December 09 12:08:18 PM

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jlbaz

Posted - 2009 December 09 :  12:09:34 PM  Show Profile
quote:
Originally posted by High Ball

Hello;

Very interesting.

Now I'm confused more then ever.

Please explain why a home meter will work with DC but not DCC.

As I understand it a DC system controls the track. O volts up to, what, 14 volts maximum. 0 volts nothing is moving. 14 volts, she's a really rippin boys.

The DCC system controls the locomotive. That with DCC the voltage is high and constant. What exactly high is I don't know. I just can't understand why a home meter won't work. I know you are right but just wonder why.

thanks.


The DCC waveform is a series of square pulses. If you try to measure it as DC, you will see zero, since the voltage with respect to either rail is positive and negative equally. Using the AC setting you will get a number that is close, though not exact, since the meter is calibrated for a sine wave rather than a square wave.

What is true is that measuring the voltage on the rails without a load is not really a useful exercise. If there is a poor connection you will still see full voltage, but as soon as there is a load there will be a drop across the poor connection and the voltage to the rails will drop. It would be more useful to remove the command station and measure the resistance from different locations around the layout back to the command station.


Jeff

--but it's a dry heat

Country: | Posts: 256 Go to Top of Page

High Ball

Posted - 2009 December 09 :  8:30:46 PM  Show Profile
Hello;

Will one locomotive running impose enough load to conduct an accurate test?

For the purpose of checking track voltage for constant voltage. Would it be o.k. to check the track in the DC mode with one locomotive running. If the voltage readings are constant or near so all around the rails would that not indicate the track connections and power drops would be o.k. for DCC as well?

thanks.


nicholas

Country: USA | Posts: 688 Go to Top of Page

jlbaz

Posted - 2009 December 09 :  9:45:10 PM  Show Profile
One loco might not really be enough of a load, and you'd want to check the voltage at the load, so you would be chasing the loco around!

The way to make this kind of measurement accurately would be to use a big power resistor, 5 Ohms or so, and go around the layout and measure the voltage at the resistor. You could use DC for that easily enough.

The important thing is to be careful as you do your wiring. Better to get quality through workmanship than through testing!


Jeff

--but it's a dry heat

Country: | Posts: 256 Go to Top of Page

peteski

Posted - 2009 December 10 :  04:30:52 AM  Show Profile
quote:
Originally posted by High Ball

Hello;

Very interesting.

Now I'm confused more then ever.

Please explain why a home meter will work with DC but not DCC.

As I understand it a DC system controls the track. O volts up to, what, 14 volts maximum. 0 volts nothing is moving. 14 volts, she's a really rippin boys.

The DCC system controls the locomotive. That with DCC the voltage is high and constant. What exactly high is I don't know. I just can't understand why a home meter won't work. I know you are right but just wonder why.

thanks.



This might be helpful in explaining.
http://www.dccwiki.com/DCC_Tutorial_%28Power%29


Peteski

Country: USA | Posts: 3324 Go to Top of Page
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