# Voltage readings on stub tracks



## fulsom56 (Sep 18, 2015)

Hi everyone, I just finished wiring my roundhouse & stub tracks leading off of the turntable. I only want power to one stub track at a time depending on where a loco. will be placed. I achieved this by wiring in a rotary switch with one leg of each stub track going to the rotary switch & then the common wire on the switch going to the red leg on my track buss. The other legs off of each stub track are all wired directly to the black wire of the track buss.

I checked operation of each stub track & it works just as intended. Voltage to the track that is powered reads approx. 13.8 volts A.C. All other tracks do have a voltage reading of approx. 3volts. I believe this is due to the leg of each track that is connected directly to the track buss.

Question........could the stub tracks that have the 3 volts applied to them damage a locomotives DCC decoder if it sits on those tracks long enough?


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## fulsom56 (Sep 18, 2015)

Here is a photo of my layout showing the control panel with the rotary switch & stub tracks in question leading off of the turntable.


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## cid (Jul 3, 2014)

Fulsom, nice looking layout there! I think your three volts may be just a spurious reading, a little high impedance leakage thru the rotary switch, maybe? But put a loco on the track while you measure it. Hopefully with any load on the track that voltage reading will disappear.


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## DonR (Oct 18, 2012)

You have a layout with a lot of switching possibilities. You sure
got a lot of yards and tracks in a relatively
small space. Be sure to post it in the Layouts of Members
thread.

I agree with CID. You need a load on the track
to get a good voltage reading. 

With DCC there's really not a necessity to depower
any loco storage tracks. The decoders draw 
relatively little current when the loco is inactive.
However, if you have a DC loco or so they must
have a dead track when idle to protect the motor
from the DCC's AC burnout.

Don


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## Lemonhawk (Sep 24, 2013)

3 volts does seem a bit high. If you were using an autoranging multimeter are you sure it wasn't 3 mv? I've fool myself several time by not noting the units. Also rotary switches can be "shorting" or "non-shorting" meaning that as your moving the wiper it will power the next position and the current position (shorting) before getting to the next position. A non-shorting switch has a gap between positions. I think either will work in your case but there may be that slight unexpected sound from as your repositioning the switch. I would love to have a turntable to play with, but no room yet! Yours is just what I want to build!


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## fulsom56 (Sep 18, 2015)

cid said:


> Fulsom, nice looking layout there! I think your three volts may be just a spurious reading, a little high impedance leakage thru the rotary switch, maybe? But put a loco on the track while you measure it. Hopefully with any load on the track that voltage reading will disappear.


I just rechecked my readings with a loco on the tracks & now get approx. .5 vac. A coworker let me use his analog meter which I set at 0-10 volt range & even without a loco. on it the most I get on any of the stub tracks is .3 volts. Absolutely right, you do need to have a loco. on the tracks to get a proper reading. Thanks for the kind words on the layout, I've been working on only that portion all winter...........Al.


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## fulsom56 (Sep 18, 2015)

DonR said:


> You have a layout with a lot of switching possibilities. You sure
> got a lot of yards and tracks in a relatively
> small space. Be sure to post it in the Layouts of Members
> thread.
> ...


Hi Don, the reason I'm depowering stub tracks with locos. on them is so I don't have to worry about run away engines-so I thought I read this somewhere. I also thought you could fry a DCC decoder with power left on for a long period-don't know why, I'm probably overthinking this.
When I get time I'll post a series of pictures showing the progression of my layout. Thanks..........Al.


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## fulsom56 (Sep 18, 2015)

Lemonhawk said:


> 3 volts does seem a bit high. If you were using an autoranging multimeter are you sure it wasn't 3 mv? I've fool myself several time by not noting the units. Also rotary switches can be "shorting" or "non-shorting" meaning that as your moving the wiper it will power the next position and the current position (shorting) before getting to the next position. A non-shorting switch has a gap between positions. I think either will work in your case but there may be that slight unexpected sound from as your repositioning the switch. I would love to have a turntable to play with, but no room yet! Yours is just what I want to build!


Hi Lemonhawk, I'm using a Amprobe multimeter with autorange but it is reading volts not millivolts so the 3 volts is correct. Talking to a coworker he had me check with his analog meter which gave me approx. .3 volts ac. With the circuitry of a digital meter, in this case, he believes a analog meter would be more accurate. 

The rotary switch is non shorting with a gap between each contact. I have it set for 11 positions out of 12 possible. Thanks..........Al.


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## DonR (Oct 18, 2012)

Al

The DCC decoders are designed to be 'on' all
the time much the same as your computer
tho it may go to 'sleep'. No harm will come
to them sitting idly on a powered track.

You may have been thinking of DC locos sitting
idle on a DCC track. That will quickly burnout
the motor.

Do you get the same reading with a loco or lighted
car on the track you are testing?

There is another possibility that might cause the
voltage leak that you are seeing. You have a
common buss to each track, but a rotary switch
on the other side of the circuit. I'm wondering if
there can induction that is somehow responsible for the leakage.
Are all of the connected stub tracks empty?

We are dealing with digital signals not just plain
60 cycle AC. On some of the big club type DCC layouts with
powerful boosters they have found the need for
snubbers on the ends of the buss to coral stray
emissions and prevent distortion of the digital info.

Don


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## tkruger (Jan 18, 2009)

Just an FYI. I had the set up you described in my layout when it was DC. I did not change the wiring when I first went to DCC. Unfortunately I found that I started to get shorting due to the rotary switch. Removing it fixed the issue. I do not know if it was shorting or non-shorting per say, I just know it was causing shorting .


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## fulsom56 (Sep 18, 2015)

DonR said:


> Al
> 
> The DCC decoders are designed to be 'on' all
> the time much the same as your computer
> ...


Don, thanks for the info. With no engine on a stub track that is not selected (power off to that track) & with a digital meter I get approx. 3 VAC. If I have an engine on that track (track not powered) the voltage drops to .3 VAC. Actually , I'm satisfied with the readings that I get & it looks like everything is working just the way it was intended. The information you guys gave me helped a lot in answering my questions. I'll be looking into the use of snubbers also. Al.


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## fulsom56 (Sep 18, 2015)

tkruger said:


> Just an FYI. I had the set up you described in my layout when it was DC. I did not change the wiring when I first went to DCC. Unfortunately I found that I started to get shorting due to the rotary switch. Removing it fixed the issue. I do not know if it was shorting or non-shorting per say, I just know it was causing shorting .


The rotary switch that I'm using came from an old medical monitor that was discarded at a hospital where I work. An electronic tech. friend of mine has been saving old equipment that I'm able to strip for various switches, push buttons, rotaries,etc. I bench tested this rotary switch & set it up for 11 positions which is how many stub tracks I'm feeding. I'm happy to see that it works out............Al. By the way, I checked out your layout. Very nice, like the scenery & there's a lot to look at.


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## DonR (Oct 18, 2012)

Maybe I misread earlier. I see you are saying .3 VAC.

That could be any kind of stray current, but not
enough to worry about IMHO.

Just out of curiosity, how does your DCC controller
react if you short across a track where you get
that reading? Does it show a short? If a loco is
running on the main when you short the track
where you get the reading does it react?

Don


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## fulsom56 (Sep 18, 2015)

DonR said:


> Maybe I misread earlier. I see you are saying .3 VAC.
> 
> That could be any kind of stray current, but not
> enough to worry about IMHO.
> ...


I just checked an I cannot create a short on a stub track with no power to it. If a loco is running on the main it does not effect it ether. If I switch on a stub track using the rotary sw. it does create a short & shut down power. Yes I am say point 3 volts on stubs with no power.


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## DonR (Oct 18, 2012)

I would be curious to hear from some of our more
high tech digital guys, but I'm thinking the 3 volts with
no load when track is off is an invalid reading or the
result of Digital inductions or some sort.

Since you don't get a short indication on a track 
not 'on' it indicates to me again an invalid reading
so at this point I think all is well.

I assume you have tested and found that locos
respond correctly on these spur tracks when
switched on.

Don


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## fulsom56 (Sep 18, 2015)

DonR said:


> I would be curious to hear from some of our more
> high tech digital guys, but I'm thinking the 3 volts with
> no load when track is off is an invalid reading or the
> result of Digital inductions or some sort.
> ...


Yes, all my engines work correctly on all spurs. I even shorted the spurs to be sure power shut down & returned as normal. As a side note, I'm powering my layout with the NCE Power Cab which is connected to a DCC Specialties PSX circuit breaker which connects to the track buss.

Also noted, concerning the 3 volts is that it is read with a digital multimeter. I've checked it with a analog meter set on 0-10 VAC setting & get only point 3 volts. I tried this on a recommendation from an electronic tech. friend of mine. Can't get to technical here but he believes in this instance a analog meter is more accurate then a digital.


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## DonR (Oct 18, 2012)

I think there is a thread here on the forum where
electronics techs discuss using a scope or other
more exotic test gear to get an accurate measurement
of the DCC square wave AC voltage. What we get
with the multimeters we have is usually sufficient
for our purposes.

Don


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## fulsom56 (Sep 18, 2015)

DonR said:


> I think there is a thread here on the forum where
> electronics techs discuss using a scope or other
> more exotic test gear to get an accurate measurement
> of the DCC square wave AC voltage. What we get
> ...


I have been considering purchasing the RRampmeter from DCC Specialties to get a more accurate reading but don't know if I want to shell out the bucks for it.


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## ncrc5315 (Jan 25, 2014)

The best way to check DCC track voltage, is by using an oscilloscope, short of that, the manual, should tell you how to check your track voltage. With Digitrax, you set an address of 00, and the speed is set to 00. Then measure from rail A to ground, and rail B to ground. Then add the two voltages together, to get your track voltage.


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## Mark R. (Jan 26, 2013)

I don't understand how you would get a voltage reading of ANYthing but 0 volts if one rail is turned off. (?)

I checked all my tracks that have the ability to be mechanically turned off on one rail, and with both a high quality digital and analog meters, they both read absolute 0 volts when turned off.

How do you get voltage when only one rail is live and the other dead ?

Mark.


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## higgsbosonman (Nov 17, 2014)

You said the rotary switch came out of a piece of medical equipment? maybe it has built in bleed resistors to each channel. I don't know what it was in before you popped it out, but if it was a medical device, they might have had it hooked to a circuit that they wanted to fully discharge when they switched away, and prevent any residual charge from forming (because shocking patients leads to lawsuits, and a lot of medical stuff plays with fantastic voltages). Test the switch itself with the ohm setting of your multimeter; does it register any resistance at all? or is it truly open circuit when off?


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## fulsom56 (Sep 18, 2015)

Hi, thanks for the continuing input. When checking the rotary sw. for continuity it is open from common to each poll that is not connected. The closed poll shows no resistance & reads 0 ohms.
Photos 1 & 2 show the switch in question.
#3 is my meter on AC auto range-nothing connected.
#4 shows 6.68 VAC with only the black lead plugged into a grounded wall outlet.
#5 has 1 lead connected to a spur controlled by the rotary sw.(1.042 VAC & no power).
#6 both leads connected .670 volts & no power.
#7 power switched to this spur shows 13.65 VAC
I cannot explain the voltage numbers that I'm getting other then it's feedback from the meter. I checked a number of wall outlets in my house & get the same readings. The rotary sw. setup works as intended & I'm more curious then anything at this point by the voltage readings. Thanks again...........Al.


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## Mark R. (Jan 26, 2013)

That's new to me .... never seen a meter read ANYthing just by attaching a single probe. (?)

Mark.


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## DonR (Oct 18, 2012)

Did you do a typo?

You claim 13.65 VAC when power is switched
on to the spur. N scale track should be DC.

I would be curious to see the readings from
a different meter. I have not seen meter readings
with only one probe connected either.

Don


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## Mark R. (Jan 26, 2013)

For a DCC system, the voltage is a form of AC, so using the AC setting on the meter is correct (kinda).

Mark.


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## ncrc5315 (Jan 25, 2014)

Mark R. said:


> For a DCC system, the voltage is a form of AC, so using the AC setting on the meter is correct (kinda).
> 
> Mark.


Actually, the wave form, is bi-polar DC, which to most devices, would "look" like AC, the correct way to measure the voltage, is on DC, and then you need to measure from rail A to ground, then from rail B to ground, and add the two numbers together, to get the actual track voltage. As a side note, I took my cheap radio shack DMM, and stuck one probe in to an outlet, and it showed ~15VAC. I next tried my Fluke 199C scopemeter, and is showed 500uV.


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## fulsom56 (Sep 18, 2015)

DonR said:


> Did you do a typo?
> 
> You claim 13.65 VAC when power is switched
> on to the spur. N scale track should be DC.
> ...


DCC is a form of AC voltage, I believe they call it square wave AC voltage.


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## fulsom56 (Sep 18, 2015)

ncrc5315 said:


> Actually, the wave form, is bi-polar DC, which to most devices, would "look" like AC, the correct way to measure the voltage, is on DC, and then you need to measure from rail A to ground, then from rail B to ground, and add the two numbers together, to get the actual track voltage. As a side note, I took my cheap radio shack DMM, and stuck one probe in to an outlet, and it showed ~15VAC. I next tried my Fluke 199C scopemeter, and is showed 500uV.


On my layout there is no ground. I have an NCE Power Cab starter set. Power comes from the supplied power supply to a PCP panel where you connect the Power Cab. The track buss wires (red & black) connect to the PCP panel. To check voltage you simply set your meter to AC volts & check across the rails - red & black. If you bought the RRampmeter you would be doing the exact same thing by placing that meter across the tracks to find your track voltage.


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## DonR (Oct 18, 2012)

A serious Senior moment, of course I know DCC
is a modified AC. No idea why my N scale DC comment.

Don


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## Lemonhawk (Sep 24, 2013)

On a Digitrax system, the ground on an outlet is not to be used on the track power, hence it will not provide any reference that should be trusted when checking any track voltage. If you were measuring between the outlet ground and either the A or B rail you could get strange voltage readings.


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## fulsom56 (Sep 18, 2015)

DonR said:


> A serious Senior moment, of course I know DCC
> is a modified AC. No idea why my N scale DC comment.
> 
> Don


I've had a bushel basket full of "senior moments" & I don't consider myself a senior.........but I'm getting there..........


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## ncrc5315 (Jan 25, 2014)

fulsom56 said:


> DCC is a form of AC voltage, I believe they call it square wave AC voltage.


I was thinking it was DC, because in the Digitrax manual, to measure track voltage, they tell say to put the meter on DC. But, when I attached an oscilloscope on the track, it is AC. I was wrong.


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