# NCE Power Pro Voltage Anomoly



## Kinbass (Apr 28, 2018)

Hey all, this is my first post. Thanks in advance for any help. Decided to dive into DCC, I bought a Power Pro command station w. Wireless Pro Cab kit off Ebay, sigh. I am struggling with it, think it is broken. 

(All of this is on multimeter 200acv)If I measure the voltage across the rails I got 10v in one orientation, if I switch the electrodes I get 0 volts. So then I put the com electrode on ground on the control module, and with + electrode I get 10v on 1 rail and 20v on the other rail. What the heck is going on?

I measured the power input from power pack, its a solid 16.4v w. electrodes in either orientation. And just to test the meter I checked a wall socket and its reading 115v as expected. 

Thanks for any thoughts.


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## gregc (Apr 25, 2015)

if the voltage from the unit is 16.4 VAC, there's nothing roken

check your connections to the track. With the unit unplugged check the resistance from each connector on the unit and a track rail.


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## Kinbass (Apr 28, 2018)

I screwed up when I said 16.4v from the "power pack", I meant from the power transformer, from the wall, powering the unit. This would be the feed into the unit via the "power" connections. 

It's the track connections that are giving me fits. They are the ones giving the 10v/0v when I put the electrodes on them, and then 10v/20v when I put the com electrode to ground and then the + electrode on each track connection. Also note the program track is reading 1.4v.


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## Kinbass (Apr 28, 2018)

One other note, these readings are directly from the connections on the front of the unit, not from any actual connected track. Thanks.


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## gregc (Apr 25, 2015)

DCC track voltage changes polarity between every 50-100 usec in order to communicate with a decoder.

The way it does this is to connect one rail to ground and the other rail to the supply voltage and visa versa. the way it does this is with what's called an h-bridge typically using MOSFET power transistors which act like switches.

This means that the average or DC voltage across the rails is close to zero and the AC voltage should be representative of (depending on meter) the supply voltage.

it doesn't matter which wires the meter probes are connected to when measuring AC. 

a digital meter typical reports the voltage as negative if the probes are reversed. Not sure about an analog meter.



Kinbass said:


> If I measure the voltage across the rails I got 10v in one orientation, if I switch the electrodes I get 0 volts.


trying to understand how you measure zero volts and wondering if you're measuring DC or AC. 




Kinbass said:


> So then I put the com electrode on ground on the control module, and with + electrode I get 10v on 1 rail and 20v on the other rail. What the heck is going on?


wondering how you measure 20 V (AC or DC?) if the supply is 16.4 VDC.

when measuring with respect to ground (a good idea) the output is alternately connected to ground and supply. The DC voltage would be the average or half of 16.4 supply voltage and the AC voltage would also be half as well.

if the power transistor connecting to supply, there would be no output. Not sure how to determine if the transistor connecting to ground is failed.

i guess a power transistor can be blown, but there's protection against shorts. I guess it's possible there's a broken solder joint.


assume you have a powerhouse command station


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## DonR (Oct 18, 2012)

Uncertain what multimeter setting you
are using. Use AC setting.

DCC controllers will put around 14 volts modified
AC on the rails any time the power is on.

To get a correct voltage reading from your track place
a loco on it as a 'load' then read the voltage.

Don


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## Lemonhawk (Sep 24, 2013)

I don't think a load on the track will help much on DCC, different story for a DC layout. Does you meter have anything other than 200v AC? Is it an autoscaling digital meter? Measure the track output (at the controller with the track disconnected. I think if you don't see around 14-16 volts (on an AC setting) then the Controller has issuers.


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## Kinbass (Apr 28, 2018)

I cant find my good meter, having to use my cheap HF backup, but it is giving me good readings, tested AC on house, and dc on several batteries. Even tested ohms on some resistors. Kind of getting that feeling I bought a lemon. Its not a power house, its a power pro. Attaching some pics to show my reading.


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## gregc (Apr 25, 2015)

can you say which are DC and which are AC measurements?

the input should be DC.

the track measurements should be AC


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## gregc (Apr 25, 2015)

sorry. i'm not sure what the input voltage should be DC/AC either.

i think the manual describes both the 5A and 10A system. I think the 5A system takes AC.


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## Kinbass (Apr 28, 2018)

Ya, I meant to put the entire meter in the pic. All of those measurements were AC. I looked very closely at the entire PCB, I see no fried components or broken solders. Very odd.


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## Kinbass (Apr 28, 2018)

I sent NCE an email, they told me to ship it to them and they will take a look at it. Apparently they do this service for free. Then, if it needs repair, they will let me know the cost before they fix it. So I am going to do that. I will post back in a month or two with the results. (they have a 4-5 week backlog right now).

Thanks all


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## fcwilt (Sep 27, 2013)

Just for grins try measuring a known DC voltage with your meter set to AC.

What you are seeing might be an artifact of the way your meter handles AC.

Frederick


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