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Building a Track Power Indicator


Sir TophamHatt
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So I was looking at making a quick track power indicator but don't know if I can change it to indicate how strong the power is.

Got the idea from the MERG Electronics for Model Railways (Part B) book.

 

I don't have all my track sections connected to the bus wire, but the ones that aren't are very short, usually brand new pieces of track, so nice and clean.

 

Any idea if I can make some sort of strength indicator so see how good/bad the power is?

 

I guess this may just be a multimeter, even on DCC powered layout.

Edited by anotheruser
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What are you trying to see?

 

At a minimum you need 2 meters; a voltmeter & an ammeter, then multiply these together. Voltage needs to be measured across the load (load typically being a loco) & current needs to be measured inline.

 

If you are searching for possible volt drop, then just placing the probes of your meter across the track will not do, because a voltmeter has a very high resistance & voltage around a circuit is split in proportion to the resistance. If you can put a power hungry load in section & measure the voltage, you will see a difference if you have a poor section.

 

If you are looking for a current indicator to make sure you don't overload your system, then an ammeter will tell you this but you would need to break the circuit in order to connect it. This will still not be accurate though, because of the sine/square wave issue.

 

 

 

You made a brief mention to DCC:

 

You will not get an accurate reading from a standard multimeter because they are designed to measure sine wave AC. DCC is square wave.

 

I don't know about other systems but NCE's Powercab has a built in ammeter, but the PowerPro does not. I believe this is because the PowerCab is the system's command station, so all the layout current passes through it but the PowerPro has a separate one. I am not sure about a PowerCab with a booster. I suspect this will not all the ammeter to work.

 

Edited to cover the differences for DCC since it got a brief mention in the initial question, which I mis-read at first.

Edited by Pete the Elaner
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Hi

The LED indicator shown in Part B of the book is a MERG PMP (Pocket Money Project) kit, but it is very simple to make using two LEDs and two 1K0 resistors and piece of Vero stripboard plus two large headed pins acting as probes/contacts to the rail.   The PMP1 kit costs MERG members £0.46 plus postage! 

All it shows is that voltage is on the rails. It doesn't show how much or how little voltage is present or what current is being drawn.  Its a very quick and simple "Is there rail volts?" tester.

 

For DCC... A single red or green LED with a series 1K0 resistor and a 1N4001 or 1N4148 or similar diode connected inversely across the LED will provide a constant visual ' DCC Power On' indication when its connected across the DCC rails or DCC Bus pair of wires.

For DC (Analogue)... simply add a second LED and resistor but this second LED is reversed to the first one.  No diodes are needed on DC when two LEDs are used and one is inverse to the other.  But either of the LEDs will only illuminate when track power is turned up. One LED would come on for forward power the other for reverse direction,

 

If you want to measure the DCC rail voltage use a multimeter set onto it AC voltage range for DCC. Many cheap domestic multimeter wont have AC current ranges!   A more upmarket multimeter may have AC Amp range   Do remember though what is read on a domestic multimeter on DCC is not necessarily an accurate reading. But never the less what voltage is read at the supply should be virtually the same every where else!

Possibly, for general DCC output monitoring, though much more expensive, is to obtain a RRAmp meter that shows both track voltage and current to track accurately. Example... http://www.dccsupplies.com/item-p-100316/rramp-meter-version-iii.htma

 

Most budget multimeters will measure DC voltage and DC current (Amp).  Remembering with virtually all meters to allow current (Amp) reading, the red test lead has to be moved to the correct Amp socket on the meter and of course the range switch is moved to the DC Amp maximum range setting. Always return the lead to the normal red socket on the meter as soon as you have finished reading current and turn off the meter range switch too.

Edit to add....

Always test Voltage with the meters leads across the rails or bus pair. 

Always test for current with the meters leads in series with one feed wire going to one rail or bus wire. This will mean disconnecting the feed wire and connecting the meters test lead to the end of the removed wire and its other lead to the place where the wire was removed from!

With any reading - Voltage or current start at the highest range setting.   NEVER connect a meter across the supply when the meter is set to current (Amp) ! 

Edited by Brian
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