Northern Tablelands Express approaching Ardglen Tunnel

Northern Tablelands Express approaching Ardglen Tunnel
Click on the above photo to see the Main North Album at Flickr

Sunday, July 9, 2017

DCC Ammeter for the Layout

Over the years, I've read/heard modellers asking many times, "When do I need to add a second Booster". Recently some modellers reported on one of the Groups that a loco or lighted Passenger Coaches Set, drew too much current, causing the DCC system to cut out.

Almost everyone has a 10 Amp D.C. range on their Multimeter and adding a 6.0 Amp Bridge Rectifier to it as shown below, you'll have a DCC Ammeter for $2.50. Seems crazy if you don't have one. Now you'll know what current is being drawn by the layout (locos, lighted Coaches etc) and when to add a Booster.

Note: If you are using an NCE Power Cab, it has an Ammeter included, set it up in Cab Parameters. If you are using the Power Cab with an SB3/5/Power Pro, the included Ammeter is not available.

The Bypass Switch: The Bridge Rectifier is necessary to measure the Amps but it reduces the Track Voltage by 1.5 Volts.
If your DCC system has a Voltage Adjustment you can compensate for this 1.5 Volt drop and you can leave out the Bypass Switch.
If your DCC system does NOT have the "adjustment" and you want to operate at the "set" voltage, install the Bypass Switch and operate it in the OPEN position for Current measurements and in the CLOSED position if you don't want to operate with the slightly reduced (1.5 Volt) track Voltage.

See below for measuring the DCC Voltage.

Add the Bridge Rectifier to one of the Track "Power Bus" Feeders as shown below by "hard wiring" the Bridge Rectifier into the Booster Track Terminals or an appropriate location and run 2 wires to the Meter and Switch (if you are using it). Shown below is the " Ammeter Adapter"for my DCC Tool Box, 10 Amp Multimeter, necessary for troubleshooting other layouts or demos etc.     

One method of making the "simple" Ammeter using a Jaycar $10 Multimeter and a ZR1314 6.0 Amp Bridge Rectifier with the "D.C." leads soldered into two Banana Plugs for easy removal/install of the Adapter. The two Back leads connect to the "A.C." leads and connect "into" one Track Feeder at the Booster as per the above diagram. You choose the easiest way to make it.

This is all that's necessary to measure the current to the layout.

The above Bridge Rectifier Ammeter compared to my Fascia Ammeter, refer below for details on how I made it..

A 5 Amp Bridge Rectifier soldered to the rear of a 5 Amp Panel Meter with the black wires goint to the Booster.

The Digital Multimeter Ammeter compared to a 5.0 Amp D.C. Panel Meter, both indicating the track current - no locos running and all quiet (no sound). The reading indicates the standby current for 35 stationary locos and a few Bus Accessories (power to my Signal Power Supplies etc), to my layout.

During an Operating Session with 6 to 8 Operators running trains, the Ammeter rarely goes above 2.5 Amps on my 600 Sq Ft Double Deck layout and there is just the one Booster. 

My Fascia Ammeter made from a Rob Paisley Model Railroad Circuits at:
made on Veroboard with the 2 very small black rectangular ZXCT1009 - 3 Terminal 'Current Monitor' Integrated Circuits, between the Copper tracks in the centre of the photo. 

Above an old 5 Amp Digital Multimeter, cut in half to fit behind my Fascia connected to the above ZXCT1009 Ammeter. I could have bought a Digital Display from Jaycar, but it was lying around not being used. The Meter is powered from the same Transformer that powers the Power Pro system.

 A 5 Amp Panel Meter fitted to one of my mate's DCC System Cabinet, showing 4 High Speed Diodes and the small Bypass Switch. The larger one (Upper R/H side), is the Layout ON/OFF Switch. The layout is divided into 6 Power Districts using NCE EB1 Circuit Breakers. The District ON/OFF Switches are installed to help troubleshooting the layout when there are the inevitable wiring issues. This is a large layout and still only using one Booster with the Meter showing less than 2.5 Amp during the running of trains. If and when it gets to 3.5 to 4.0 Amps, we'll add a second Booster.

Measuring DCC Track Voltage is as easy as using your Multimeter and selecting A.C. Volts. While this may not be as accurate as a specialist DCC Voltmeter like Tony's RRampmeter, it is good enough for troubleshooting voltage drops. With your Mutimeter, measure the voltage at the Booster Track Output Terminals then measure at the appropriate location. Compare the two readings. The "difference" in the readings is the voltage drop between the two locations. 
NOTE:  When making a voltage drop measurement, always have a load like a 21 Watt Automotive Lamp (1.5 Amps), across the track at the "Track" location. 

For more details on Meters for DCC see my web page at:

1 comment:

  1. Very useful, simple approaches Marcus. Thanks for sharing.