Above photo is my Gosford complete with the Overhead. Click on the 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 Yahoo/Facebook Groups, that a loco or lighted Passenger Coaches Set, drew too much current, causing the DCC system to cut out.

Determining how much current a Booster is supplying to the layout, is not about how big a layout is, how many locos you have, what scale you model etc, it's about what current is "actually" flowing. Yes quantity and size are factors.

Determining the Booster Output Current without an Ammeter, is just a GUESS.

I built a DCC Ammeter (discussed below), from Allan Gartner's Wiring for DCC pages, many years ago, see:
and found that locos (decoders) sitting on "powered" track (not moving), draw approximately 30 mAs and running modern HO loco (last 20 years or so), draw between 100 - 400 mAs.

Install a $2.50 Bridge Rectifier from Jaycar (Part No ZR1314), connected to a 10 Amp Multimeter (similar to the $10 Jaycar QM1500) or Panel Meter, as shown below, you'll then know what your layout is drawing and what each loco uses and it only takes 10 minutes to make/install.

Seems crazy if you don't make a DCC Ammeter.

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.

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.     

Shown above is the 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.

The above Bridge Rectifier Ammeter compared to my Fascia Ammeter, made from a Circuit from Rob Paisley's Model Railroad Circuits at: 

A 5 Amp Bridge Rectifier soldered to the rear of a 5 Amp Panel Meter and the Meter/Bridge Rectifier assembly connected in SERIES with one of the Track Feeder wires, via the two black wires.

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. 

Caution: The 6 Amp Bridge Rectifier used above gets quite warm at 2.0 Amps. Operating at higher currents over an extended period of time, I'd suggest mounting the Bridge Rectifier on a Heat sink. 

 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 Amps 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 (see below), 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 12 Volt 21 Watt Automotive Lamp (1.5 Amps), across the track at the "Track" location. 

Specialist DCC Volmeter/Ammeter
For those of you that don't want to "make" the above DCC Ammeter or would like a very professional looking Meter Set, easily mounted into your layout's fascia, the A$130 RRampMeter  from DCC Specialties may be more suitable, see:
and can be purchased here in Sydney Australia from Models n More at:

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