5 Amp - DCC Ammeter


February 2021 at 16:55 - The DCC Ammeter Circuit Board Is No Longer Available.

  The circuit shown on this page uses inexpensive digital multimeters or low cost panel meters (links below) to measure currents in DCC systems.

  Using a milliammeter as the readout means that the circuit does not require re-calibration if a different meter is connected to the circuit. The meter will normally be set to the 20 milliamp range which allows the highest output reading range. A 2 mA setting would give a 0 to 2 amp read out.

  The DCC Ammeter uses two - ZETEX - ZXCT1009 - three terminal 'Current Monitor' integrated circuits to measure the current.

  The DCC Ammeter can used in circuits of between 7 and 20 volts. The 20 volt maximum can be increased if needed, see the diagram further down the page.

  The 2010 DCC ammeter circuit is designed for a 5 amp continuous current but can operate at up to 7 amps for short periods.

DCC Ammeter (2010) Schematic

DCC Ammeter Operation

Input To Output Current Ratio

  For the values given, R1 and R2 equal 0.1 ohm, when the load current is 1 amp the current from the output terminal of a ZXCT1009 will be 1 milliamp. This gives an output ratio of or 1000:1. (See the ZXCT1009 datasheet for more information.)

  Therefore, the output current from the ammeter is 1 milliamp per ampere of load current.

  The milliammeter will normally be set to the 20 milliamp range which allows the highest output reading range. If the meter is set to the 2000 microamp (2 mA.) range the readout will only indicate as high as 2 amps but gives better resolution for low current measurements.

Calibration Of The DCC Ammeter (2010)

  No external calibration is required for this circuit. The accuracy is mostly dependent on the 1 percent tolerance of the 0.1 ohm resistors.

DCC Ammeter Circuit Notes

DCC Ammeter (2010) - Parts List

Part Number   Description   Digi-Key Part #   Qty
IC1, 2 - IC Current Monitor SOT-23 - ZXCT1009FCT-ND - 2
D1, 2, 3, 4 - Diode 100V 4.0Ns DO-35 - 1N4148FS-ND - 4
R1, 2 - 01. Ohm resistor 1% - 5W - LVRC-.10RCT-ND - 2
- - 2 Position Terminal Block - 3.5mm - ED1514-ND - 2

Panel Meters

  Panel meters can be adapted to the circuit by adding the appropriate voltage dropping resistor. The value of the resistor depends on the meter itself but 1,000 ohms for a voltmeter and 10 ohms for a 200 millivolt panel meter.

Analog Meters

  There a number of low cost panel meter sources that could be used with the DCC ammeter circuit. Below is a list of links to meters and suppliers of examples of these meters.

  Using the analog meters will depend on their ohms per volt specification. An analog voltmeter is the best choice, the 'V' symbol on the face could be changed to an 'A' with little work.

Digital Meters

  The 200mV, digital meters should only need a 1K load / scaling resistor to be connected. These meters need a power supply which is typically a 9 volt battery. Other power supplies are shown below.

  There are many digital and analog meters. I don't have the specification sheets for these meters so the exact connection to the ammeter is not know but should be easy to figure out.

  Below are links to several meters that could be adapted.

Analog And Digital Meter Examples

A 200 milivolt range is good for the digital digital meters

Futurelec - 200mV Meter

Abra Electronics



Images Of Various Meters That May Be Suitable

Meter Images

Additional Circuits

Operating Voltages Greater Than 20 Volts

  The DCC ammeter can be used for systems that operate at greater than 20 volts by adding a voltage drop to the meter portion of the circuit.

Using Voltmeters As The Output Indicator

Analog (Or Digital) Voltmeter

  A voltmeter can also be used as a display if a calibrating resistance is placed across the outputs of the current monitors.

  The 1K variable and 470 ohm resistors are used to calibrate the voltmeter circuit against a known DC or DCC load or another DCC capable meter. The voltmeters reading is adjusted the reading is 1 volt per amp measured.

  An advantage of using a voltmeter as the display is that different meters should nt need calibration.

200 Millivolt Digital Panel Meter

  A digital panel meter with a 200 millivolt range can also be used with the ammeter circuit.

  Due to the low resistance of the 10 ohm shunt resistor, it does not need a 1 percent tolerance resistor if one is not readily available.

Alternate Power Supplies For the Meter

  The circuit uses a full wave bridge rectifier and a zener diode to replace the multimeter's battery. Capacitors C2 and C3 isolate the meter's circuitry from the track circuit.

  The parts values given in the circuit above are based on the digital multimeter having a current draw of approximately 1 milliamp from its 9 volt battery. The parts values were determined using actual circuit conditions.

  A 1N757, 9.1 volt zener type diode is used in the circuit above but any combination of zener's, forward biased ordinary diodes or LEDs that can produce a voltage drop of between 8.0 and 9.5 volts at 1 milliamp would also work.

  When the power to the track is ON, the optoisolator will act as a closed switch and the meter will have power.

Non DCC Ammeter Circuits

Dual - ZXCT1009 - DC Ammeter

  The following is a Dual - DC Ammeter circuit made with the DCC Ammeter circuit board shown at the top of this page.

  The only changes needed to the original ammeter circuit are the removal of the four blocking diodes and connecting the meters directly to the outputs of the current monitor ICs.

  A toggle switch could be used to select outputs so that one meter could be used for both outputs.

  The circuit board could also be used to make two separate DC ammeter circuits.

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Please Read Before Using These Circuit Ideas

  The explanations for the circuits on these pages cannot hope to cover every situation on every layout. For this reason be prepared to do some experimenting to get the results you want. This is especially true of circuits such as the "Across Track Infrared Detection" circuits and any other circuit that relies on other than direct electronic inputs, such as switches.

  If you use any of these circuit ideas, ask your parts supplier for a copy of the manufacturers data sheets for any components that you have not used before. These sheets contain a wealth of data and circuit design information that no electronic or print article could approach and will save time and perhaps damage to the components themselves. These data sheets can often be found on the web site of the device manufacturers.

  Although the circuits are functional the pages are not meant to be full descriptions of each circuit but rather as guides for adapting them for use by others. If you have any questions or comments please send them to the email address on the Circuit Index page.

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27 February, 2021