Using a Shunt Resistor with TPDIN-Monitor-Web2

  • 17 April 2017

    Using a Shunt Resistor with TPDIN-Monitor-WEB2


    Background: Using a shunt resistor can allow you to measure very high currents using the TPDIN-Monitor-WEB2. A shunt resistor is an external high current capacity resistor that is placed in-line with the current circuit. The shunt is usually constructed of an alloy called Manganin (86% Copper, 12% Manganese, 2% Nickel) because it has a stable resistance over temperature. The TPDIN-Monitor-WEB2 measures the voltage drop across the resistor and displays the appropriate current.


    1. To calibrate the TPDIN-Monitor-WEB2 for a particular shunt resistor, you need to enter the shunt resistance into the Shunt Resistor Ohms field on the System page of the web interface. The Max Current and Min Resistor Watts displayed are for information only.


    2. Selecting a shunt resistor depends on how much current you need to measure. You can use the tool above to find the resistance needed to meet your Max Current requirements by changing the Shunt Resistor Ohms value until the Max Current displays your required current and then finding a shunt with the proper resistance and minimum watts value. For instance in the example above you may need to measure up to about 300A. You will need to find a shunt resistor with 0.000100 Ohms and at least 11W power capacity.


    3. Another way to select a shunt is to find an available shunt with a current rating higher than your required current. Most common shunts are 75mV shunts. The TPDIN™ shunt input is +/- 33 mV. When using a 75mV shunt you will need to de-rate for a 33mV input.

    a. For example, a 100A 75mV shunt will only be able to display up to +/- 44A on the TPDIN-Monitor-WEB2 (75mV/33mV = 2.27 100A/2.27 = 44A)

    b. Another way is to look at shunt resistance: 100A 75mV shunt , (E/I=Ω), 75mV/100A = 0.00075Ω. Enter the 0.00075Ω to the System page and you will see Max Current is 44A.

Starting a Generator with TPDIN-Monitor-WEB2

  • 19 December 2016

    Background: Many customers want to use the TPDIN-Monitor-WEB2 to be able to sense the battery voltage and start a generator when the voltage gets too low. You can use the following method to accomplish this with the TPDIN-Monitor-WEB2.

    1. Use one of the Normally Open Relays – Relay 3 or Relay 4.
    2. On the System Page set the Cycle Delay which should equal the generator start time, normally 15-20seconds.

    1. On the Relays Page setup Relay 3 or Relay 4 controls.
      1. Voltage Control
        1. Select the Voltage channel that is monitoring the battery voltage in the drop down box.
        2. Set the voltage “From” to the low limit and the “To” to the upper limit. Normally the upper limit should be higher than any possible battery voltage.
        3. Set the action as “Open else –“ (don’t care)
        4. Periodic Control
          1. Set the Periodic Control to control the retries. In the example below we have it set to retry every 5 minutes.
          2. Set the action as “Cycle else Open”

    1. In this example the functionality will be as follows:
      1. When the Voltage is between 11.0V and 22.0V the relay will be held open.
      2. If the voltage drops below 11.0V or exceeds 22.0V the periodic control will take over and the relay will cycle every 5 mins for 15seconds and it will continue to cycle until the battery voltage exceeds 11.0V.
      3. As soon as the generator turns on, the voltage will rise quickly about 11.0V and disable the Periodic Control.
      4. You can adjust the limits to suit your specific application.
    2. Some generators have a Start Switch and a separate Stop Switch. If you need another relay to turn off the generator use the other Normally Open Relay (Relay 3 or Relay 4). You will need to use I3 or the shunt input (using an external current shunt) to monitor current going into the battery from the charger.
    3. On the Relays Page setup Relay 3 or Relay 4 controls.
      1. Current Control
        1. Select I3 (+/- 10A capability) or Shunt Current (If using an external current shunt)
        2. Set current limits “From” 2.0 Amps “To” 20.0 Amps.  You need to monitor battery current so you know when to disengage the generator. Normally when the battery charging current is around 2A, the batteries are fully charged. This number depends on your total load because your load will add to the battery current measured and it also depends on the size of your battery array. The “To” amps should be higher than any current you might encounter or the maximum current possible from your charger.
        3. Set the action as “Open else Cycle”

    1. In this example the functionality will be as follows:
      1. When the current is between 2.0A and 20.0A the relay will be held open.
      2. When the current falls below 2.0A or exceeds 20.0A, the relay will cycle for 15seconds and will turn off the generator.
      3. You can adjust the limits to suit your specific application.