Calculating Voltage Drop

From PTI Security Systems
Jump to: navigation, search


Most PTI AI Devices require a minimum of 12V (AC or DC) to function. PTI Power Supplies are set to provide approximately 14VDC output unloaded and 12VDC output at rated amperage. Long runs of wire and multiple remotes powered on the same line can cause the voltage to drop below the required 12V. Multiple Power Supplies, separate wire runs, or larger gauge wire may be required to compensate for this voltage drop. Use the calculation examples below to calculate voltage drop at each remote location while preparing the wiring plan for your site. Please read the entire document before beginning and be sure to follow all steps in order. Planning the wiring of a site and calculating voltage drop is a process that requires a high degree of technical knowledge, PTI recommends that this be done by a knowledgeable, trained professional.

  1. To calculate voltage drop, it is helpful to draw a diagram of your site showing each remote, power supply, and the distance between them. You must know the measurement in feet between each remote as well as where the lines will go and how they will be run. To perform the calculation, you use the actual length of wire between each remote which includes the straight line distance plus any extra wire needed for turns, depth for burial, or height to the conduit if overhead. For the calculation to be correct, you must have the measurements as exact as possible. If you are unsure, it is better to round up by 10% to be safe.

  2. You must know the current draw for each piece of equipment on a given line.[1] The current draw in milliamps (thousandths of an amp) is given below for PTI AI Devices. When powering other equipment such as door strikes, HID readers, maglocks, or sirens, be sure to consider the current draw specifications for that equipment as well. We recommend that you do not power door strikes, maglocks, cameras or sirens from the same power supply as remote keypads and multiplexers as these items can cause power spikes, under powering the AI devices. We recommend that you use a separate power supply for these items. Refer to the manufacturers specs for current draw to calculate voltage drops for these items.
  3. A/I Device Type Current Draw
    VP KeypadA touchpad device used for access control. PTI has three series: the Falcon Series, VP Series, and Apex Series. Each series has several different options. 300ma
    APEX KeypadA touchpad device used for access control. PTI has three series: the Falcon Series, VP Series, and Apex Series. Each series has several different options. 300ma
    Hardwired Door Alarm MuxDoor Alarm Multiplexers take multiple inputs from individual door contacts and convert them to a single output back to the controller. Camera Multiplexers are similar in that they take multiple inputs from different cameras and create a single output back to the recorder. (16 - 96 Ch) 300ma
    8 ChannelIndividual input point on a multiplexer, Apex keypad, or XT that allows a door alarm sensor or contact to be connected to the system. One channel equals one door. Relay Board 500ma
    PWIE Board 300ma
    Wireless MultiplexerDoor Alarm Multiplexers take multiple inputs from individual door contacts and convert them to a single output back to the controller. Camera Multiplexers are similar in that they take multiple inputs from different cameras and create a single output back to the recorder. 500ma
    RB5 Relay module 120ma
    HID Proximity reader 30ma
    Pinhole camera option on keypads B&W / Color 100ma / 240ma
  4. You must know the resistance in Ohms per feet for the wire that you are using. Refer to the Wire Recommendations page for this. PTI strongly recommends that you do NOT use wire gauges smaller than 18 AWG for power or data when installing our gate system. Larger gauges are acceptable (16, 14, 12, and 10).

  5. The Voltage calculation must be done separately at each remote unit on a line, beginning with the first remote closest to the power supply and calculating at each remote further away from the power supply through the last one on a line. The calculation is as follows: V - (S * D * R) = X. Refer to Examples I – IV below. It is important to do this calculation in the right order, completing the calculations in parenthesis first and multiplying the results before subtracting from V. If you do this in the wrong order, the answer will be incorrect.
  6. S Sum total of the amperage for the AI DeviceAccess Interface Device. A general name referring to all PTI Keypads, Multiplexers, Relay Boards, and Wiegand Protocol Devices. In previous PTI systems these were occasionally referred to as remotes or remote devices. you are currently calculating for, plus the amperage for any AI devices connected to the same power wire and are further down the power wire from the power supply and the AI device that you are currently calculating for.
    Multiplied by
    D Length of wire (in feet) between previous AI DeviceAccess Interface Device. A general name referring to all PTI Keypads, Multiplexers, Relay Boards, and Wiegand Protocol Devices. In previous PTI systems these were occasionally referred to as remotes or remote devices. and the AI DeviceAccess Interface Device. A general name referring to all PTI Keypads, Multiplexers, Relay Boards, and Wiegand Protocol Devices. In previous PTI systems these were occasionally referred to as remotes or remote devices. you are currently calculating for. If this is the first AI device in the chain, it is the wire length from the power supply to the AI device.
    Multiplied by
    R Resistance in Ohms per foot of wire. (Varies by the wire type you are using)
    Subtracted from
    V Voltage coming into the AI device from the power supply (14V) or from the previous AI device in line (Calculated).
    Results in:
    X Voltage at this AI device after the voltage drop calculation. Use this number as V in the calculation for the next AI device in line further away from the power supply.
  7. When all of the calculations are done for a particular line, verify that there is a minimum of 12V available at the last Ai device. If the voltage drops below 12V anywhere on the line, there are three possible solutions:
  • As long as the power supply amperage is rated high enough to handle all of the AI devices on one power supply, consider running some of the devices on a separate line. You will have to run additional wire, but this is the best way to deal with this issue.
  • Install an additional power supply next to the first one and run some of the devices on this separate line. Connect the negative wire from one power supply to the negative but keep the positive system wires for each line separate. This keeps the ground as a common reference point without interfering with the voltage.
  • Install an additional power supply on the line elsewhere on the site. This can be anywhere along the line that is convenient and where the remaining devices on the line will be adequately fed by the added supply. An RB5 Relay module is required for this so that one person, if a service situation requires it, can press the reset button at the main power supply and reset the entire system. Resetting the main power supply cuts the power to the RB5 that in turn cuts the power output from the other power supply. You must remember to include the current draw of the RB5 in the calculations.

Examples:

(All examples use 18AWG wire)

Example 1:

Voltage Drop1.png
  • Voltage at Entry Keypad A: (14.00V) – (.300 A + .300 A + .500 A + .300 A + .300 A + .300 A + .030 A) x (40 Ft. x 0.00692 Ohms) = 13.44V
  • Voltage at ExitTo close a program or window, generally by clicking on the red ⌧ in the upper right corner of the window. Also refers to a user leaving a facility by entering their code at a keypad that operates a gate or door, allowing egress from the site or building. Keypad B: (13.44V) – (.300 A + .500 A + .300 A + .300 A + .300 A + .030 A) x (10 Ft. x 0.00692 Ohms) = 13.32V
  • Voltage at 8 Ch Relay C: (13.32V) – (.500 A + .300 A + .300 A + .300 A + .030 A) x (100 x 0.00692 Ohms) = 12.45V
  • Voltage at MuxDoor Alarm Multiplexers take multiple inputs from individual door contacts and convert them to a single output back to the controller. Camera Multiplexers are similar in that they take multiple inputs from different cameras and create a single output back to the recorder. D: (12.45V) – (.300 A + .300 A + .300 A + .030 A) x (15 x 0.00692 Ohms) = 12.35V
  • Voltage at MuxDoor Alarm Multiplexers take multiple inputs from individual door contacts and convert them to a single output back to the controller. Camera Multiplexers are similar in that they take multiple inputs from different cameras and create a single output back to the recorder. E: (12.35V) – (.300 A + .300 A + .030 A) x (65 x 0.00692 Ohms) = 12.07V
  • Voltage at Weigand F: (12.07V) – (.300 A + .030 A) x (75 x 0.00692 Ohms) = 11.90V (Insufficient voltage)

    Example 2:

Voltage Drop2.png
  • Voltage at Entry Keypad A: (14.00V ) – (.300 A + .300 A + .500 A + .300 A) x (40 Ft. x 0.00692 Ohms) = 13.61V
  • Voltage at ExitTo close a program or window, generally by clicking on the red ⌧ in the upper right corner of the window. Also refers to a user leaving a facility by entering their code at a keypad that operates a gate or door, allowing egress from the site or building. Keypad B: (13.61V) – (.300 A + .500 A + .300 A) x (10 Ft. x 0.00692 Ohms) = 13.53V
  • Voltage at 8 Ch Relay C: (13.53V) – (.500 A + .300 A) x (100 x 0.00692 Ohms) = 12.98V
  • Voltage at MuxDoor Alarm Multiplexers take multiple inputs from individual door contacts and convert them to a single output back to the controller. Camera Multiplexers are similar in that they take multiple inputs from different cameras and create a single output back to the recorder. D: (12.98V) – (.300 A) x (15 x 0.00692 Ohms) = 12.95V
  • Voltage at Weigand F: (14.00V) – (.300 A + .030 A + .300 A) x (90 x 0.00692 Ohms) = 13.61V
  • Voltage at MuxDoor Alarm Multiplexers take multiple inputs from individual door contacts and convert them to a single output back to the controller. Camera Multiplexers are similar in that they take multiple inputs from different cameras and create a single output back to the recorder. E: (13.61V) – (.300 A) x (75 x 0.00692 Ohms) = 13.45V

    Example 3:

Voltage Drop3.png
  • Voltage at Entry Keypad A: (14.00V ) – (.300 A + .300 A + .500 A + .300 A) x (40 Ft. x 0.00692 Ohms) = 13.61V
  • Voltage at ExitTo close a program or window, generally by clicking on the red ⌧ in the upper right corner of the window. Also refers to a user leaving a facility by entering their code at a keypad that operates a gate or door, allowing egress from the site or building. Keypad B: (13.61V) – (.300 A + .500 A + .300 A) x (10 Ft. x 0.00692 Ohms) = 13.53V
  • Voltage at 8 Ch Relay C: (13.53V) – (.500 A + .300 A) x (100 x 0.00692 Ohms) = 12.98V
  • Voltage at MuxDoor Alarm Multiplexers take multiple inputs from individual door contacts and convert them to a single output back to the controller. Camera Multiplexers are similar in that they take multiple inputs from different cameras and create a single output back to the recorder. D: (12.98V) – (.300 A) x (15 x 0.00692 Ohms) = 12.95V
  • Voltage at Weigand F: (14.00V) – (.300 A + .030 A + .300 A) x (90 x 0.00692 Ohms) = 13.61V
  • Voltage at MuxDoor Alarm Multiplexers take multiple inputs from individual door contacts and convert them to a single output back to the controller. Camera Multiplexers are similar in that they take multiple inputs from different cameras and create a single output back to the recorder. E: (13.61V) – (.300 A) x (75 x 0.00692 Ohms) = 13.45V

    Example 4:

Voltage Drop4.png

Voltage at Entry Keypad A: (14.00V ) – (.300 A + .300 A + .500 A + .300 A + .120 A) x (40 Ft. x 0.00692 Ohms) = 13.58V
Voltage at ExitTo close a program or window, generally by clicking on the red ⌧ in the upper right corner of the window. Also refers to a user leaving a facility by entering their code at a keypad that operates a gate or door, allowing egress from the site or building. Keypad B: (13.58V) – (.300 A + .500 A + .300 A + .120 A) x (10 Ft. x 0.00692 Ohms) = 13.50V
Voltage at 8 Ch Relay C: (13.50V) – (.500 A + .300 A + .120A) x (100 x 0.00692 Ohms) = 12.86V
Voltage at MuxDoor Alarm Multiplexers take multiple inputs from individual door contacts and convert them to a single output back to the controller. Camera Multiplexers are similar in that they take multiple inputs from different cameras and create a single output back to the recorder. D: (12.86V) – (.300 A + .120 A) x (15 x 0.00692 Ohms) = 12.80V
Voltage at Relay Module: (12.80V) – (.120 A) x (125 x 0.00692 Ohms) = 12.70V
Voltage at Weigand F: (14.00V) – (.300 A + .030 A + .300 A) x (10 x 0.00692 Ohms) = 13.96V
Voltage at MuxDoor Alarm Multiplexers take multiple inputs from individual door contacts and convert them to a single output back to the controller. Camera Multiplexers are similar in that they take multiple inputs from different cameras and create a single output back to the recorder. E: (13.96V) – (.300 A) x (75 x 0.00692 Ohms) = 13.80V



Notes:

  1. The actual amperage rating of the Power Supply (1, 2, 4, 6, or 10A) has no bearing on the voltage calculation. You still must select a power supply with sufficient amperage rating to support the total current draw of all AI devices connected to that supply. See PTI Power Supplies for details on this.