Supplying your analog security cameras
with the proper amount of power is essential. It’s especially important because problems can occur if there’s too much or too little power. If your camera is not getting enough power, it may lose signal. And, if your camera receives too much power, it may damage or short out your camera.
When it comes to camera power, the most components to consider are voltage, amperage and voltage drop. We decode the basics below:
Volts, amps and watts are all units of measure for electricity. The electrical units for power, voltage, resistance and current are all interlinked. If you alter one, the values of the other variables change.
An ampere (Amp) is the amount of current in a circuit.
A volt (V) is the strength of the current as it flows through the circuit.
A watt (W) is the total amount of electrical power released by the circuit per second.
One watt is equal to one volt multiplied by one amp. You can calculate the current flowing through the components if the wattage and voltage are known.
In order to make an electrical current flow through a resistance, there must be a voltage across that resistance. Ohm’s Law states that the electrical current flowing through a conductor between two points is directly proportional to the potential difference across the two points.
V (volts) = I (amps) x R (ohms)
The law demonstrates the relationship between voltage (V), measured in volts, current (I), measured in amps or milliamps, and resistance (R), measured ohms or kilohms.
Direct Current and Alternating Current
The flow of electrical currents along a wire or cable can occur in one direction, or both directions along the wire. Direct current (DC) flows in one direction, while alternating current (AC) flows in both directions; first in one direction, then the reverse direction along the conductor.
Most video security cameras will use either 24 volts AC or 12 volts DC. Traditionally, when CCTV security cameras were first introduced, they were 24 Vac,
but now 12 Vdc video security cameras are more common. Some video security cameras are dual voltage, enabling you to use either an AC or DC power source, eliminating the worry of whether or not your power source is compatible with your security camera.
Calculating Voltage Drops in Analog Cameras
As we mentioned above, it’s important that your security cameras are receiving the correct amount of power and calculating voltage drop is important. Voltage drop happens between the security camera, the cable and the power supply.
Regarding camera voltage drops there are a few things to keep in mind:
1. The longer your cable run, the greater the voltage drop
2. The thinner the wire, the higher the voltage drop
3. The larger the Amps (as with more powerful security cameras), the greater the voltage drop
4. The higher the source of voltage, the lower the percentage of voltage drop
Below are a couple of camera voltage drop scenarios:
Voltage Drop Scenario 1
At 12 Vdc, a 300 mA camera at 100 feet on standard 18 AWG (American wire gauge) will have a voltage drop of 0.38 volts. Industry standard is +/- 10%, which is 1.2 volts. In this example, you are within limits.
American wire gauge is a standardized US wire gauge system. The voltage drop of a conducting wire depends on the amount of current being carried and the electrical resistance. A thicker gauge wire carries more electrical current with less resistance over a given length, which makes it a better choice for limiting voltage drop over longer distances.
Voltage Drop Scenario 2
At 12 Vdc, a 0.8 amps or 800 mA camera (which is not unreasonable for an IR camera) at a distance of 150 feet on 18 AWG would give you a drop of 1.54 volts, which is greater than acceptable limits.
The way to get around this is to have a shorter cable run, or increase the size of your power wire. In this example, increasing the power wire to 16 AWG would decrease the voltage drop to 0.96 volts, which is within limits.
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