Voltage drop is a term that we hear about all the time in the surveillance
industry. While many people talk about it and use the charts and calculators
provided by different sources, I think a smaller amount of people fully
understand the physics behind it. Today I want to give a quick review of the
ideas behind voltage drop and then some practical tips for installing security
cameras or any other equipment.
Equation
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Equation
Here is the equation for Voltage Drop:
Voltage drop=( 2 * (length of run in ft.) * (resistance
factor) *(current load in Amps))/1000
The length of the run is pretty simple; it is how long the cable is
between the camera and the power supply.
The resistance factor is determined by the wire used and there is a chart in the NEC Chapter 9, Table 8 (rule of thumb, thinner wire will have higher resistance).
The current will be defined by the camera and will be found on the spec sheet.
The resistance factor is determined by the wire used and there is a chart in the NEC Chapter 9, Table 8 (rule of thumb, thinner wire will have higher resistance).
The current will be defined by the camera and will be found on the spec sheet.
Voltage Drop Example (300mA Security Camera)
Here is a quick example: 200 ft. run, 18 Gauge wire, 300mA camera
VD=2 *(200)*7.7 Ω *.3A/1000
VD=.924 V
VD=2 *(200)*7.7 Ω *.3A/1000
VD=.924 V
Voltage Range
Cameras need a certain amount of voltage. There is normally a range
of ±10% of the rated voltage, so for this example we will say that a 12v camera
can work in a range of 10.8v up to 13.2v (±10% of 12v is 1.2v). If a CCTV
camera gets too much voltage, it will fry, and too little will not power it
on. So if the power supply is exactly 12V at the source, then it
will drop .924V in 200ft and supply the camera with 11.076V, which is in the
range of operation.
Voltage Drop
One thing to remember is that the number for the voltage drop is not
dependent on the supplied voltage. So if a 12V camera loses 2 volts,
it wouldn’t power on because that is a 17% loss, but if a 24V camera
loses 2 volts, it will work because that is only an 8% loss. So 24V
cameras can run farther.
So the final test in for your setup is determining the Voltage percentage
drop:
VD%=( VD/Source Voltage)*100
From our example above:
VD%=(.924/12)*100
VD%=7.7% (which is in the range)
VD%=(.924/12)*100
VD%=7.7% (which is in the range)
If
the proper power is not supplied to your CCTV equipment, it can cause it to
lose signal or in some cases cause your camera(s) to fry! Two essential
things to consider include Voltage and Amperage.
Most
of the below data concerning voltage and amperage can be considered for 99% of
systems. Cameras will usually use either a 24VAC or 12VDC current.
Basic
voltage & amperage reference guide for proper power supply to your CCTV
equipment.
Wiring Tips
All of this stuff is neat and I hope that is explains the science behind
it all little more. Just remember:
Longer Run = more Voltage Drop
Thinner wire (higher gauge) = more Voltage Drop
Larger Amps (more powerful camera) = more Voltage Drop
Higher source voltage = Less Voltage Percentage Drop
Thinner wire (higher gauge) = more Voltage Drop
Larger Amps (more powerful camera) = more Voltage Drop
Higher source voltage = Less Voltage Percentage Drop
For Installers
Final point, there are times in which installers have called in because a
camera is not working and they claim that the wire is supplying enough volts.
The problem with that is that they unplug the camera and connect a Voltmeter to
the two wires. The Voltmeter has a very low amp draw, and will show less
voltage drop because of that. Once the camera is reintroduced in the circuit,
the voltage drop will change, making the measurement ineffective. So we need to
run the numbers on paper to determine the drop.
Voltage has to be an exact match. A 12V DC device needs a 12V DC adapter (10% toll).
Amperage is the amount of power your device uses. The adapter you order has to be able to supply AT LEAST the amount of Amps your device draws. If your device states it is 12V 3A, a 3A adapter can handle that load, but so can a 4A and 5A. The higher amperage (amp) power supply will not have to work as hard to handle a smaller load, and will run cooler and more stable.
If the Amperage of your device is uneven, such as 3.13A or 4.16A, always round up. 3.13A rounds up to a 3.5A adapter, a 4.16A device will round up to a 4.5A or a 5A.
If you match these two specification (V and A), the power supply will work for your device.
Voltage:
All of the power supplies we sell are 12V DC. They take any input from 100V up to 220V AC, which is what comes out of your wall socket, and output 12V DC. This is what most digital devices such as LCD screens, DVD players, Hard Drives, Audio Gear, and most other digital devices use. We only carry 12V DC power supplies, so if your unit is not 12 Volt, you will not find the correct adapter here.
Amperage:
Once you have confirmed that you need a 12 Volt power supply, you will need to find out how much power your device draws. This is called amperage. Next to the 12V in the specifications there will be another number followed by a capital "A" for Amps. You will need a power supply that can supply enough power for your device. If your device says it draws 3 Amp (3A), you need to use a power supply that can put out at least that many Amps. If your device states it needs 3A, then you can use a 3A, or 4A, or 5A unit. All will work.
If the Amperage of your device is uneven, such as 3.13A or 4.16A, always round up. 3.13A rounds up to a 3.5A adapter, a 4.16A device will round up to a 4.5A or a 5A.
Connector:
All our power supplies have a connector that is standard for a 12V DC device. Most 12V DC devices use the standard tip. This tip is 5.5mm (outer barrel) by 2.5mm (inner barrel) and is center positive. It is a simple round barrel connector. To repeat, if you match the voltage and amperage, then you should not have to worry about the connector type accept in the rare occasion when your device has an unusual connector such as a double barrel, or a 4-pin, but these are easy to spot as the jack where the adapter plugs in will not be a simple circular barrel with a pin inside.
Quick instructions on selecting a power supply:-
The only information you need to have in order to find the correct power supply for your device is the Voltage / Volts (V) and Amperage / Amps (A).Voltage has to be an exact match. A 12V DC device needs a 12V DC adapter (10% toll).
Amperage is the amount of power your device uses. The adapter you order has to be able to supply AT LEAST the amount of Amps your device draws. If your device states it is 12V 3A, a 3A adapter can handle that load, but so can a 4A and 5A. The higher amperage (amp) power supply will not have to work as hard to handle a smaller load, and will run cooler and more stable.
If the Amperage of your device is uneven, such as 3.13A or 4.16A, always round up. 3.13A rounds up to a 3.5A adapter, a 4.16A device will round up to a 4.5A or a 5A.
If you match these two specification (V and A), the power supply will work for your device.
Detailed Instructions:
In order to find the correct power supply for your device, you will need two pieces of information. These are Voltage (measured in Volts or V) and Amperage (measured in Amps or A). You can find this information off the back of the old power supply, or off the back of the device itself. If you do not find it on the device, you can check the manufacturer's website, or in the device's manual under "specifications".Voltage:
All of the power supplies we sell are 12V DC. They take any input from 100V up to 220V AC, which is what comes out of your wall socket, and output 12V DC. This is what most digital devices such as LCD screens, DVD players, Hard Drives, Audio Gear, and most other digital devices use. We only carry 12V DC power supplies, so if your unit is not 12 Volt, you will not find the correct adapter here.
Amperage:
Once you have confirmed that you need a 12 Volt power supply, you will need to find out how much power your device draws. This is called amperage. Next to the 12V in the specifications there will be another number followed by a capital "A" for Amps. You will need a power supply that can supply enough power for your device. If your device says it draws 3 Amp (3A), you need to use a power supply that can put out at least that many Amps. If your device states it needs 3A, then you can use a 3A, or 4A, or 5A unit. All will work.
If the Amperage of your device is uneven, such as 3.13A or 4.16A, always round up. 3.13A rounds up to a 3.5A adapter, a 4.16A device will round up to a 4.5A or a 5A.
Connector:
All our power supplies have a connector that is standard for a 12V DC device. Most 12V DC devices use the standard tip. This tip is 5.5mm (outer barrel) by 2.5mm (inner barrel) and is center positive. It is a simple round barrel connector. To repeat, if you match the voltage and amperage, then you should not have to worry about the connector type accept in the rare occasion when your device has an unusual connector such as a double barrel, or a 4-pin, but these are easy to spot as the jack where the adapter plugs in will not be a simple circular barrel with a pin inside.
Also Visit: http://arindamcctvaccesscontrol.blogspot.in/2013/01/camera-power-considerations.html