Battery Backup for Outdoor CamerasBy Ethan Ace, Published on Feb 26, 2012
Pole-mounting cameras, especially for use in parking lots and municipal surveillance systems, is a growing trend. However, power in these locations may be unreliable, subject to fluctuations and outages. Supplying backup power to cameras and transmission equipment becomes an important consideration, to prevent loss of video, and exposing the facility or municipality to risks or liability.
Typically, three ways exist of providing backup power to these cameras:
- Indoor UPSs in outdoor enclosures
- Outdoor low-voltage power supplies
- Outdoor UPSs
In this note, we examine each of these options and give our recommendations on when each should be used.
Indoor UPS in Weatherproof Box
Though not recommended, some integrators install indoor UPSs in weatherproof boxes in order to power equipment, since historically, there have been few options for outdoor battery backup. Non-rack mount models, especially those in "power strip" form factors are often used because of their small size, making them easier to fit in an enclosure. The APC Back-UPS and Minuteman EnSpire series are two examples of this type. UPSs such as these can be found for under $100 online.
Using indoor UPSs outdoors is generally not recommended where other options are available, for these reasons:
- Not intended for outdoor use: First and foremost, it goes without saying that these UPSs are intended for indoor use only. Even in climate-controlled housings, moisture variations and temperature fluctuations will occur, which will put stress on plastic housings, corrode components, and reduce battery life.
- 110 VAC output only: Indoor UPSs do not offer low-voltage output, such as 12 VDC or 24 VAC, requiring transformers for any equipment which requires these voltages.
- No monitoring functions: Interior UPSs generally do not offer any means of monitoring their status, which outdoor-rated units often carry.
Outdoor Camera Power Supplies
Some manufacturers have begun providing battery-backed outdoor camera power supplies. These units supply 12VDC or 24VAC (or both) to one or more cameras, with battery backup, with all electronics housed in a weatherproof enclosure. The Altronix ReServ line is the most common example of these units. They are more expesnsive than indoor UPSs, but well under most outdoor UPSs, found for about $300 online.
The main drawback with this style of power supply is that it does not provide any option for voltages other than 12 or 24 volts. In some cases, 48VDC or 110VAC may be needed to power wireless radios or switches, making a low-voltage supply unsuitable.
Historically used by the telecom and wireless markets, outdoor UPS units generally output 110VAC, often with additional outputs for 12VDC, 24VAC, or 48VDC, making them more flexible than other options. They are also available in a wider array of sizes, to accomodate larger loads, or more batteries, for extended runtimes. This flexibility does come at a price, with prices starting at about $700 for even small units, and ranging into the thousands for larger-load units equipped with multiple voltage outputs, alarm contacts, or network monitoring capability. Alpha [link no longer available] and Ventev [link no longer available] are perhaps the best-known manufacturers of outdoor UPS.
Which Option Should I Use?
When selecting one of the above options, output voltage is the first deciding factor. If 110VAC power is required, low-voltage supplies are not usable, and a true UPS must be used. Conversely, if all components accept 24VAC or 12VDC power, a multi-output low-voltage supply should be suitable.
Budget is also a limiting factor. While it is not preferable, using an indoor UPS in an outdoor enclosure is better than providing no protection at all. However, users should be aware that failure rates are likely higher than units truly intended for outdoor use. The higher initial investment cost of an outdoor unit may be offset by replacement costs and service labor to replace failed indoor UPSs.
An often overlooked factor is the ability to monitor the status of the battery backup. This may be achieved through SNMP monitoring, but is more simply handled via camera I/O. Many power supplies have contacts for two states: on-battery and battery low. Additional statuses such as charge or battery trouble may be provided, as well. By connected these contacts to inputs of IP cameras, operators may receive notifications via email or VMS event (dependent on what camera and VMS support). This lets them know there is an issue at a location before video is lost.