Before we answer the question, one must consider what is exact function and differences between the two sources relevant to CCTV application. UPS devices come in 3 types (you can find tons of material on the differences online)
- Offline - 10ms or lower switchover time, no mains power conditioning
- Line Interactive - sub 10ms switchover time, Automatic voltage regulation + Surge protection + other mains power conditioning (based on model)
- Online or Double Conversion - 0 ms switchover time, Completely clean power from inbuilt alternator.
(3) are the best, used for very sensitive application like medical instrumentation, Data center, etc. and therefore expensive. However, you will not see them easily available in sub 1-KVA capacities. Big centralized/de-centralized wired IP systems whose power requirement itself is in KVAs, should use this AFAP (we use this in our system with VRLA/SMF battery bank)
(1) May create risks for equipment if the basic power supply is not clean (fluctuations, brownouts, frequency problems, etc) like Diesel Generators. One would be better avoiding this type of setup, if the quality of power cannot be guaranteed, despite having SMPS functionality in camera chargers and recorders which may tolerate some anomalies. It can avoid expensive non-warranty repairs.
(2) is sort of middle ground. Balance between cost and capability. They can be used if the power supply (discom and backup generator) is relatively stable/clean and so some cleaning themselves. They are somewhat suitable for consumer grade equipment , but definitely not for enterprises.
Here is a summary of common electrical power supply faults and the equipment/protection device required:
Pure inverters should not be used at all. Infact they are more suitable as secondary sources akin to Diesel generators. As their switchover time from mains to battery is in seconds, which will result in camera and NVR reboot (along with chance of storage media corruption) when a a switchover between primary(mains) and secondary sources (battery) takes place. Also to be avoided are non sine-wave inverters (they are bad for *most electrical or electronics equipment). These days non-sinewave and pure inverters are rare. What is *commonly available (and more cost-effective) are Home/Office Inverter UPSes that combine both *offline UPS AND *Inverter into one device, making the picture confusing. However these are more suitable for home UPS application and for not-so-sensitive electrical devices like lights, fans, refrigerators, etc. But they may not be the best choice for sensitive electronics equipment like IP CCTV Cameras and Recorders, Servers, etc. Therefore we recommend that a centralized/decentralized IP CCTV not be run of a Inverter UPS in the interests of maximum safety, though it may run fine in the short term like a Desktop PC would on a home Inverter UPS enabled power socket.
A very similar phenomenon is observed when powering an Wireless IP CCTV camera by 5V USB power-bank and 5V DC-DC USB UPS. The former (assuming passthrough charging is supported) acts more like an inverter. Whenever the charging port loses power (or it comes Back), camera will reboot immediately as their is a little delay in switching to (from) inbuilt battery. The latter option provides true un-interrupted power supply as no abnormal behavior is observed during switchover.
For our apartment system, we use redundant online UPS units with VRLA/SMF batteries. And for Wireless cameras, we recommend either using battery or any deployed single-phase home UPS (not Home Inverter-UPS) supply or DC-DC UPS if home UPS supply is not available on nearby socket to which the wireless camera is plugged into.
- Suman Kumar Luthra @ APRC-P3 Telecom Sub-Committee
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