Reference Setups
Lets assume a CCTV system of 4 wired IP cameras for a small home.
Camera Power = 6W x 4 = 24W
PoE switch (unloaded) = 5W x 1 = 5W
NVR + 1xHDD + 1xWifi/4G dongle = 20W
We assume smartphone as the viewing screen. So totally 50W load for a small minimalistic setup
As of 2020, for India, and in big urban city area, 3-4 hours of power cut (load-shedding) per day can be expected in summer season while in smaller towns it may go upto 6-8 hours or even more. So our requirement is both Uninterrupted supply and long backup time on secondary/standby power source.
Backup-Option-1
Lets look at the capabilities of one of the most popular compact PC UPSes available in the Indian market, which makes it suitable to be kept in 4U/6U racks and therefore quite a favorite among novice CCTV system integrators:
APC Back-UPS 600, Model No. BX600CI-IN, Line-Interactive Topology
Their will be many other similar devices (1-PC backup category) from other brands like iBall, Numeric, MicroTek, Vguard, Emerson, etc with almost similar capabilities. They are inexpensive & all all cost in the Rs. 1500-3000 price band . Typical specification (here of the APC unit) can be like:
Battery (Inbuilt) = Model RBC2 (12V, 7Ah)
VA Rating = 600 VA
Charging Time = 6 hours // for this much time utility power we will surely get every day
We assume no-load shutdown or any time based auto switch-off function (to extend battery life) is disabled & UPS battery runs down to deep discharge state.
Based on the above data from the specification sheet, what we can derive is:
Charging Current = AH rating / Charging Time = 7 / 6 ~ 1.17A
Max Load supported safely = 60% of VA Rating = 0.6 * 600 = 360W // >> 50W CCTV system loadj
Total energy stored in fully charged battery = 12 x 7 = 84 Wh
Assuming UPS efficiency as 70% (conservative) or a Power factor of 0.7, the actual energy that can be used is 84*0.7 = 58.8Wh
Backup time = 58.8/50 ~ 70 minutes // If a fixed/mobile broadband wifi router is also used it will be less than 1 hour
This is way lesser than a typical power cut during the day and therefore with such a device we cannot provide 24x7 uninterrupted power in all seasons.
In a large IP CCTV setup, a typical 24 port switch supplies about 200W of power and if its fully loaded with cameras and backed by its own UPS will give no more than 17-18 minutes of backup time, if no DG/Solar/Inverter backup is available.
Some UPS vendors claim Power factor of 0.8 & 0.9 (the fine-print will usually spell out the economics with the truth), but even if true, it is not going to make a very big difference to the backup capability and have any sort of noticeable impact.
Backup-Option-2
Again we consider the the smallest Home Inverter UPS solution of Indian market:
Amaron 400VA Home-Inverter UPS + 80AH Tubular/SMF battery
From the specification, we know that it can support 8A and 10A charging currents. Generally homes will not use this as its too low powered (minimum 900VA and 150/180AH batteries are used) and this may be popular only in small shops supporting few lights, 1 fan and maybe 1 led tv for shopkeeper entertainment. This device setup is bulky, not suitable to be kept in racks and will cost atleast 5 times the above APC UPS (maybe half the IP camera system cost itself)
Anyways, the following are derived:
Charging time = 8-10 hours
Battery Voltage = 12V
Stored energy = 80X12 = 960 Wh
Again assuming a power factor of 0.7, usable energy = 960 x 0.7 = 672 Wh
Backup Time = 672 / 50 = 13.44 hours.
Almost no system integrator uses this setup, due to cost and bulk, but it can support our setup rather well in most parts of the country in any season. the Inverter UPS above can be paired with a 150ah battery to serve the entire home well. In many cases the site will have an older inverter setup which cannot switchover in 10ms, but takes 100ms or more causing cameras and recorders to reboot. This can be overcome wither by deploying the APC UPS above (better protection to line interactive topology) or asking the tenant to just upgrade to a home Inverter-UPS solution (less preferable as they are mostly offline UPSes).
And even for a large 200W 24 camera deployment, this setup may work acceptably for most cases with battery upgrade required in others.
Backup-Option-3
We can deploy high capacity (VA) online/Line interactive UPS with atleast a 65AH internal/external battery for IP CCTV system and where the UPS can actually be used both as a emergency and standby source. But the weight and form factor will again make it unsuitable for keeping inside wall mount racks (may take 6U rack space for both battery and UPS). Also the cost will be too high, perhaps even higher than the cost of the IP CCTV system itself , making this thoroughly impractical.
Backup-Option-4
This involves deploying 12V DC-DC LiIon UPS at each camera (4 nos.) and local (not PoE Power) which will give a backup time of 4 hours with a typical 22Wh DC-DC UPS. The NVR is 12V powered and consumes 20W. The same UPS will give it a backup time of about 1 hour. Another DC UPS will be required for the 5V 10/100 networking switch which can again run for about 12 hours. So with 6 DC-DC units, we can backup the setup with lightweight units for about 1 hour only (the least) and the cost maybe equal to or more than smallest Home Inverter UPS (option 2). The NVR is the problem. If we remove NVR and go for cloud storage, we can get a backup of 4 hours at about 4 times the cost if Option 1. May work in few deployments only and definitely not cost effective (practical) for a CCTV application only.
The main problem is that we need atleast a 48/65 AH battery to support such a small system for 6-8 hours power-cut. And we don't get this cheap enough , light enough (30 Kg+). The UPS unit also which can support such heavy battery will atleast be 1 KVA unit and cost upwards of Rs. 10,000/-. The only viable option seems to be using a shared Home Inverter Setup (standby source cum offline-UPS).
So the most important general conclusions (not limited to the above CCTV deployment study) that we can derive are:
(1) we can learn here is that UPS is not a suitable secondary source. Its just emergency source to manage a transitions (small blackouts) between primary (distribution company's supply) and backup source (DG/Solar/Inverter). Its *unique value is just the "U" and not the "PS". They should consider renaming UPS to EPS (E=Emergency)
(2) Secondary sources can be Diesel Generators or Solar-Inverter or Inverter-UPS. These need *capacity of long operation running into hours. Therefore use ones with external battery for maximum flexibility, expansion & maintenance
(3) If the secondary source installed cannot guarantee un-interrupted power and causes sensitive equipment (like Desktop PC, Router, TV STV, etc) to reboot, then you may deploy site specific small line interactive UPS or a line-Interactive/Online Home-UPS with *inbuilt battery but UPS based on load of small electrical and electronic appliance (not include big refrigerator, AC, washing machine, dryer, oven etc). Sich UPS are required to run for a short time only and therefore it does not high battery capacity, which is what UPS with inbuilt battery offer. It will also be child safe.
- Suman Kumar Luthra @ APRC-P3 Telecom Sub-Committee
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