Backup Power for Large Security Systems

Author: Brian Rhodes, Published on Jul 31, 2013

Choosing the right backup power system depends on system size. While small and medium systems greatly benefit from using UPS battery backup sources, larger systems need a centralized generator power source. How are these systems designed and specified, and what type of maintenance effort is needed to keep them ready to go at a moment's notice? We look at generator backup for large systems in the note.

Condo / Office Example

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Backup *********

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Transfer ********

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Dealing **** '*** ****'

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Electrician *************

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Comments (11)

Brian, another good "nuts and bolts" article. I agree with the ATS and generator system.....if it can be done. What I mean by this is a power solution like this cannot be an afterthought. It usually must be part of the original construction process. Depending on the complexity of the site, a electrical engineer may need to "draw" this into the original construction documents but at a minimum it must be in the scope of work for the electrical contractor. In this case, 24 sites need dedicated power in some form or fashion to feed the power supplies and/or PoE switches scattered throughout ..........and all fed from the single gentran panel/load center. This could be a showstopper and probably not feasable in existing structures without significant work and cost... if at all.

"Using UPSes on 'headend' equipment is needed when using backup generators." 100% correct and I would even recommend using surge surpressors on the PoE switches (assuming that is what is powering the cameras) to handle the In Rush when the ATS flips and all that current comes on in one instant.

This type of top notch engineering and construction for surveillance is rare (for certain verticals). Competition is brutal in the bid market. Usually and sadly, money is so tight its like trying to squeeze between two coats of paint:)

Unless the customer is very well versed and time invested and there are no other solution providers being considered, you'll rarely win a job doing it 100% right. It almost always comes down to price, and funcitonal enough to sign off on the job is what usually gets done.

^^^ In my experience, this is very true. And a sad reality.

I respectfully suggest there may be some math adjustments to the above example:

For the distribution panels with 11 cameras x 15w that is 165W. I would recommend getting much larger UPS say 1800W. That gives 5 distribution panels instead that would handle 520 cam at 104 cameras each or 104 x 15= 1560W each per UPS. To get the 8 hour discharge time you will need batteries for each UPS of: 1560W/ UPS eff/Voltage of battery system/derating of battery for 5year use/ derating for listed battery capacity (20hr) with 8hr discharge capacity. UPS eff is 85%, derating for 5 year use is 0.8, derating for 8hr discharge instead of a 20Hr rated battery the derating is 0.9.

All in: 1560W*8hr/0.85/12V/0.85/0.9 = 1700AH

We build these size of units and typically costs are in the order of $400 per 250AH battery. Batteries, UPS and racks would be about $5000. For 5 distribution panels would be 25K.

There are additional costs for generator systems not mentioned including an automatic transfer switch which will be $2500+. The costs for installation also needs to include the building services required for fresh air, exhaust, noise reduction. For servicing, space will need to be alloted in the building (+100sqft). However, for the example given a (high rise building) it would already have a generator for backup power for the elevator, smoke control and fire alarm. The incremental cost for adding an additional 10KW to say a 25KW generator would not be significant.

We maintain about 200 emergency generator systems and the reliability of these systems is directly related to the maintenance they get. For example for our central station we perform the following maintenance: weekly run test at no load, once a month we simulate power failure and run the station at 80% load for 1/2 an hour, semi-annual service by the mechanic, and full load run test with dummy load for 2hr. Proper maintenance costs is significant for generator systems.

We have found that diesel engine generators will prematurely fail and need to be replaced with less than 100 hr on them because of poor maintenance, or oversized for the connected load.

I probably should stop now.

Robert,

"We have found that diesel engine generators will prematurely fail and need to be replaced with less than 100 hr on them because of poor maintenance, or oversized for the connected load."

Not sure I agree there. I would assume longevity depends on many factors, but if not diesel, what?

Also, I've replaced UPS batteries for substantially less than either the $700 quoted by Brian or the $400 you cite. But then again, you are quoting 250AH batteries, whereas the UPS's I have dealt with used much smaller batteries, ranging from the size used in old VHS camcorders to approximately automobile-size.

Hello Robert, Carl:

Great comments, and thanks for reading!

Re: pricing - I've pulled all pricing from the net, and plugged in OEM replacement parts, which isn't to say it is the cheapest or smartest way to buy these components. The magnitude of contrast is the useful part, and the overall analysis stands pat.

Re: efficiency/derating values - I appreciate you adding those in Robert. I excluded them from our example for the sake of readability, and because I was uncomfortable defending 'general values' that describe all UPSes. My followup question, how do you calculate efficiency and derating values? Are those given on manufacturer spec sheets? Do those values change depending on how they are used?

Re: additional generator costs: again, thanks for adding those in! Based on my own experience, I presumed mounting this equipment typically outside, with noise abatement part of package design, but your point is well made and defined. Thanks.

When diesel gens 'prematurely fail', is the cheapest option swapping them out? Or can they be rebuilt in-place?

The problem with diesel engine failure to low loading is called wet stacking. It also affects other engine types. See the link below.

http://www.generator.com/experts.php

You want to use the largest batteries in a connected set to reduce the number of battery connections. Too many batteries in parallel can be the source of voltage drops on poor connections leading to imbalance float charging. Sealed batteries can handle a little bit of overcharging, however, undercharging will kill the battery. A bad battery in a connected set will then effect the others. When repairing a battery set with a single failed battery, I recommend to our technicians to replace the entire set as they are now of disimilar ages. That also means when you build a battery set of any size, don't mix the sizes, manufacturer or age.

250AH batteries are 150# each. The're size is referred to as 8D.

Carl, I hope that helps.

Hi Brian:

To get the various derating you need to get your hands on the manufacturer graphs for the type of battery. The following is typical for an AGM type battery. For 4 years to be safe, you need to derate the battery 80%

For determining the actual available capacity for a battery, the manufactuer will give its capacity based on a particular discharge period. For most standby it is 20hr, for traction batteries (golf carts, wheel chairs, fork lifts,..) they are usually specified on an 8 hr discharge period. The manufacturer will give the available capacity of the battery depending on the discharge period 20, 10, 5, 3, 2, 1, 30min are typical. For the example you gave I looked up a 20AH battery, it gave the following capacity for the discharge times:

20hr 20AH

10hr 19.6AH

5hr 15.3AH

For 8 hr, I just proportioned the difference:

15.3 + (8-5)/(10-5) x (19.6-15.3) = 17.88

The derating factor is then 20/17.88 = 0.89

Brian, very good article and also very valuable comments!

In some large systems only a portion of the overall video system gets emergency power, as not all sites/locations are high-risk. But a UPS is still very important for the video servers even at low risk sites, to enable them to perform an orderly shutdown and not corrupt any databases. This includes correct sequencing of shutdown and restart of the data storage if it's not a server-and-storage single box. With external storage, you have to have the correct sequence for application shutdown, server shutdown and storage shutdown as well as for startup, to avoid data corruption and avoid errors on startup (such as storage not being found). There are timing issues involved in this, too. The main thing is to make orderly shutdown and startup on power restoration fully automatic.

I know of one recent case where police requested video based on a reported crime, yet due to power outage the video database got corrupted, and no video could be retrieved. I also know that some VMS systems store video in data files in a folder structure that allows video to be easily retrieved even if the indexed database (that includes alarm linkages and facilitates searching) is lost. But application architecture design is a little bit off topic for an article about backup power.

Excellent article and commentary!

Both generators and UPS's can be configured with trouble alarms which indicates such things as low battery, AC failure, temperature and fuel limits and a host of other things. Many if not all the security systems I have evaluated over many years, either do not have these features, or the alarm outputs are unconnected. Why? I have asked that of the integrators installing these systems, and to a man, they are at a loss for an answer.

Has any anyone ever dealt with hydrogen fuel cells? I was pitched these units some years ago, and they seemed like a wonderful solution.

Good article. I must quibble, however, with your sloppy use
of the technical terms (physical units) of power and energy.

The article says,

* Each Distribution Panel Supplies 11 cameras
* Each Camera consumes a maximum 15 Watts
* Cameras need to work for at least 8 hours on backup power.
* (11X15=165W/h * 8 hours =1320 W)

Saying 165 Watts/hour is nonsense considering what is mean
to be conveyed:

The unit Watt is the rate of using energy.[1] The equivalent
statement regarding driving a car, where the speed is the rate
of covering distance, would be 75 miles per hour per hour.[2]

The correct statement of that situation would be,

* Each Distribution Panel Supplies 11 cameras
* Each Camera consumes a maximum 15 Watts
* Cameras need to work for at least 8 hours on backup power
* 11 cameras x 15 Watts/camera = 165 Watts, continuously for
however long is desired
* 165 Watts x 8 hours = 1320 Watt-hours, or 1.32 kWh

Here the power required from the UPS, no matter how long the
cameras were required to be run, is 165 Watts. The amount of
energy required to run them for 8 hours is 1.32 kWh. Since APC
has changed their website since the article was written, use,
<this link> to figure out what size of UPS to use.

Using 165W plus 10% "Extra Power for Future Expansion" with a
run time of 8 hours, the UPS Selector gives a "Best Price"
recommendation of,

APC Smart-UPS XL 1000VA USB & Serial 120V
+ (2)SUA24XLBP Battery Unit $1,458.98
Run time: 655 minutes
Part Number(s): SUA1000XL + (2)SUA24XLBP
% of Max Capacity Used: 21 %

This is overkill for the application, providing 655 minutes of
run time instead of the required 480 minutes.

The projected cost of this option would be 24 x $1460 ~ $35,000,
roughly one-half of the estimate of the article based on sloppy
use of physical units.

Physical units are used correctly in the analysis of the generator
case, but now instead of 11 cameras/panel x 24 panels = 264 cameras,
we are presented with the case of 520 cameras. We have here an
apples-to-oranges comparison.

A correct comparison would require a 5 kW generator to run the cameras,
lowering the cost of the generator option.

The final conclusions of the article are correct, but could have
been different because of the errors.

BTW, the analysis by Robert Baxter @ 08/01/13 01:12pm is good, and,
like him, I probably should stop now.

[1] Technically speaking the 1 Watt = 1 Joule / second

[2] 75 miles per hour per hour is a valid physical unit, but it is
a unit of acceleration and tells how long it would take to get
to a given speed (a given rate of covering distance).

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