UPS and Joules

[01101001]

A tad confused here.

I've searched this board and read several threads on UPS and see that the concensus leans towards APC as one of the top brands while the CyberPower brand is less popular. I've had a small CyberPower UPS for a couple of years now and it has always been there for me when things go 'brown' or 'black' so my loyalties are leaning in that direction. The only reason for a UPS upgrade is the need for more battery-protected outlets.

I've come to learn that the higher the rating the better surge protection you have so in comparing similar APC and CyberPower units I was struck by the difference in joules ratings.

I see similarly priced units from both companies with similar specs -- both units are 1500VA with AVR & both have 6 battery-protected outlets. However, the CyberPower CPS1500AVR (900w) has a joules rating of 1800 while the APC BR1500 (865w) has a joules rating of only 460. I suspect joules ratings can be iffy, but this is a big difference.

What am I missing ?

 

[Ice Czar]

snakeoil and spin

read these

http://www.apttvss.com/white/white-joule.asp

From this IEEE document, one can conclude that energy delivery capability of a surge can be difficult to calculate when that surge is absorbed or shunted by a nonlinear device. Why then is it necessary for SPD manufacturers to print energy dissipation figures in joules? Because they are utilizing linear devices; or are they? Typically, manufacturers that don’t advertise joule ratings are not utilizing this technology in their device. However, there are some manufacturers that do advertise joule ratings and the values they print are a calculation of the energy dissipation capability of each individual discrete component as listed by the manufacturer of that discrete component. These manufacturers often publish these joule rating values to disguise or distract from other less flattering values. Seldom do reputable manufacturers utilizing nonlinear components advertise joule ratings. This is primarily due to the fact that nonlinear components have a variable joule rating value that is influenced by the characteristics of a particular surge event. The manufacturers that do utilize nonlinear components and advertise joule ratings, tend to calculate their joule rating by virtue of summing the highest value in the scale of the joule values for that particular nonlinear component. This is truly a deceptive maneuver on their behalf. You will notice the variable values listed below.Transient energy ratings are a source of some confusion in the industry. The rating, in joules (watt-second), is the maximum allowable energy for a single impulse of 10/1000 m s current waveform with continuous voltage applied. For cases where the transient is from a source external to the equipment, an approximation technique can be used to estimate the energy of the transient absorbed by (in the case of an MOV) or shunted by (in the case of a gas tube) the suppression device. The method requires finding the transient current and voltage through the device.

Where I is the peak current applied, Vc is the clamp voltage which results, t is the impulse duration and K is a constant. From this it can be seen that energy dissipation is directly proportional to the clamp voltage and the duration of the impulse. The higher the impulse duration, the clamp voltage, or the peak impulse current, the higher the energy rating of the device. There is a trade-off here between low clamp voltage and high joule ratings. Since the object in surge suppression is to minimize the voltage spike that protected equipment experiences, it is much more advisable to focus on the clamp voltage as the primary quantity to specify. Most SPD units manufactured by reputable manufacturers utilize MOV technology. The larger the MOV, the larger its joule rating (the factor K above is a function of MOV size)

Whether or not the joule rating is an effective means of measuring a surge device’s energy absorption capability is up for personal speculation and evaluation, but one must remember that joule rating is not criteria defined by NEMA LS1 or ANSI/IEEE as criteria deemed essential for a surge suppressor. Energy absorption characteristics are best defined and evaluated using "Maximum Surge Current" capability. The parameters surrounding this performance criteria are far more defined.Here’s an "intriguing" quote from a manufacturer of SPD devices that advertises joule ratings in their literature:

For those who would apply a Joule rating to a surge protector, we advise caution. While a high Joule Rating may describe the ruggedness of a protector and its ability to survive high energy surges, a high Joule Rating may not adequately describe the protective capability of the protector.

A Joule is a Watt-second. A Watt-second is the product of the voltage in volts, the current in amperes and the time in seconds. In the test simulations prescribed by various ANSI/IEEE standards, the current amplitudes and the waveforms (i.e. time) are definitively specified. Only the voltage drop accross the surge protector is unknown. This voltage drop is referred to as the suppression voltage of the protector. The lower the suppression voltage, the lower the voltage appearing across the circuit or device being protected. Therefore the lower the suppression voltage, the lower the energy dissipation of the surge protector in Joules.

Remember, the theoretical ultimate in protection would be a surge protector whose suppression voltage is zero relative to the normal AC system voltage. This would result in a Joule Rating of Zero.

combine the real meaning of a Joule Rating with its Marketing meaning and its largely a useless measure
factor in the different approaches to protecting devices and well....


SPD = Surge Protection Device
there is alot more on that site, as there is here > http://brickwall.com/nofail.htm

 

[01101001]

Thanks for the info and links. Its an interesting (if complex) read.

It all makes me wonder though, if there are such deceptive practices for joule ratings (all the major players seem to list joules ratings in their advertising or spec sheets) who can we trust? I mean, are listed wattages accurate? Is one guy's AVR as good as the next? Etc., etc.

I'm just a home user in search of a quality unit that will give me reasonable protection for a reasonable price -- a 2 outlet, non-destructive SPD for $175US is simply out of my league. The APC 'UPS Selector' offered 3 recommendations priced from $389 to $819US -- not only is that out of my league its hard to believe I really need to spend that much moola. Another spin perchance? I don't need hours and hours of up-time on battery or state-of- the-art equipment -- just something reliable and dependable.

How do I discern a quality UPS from a consumer-grade one dripping in snake oil?

 

[Ice Czar]

well there is a big difference between mission critical and reasonable precautions

and what youve spent on your rig, and where you are play alot into that
if your in Florida widely considered the Lighting capitol of the world (and a common target for hurricane induced power issues) its one thing compared to somewhere with a more stable power source

and if your typing from a workstation that cost more than your first couple of cars an investment of a few hundred dollars isnt alot to make, if you also cosider that a non-MOV based solution is an infrastructure investment that you spread out over decades instead of years it looks alot better too

Then there is the old school on-line UPS route, you can find double inverter Liebert UPSs on ebay for a pretty reasonable amount of money (GXT GXT2) or the DIY Ghetto Solution

but the ticket for affordable surge protection not UPS on the cheap was provided by our very own gee

I check in every once in a while. If there's an interesting thread, i'll post in it.

And having designed AC protection for very expensive equipment... you can't beat a circuit breaker upstream from a MOV. For spikes they act fast and absorb a huge amount of energy, and during big surges, they'll just pop the circuit breaker.

promises promises, eh? - http://dkc3.digikey.com/PDF/T052/1135.pdf

For 120VAC operation, you want part # ROV20-201K-S... they offer 114J apiece. They're $4.70 for 10 at Digikey, and to meet the $25 minimum order you're basically buying 60 of them - enough to make a 6840 joule power bar. Put 1 from ground to neutral, 1 from ground to hot, and 58 between line and neutral. This will take up a *lot* of space.

Another way to protect your stuff is to use a PFC power supply - Most power supplies with a 120/240 volt switch can't handle any more than 140 volts on the input, before they pop their main input cap. But a PFC supply running at 120 volts can get a 230 volt surge (which will make a regular supply explode) and it'll just alter its duty cycle and carry on its merry way, powering your computer off the surge.