UPS Battery question

Wow! 408 Vdc. Be careful out there.

There are other groups (e.g.: homepower) that worry more about batteries but because of manufacturing variations even cells purchased from the same make and the same run may have differences.

What that means it that you ALWAYS have to pay attention to problems that variations between cells can cause. The standard technique was to provide an "equilization chage" whereby some cells are fully charged and a few cells end up being over charged and lose a little water.

Likewise when you draw power from the battery to have to ensure that none of the cells is comletely discharged as those cells will be reversed and suffer great damage.

With over 200 individual cells you really, really need methods of automating the checking of the conditions of the cells. Namely you should consider a system that can read the potential of each cell (or at least every group in a physical battery) and do some spreadsheet type analysis to see if some are acting a little TOO different.

Of course, in most larger UPS applications the batteries are only to keep things running until you can start the generator out back. That's the way the telephone companies always did it.

Have you considered adding a DC output flywheel instead of battery banks? Since hours of emergency operation can be provided only by a generator anyway, large battery bank is a very expensive way (not to mention being lethal voltage at 408VDC and lead/battery acid being very dangerous to health & environment) to provide a few hours of emergency operation. A DC flywheel can replace a battery bank by providing about 20 to 30 seconds of ride-through for the generator to come upto speed & take over within 10 to 15 seconds, and low speed flywheel is a proven solution for the past 20+ years. Two companies that make DC flywheels (for large UPS systems) are Power Systems & Controls

Richmond, VA and Pentadyne (don't know website, but a little googling will get you the website, I am sure) somewhere in the western USA.

"Nam Paik" a écrit dans le message de news: snipped-for-privacy@posting.google.com...

Paralleling two different strings of batteries not recommended at all. For the economy of using existing batteries you're risking a complete failure:

- The charging is different, risk of over / undercharge

- When called for one string may charge feedback the second one, and it might give an undervoltage signal to the UPS which in turn jumps to the bypass for the last ditch, that means "unprotected" if the bypass is available and "dead" if it is not.

I wouldn't do it.

SGT

Perhaps I've missed something, but I haven't seen a flywheel based system in wide-spread use since the IBM power line stabilization systems marketed during the early 1960s. Even IBM discontinued them when battery-backup UPS became available shortly after that time. Then too, it was the goal of the IBM product to stabilize computer operation during only the loss of a few cycles of commercial power.

Then too, a flywheeel system providing anything approaching 20-30 seconds of emergency back-up would be incredibly expensive, bulky, and heavy compared to the cost of a battery-backup UPS, let alone providing 5-30 minites of backup power.

The classic problem with flywheel systems (beyond weight and size) is that the flywheel's angular velocity begins to decellerate immediately on the imposition of a load, plus its energy storage capacity is severely limited by both its mass and initial angular velocity.

Just my observation.

Harry C.

snip snip make it fit in the window :)

Flywheels are becomming popular for short term energy storage. They are much more dense energy storage than batteries, are cheaper and more reliable. They generally drive a synchronous 3 phase motor which acts as both a motor and generator. The power goes through a AC-DC-AC converter to keep it the same as the grid frequency. There are several commercial products around and are used for short term power backup until a diesel genset can be started. As was stated earlier, UPS are usually used in the gap between mains failure and diesel backup. Batteries provide better longer term and longer use than a flywheel, but for short time evergy storage < 3 mins, flywheels are very good. THey can also be found in peak demand reduction schemes and other power system stabilisers.

pretty fascinating anyway

James

Do you have any "back of the envelope" numbers on a typical installation.

Stuff like: A flywheen that's 3' in diameter that weighs _____ lbs in slowing down from 3600 rpm to 2000 rpm provides ____ kW of power for ______ minutes.

I realize that we could "work this out" for ourselves but I am lazy!

In fact, such AC - DC - AC flywheel plus diesel genset can entirely replace any UPS plus battery bank. Flywheel provides ridethough of 20 to 30 seconds & by then diesel gen set should be online. A collegue of mine told me to avoid the new high RPM (30,000 or more) magnetically suspended, vacume operated flywheels since high cost, low reliability (vacume pump failure rate is high), high noise levels are still key weaknesses. More conventional 1800 RPM flywheel systems just require periodic greasing of ball bearings & diesel fuel treatments as diesel tends to grow gunk & clog up the fuel filter. Other than that the low RPM flywheel systems are almost failure-proof.

When all the technical problems are worked out (maybe 10 to 20 years from now?), an ideal power backup system might be a refrigerator sized energy storage cabinet with 100,000+ RPM flywheel providing minutes of ridethrough for megawatt load and cross our fingers, emission & very low noise Hydrogen Fuel Cell backup megawatt power generator (full power within 5 minutes instead of hours that it takes now) with natural gas, LPG, methanol or ethanol as fuel for days of operation.

By then, large UPS with large battery bank will be a relic of the past. 30 years from now, 20 somthing engineers might say "What? Sulfuric acid and lead in the basement and smoke-belching, noisy & dangerous combustion engine generator as UPS? Neanderthals & Babarians !!! ".

Nam, I suspect you taken the sales pitches for investment in start-up, speculative firms far too seriously.

As a wake-up call, just review the physics of a flywheel energy storage system along with the practical constraints. Then too there are the serious safety issues associated with containing and maintaining any flywheel having serious moments of intertia and operating at high RPM, as well as the motor/generators systems that they must drive. Realize that the safety housings for such devices may well outweigh the flywheels themselves.

Sadly, it is both easy and common for non-technical business promoters to hype impractical/impossible schemes like these. Engineers on the other hand are constraing the focus of their attention to those things that are both practical, reliable, and realizable.

Also, in electrical and electronics work, the fly in the ointment has historically been the need to rely on mechanical devices to supply certain critical functions that have not been able to be met by static device. In computers, for example, it was a great advance when CRT Terminals replaced mechanical page printers; In telephone switching when the mechanical stepping relays were replaced with digital switches, and when the only moving parts in the electrical transmission system became limited to the generators themselves and some rarely activated mechanical switching devices.

Flywheel energy storage, except for a very specialized venue of mechanical transportation schemes is a relic of the past. Not even the recent past, but the distant past!

Harry C.

p.s. Back around 1960 I was involved in the Stellerator Project at Princeton University. The machine employed a flywheel to accumulate the energy to provide a pulse of current to the magnets. This was a very LARGE flywheel, which took a 2,400-HP motor nearly 15-minites to drive it up to 6,000 RPM. It was connected to a d.c. generator that provided a high current pulse to the magnets. In operation, each pulse to the magnets pulled enough energy from the flywheel to drop it from

6,000 RPM to around 200 RPM in roughly 100-ms. Later versions of similar systems employed capacitor banks to achieve supperior results.

You did great so far, but let's add: What happens to the frequency produced by the generator that the flywheel is driving?

Harry C.

Harry,

Your advice not to take sales pitches from these flywheel makers is well taken.

In 1997, a V.P. of Engineering of a new hydrogen fuel cell manufacturer (with several professors, PhD scientists and engineers in his R & D team and he himself being a PE with 25+ years with a major power company) got me introduced to the possibility of HFC. I guess I got the stars in my eyes because the possibility of pollution-free automobiles and primary/backup power generation would truly revolutionize transportation & power industry. Not to mention the possibility of significantly enhancing the hydrocarbon fuel to useful electric energy (measured in joules per liter of fuel) which would conserve world's oil reserve.

I have been closely monitoring developments & commercialization of HFC, flywheel, new batteries and ultracapacitors ever since then. Nearly 6 years later, I must say that the commercialization of HFC and ultracapcitors have been painfully slow. GE Powe Systems (who had boldly announced "GE will be the first one to supply one million units of natural gas powered 7 to 10 Kwatt residential HFC microgenerators" on their website in 1998 & 1999) quietly dropped the GE microgen web pages sometime in 2000 and sold off their investment in Plug Power (a HFC pioneer in NY area) sometime in 2000 or 2001 after spending tens of millions of dollars buying Plug Power & several years of commercialization effort.

Other smaller & start-up HFC makers have also dramatically lowered their targets from "millions of units" down to "hundreds or thousands" of systems per year type applications. Except Ballard Power Systems (who is being funded by the Canadian government, Ford, GM, Toyota, and other major car makers for development of HFC automotive engine). The Bush administration also announced its commitment to hydrogen fuel cell automobile recently (EE Times cover page article on Feb. 10, 2003 as well as on USA Today feature articles in 2002).

Bush Administration's goal of production all HFC cars by 2010 might be somewhat optimistic based on the technical difficulty of developing a viable liquid fuel to pure hydrogen reformer that is compact, mobile, lightweight & cost effective (tall order even for hundreds of scientists now trying to crack this tough nut).

But, I still remain an optimist. Yes, even after spending hundreds of millions of dollars (maybe billions collectively) during the past 10 years of R & D by dozens of companies, universities & government labs in HFC, high-speed magneti suspension flywheel energy storage/UPS systems, ultracaps & new batteries, commercialization is still years (maybe decades) away. But given 10, 20 or 30 more years (& more billions in R & D funding), I still believe that widespread commercial use of above technologies are still possible & very likely.

Perhaps we should remember that something as simple & obvious as conversion from black & white TV to color TV took something like 20 or

25 years and that first PC's came out in late 1970's and massive commercial usage occurred about 20 years afterwards. Maybe instead of "wheel of justice turns slowly", a new proverb should be "wheel of new technology adoptation/commercialization turns very, very slowly"?

Interesting possibility. Still name one commercially manufactured power back-up system of this type having any success in the market.

Harry C.

The new flywheel systems run very high speed inside vacuum chambers on magnetic bearings. The output is converted to DC, then to utility-grade AC for delivery to the load. This allows a large portion of the energy to be used. There are trade-offs between power and ride-through time, but minutes, and in some cases hours, are possible. Most of the problems that you mentioned do not exist in today's systems.

Ben Miller

whats the q?

I'll second that. Rotary UPS's are in wide-spread use in financial markets (stock exchanges, major banking facilities) world-wide. The reason? They don't fail..

The ANZ Bank HQ in Australia uses a single Piller 400kVA rotary UPS to run the whole building.

Cameron:-)