[Nut-upsdev] Questions on the state of the UPS market

Robert Woodcock rcw at debian.org
Fri Jan 16 01:15:32 UTC 2009

On Thu, Jan 15, 2009 at 07:35:02PM -0500, Eric S. Raymond wrote:
> The source of my confusion is this.  I learned years ago to
> distinguish between three categories of product:
> 1. Line conditioners (LCs) and surge suppressors.  The are just spike
> filters, with no battery.
> 2. SPS = Standby power supply.  These normally filter mains power,
> switching to a battery when the mains have a dropout.
> 3. UPS = Uninterruptible Power Supply.  These continuuosly feed power
> to a battery, which discharges continuously to run the equipment.
> When the mains go down, the battery stops charging. 
> My problem is this: The way these products are now labeled, I
> could not work out a way to tell which are which. Some look so
> small that they almost have to be mere line conditoners, because
> there;s no room in the case for a serious battery pack.  Others
> could be SPS or UPS devices, but I can't tell which.  All are now
> just labeled "Battery Backups"!
> 1a: Does anyone have good heuristics for telling the LCs, SPSes,
> and UPSes apart based on the packaging or the specs visible on them?

These categorizations are still useful today, although your terminology
is different.

If they have a battery, they are #2 or #3. If not, they are #1.

Some of the fancier ones in category #2 are "line-interactive", which
try to buck or boost voltage to maintain output compliance without
going on battery. But they still pass whatever hiccups get through
the filter to your equipment. You may or may not see any that do this
for under $200. They'll use words like "line-interactive", "buck/boost",
"AVR", etc., in their specs.

UPSs of type #3 are commonly referred to as "online" or
"double-conversion". Good luck getting anything like that for $200.
APC doesn't even have one in their lineup (as far as I can tell, the
entire Smart-UPS and Back-UPS line is #2).

> When I last seriously examined the market (mid-2005), SPS designs
> appeared to be on their way out because the switching electronics for
> full UPS operation were dropping in cost fast enough to make SPS
> designs a pointless economy.  In the 2005 and 2007 revisions of the
> UPS HOWTO, I must have believed SPSes were one with the dust of
> history, because I didn't mention them anywhere.

Unfortunately they'll always be cheaper to make, and more compact.
Since SPSs pass a fixed amount of energy through their inverter,
they can get away with using a block of metal for a heat sink, instead
of using active cooling.

(This is a big reason not to hack external batteries onto a UPS that
isn't designed to attach to them.)

> I'd still believe that, except that it's 2009 and I saw at Ardmore
> that APC is still selling not only units with serial-port interfaces
> but units that I know for a fact have the old-fashioned single-pin
> dumb interface.  And if they're still selling *that* kind of obsolete
> crap, I have to think maybe there are still SPSes in the world.
> 1b: Is the SPS in fact dead as a technical category?  If not, why not?

I'd say it's more pervasive now than in 2005. Price/profits/ignorance.

> Oh, and this, too:
> 1c: RS232C, on consumer devices, in 2009?  Ferfuckssake, *why*? 
> It's not like USB chips are expensive or anything. I know all about
> this from GPS-land, actually; pl2303s are so cheap that even if the
> vendors wanted to retread their RS232 designs, the cost of goods to
> refit them with USB-to-serial conversion is close to zip.  Does anyone
> have a clue why this interface type didn't die five years ago?

Because the stuff they're currently selling is based on 5+ year old
designs. Same reason why if you buy an alarm system or fire system,
you get, among other things, a circuit board with gobs of discrete
components on it.

Ethernet interfaces are similarly cheap (< $3). Unfortunately, the
products weren't initially designed with them in mind, so what you
get for your $100-$300 is a computer on a card that has an ethernet
port on the back.
Robert Woodcock - rcw at debian.org
"Obscenity is whatever happens to shock some elderly and ignorant magistrate."
	-- Bertrand Russell

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