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From: BillW50 on 27 Mar 2010 15:33
In news:cdKdneHU4KiUDjHWnZ2dnUVZ_j2dnZ2d(a)earthlink.com,
Billsey typed on Fri, 26 Mar 2010 05:57:07 -0500:
> For my own part, I have UPSs at home, that I use with my computer
> equipment; with my audio equipment, though, I use an ISOLATION
> TRANSFORMER-not a UPS.

And what do you think you are gaining by using an isolation transformer?
As an isolation transformer will be more than happy to transfer any
frequency say above 45 hertz or so. And the biggest danger from
equipment running off of AC isn't from 45 hertz or lower, but from those
high spikes on the power line. Sometimes hundreds and even thousands of
volts peak. And an isolation transformer won't stop any of them and will
let them right on through.

The only good thing about an isolation transformer for audio equipment
would be any ground loop would be gone (if the isolation transformer
isn't grounded on the output and/or the equipment isn't either).
Otherwise you are not gaining anything really.

--
Bill
Gateway MX6124 ('06 era) 1 of 3 - Windows XP SP2


From: Barry Watzman on 27 Mar 2010 19:02
I have oscilloscope photographs as JPEG files. Send me an E-Mail and I
will send them to you. It's a square wave with "zero-volts space"
between the positive and negative pulses. Although I can appreciate
your interest in seeing them ... and I don't have any problem with that
.... you should be able to draw it on your own from that description.
And yes, it was an APC (brand) UPS.

[BTW, although it's not my photo, the image at:

http://www.halfgaar.net/media/ups-unloaded

is similar to what I saw, although on my UPS, which WAS loaded (with a
100 watt light bulb), the positive and negative square wave pulses were
wider, and there was less "zero voltage" interval in between them.]

As to "What is the fundamental difference between a computer (laptops
excluded for obvious reasons) and most consumer electronic equipments
which would make UPSs acceptable for the former and not for the latter?"

Computers (at least modern ones ... although not my 1970's Sol-20's and
IMSAI's) are run exclusively from switching power supplies. Switching
power supplies don't give much of a damn as to what you feed them, many
of them would even work from DC. And while, as you say, "computers do
have motors" ... those are run from the DC output of the switching power
supply. NOTHING except the power supply itself runs from the incoming
AC line. That is true of SOME consumer electronics, but other products
have different kinds of power supplies that may not tolerate the square
wave output of a UPS (the operative words here are "MAY not"). I have
no idea how a transformer reacts to such an input, and also many
consumer electronics have devices and/or circuits that are run, in one
way or another, directly from the incoming AC power line.

Of course there ARE sine-wave UPS'; but you will pay more for them ... A
LOT MORE (we are talking about multiplying the total price by integers
here) ... than for square wave UPS (which the UPS manufacturers have
other names for, however).

Barry

John Doue wrote:

> Hi Barry,
>
> Could you post somewhere a copy of the output you saw from an APC UPS?
> Have you tested this way several models? If as you say - and I do not
> doubt you - it is squarely (forgive the pun, too tempting) a square wave
> with a no output in between, I am shocked too.
>
> As most people here I guess, I did not wait for Billsey post to read the
> warnings of UPS manufacturers: they have been there for as long as I can
> remember. But one point bothers me:
>
> What is the fundamental difference between a computer (laptops excluded
> for obvious reasons) and most consumer electronic equipments which would
> make UPSs acceptable for the former and not for the latter? Computers do
> have motors (hard disk, motorized trays) as VCR, tape recorders and CD
> players do , and LCD displays, as TVs do. That point escapes me, but
> admittedly, I do not have or claim to have any in-depth knowledge in
> electronics beyond what I learnt, almost centuries ago! I would very
> much appreciate if you took the time to explain this, since this would
> go a long way complementing common sense and avoiding blinding
> compliance to self-protecting manufacturers mentions.
>
> I personally never have had any problem with any of my various audio and
> video equipment that could be even remotely related to a UPS (I only use
> APC UPSs), and I have never had people I know report any such problem.
> Since usual consumer grade UPSs only provide power in case of sudden
> loss, and then for a very limited time, there would have to be a severe
> incompatibility to cause damage.
>
> One other way to look at the issue might be that, UPS manufacturers do
> not bother to improve the quality of their outputs ... knowing perfectly
> well that it is *acceptable* for most equipments. The improvement of
> output quality would not be cost effective considering they would still
> not be able to claim perfect compatibility with any equipment, which
> would be foolish in any case.
From: John Doue on 28 Mar 2010 06:02
On 3/28/2010 1:02 AM, Barry Watzman wrote:
> I have oscilloscope photographs as JPEG files. Send me an E-Mail and I
> will send them to you. It's a square wave with "zero-volts space"
> between the positive and negative pulses. Although I can appreciate your
> interest in seeing them ... and I don't have any problem with that ...
> you should be able to draw it on your own from that description. And
> yes, it was an APC (brand) UPS.
>
> [BTW, although it's not my photo, the image at:
>
> http://www.halfgaar.net/media/ups-unloaded
>
> is similar to what I saw, although on my UPS, which WAS loaded (with a
> 100 watt light bulb), the positive and negative square wave pulses were
> wider, and there was less "zero voltage" interval in between them.]
>
> As to "What is the fundamental difference between a computer (laptops
> excluded for obvious reasons) and most consumer electronic equipments
> which would make UPSs acceptable for the former and not for the latter?"
>
> Computers (at least modern ones ... although not my 1970's Sol-20's and
> IMSAI's) are run exclusively from switching power supplies. Switching
> power supplies don't give much of a damn as to what you feed them, many
> of them would even work from DC. And while, as you say, "computers do
> have motors" ... those are run from the DC output of the switching power
> supply. NOTHING except the power supply itself runs from the incoming AC
> line. That is true of SOME consumer electronics, but other products have
> different kinds of power supplies that may not tolerate the square wave
> output of a UPS (the operative words here are "MAY not"). I have no idea
> how a transformer reacts to such an input, and also many consumer
> electronics have devices and/or circuits that are run, in one way or
> another, directly from the incoming AC power line.
>
> Of course there ARE sine-wave UPS'; but you will pay more for them ... A
> LOT MORE (we are talking about multiplying the total price by integers
> here) ... than for square wave UPS (which the UPS manufacturers have
> other names for, however).
>
> Barry
>
> John Doue wrote:
>
>> Hi Barry,
>>
>> Could you post somewhere a copy of the output you saw from an APC UPS?
>> Have you tested this way several models? If as you say - and I do not
>> doubt you - it is squarely (forgive the pun, too tempting) a square
>> wave with a no output in between, I am shocked too.
>>
>> As most people here I guess, I did not wait for Billsey post to read
>> the warnings of UPS manufacturers: they have been there for as long as
>> I can remember. But one point bothers me:
>>
>> What is the fundamental difference between a computer (laptops
>> excluded for obvious reasons) and most consumer electronic equipments
>> which would make UPSs acceptable for the former and not for the
>> latter? Computers do have motors (hard disk, motorized trays) as VCR,
>> tape recorders and CD players do , and LCD displays, as TVs do. That
>> point escapes me, but admittedly, I do not have or claim to have any
>> in-depth knowledge in electronics beyond what I learnt, almost
>> centuries ago! I would very much appreciate if you took the time to
>> explain this, since this would go a long way complementing common
>> sense and avoiding blinding compliance to self-protecting
>> manufacturers mentions.
>>
>> I personally never have had any problem with any of my various audio
>> and video equipment that could be even remotely related to a UPS (I
>> only use APC UPSs), and I have never had people I know report any such
>> problem. Since usual consumer grade UPSs only provide power in case of
>> sudden loss, and then for a very limited time, there would have to be
>> a severe incompatibility to cause damage.
>>
>> One other way to look at the issue might be that, UPS manufacturers do
>> not bother to improve the quality of their outputs ... knowing
>> perfectly well that it is *acceptable* for most equipments. The
>> improvement of output quality would not be cost effective considering
>> they would still not be able to claim perfect compatibility with any
>> equipment, which would be foolish in any case.

Thanks, Barry; I now have a better idea of the shape of the wave from
your description. Thanks for the URL. A picture is decidedly worth
thousand words ...

I think we have covered much of the ground here. I understand that the
equipements using, at least partly, directly AC might have problems, but
I guess that they are becoming a disappearing species.

As opposed to UPS, Pure inverters do cause failures and the warnings on
them are very specific and clear. Any attempt to use them do result in
almost instant failure. But their fonction is totally different.

So I believe, your explanations combined with Bill's make it clear that,
even if the shape of the wave is surprising at first look, the its
design has been proven valid. I also believe that people who own very
special and expensive equipments, which by their conception could be
harmed by UPSs, are probably technically inclined enough to assess the
pros and cons of using UPS.

Of course, it would nice to have a clear cut situation but a modicum of
common sense, education ... and as a last resort, experience helps a lot
avoid dangerous situations.

--
John Doue
From: Barry Watzman on 28 Mar 2010 11:12
Re: "As opposed to UPS, Pure inverters do cause failures and ..."

I don't think that there is any difference between what you call a "pure
inverter" and a typical UPS. A UPS is just a packaging of a number of
components in one device:

-Inverter
-Battery
-Battery charger
-Surge suppressor & noise filter
-Power fail detect and Transfer switch
-[usually] Computer status reporting & communication

I think that you are suggesting a distinction between the inverter in a
UPS and a general purpose inverter (cigarette lighter to 120v
receptacles) that, for the most part, simply does not exist. [Does not
apply to true sine-wave UPS', of course.]

[Obviously, there are hundreds of manufacturers of both UPS' and
Inverters, and tens if not hundreds of thousands of designs, so any
discussion of this is going to be a generalization that doesn't apply to
absolutely all devices.]


John Doue wrote:

>
> Thanks, Barry; I now have a better idea of the shape of the wave from
> your description. Thanks for the URL. A picture is decidedly worth
> thousand words ...
>
> I think we have covered much of the ground here. I understand that the
> equipements using, at least partly, directly AC might have problems, but
> I guess that they are becoming a disappearing species.
>
> As opposed to UPS, Pure inverters do cause failures and the warnings on
> them are very specific and clear. Any attempt to use them do result in
> almost instant failure. But their fonction is totally different.
>
> So I believe, your explanations combined with Bill's make it clear that,
> even if the shape of the wave is surprising at first look, the its
> design has been proven valid. I also believe that people who own very
> special and expensive equipments, which by their conception could be
> harmed by UPSs, are probably technically inclined enough to assess the
> pros and cons of using UPS.
>
> Of course, it would nice to have a clear cut situation but a modicum of
> common sense, education ... and as a last resort, experience helps a lot
> avoid dangerous situations.
>
 | 
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