[TriLUG] UPS Recommendations?

[Joseph Mack NA3T]

On Sun, 16 Jan 2011, Randy Barlow wrote:

> I've read that typical inexpensive UPS's (I think we 
> should call them LIPS - Less Interruptible Power 
> Supplies), don't actually produce sine waves, but 
> approximations of sine waves, often with stepping or 
> triangulation when they switch to battery power.

They used to produce square waves. Now they produce modified 
square waves (hope this ASCII art survives mailing)

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this is a better approximation to a sine wave and clocks at 
twice the rate, making it easier to build.

A peak reading AC voltmeter (which is many meters) will not 
show 120V for non-sinusoidal waves like this, even though 
the RMS voltage is 120V. Best test is to try a 100W light 
bulb.

A square wave device like a UPS is not designed for 
inductive loads (eg motor running under load). I don't 
expect anything will blow. You just may not be able to 
deliver any power to the motor. I don't know much about 
this.

> I also read that such signals can be damaging to the UPS 
> and the power supply.

not true.

I've been using the output from switched power supplies (the 
one's generating the above waves) sine the 60's and never 
blown a thing attached to them. The only people saying this, 
I expect, are the makers of sine wave power supplies.

> It seems that Pure Sine Wave UPS's cost a whole lot more.

they're enormously more difficult to build.

Joe

-- 
Joseph Mack NA3T EME(B,D), FM05lw North Carolina
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