On Tue, 2006-12-05 at 20:38 -0700, Joseph Sinclair wrote:
> Here's what I think you're looking for:
> 1) all surge suppressors route surges to ground, there isn't a commercial capacitor available that would absorb a UL-spec surge of 2000+ Joules, and even if it did, you'd have to drain it somewhere or it'll pour into your equipment anyway. Note, capacitors don't hold charge for long, even a very large capacitor usually drains to 0V within 10 minutes to 2 hours (depending on type and surrounding circuitry). That's why they aren't used in place of batteries except in special applications.
> 2) Surge suppressors vary mostly by how outlets are isolated (or not), whether the power is filtered (or not), maximum surge capacity, and the type of surge bypass (MOV, inductive coil, or both).
> 3) All commercial surge suppressors intended for consumer use use MOV (Metal Oxide Varistor) bypass, it's fast to respond and it's cheap. Some add inductive coil (which is better for HF/VHF pulses typical of atmospheric-discharge inductive coupling). This means they are "burnt out" if they stop a surge, this is OK, since the suppressor is (usually) a LOT cheaper than what it's protecting. It's also why I put surge suppressors between a UPS and the outlet, it's cheaper to replace the suppressor than the UPS.
> 4) Watts=Volts*Amperes ONLY holds for DC power. For AC it's a much more complex (differential) equation because in reality both voltage and watts are constantly changing, not the static values quoted. For household power the actual values at the outlet are 115V(rms) and 15A(rms), where (rms) denotes the root-mean-square equation applied to an AC waveform to generate a value that works for pure resistive loads. VA is much simpler to calculate, so that's why UPS's are rated in VA. For most electronic devices the equation is roughly Watts=(3/5)VA, but that's only an approximation, and it's always good to maintain a 20-30% headroom when buying a UPS to account for load variance. It's worth noting also that most printers have VERY non-linear loads, and can spike a lot of VA on startup
> without drawing a lot of Watts.
> 5) The reason the UPS you noted is cheaper than the Isobar suppressor is that the output of the Isobar is ultra-clean pure sine-wave power. The UPS output is passthrough (i.e. not filtered) when power is on, and a very noisy stepped waveform when power is out (which is not very good for your equipment). Basically, the UPS you noted is using really cheap components, compared to the high-quality components in the Isobar.
>
> ==Joseph++
----
yeah - that's what I would have said ;-)
Warning...do not expect to beat Joseph at Trivial Pursuit.
Did you ever think about trying to get on Jeopardy?
Craig
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