[conspire] Another motherboard was _not_ burned out today

[Rick Moen]

I wrote:

> UPSes follow one of two basic design patterns.  The older one has the
> battery _not_ inline to the downstream devices.  The newer one does have
> the battery inline.  Neither typically provides meaningful power
> regulation but the older type provides none at all.

I cannot find my prior write-up on this subject, so here's a quick
attempt:


Offline/Standby type:  The charger -> battery -> inverter circuit is
rigged in parallel to normal power.  Thus, there's no isolation
whatsoever of the equipment from incoming utility power 99.9% of the
time, because the equipment is directly connected to incoming power
except on the very rare occasions when the UPS kicks the battery in.
At best, the manufacturer will have kicked a few bucks into some
primitive protection such as a MOV.

Line-interactive type:  UPS's front-end circuitry puts the power through
an autotransformer, then the charger -> battery -> inverter circuit.
The autotransformer switches taps as required to level out overvoltage
surges and undervoltage brownouts.  This is significantly better than
nothing.  It is not, however, particularly fast:  Switching taps takes
on the order of a couple of seconds.  So, the only protection you get
against spikes (the more-rapid variations than 'surges') is what you get
from brute-forcing incoming power through a charger, a big lead-acid
battery, and an inverter circuit.

At which point, you would ask yourself:  'Wait, I'm using an
autotransformer, a charger, a big lead-acid battery, and an inverter as
a voltage conditioner.  Maybe it'd be more efficient, and not entail
replacing the battery pack every few years at high expense, to use a
voltage conditioner instead.'


(There is also a third type of UPS, but one that is found only in
extremely expensive units delivering well over a kilowatt.  It is called
the 'Online' aka double-conversion style, rectifying to DC for passing
through the rechargeable battery (or battery strings), then inverting
back to 120 V/230 V AC for powering the protected equipment.  These are
quite expensive.)