[Noisebridge-discuss] Fwd: [BerkTIPGlobal] Fwd: Re: [HH] UPS Tutorial & Teardown

giovanni_re john_re at fastmail.us
Tue Aug 13 18:11:02 UTC 2013


----- Original message -----
From: "Peter (peabo) Olson" <peabo at peabo.com>
To: hardwarehacking at blu.org, Tom Metro <tmetro+hhacking at gmail.com>
Subject: Re: [HH] UPS Tutorial & Teardown
Date: Mon, 12 Aug 2013 23:11:39 -0400 (EDT)

On August 12, 2013 at 2:28 AM Tom Metro <tmetro+hhacking at gmail.com>
wrote:
> Here's a video that describes the 3 major architectures for
> uninterruptable power supplies, then tears apart an APC rack mount UPS
> to match up the real components to the theoretical block digram:
>
> http://www.youtube.com/watch?v=Fj7e3WGUKO8&feature=em-subs_digest
>
> I went into it figuring I already knew how a UPS worked, but still
> learned some things. (AVR UPSs really just use an auto transformer and a
> couple of relays to implement voltage boosting/reduction? That's
> surprisingly granular.)

The mind-bending moment occurs towards the end, when he tries to find
the
circuit which charges the backup battery.  It seemingly is not there.

Imagine an H-bridge driving the primary of a transformer that is
producing AC
out when the UPS has no line input.  Cool.  Imagine the same H-bridge
when line
input is available.  It is sort of backward.  Enough that the protective
diodes
of the MOSFETs are conducting.  What do you have then? A bridge
rectifier
supplying current back to the battery, which coincidentally has some
hefty
capacitors to filter the voltage and help charge the battery.

Ingenious.  Well it is a little more complicated, but that is the basic
nifty
insight :-)

peabo
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