In article ,
Day Brown wrote:

I live out in the ozark boonies, at the very end of the grid with
really dirty power and lotsa lightning on the lines strung out hundreds
of feet above the valley floors.

And now, we've got the 3rd UPS crap out in 2 years. Getting old.
Besides, the usual 20 minutes backup sux. Power's often out for 1/2 hour
or more.

Well, I could hook up an inverter to run the systems off, and then hook
up a large battery charger to keep the battery fully charged. But, now,
I wonder if it wouldnt make more sense to yank the PC power supply out
of the case, and use two 12 volt car batteries in series to run the PC
motherboard with a 24 volt charger. Gonzo more efficient.

Center tap the series to get the +12 and the -12 the motherboard wants,
and then use DC-DC converters to get the +5,-5, and the +3.3 vdc...
but given the amps on the +5 and +3.3vdc, it'd be nice to use 24vdc to
power the DC converters. the high amp low voltage DC converters are
kinda expensive. And besides, I got plenty of room under this desk; it
could be the size of a shoebox or more. I dont see any sense in paying
more for something they designed to fit in a rack frame.

So, lessee if this makes sense. use a low frequency oscillator. That
way, if it aint oscillating, I can *hear* that, and dont havta drag out
the scope. so what if it needs a bigger ferrous core. Horse shoes aint
expensive. I got hundreds of feet of 12 awg wire. Got some 25 amp full
wave bridges. Use lotsa iron and copper and quit worrying about fast
snubbers to protect the MOSFETs.

And, between the gauss of, say a 10 amp 24 volt charger, and the ability
of the car batteries to soak up spikes, lighting would havta fry the
wires in the wall before it'd crash the system.

Any other hints?


Find a surplus motor/generator set or else build one. You can have an AC
motor drive a DC motor/generator and an AC generator. The AC motor
provides power when public power is more or less normal. The DC
motor/generator is used to keep the batteries charged. The AC generator
powers your equipment. If power is lost to the AC motor, the DC
motor/genarator becomes a motor and continues to drive your AC
generator. If designed properly, the switch over glitches will be minor
and should not bother your equipment. The mechanical inertia of the
system along with proper feedback controls should be able to maintain a
more or less constant output on your AC generator.

I know it works as I have worked on military systems which use this
scheme.

Al