Automatic transfer switch

 

I've set up an array of batteries with an inverter to power a few
computers. When the AC fails, I'd like for the computers to
automatically switch over to the battery power. Can anyone recommend a
good and inexpensive automatic transfer switch which can accomplish
this?

I imagine the setup will look like this


AC--------->Switch---->Computer
                     ^
Batteries->Inverter

Thanks!

 

jevansts wrote:

possibly better:
AC > battery charger > batteries > inverter > computer(s)

kind of an UPS, but with higher capacity depending on your battery amp
hours.

//lm

 

In order to have that kind of transfer (within a cycle or two) the inverter
needs to be synchronized to the grid before the power failure occurs.  Most
simple inverters do not have this capability.

Also simple modified sinewave inverters do not have ability to ground their
common side of plug to neutral of house AC.  You will need an isolation
transformer to allow this.

RC

 

wrote:


Sure they do.  They couldn't do bumpless transfer unless they did.
Miss even a whole cycle and a PC power supply will drop the "line
good" line and reset the computer.  And if they miss that cycle then
they have to wait several more, in case there is an electric motor
attached.  If there is and the motor is turning and there is any
residual excitation in the stator then it'll induction-generate out of
phase and may/probably will trip the inverter on overload.

Line sync is as simple a coupling some line voltage to the oscillator
with a simple capacitor to injection-lock the oscillator.  That's the
way most every one I've looked at does it - the 60 hz oscillator runs
all the time injection-locked to the 60hz line.  A missing pulse
detector gates the power stage on when the line voltage fails.  The
transfer is almost seamless.


Make that "some simple inverters".  Certainly not all.  Even those
that float the neutral don't matter since there is never a need to
connect the neutral and ground on an isolated system like that.

John



John De Armond
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http://www.neon-john.com
Cleveland, Occupied TN
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