Power Supply Question
 

Hi

I have two power supplies giving 110V AC as outputs - I want to connect the
two together in some way so that give 110V output. Can someone pls tell me
how this can be donbe safely. I am trying to create a backup system so if
one fails I can remove one supply and still not disrupt power from system
and then replace the bad one with new. it is like putting two ac sources in
parallel - is that possible



Thx

SS

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SS wrote:

Hi

I have two power supplies giving 110V AC as outputs - I want to
connect the two together in some way so that give 110V output. Can
someone pls tell me how this can be donbe safely. I am trying to
create a backup system so if one fails I can remove one supply and
still not disrupt power from system and then replace the bad one
with new. it is like putting two ac sources in parallel - is that
possible



Thx

SS

Hi,
You can't really put two AC supplies in parallel because if they get
out of phase they'll start eating each other's power as fast as they
possibly can and will blow up (but I'm guessing you already knew
that). If you need to put both power supplies together, you could try
to figure out how to phase-lock them. If you just need redundancy,
maybe you should only actually power your circuit with one supply at
a time and keep the other "hot" but not in use; when power fails, you
instantly switch over to the backup supply. If you're just running
lights this'll work fine and you'll hardly notice a flicker, and most
digital electronics runs off DC with its own internal power supply
which can keep it running if the mains supply vanishes for a few
fractions of a second with internal capacitors.

Chris
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You can't really put two AC supplies in parallel because if they get
out of phase they'll start eating each other's power as fast as they
possibly can and will blow up

Are you sure you're right, here? After all, the National Grid is supplied by
no end of alternators all in parallel. Once an alternator has been put on
line it remains in phase automatically because it can't do anything else.
It's getting it on in the first place that's the trick (but not a big one).
Lamps across each pair of phases will go out when the phases are in phase,
so to speak, and the alternators can then be switched together.

Rob Graham

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Robin Graham wrote:

You can't really put two AC supplies in parallel because if they
get out of phase they'll start eating each other's power as fast as
they possibly can and will blow up

Are you sure you're right, here? After all, the National Grid is
supplied by no end of alternators all in parallel. Once an
alternator has been put on line it remains in phase automatically
because it can't do anything else. It's getting it on in the first
place that's the trick (but not a big one). Lamps across each pair
of phases will go out when the phases are in phase, so to speak, and
the alternators can then be switched together.

Rob Graham

Hi,
That makes sense in big national generators. As you say, the problem
is *getting* the generators in phase to start with, and making sure
they don't drift out. Alignment circuitry and things are a tiny
fraction of huge national-power-grid generators, but I'm guessing
they're a larger percentage of the components in a little homebuilt
system (and I'm assuming SS is not asking how to build a national
electrical grid on alt.electronics - you never know though G).
Still, on second thought, it probably shouldn't be too complex even
for a personal project; assuming you get both generators running at
the same *speed*, then *phase* matching is probably pretty easy.

Chris
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Are you sure you are right? Run an amplifier in bridge mode and you
basically have 2 electonic generators connected in antiphase and you will
get lots of power without one side trying to catch up with the other.

I always thought that the national grid machines synced up because a
generator can also act as a motor and any out of phaseness with the grid
means the grid will drive the generator till it goes back in phase.

Gareth.



"Robin Graham" wrote in message
...
You can't really put two AC supplies in parallel because if they get
out of phase they'll start eating each other's power as fast as they
possibly can and will blow up

Are you sure you're right, here? After all, the National Grid is supplied
by
no end of alternators all in parallel. Once an alternator has been put on
line it remains in phase automatically because it can't do anything else.
It's getting it on in the first place that's the trick (but not a big
one).
Lamps across each pair of phases will go out when the phases are in phase,
so to speak, and the alternators can then be switched together.

Rob Graham

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Gareth Magennis wrote:

Are you sure you are right? Run an amplifier in bridge mode and you
basically have 2 electonic generators connected in antiphase and you
will get lots of power without one side trying to catch up with the
other.
[snip]

Hi,
Yes, that's true, BUT: a bridge amplifier uses two antiphase supplies,
one on each side of the load circuit. The output voltage will be
twice the output voltage of one of the "half-amplifiers". The
original poster asked about outputting 110V from two 110V supplies,
so I assume (s)he wanted the supplies to be in parallel (i.e. grounds
both on one side of the load, hots both on the other side). This is
basically like taking an amplifier in bridge mode and connecting a
zero ohm "speaker" to it. ;) You'd better be in phase!

Chris
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Hi,
I couldn't and still can't find the original post, but we seem to agree with
each other in that they absolutely have to be in phase.
My point was also that machines connected to the grid will not behave like
the above situation and will lock automatically, so long as they don't
explode first.


Gareth.


"Chris" wrote in message
news:RqM2d.67798$XP3.39422@edtnps84...
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Gareth Magennis wrote:

Are you sure you are right? Run an amplifier in bridge mode and you
basically have 2 electonic generators connected in antiphase and you
will get lots of power without one side trying to catch up with the
other.
[snip]

Hi,
Yes, that's true, BUT: a bridge amplifier uses two antiphase supplies,
one on each side of the load circuit. The output voltage will be
twice the output voltage of one of the "half-amplifiers". The
original poster asked about outputting 110V from two 110V supplies,
so I assume (s)he wanted the supplies to be in parallel (i.e. grounds
both on one side of the load, hots both on the other side). This is
basically like taking an amplifier in bridge mode and connecting a
zero ohm "speaker" to it. ;) You'd better be in phase!

Chris
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