What do you call a circuit that switches from household
110 to batteries when the electricity goes out (and back
to the mains when the electricity comes back on)?

Is there a proper name or description for this type of circuit?

 

it could be called a transfer switch

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UPS. United parcel Service.
Uninterruptible Power Supply.
I spelled it wrong on the other website.

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Even if you build it yourself?

How about a "dropout switch" or a "changeover switch?"

I am very familiar with pre-packaged UPS systems. You
give me an idea. Could I just steal the major components of
an off-the-shelf UPS and just replace the connected battery
with one or more car batteries connected in parallel?

I don't see why not as long as I don't exceed the capacity
of the inverter built in...

 

Some UPS's have a tiny battery (that is why you want a bigger one) that lasts for only a couple of minutes so a computer can shut down. Then it also has tiny heatsinks.
It will smoke if you tried a huge battery and have it operating long enough to get very hot.

Its charging circuit also might croak.

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That all makes sense. Oh well, I know I can connect a battery charger
to a car battery and then to an inverter. I can then run the fans off the
inverter full-time. This is hard on all of the equipment involved though.
I would rather not wear the battery charger and inverter out so soon.
Seems like it could even be a safety issue somehow to me.

Anyway, what is a simple switch/relay configuration I can build to solve
this problem?

Can you point me to any articles or threads about it? I'm more than
happy to read so you don't have to type...I'm very new to electronics
and don't quite know what I'm looking for...

Could I use some type of relay with an AC power supply, that just
switches the fan input over to the battery/inverter system on the
other contacts? If so, what type of relay is this?

 

Maybe I can use a "double throw, double pole, break-before-make" relay
to make the transfer. If I power the switching with a transformer on the
mains, when the mains power failed, it would then switch over to the battery/inverter supply.

Does this make any sense? Would it work? If so, where do I find such a
relay?

 

because the batteries in UPS are so expensive to buy, you can find ENORMOUS UPS (6u x 19" x 3' or 4' deep) on ebay. These are designed for server farms ect, where they are required to keep LOTS of servers alive for reasonabley long periods.

I would have thought you could hack one of these.

I used a UPS (dead batteries, £10 collect only) as the basis for my power supply in my works van. I needed 'clean' power for my computers, but only had a 2-stroke petrol generator. I connected that to the ups and my computers, so that the power was filtered by what was probably a very well made (and expensive) filter when the unit was new. Even with the dead batteries, there was enough power in them to allow the ups to do its thing, and covered the 5mins or so it took to re-fuel the generator.

for example i just found 2x 3000VA sitting at £5.50

What sort of current are we talking about?

If its heavy current then you would need a contactor, if its low current then any DPCO rated for the current would be fine. You wouldnt want much in the way of filter caps in your transformer, as it could delay the coil de-energising, meaning that your 'emergency' circuit wont kick in immediatly.

 

Industrial UPS...good idea.

I need about 250 watts for about 4 hours (slightly overestimated for safety)
at 110 watts.

As best I can calculate, a UPS style system with a marine battery on a
charger should work great. I think a battery powered timer should be
able to handle the trickle mode of a battery charger.

So, I want a DPCO instead of a DPDT? Is it the "stable off position in
the centre" that prevents some problem in my circuit? Would they be
good for 250 Watts/2.3 amps at 110 volts?

Would a device like the one at the link below work?
http://www.newark.com/86H6705/electr...questid=119348

 

DPDT/DPCO is same thing i think, 2 poles each with 2 positions, the stable state would be the n/c contacts.

You would wire your backup mains power through the n/c contacts, and your normal mains power through the n/o contacts. Wire your 'load' to the common contacts, and use a transformer plugged into the normal mains for the relay coil. where is mains, the circuit uses mains, when it fails, the coil de-energises and connects the 'load' to the backup mains.

2.3 amps would be no problem at all for a suitable relay

that relay you linked to is a bit big and industrial, there are many smaller, and still capable relays. You will probably find 12v relays easier to power as 12v wall warts are a lot easier to find (and cheaper)

 

Can you suggest any online suppliers for such a DPDT or DPCO? Yes,
12 volts is much more common. I really have no idea where I can
find such a relay that I can solder or otherwise attach wires...

 

How about:

http://www.alliedelec.com/Search/Pro...9532003E7FE17F

 

I have been using 300 watt (or so) ups with car batteries for a long time. Here in the US Virgin Islands the power goes out a lot. It's a comfort to have a fan and a lite when the power is out. I get the ups for free, toss the gel-cells and run a wire out to the battery. The ups keeps the battery up, and I've only had one drop dead. Audioguru is right about heat sinks and overloading the unit. I now look for units with fans. I have a Powerware Personal 1000 I'm trying to revive, but can't find schematics. It's blowing the internal 30 amp fuses on the 30 volt side.

 

Hi downplay

What do you wan't to run on it ????

keep in mind that UPS normaly don't handle peak surges that well

so if you have some inductive loads that needs a big starting current to run you still might have a problem that it can not handle it

Robert-Jan

 

That is exactly my setup. People toss a working UPS in the trash because it costs little more to buy a new one than it does to replace the battery. So I just take it and connect an externel battery. I use an old car battery whi is no longer good for cranking but still has plenty of life left in it and is also free.
The OP is looking for about 200 W which can easily be handled indefinitely by almost any UPS. The problem is getting the battery to last for 4 hours. I would say you need about 200 Ah which is about 4 car batteries. A 200 Ah deep cycle battery would be best.

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