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Old 04-03-2013, 10:42 AM   #1
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Universal Power Interrupter - what actually does the detecting and forces the switch?


Does anyone know what the part(s) are called that a UPS uses to determine when theres no power and it should kick itself on to supply power from its own power supply?

I know some work by constant powering batteries through DC voltage, and switch it to AC, when power outage occurs.

What is the name of the device, switch, apparatus that actually does the detecting and the switching. I asked this in a different forum and they all sent me to howstuffworks and wikipedia that just explain the overall process. I need the actual details and product parts.

Also, anyone know how the UPS detects a return to regular power, and switches itself off to allow the electric company
power to resume offering power?

Thanks

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Old 04-03-2013, 11:13 AM   #2
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Universal Power Interrupter - what actually does the detecting and forces the switch?


My guess would be some sort of relay.

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Old 04-03-2013, 11:15 AM   #3
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Universal Power Interrupter - what actually does the detecting and forces the switch?


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Originally Posted by jratftcc View Post
Does anyone know what the part(s) are called that a UPS uses to determine when theres no power and it should kick itself on to supply power from its own power supply?

I know some work by constant powering batteries through DC voltage, and switch it to AC, when power outage occurs.

What is the name of the device, switch, apparatus that actually does the detecting and the switching. I asked this in a different forum and they all sent me to howstuffworks and wikipedia that just explain the overall process. I need the actual details and product parts.

Also, anyone know how the UPS detects a return to regular power, and switches itself off to allow the electric company
power to resume offering power?

Thanks
Method 1 -- A relay is held in position for utility power direct from power cord to load receptacles using a solenoid. If utility power is lost, the solenoid lets go and the relay contacts switch to battery power. There is a moment, perhaps 1/30 second, that power to the load is cut but even computer power supplies should be able to keep the DC power to the computer circuits steady despite the interruption. The better UPS units have an electronic circuit that tests the resuming AC power for stability over several seconds' time before energizing the solenoid to switch the load back to AC power.

Method 2 -- The load is always on battery power. When AC power is on, the battery charging circuit is active to put at least as much power back into the battery circuit as is being drawn by the load,so there is no net outflow from the batteries. Sensing circuits in the line going to the batteries proper, together with voltage regulators, keep a trickle charging current of the proper amoun going to the batteries as the load changes. This method is less energy efficient because all of the power used by the load during normal AC operation is first converted to battery charging voltage (typically 14 or 26 volts DC) and then converted back to 120 or so volts AC as the UPS unit under battery conditions normally does.
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Last edited by AllanJ; 04-03-2013 at 11:34 AM.
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Old 04-03-2013, 11:18 AM   #4
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Universal Power Interrupter - what actually does the detecting and forces the switch?


These can be quite simple with just a relay connected to AC or a AC to DC power supply and that connected to a DC relay. You lose power and then so does the relay. And a relay is an electric switch.

Others can be more complex with microcontrollers monitoring line voltage and frequency. If the power quality drops below a certain level, then it switches. For those search google.com for the words...

ac power monitor
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Old 04-03-2013, 07:59 PM   #5
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Universal Power Interrupter - what actually does the detecting and forces the switch?


Will a single phase monitor do the job Im asking?
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Old 04-03-2013, 11:28 PM   #6
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Universal Power Interrupter - what actually does the detecting and forces the switch?


It could be a simple as a relay,
but I think its more likely just some diodes,
Under normal operation they would be reverse biased,
But the instant power fails it becomes forward biased,
This way is much quicker, and no moving parts to fail.
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Old 04-03-2013, 11:32 PM   #7
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Universal Power Interrupter - what actually does the detecting and forces the switch?


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Will a single phase monitor do the job Im asking?
What are you doing? What will this control?

If there is a device you are using which plugs into a regular house 120 volt outlet, then that would be single phase. (Like a home computer.)
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Old 04-04-2013, 03:11 AM   #8
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Universal Power Interrupter - what actually does the detecting and forces the switch?


I was looking at building my own UPS and I was going to use a relay plugged into AC and the relay simply switches off and diverts to the inveter (that would always be running) but one issue I ran into in my testing is that the relay does not switch fast enough as there will actually be a bit of voltage left in the relay itself and the converter that is powering it (most relays take a low voltage DC source like 12v so you need to convert it). So my guess is most UPSes have a microcontroller that monitors the AC voltage and if it misses a single sine it tells the relay to switch.

Ended up just buying an inverter-charger. It's basically a UPS but it's designed to hook up bigger batteries to it and it will charge them when the power is on and then switch to inverter when the power goes out, and it's instant enough for servers to not see it.

Though at some point I think I want to build a sort of dual conversion setup so there is zero hit to the equipment. With a relay type setup there is always that slight chance that something causes it to not trip fast enough. Brownouts can be bad for that as it may not brown out bad enough for it to decide it should go on battery, so the equipment sees the brownout. I've seen many situations where laser printers will cause computers to shut down despite them being plugged into a UPS. with a dual conversion setup it's always running off batteries/inverter. Though you need more expensive batteries/charger for that. Another way of doing it that I actually want to look into is to do a partial dual conversion setup. You have the rectifier powering the inverter which powers the equipment. Between the rectifier and inverter you have a capacitor bank, and then a relay. That relay will connect to the batteries only if the power goes out. That way you can get away with cheaper batteries, and a cheaper charger. The charger does not need to be able to handle the full load, like a true dual conversions setup. The batteries also don't need to be designed for constant use. My current setup is only about 700w and I've been toying with the idea of doing a 2-3kw one so I'd probably do something like this.

Oh and I have taken apart some UPSes (great way to get resistors, diodes and other components) and they will have quite a few relays in them. The last one I did had 5 of them. Low(7a or so) amperage AC rated ones.


Last edited by Red Squirrel; 04-04-2013 at 03:16 AM.
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