UPS, Inverters, AVR and MOV Explained

[Forkinhades]

A sticky to try and simplify these terms, and to give us stable electricity in Thailand. Now that we understand to protect ourselves from electrical shocks, and fires. Now we need to try and protect our devices from under-voltage, over-voltage, and spikes in voltage. First let me expand on the terms.

UPS = Uninterrupted Power Supply
AVR = Automatic Voltage Regulation
MOV = Metal Oxide Varistor


Firstly, so what do you need a UPS or Inverter?
This is one of the basic confusion people face, so let me start with answering this first. UPS and Inverter are words used interchangeably though they are not exactly same. UPS is just a system which allows INSTANT switchover to the power back-up source in case of a power failure. The power back-up source can be a battery or something else. Whereas an Inverter is a system which converts direct current to alternate current hence enables using a battery for backing up equipments running on AC power supply. Inverter uses a battery to provide power back-up. Computer UPS comes with in-built battery which works as back-up power source and can provide back-up for 15min. to 30 min. So if that much of back-up is sufficient for you, you should be fine with buying just a UPS for your need. But Inverter comes with more powerful battery and can provide support for electrical equipments, computers, home appliances etc. and also gives more hours of back-up. Most of the inverters come with in-built UPS which ensures that power failure doesn't cause fluctuation and your system switches instantly to Inverter's Power Back up battery.


AVR = Automatic Voltage Regulation.
What it does is to regulate the mains voltage within a limited range. In the case of your UPS, it boost +12% when the incoming voltage is too low. Let’s say the incoming voltage is at 200 volts, the output then goes to 224Volts, +12% of 200 volts, which is still acceptable for most UPSs. When the UPS output reaches let’s say, 230V with the boost mode on, then the UPS sends a command to a component called relay so that the +12% compensation is turned off.
Basically the voltage regulation is a series of power transformers, it can either be step-up transformers or a step-down transformers They basically do the same thing a 220V to 110V step-down transformer does, or a step-up transformer does, when it gets 110V and transforms to 220V. The UPS senses the incoming voltage and commands a series of relays to select a different transformer output or “tap”, as they call it.
An automatic voltage regulator can only work within a limited range.
A voltage regulator transformer can have a much higher range as its developer wants, but it makes the unit much heavier, it wastes more energy and generates more heat. It doesn’t matter what range the AVR has, it is still slow for suppressing voltage surges

MOV – Metal Oxide Varistor

Surge suppression is basically made to protect against high energy and fast rising surges or spikes that can be caused by lightning, electric motors being turned on or turned off, etc. Surges are essentially fast rising spikes and voltage swells are slow rising and low energy in nature. Surge suppression can in some cases reduce voltage swells, but this is not its main purpose.
Surge protection is basically comprised of a component called MOV – Metal Oxide Varistor.
An MOV works at diverting surges to ground. When operating at its nominal voltage, or the mains voltage, the varistor acts like a resistor with its resistance tending to the infinite, so it does not conduct electricity to ground at this state. When there is a fast surge, it instantaneously reacts (in nanoseconds) by decreasing its internal resistance, allowing the excess energy to flow to ground.

The voltage regulator cannot act as fast as an MOV for suppressing high power and fast rising surges and would not be capable of that because of the nature of a power transformer. High energy surges must be diverted to ground and power transformers do not do that. Compared to the speed of an MOV, the voltage regulator is like a turtle.
There are some disadvantages regarding the use of MOVs for suppressing voltage swell. MOVs degrade very fast if frequent voltage swell are imposed to it, it gets too hot and it’s internal chemistry degrades. MOVs are made to react fast and come back to it’s initial state very quickly as well, which happens when a power surge occurs. That’s why manufactures of surge protective devices use an MOV that only triggers itself when the voltage is much higher than the mains voltage. If the MOV starts to conduct too early, it will degrade itself very quickly and on all power grids a relatively high number of fast duration swells, do happen

What an MOV doesn’t do…
An MOV does not provide equipment with complete power protection. In particular, a MOV device provides no protection for the connected equipment from sustained over-voltages that may result in damage to that equipment as well as to the protector device.
An MOV provides no equipment protection from inrush current surges (during equipment start-up), from over current (created by a short circuit), or from voltage sags (also known as a brownout); it neither senses nor affects such events.

To Summarize
The AVR and the surge suppression solve two different problems. They’re complimentary technologies but do not ensure total power protection (Over Voltage Cut Off Device)
The AVR can adjust the voltage of the line within a limited range to compensate for the voltage being too high or too low. However, the AVR does not respond quickly enough or have wide enough compensation to handle surges.
Surge protection is capable of putting huge surge voltages into ground very quickly, but won’t adjust the long-term voltage of the line as the AVR does.
Both however are ineffective against sustained high voltages. in neutral open condition , they themselves will need protection.

[JesseFrank]

I never opened up a UPS, but would it be easily doable to replace the charger with a heavier one and then connect a larger external battery ?

[Crossy]

I never opened up a UPS, but would it be easily doable to replace the charger with a heavier one and then connect a larger external battery ?

Nah, they're all rather heavily integrated as a cost saving measure.

Nothing to stop you bringing out the battery terminals for external batteries, if you don't need rapid re-charging the internal charger should be ok with batteries up to 2-3 times the capacity of the internals.

If you use a decent PSU as an external charger (use a blocking diode on its output) then there's little danger of hurting the UPS. I would NOT use a regular battery charger, output is too unpredictable. You may want to include a relay that only connects the external batteries when the mains fails for a bit of extra security.

[JesseFrank]

If you use a decent PSU as an external charger (use a blocking diode on its output) then there's little danger of hurting the UPS. I would NOT use a regular battery charger, output is too unpredictable. You may want to include a relay that only connects the external batteries when the mains fails for a bit of extra security.

Do you mean that I can connect a PSU to the outputs of the internal charger and charge the external battery that way ?

How large of a battery would be possible to use in that case ? I'm thinking about a 125 Ah battery.

I was thinking about purchasing one of these that would cost me about 12.000 Baht include shipping, but if it is possible to modify a UPS in the way I explain above, it maybe better and cheaper in the long run.

http://www.ebay.com/itm/800W-12V-pure-sine-wave-solar-smart-UPS-inverter-charger-max-50A-/141103392587?pt=LH_DefaultDomain_0&hash=item20da6ae74b

[Forkinhades]

^ I would have thought that you can swap out the battery, extend the battery leads and put a higher rated Ah Deep Cycle Battery next to the UPS?

Thoughts Xy?

EDIT: Just read your first post Xy ....Coffee!

[Forkinhades]

^ So what issues would one have with swapping out a 7Ah battery, and replacing with 120Ah? Just a longer charge time? Or any other factors to consider?

[JesseFrank]

How about this.

I have 3 UPS circuits in my house, which all connect from the same location.

Each circuit has more or less 500 Watt connected to it.

A leonics OA 750 VA 450W cost 3290 Baht. If I buy 3 of these items, can I connect them to a single high Ah battery, which get charged by an external automatic charger ?

[Crossy]

^ So what issues would one have with swapping out a 7Ah battery, and replacing with 120Ah? Just a longer charge time? Or any other factors to consider?

The baby charger in the UPS may never manage to charge such a large external battery, its current would be swallowed by the losses in the battery

Time for an external charger, plenty of 10-15A switching PSUs that will do the trick (make sure it's rated at about 16V), include a suitably large blocking diode so the battery doesn't feed back into the PSU when the mains is off (some units don't like the backfeed so best to be safe).

QED

[Crossy]

How about this.

I have 3 UPS circuits in my house, which all connect from the same location.

Each circuit has more or less 500 Watt connected to it.

A leonics OA 750 VA 450W cost 3290 Baht. If I buy 3 of these items, can I connect them to a single high Ah battery, which get charged by an external automatic charger ?

I don't see why it shouldn't work like that.

[Forkinhades]

An invertor might be of better use...

Sent from my SM-G900F using Thaivisa Connect Thailand mobile app

[Crossy]

An invertor might be of better use...

Depends, do you need automatic changeover to battery, fast enough that your PC doesn't die? Both those are already built into a purpose built UPS.

[bankruatsteve]

I like the topic, but y'all are confusing me RE: inverter vs. UPS. Obviously, a UPS contains an inverter but you also say that most "inverters come ... with UPS". ???

[JesseFrank]

An invertor might be of better use...

Depends, do you need automatic changeover to battery, fast enough that your PC doesn't die? Both those are already built into a purpose built UPS.

Yes I need the UPS function, but the inverter I posted a link in post #4 has this UPS function built in, and even has a connection to start up a generator, but the 3 UPS units will save me a few thousand Baht.

So as a fact, is it possible to use 3 UPS units, from which I disconnect the charging function of 2 of them, then use a PSU connected to the charging leads of the third one to charge the 120Ah battery ?

Why does the PSU need to be rated at 16V if the battery is only 12V ?

[Gary A]

I'm a solar fan and my computer, printer, lights and fans are totally off the grid. This doesn't mean that you have to have solar set up for your computer. A small automatic battery charger, a fairly large deep cycle battery attached to a small inverter will keep your computer off grid and will give you very stable voltage. All that will be cheaper than a huge UPS, it is easily repairable, if needed, and will serve the purpose very well. I started out that way after my first small UPS died and then a larger one died. Adding a couple solar panels eliminated the automatic battery charger. You will need a solar charge controller if you use solar panels. I could find no one who wanted to or could repair a UPS. A UPS unit with a 150 AH battery will be VERY expensive. The battery and automatic charger with a small pure sine wave inverter would be a perfect power supply for an apartment or condo.

[Crossy]

On 23/06/2014 at 11:33 AM, JesseFrank said:

Why does the PSU need to be rated at 16V if the battery is only 12V ?

 

A fully charged 12V battery is about 13.8V, to float charge that you need a regulated charge voltage of around 14.5-16V (the battery spec will tell you what voltage to use).

[JaiMaai]

What would be my most cost effective solution
to provide power for up to an hour (just had an outage this long?
I would want to power:
A fibre optic router
An android TV box
A 48in LED TV
A floor fan
(and possibly a low wattage lamp depending on the time of day)

I'd imagine the tv and fan will be the most power hungry but is this doable?

Sent from my SM-J200GU using Tapatalk

[rijb]

Good question.  I'm looking for the same solution.