Installing an Automatic Voltage Regulator (AVR)

[Crossy]

Background

 

Many of us suffer from power supply issues, chronic low-voltage, supply variations and the like. This can lead to premature failure of expensive technology and less expensive water pumps and other appliances with motors. It also has some annoying effects, flickering lighting, fans that run slow, constantly beeping computer UPSs.

 

Of course your first port of call should always be the supply authority (MEA or PEA), good luck with that the usual response being "you have electric, no problem".

 

Assuming you've struck out with PEA, enter the AVR (Automatic Voltage Regulator), a magical device that takes whatever your supply happens to be (from 130V to 260V) and spits out 220V. Pure magic eh? Of course not, you never get something for nothing, but more of that later.

 

Unfortunately an AVR isn't a magic bullet or cure-all for your electrical issues so let's have a look at the sort of problem many of us face.

 

The Issues

 

Consider looking at an AVR if you suffer from:-

 

• Chronic low voltage, supply 200V or less most of the time.
• Chronic high voltage, supply 250V or more most of the time (yes, it does happen).
• Intermittent low voltage, voltage dips for short or long periods, caused by external influences (other people's loads).
• Intermittent low voltage, voltage dips for short or long periods, caused by internal influences (your loads).

 

An AVR can NOT bridge over switching dips caused by poor HV switch management which can cause your computer to crash, if these are an issue you need a UPS (and possibly an AVR too).

 

Ok so what does an AVR look like?

 

Here we go, the selection at our local Global House, we now know what they cost too.

 

 

 

To be continued.

 

[bankruatsteve]

Just to add that high voltage issues (for me anyway) start at about 235v.  My treadmill would have me running instead of what is supposed to be a walk.  My pumps sound "funny".  My inverter fridge will beep and re-set itself (or whatever it does isn't normal) - that has never knocked it down but can't be a good thing.  Over 240v of xo my TV's and sound system will shut down, etc.  While I haven't had over 250v (that I know of) since installing a LiOA AVS, I'm guessing the output would be around 233v for that situation.

[Crossy]

Our Problem

 

We've been in our home for 5 years or so, our supply is single-phase 15/45 from PEA we are about 160m from the village transformer. Until recently we really had few problems, the supply went up and down somewhat but it was generally stable.

 

One thing we did see quite often was loss of a HV phase, this put our supply down at about 110V for some time, our water pumps and aircon did not like this so I installed an under/over voltage switch, power out of range, disconnect (and as a by product start the generator).

 

This was bearable until the "disco incident". Last week we had family to stay meaning that (unusually) all our bedroom aircons were running. All was fine until I (yes, it was my fault) jumped in the shower, 30 seconds after I turned on the water heater all the lights went out, 1 minute later they came back on, but again after 30 seconds out they went again. I turned off the shower and everything recovered.

 

Wifey, who was watching TV in the lounge reported "thumping" noises coming from the electrical panel. Evidently this was the sound of the over/under contactor doing its thing.

 

Turning off our bedroom aircon allowed me to shower successfully.

 

Investigation

 

In the cold light of day I did some measurements, simply using the water heaters as a variable load and checking the supply voltage (I turned off the over/under unit).

 

This is what I found;-

 

 

Evidently our supply was already low when I decided to take a shower and pushed it over the limit, of course removing the shower load allowed the supply to recover and re-connect, until the shower pulled it down again. Enter the disco-effect.

 

Something needed to be done.

 

Task A was to move the shower load to the input side of the under/over trip, so if we pulled the voltage below the limit at least it stayed there, but this alone isn't the ideal solution.

 

EDIT The slope of the above graphs makes our supply impedance something like 0.5 ohms, this is laughably large (0.1 ohms is much more respectable) our PSC (prospective short-circuit current) is about 500 Amps!

 

More soon.

 

 

 

[Crossy]

Choosing your AVR

 

Having decided that you need an AVR how does one decide what size is needed in your particular situation?

 

Obviously, knowing what you are going to be running from the AVR is a good starting point.

 

What should we NOT run from the AVR?

 

The main thing to avoid putting on your AVR is your water heaters, they will function just fine on a reduced supply voltage (OK they will heat more slowly) and that's a considerable load that you won't need to size the AVR for. If you have an electric oven, this too will work fine without going via the AVR.

 

I would run everything else from the AVR.

 

Of course, much depends upon how your home is wired, we are lucky in that it's relatively easy to move loads to and from the AVR, I designed the wiring that way, others may not be so lucky of course.

 

A worked example

 

Let's say that, like us you have 3 off 12,000 BTU aircons plus assorted other appliances, washer, kettle, microwave and the like. The aircons will use about 16A (say 4kVA) when the compressors are running, let's add the same again for the other appliances, so a total of 8kVA then.

 

Soooo, a 10kVA AVR will do the trick then?

 

Sadly this isn't the case

 

Perusing the units in Global House it rapidly became apparent that the ratings were, shall we say, "enthusiastic".

 

For example, the V.E.G. "SVC-D20000VA" unit, whilst nominally 20kVA has an 80A incoming breaker. With a supply of 220V 80A is about 17.6kVA already rather less than 20kVA, if we consider the worst case situation of an incoming supply of 130V (the minimum where the unit still regulates) 80A gives us 10.4kVA!!!

 

Of course our aircon will be cycling and the 80A breaker will be unlikely to open before 85A but we have to look at worst case here.

 

For our example the 15kVA unit would likely be just fine, we bought the 20kVA! Purely because I'm an engineer and wanted to do some experiments.

 

You can always tell when you are in the home of an engineer. Most of us would be happy with a single distribution board, this is Crossy Mission Control:-

 

 

To be continued.

 

 

[bankruatsteve]

Crossy, how many amps have you ever mustered at a high?  For me, it's only been about 25a when I have the oven and shower going at the same time - well, along with all the normal stuff.

[carlyai]

May I be so bold as to say that today I found another reason why you should oversize your AVR.
I haven't investigated this, but today when I did my monthly ++ diesel genset run, the main bedroom aircon plus a few other things, was up around 10 A. Bit strange as I usually have 2 aircons plus some extras to get the diesel load up to 12 to 14 A.
I am sure the aircon needs cleaning, as when it does it makes a an oscillating shhhh .......shhhh ......shhhh noise.
So I'm guessing that the dirty inverter aircon is drawing maybe 3 or 4 Amps more than a clean one. Just a guess mind you.
So, if you are sizing an AVR you may have to also take into account extra unthoughtof loads.

Sent from my SM-J700F using Tapatalk

[Crossy]

10 hours ago, bankruatsteve said:

Crossy, how many amps have you ever mustered at a high?  For me, it's only been about 25a when I have the oven and shower going at the same time - well, along with all the normal stuff.

I guesstimate that the event which triggered me to get off my arse and install the AVR peaked at about 40A and had pulled the supply down to 180V (20% low).

 

A 15/45 ought to be able to supply that level of oomph without the supply going out of range (-10% = 198V).

 

[longball53098]

14 hours ago, Crossy said:

Choosing your AVR

 

Having decided that you need an AVR how does one decide what size is needed in your particular situation?

 

Obviously, knowing what you are going to be running from the AVR is a good starting point.

 

What should we NOT run from the AVR?

 

The main thing to avoid putting on your AVR is your water heaters, they will function just fine on a reduced supply voltage (OK they will heat more slowly) and that's a considerable load that you won't need to size the AVR for. If you have an electric oven, this too will work fine without going via the AVR.

 

I would run everything else from the AVR.

 

Of course, much depends upon how your home is wired, we are lucky in that it's relatively easy to move loads to and from the AVR, I designed the wiring that way, others may not be so lucky of course.

 

A worked example

 

Let's say that, like us you have 3 off 12,000 BTU aircons plus assorted other appliances, washer, kettle, microwave and the like. The aircons will use about 16A (say 4kVA) when the compressors are running, let's add the same again for the other appliances, so a total of 8kVA then.

 

Soooo, a 10kVA AVR will do the trick then?

 

Sadly this isn't the case

 

Perusing the units in Global House it rapidly became apparent that the ratings were, shall we say, "enthusiastic".

 

For example, the V.E.G. "SVC-D20000VA" unit, whilst nominally 20kVA has an 80A incoming breaker. With a supply of 220V 80A is about 17.6kVA already rather less than 20kVA, if we consider the worst case situation of an incoming supply of 130V (the minimum where the unit still regulates) 80A gives us 10.4kVA!!!

 

Of course our aircon will be cycling and the 80A breaker will be unlikely to open before 85A but we have to look at worst case here.

 

For our example the 15kVA unit would likely be just fine, we bought the 20kVA! Purely because I'm an engineer and wanted to do some experiments.

 

You can always tell when you are in the home of an engineer. Most of us would be happy with a single distribution board, this is Crossy Mission Control:-

 

 

To be continued.

 

 

So just happens I was at a Global in Rayong yesterday looking at the selection of AVRs. The VEG looks better but I am a novice. Crossy, why did you buy the VEG over the Lioa unit? I see both brands have to be wired for the connections. I am considering a smaller unit that has sockets for one or two plugs to feed my PC UPS and such.

I see another made in Thailand brand from http://www.siliconthai.com/.  But I do not know where they have them to see one.

[Crossy]

16 minutes ago, longball53098 said:

So just happens I was at a Global in Rayong yesterday looking at the selection of AVRs. The VEG looks better but I am a novice. Crossy, why did you buy the VEG over the Lioa unit? I see both brands have to be wired for the connections. I am considering a smaller unit that has sockets for one or two plugs to feed my PC UPS and such.

I see another made in Thailand brand from http://www.siliconthai.com/.  But I do not know where they have them to see one.

The V.E.G. unit got my vote (and cash) because:-

• It looks rather less industrial than the LiOA (it needs to live in the corner of our lounge area)
• The connections are inside the unit (the LiOA has exposed terminals on the back)

The V.E.G. also has a slightly wider input range (130V - 260V) but that's not really important to us.

 

There are loads of small units around suitable for powering your PC both with leads and plugs already or needing some DIY wiring. Just make sure you get one with enough oomph.

 

 

[Crossy]

Connect it something like this, use wire sizes appropriate for your main breaker. We have a 63A main breaker so 10mm² is OK.

 

 

Whilst we are on the subject of cable I recommend the use of THW(f) sometimes referred to as VCF or 60227 IEC 06. It has similar ratings to standard THW but is much more flexible so it's far easier to wrestle into those tight spaces.

 

Of course the negative (there's always a negative) is that the big DIY places tend not to carry it. You can get it from SK Universal http://www.sk-wires.com/ their English speaking contact k. Bell answers email promptly. But you can only buy in 100m rolls and 10mm² is 4,500 Baht a roll

 

Alternatively, you can do as I did and run 4 lengths of 2.5mm² instead. Despite what the purists will say this is a perfectly valid solution and you can get 2.5mm²  THW(f) in Global House. As a bonus the 10mm² is rated at 69A in free air whereas 4x2.5mm² adds up to 116A, it needs de-rating somewhat for grouping factor once it's in a conduit but it's certainly not going to be significantly worse.

 

 

 

[Crossy]

Ok some real installation photos.

 

Firstly the incoming supply and under/over unit.

 

 

Now the AVR with the front open.

 

 

And the AVR connections.

 

 

The observant amongst us will notice that there is no output neutral connection, the more observant will notice that the input and output neutrals are actually connected together. Since all are neutrals are commoned in the main board there's no need to run both cables, saves some wire.

 

I ran the cables to the AVR in a length of 50x50mm PVC trunking, plenty of room, the length to the AVR itself is covered in spiral-wrap, cable ties in the trunking and the AVR anchor everything.

 

 

 

[Crossy]

A word about water heaters

 

Yes, I know I said not to connect your water heaters to your AVR, but here is some information that you may not know.

 

A water heater is essentially a resistance which gets hot when current flows. The power dissipated by a resistor according to Mr Ohm (yes he was a person) follows the equation P=V²/R. Resistance, at least at the temperatures we are interested in, is constant.

 

So how does our heater react to low supply voltages?

 

Plotting heater power vs supply voltage gives us this:-

 

 

Note that your heater is down to 50% power by the time the supply is 155V (70% of nominal), so your shower is only half as hot (or, importantly for us Brits, the kettle takes twice as long to boil). Even at 200V which is only 10% down on volts the heater is only providing 80% rated power.

 

Running your water heater via the AVR ensures you have a hot shower, but the supply currents can get frightening, certainly enough to open your incoming breaker (trust me, I tried it). Don't run your water heater via the AVR.

 

Your kettle has a lower power consumption (2kW or so) so you can safely run via the AVR and get your cuppa in the normal time

 

 

 

 

 

 

 

 

[Crossy]

Important Note

Unlike many appliances it is vital that you get the polarity correct for your AVR.

 

Sadly it's not always obvious which connection is which.

 

All of the units I have seen have a direct connection of the neutral input to output, this MUST be your neutral connection.

 

You can verify with your meter or by using your Mk1-eyeball.

 

 

[dinga]

Right = 1st the apology (I'm completely clueless re, matters electricity)

 

Next the problem:  after the installation of an air conditioner and fridge (both brand new), both sh1t 'emselves after 2 days.  Techos say that the problems were due to lightening storms - and presumably a large spike in the voltage down the lines.  The Safe-T-Cut tripped but presumably not fast enough to prevent the frying of the electrics in the two appliances (only the fridge was turned on at the time).  Repair costs = 2,000 baht

 

Is there anything I can do to prevent a re-occurance?  Will an AVR do the trick?  Something else?

[Crossy]

6 hours ago, dinga said:

Is there anything I can do to prevent a re-occurance?  Will an AVR do the trick?  Something else?

AVR probably not, MOVs are your friend, try a forum search.

 

[Crossy]

I'm going to close this to further comments and pin.

 

If you have any questions please start a new thread.