AVR and a/c

[zlodnick]

We have low voltage problems. In the morning, we have 225v, but as the day goes on the voltage slowly drops. When I turn on our 9k btu inverter unit the voltage drops a volt or two. When I turn on the 18,000k non-inverter, the voltage drops about 20 volts. After an hour or so, it's down to 180v, so I shut it off.

 

PEA came 4 days in a row, but couldn't fix it. 

 

I've been thinking maybe change the non- inverter for an inverter unit or get a AVR. Crossy said you can get an AVR for just one appliance or the whole house. Everything seems to work ok except for the 18,000k a/c.

 

Global house has plenty of AVRs, but I'm sure the average homeowner, like me, has no idea how to select or install one. The only real electrician in our area has retired. I'm wondering if Global  House can give customers contact information of qualified electricians in the KhonKaen area?

 Any advice will be appreciated.

[Crossy]

Before shelling your hard earned $$$ on an AVR have you verified that it's your incoming supply that's dropping off?

 

Check at your main breaker and at the meter.

 

 A drop of 20V with only a couple of kW load suggests there's something pretty seriously wrong here.

 

Are you a long way from the village transformer?

 

Unfortunately, many local PEA offices have the attitude "you have electric, so no problem".

 

If you do decide on an AVR I'd suggest something around the 3kVA mark to supply just your 18k A/C.

[zlodnick]

Thanks crossy neighbors have same problem  250 meters to transformer

[JBChiangRai]

You're going to have other problems in the future, especially if people build near you and draw power.

 

I would personally go for a whole house AVR.  We have bought the LioA AV's from Global House, lots of the 10KVA, one 15KVA and one 20KVA for houses we built on this estate. Excellent quality, never had a problem.

 

I did once buy a different make from Global House because I liked the digital display, complete rubbish, we had to replace it.

 

 

[Crossy]

It

9 minutes ago, zlodnick said:

Thanks crossy neighbors have same problem  250 meters to transformer

 

 

If you've not already I would get all of the families with the same issue together hand head en-mass down to your local PEA office and ask to see the boss.

 

You may wish to take a bottle of a suitable "lubricant" for the supervisor

 

[JBChiangRai]

4 minutes ago, Crossy said:

It

 

 

If you've not already I would get all of the families with the same issue together hand head en-mass down to your local PEA office and ask to see the boss.

 

You may wish to take a bottle of a suitable "lubricant" for the supervisor

 

 

Funny you should say that.  This was our experience.

 

There are about 70 A/C units in this moo baan.  We built all the houses here.  We had a single phase supply and about 250m to a small transformer rated at 100 amps per phase.

 

In April 2022 we had the fuse at the transformer blow.  PEA came and replaced it.  10 minutes later it blew again, this repeated 4 or 5 times so they came to our moo baan and measured the current draw at each meter.  All the meters are outside the moo baan as all cables inside are copper and underground.  My house was drawing the most at 56 amps.  They came to my house and asked me to use less power, I refused.

 

We went to visit PEA, 3 houses were represented, and ultimately they agreed to bring 3 phase down to the moo baan and moved the houses across all 3 phases.  They also promised to upgrade the transformer, they never did that.

 

We still have low voltages but right from the get-go I fitted AVR's in all the houses as part of the build project and they cope admirably.

[zlodnick]

Thanks for the replies,

 

I just talked to a neighbor. He has 3 non-inverter 9k units and said he had no problem. He said the power dips around 6-7 pm. They slow down for a couple hours then get back to normal speed. Another neighbor is the same way. They just turn it on and forget about it. 

 

 Our 9k unit runs fine . The 18k unit runs great but I get nervous when it gets down below 180v. Maybe I should just take the neighbors  "mai ben rai" attatude and not worry about it.  How low does the voltage have to get and for how long before there is a problem?

 

 Anyway, I'm going to Global House tomorrow. I think buying an AVR is the easy part. Finding some one to install it could be a problem.

[bluejets]

On 4/23/2024 at 10:56 AM, zlodnick said:

Thanks crossy neighbors have same problem  250 meters to transformer

If it's fed via similar size cabling as all other domestics in Thailand, that'll do it.

AVR won't fix a voltage drop problem.

[sometimewoodworker]

12 hours ago, bluejets said:

AVR won't fix a voltage drop problem.

That is precisely one of the fundamental functions of an AVR/AVS, it regulates over and under voltage to maintain the optimum (220v, other voltages are available, ) output. There are certainly some extremes that it can’t fix but then usually  has a Hi/Low voltage cut contactor for the extremes, if not they are simple enough to fit.

[bluejets]

8 hours ago, sometimewoodworker said:

That is precisely one of the fundamental functions of an AVR/AVS, it regulates over and under voltage to maintain the optimum (220v, other voltages are available, ) output. There are certainly some extremes that it can’t fix but then usually  has a Hi/Low voltage cut contactor for the extremes, if not they are simple enough to fit.

The problem is the complete picture as is often missed by inexperienced posters.

Power requirements made up of voltage and current, among other things on AC.

If the cable creates a voltage drop, no end of voltage correction will enable more current to flow over a given cable size, pure physics.

The fix is blatantly obvious, install a mains cabling system with maximum demand calculations that allow a maximum voltage drop of the standard allowable of 5%.

..........or shift the house closer to the main supply .....🤣

[JBChiangRai]

18 minutes ago, bluejets said:

The problem is the complete picture as is often missed by inexperienced posters.

Power requirements made up of voltage and current, among other things on AC.

If the cable creates a voltage drop, no end of voltage correction will enable more current to flow over a given cable size, pure physics.

The fix is blatantly obvious, install a mains cabling system with maximum demand calculations that allow a maximum voltage drop of the standard allowable of 5%.

..........or shift the house closer to the main supply .....🤣

 

Typically, the AVR will correct the voltage drop and draw more current across the wires to the house.  There is a point at which it can no longer correct the voltage, on my LiOA unit it's 150v.  Drawing more current across the wires to the house also decreases the voltage.  The wires from the meter are almost always big enough.

 

Generally, the whole process is transparent and since the PEA meter measures power used (Voltage x Current) it makes little difference if your cable from the meter is big enough.

 

Having an AVR is detrimental to your neighbours when the voltage drops because you continue drawing full power.

 

A lot of electronics with switching power supplies (computers, inverter A/C and refrigerators) also act as an AVR and they draw more current when the voltage drops to compensate.  If the voltage drops too much then they usually blow a fuse or blow up.

[sometimewoodworker]

1 hour ago, bluejets said:

The problem is the complete picture as is often missed by inexperienced posters.

The assumption of an inexperienced poster can often be made when not every scenario has been explained in the detail and manor that someone who has seemingly only ever been exposed to a subset of situations is expecting.

 

From experience as well as the knowledge of the basic physics that @JBChiangRai has well explained, the cure suggested of larger cabling could be a part of the problem that @zlodnick is experiencing, this is unlikely to be the fix as the PEA has visited on 4 consecutive days, and while there is a significant lack of belief by some in the competence of the training required to become an electrician for the PEA this is a canard, the PEA has excellent well trained employees, though I don’t know if they also have muppets, it is less likely that all of local staff are incompetent.

 

The statement that the the only other “fix” than larger supply from the meter to the house, would be to move the house closer to the supply is a possible answer but again is fanciful, impractical, likely impossible and does not guarantee a cure.

 

There are other, more likely, correct answers that have not been thought of but @zlodnick will have difficulty getting implemented.

• The first, least likely answer, is that the PEA were incompetent in their calculations and the mains cables are too small.
• The situation is much more probably that when the current low voltage transformer (low voltage, in that it is suppling 220v) was installed the PEA load calculations assumed the usual load demand for Thai houses. Over time the households gained wealth and now are making a significantly larger demand. Also likely foreigners have built or upgraded houses.
• This means that in the daytime when many are out of the houses the PEA calculated load is not exceeded, but come evening when the microwaves, IR cookers, TVs, hot showers and AC units are all getting used there is insufficient PEA power or the installed transformer was undersized so isn’t able to cope with demand.

 

If the second scenario is correct the only people who can fix the problem are the PEA who likely don’t have the budget (though reducing tea consumption could help).

• One of the fixes the PEA  may be able to do is to change the transformer tap. Commonly there are 3 available on the transformers this may be an answer unless the transformer is maxed out already.
• Another fix that is possible is to change which phase the transformer is on, this is dependent on the location of the 3 phase supply (usually at 22k)
• A third fix, though the most expensive, and dependant on the PEA load availability, is installing, at the customer’s expense a new transformer (this then becomes PEA property and can have other users added without consent from the person paying for it.

All in all an AVR is a relatively cheap answer to test and while it will increase the load on the current section of the network it maybe enough for @zlodnick. It may also make the voltage drops for other users annoying enough that they will put more pressure on the PEA and persuade them that your section is higher on the list for upgrading.

[zlodnick]

Went to PEA today and right to the boss man. He was very friendly and knew all about our situation.

 

He said they are going to install 3 phase on our road. Didn't ask when, but I hope soon. 

 

Right now it's 42c and we're relying on our 9k btu  Mitsu inverter in the bedroom. The 18k non-inverter in the living room can't handle the low voltage. I turn it on at 210v and it will run for an hour then at 180v it starts blowing warm air. Would an 18k inverter do any better?  Just a thought.

[brianthainess]

Wow thanks all, now I know why my A/C feels crap in the day, but feels a lot colder at night, I always thought it was the ambient temperature, now maybe it is my voltage that's the problem.

[Crossy]

1 hour ago, zlodnick said:

Would an 18k inverter do any better?  Just a thought.

 

Inverter units are much more tolerant of low supply voltage, but they behave as constant-power loads, lower voltage means they pull more amps => even lower voltage ... Exactly the same real issues as using an AVR.

 

I'd hang on until PEA come up with a solution unless you can get a suitable AVR (about 3kVA) to just run your larger A/C for a sensible price to bridge you over the hot period.