how to reduce the mains voltage

How about a variac to lower the voltage. (kinda spendy... might be better to invest in new AC unit.)

George H.

That would be ideal, but at a cost of ~$140 versus a transformer costing ~$35.

I agree about the cost advantage of the variac/transformer. I was about suggest a variac too but refreshed my newsreader before hitting the Send button and saw that George had beaten me to it.

This reminds me of the time some 35 years ago when the power supply in a friend's TV kept breaking down. It turned out that the mains voltage in their house was persistently high. I improvised a step-down autotransformer with a 12-0-12V 1A transformer and fitted that inside the TV. It never broke down again.

Where I live we get 250 volts pretty steadily. In my shop are several CNC machines, one of which cannot easily tolerate the 250 volts. So I use two buck/boost xmfrs wired in a particular buck configuration to lower the 3 phase voltage going to that one machine. Since doing so the machine has not once alarmede out due to over voltage. I also wired up a little 120 to 12 volt xmfr in buck configuration to lower the 125 volts from the outlet to the 110 volts needed for a tube amp. There are directions online on how to select the proper sized xmfr for the load it will be seeing and how to wire the thing in buck configuration. Eric

Your bill went up because of light bulbs and shit with heating elements, maybe the microwave if you use it alot, and of course if you have an electric stove.

Those types of motors usually run more efficiently on slightly higher voltage. Voltage up, current is the same or lower. Well power actually, it might be the same current but the phase changes the power factor. You pay by the watt, not the amp.

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It doesn't make much sense to me; ask, instead, the power company to adjust the line voltage to an acceptable value. The taps in their transmission line drops are the solution to many such problems, if they know that you have found an excessive voltage. I'm not sure

I think you are mistaken.

Some years ago I put a voltage stabilizer on a large fan. (adjustable AC voltage regulator intended to be used for large motors) As I adjusted the voltage lower the current dropped linearly until it reached about 95 VAC then started rising exponentially as I dropped it lower.

Torque of the motor may be dependent on voltage, but the torque required for a refrigeration compressor varies with time. Starting up with the system equilibrated, there's little back-pressure on the compressor so it is lightly loaded, as back pressure builds the torque necessary to maintain synchronous speed increases.

The only other change in my habits, I shower more with hot weather - but use less hot water showering...

I still use 4 compact fluorescent bulbs in closets where they stay off, every thing else is LED. I use the electric range less - in summer.

I get a monthly report card from my power company with a graph of the last 13 months. I normally track well below the average and below their idea of what an energy efficient home should use. Last month I was up to "average." I believe it too. Years ago I mistakenly opened my neighbors power bill (without looking at the addressee) and found he was paying $120 when I was paying $30.

But if you have a momentary power dropout, it has to restart into the full back-pressure of the evaporator. If the A/C isn't a tiny one, I sure wouldn't be mickey-mousing anything that would increase the mains impedance.

Electrical codes contain a lot of non-obvious and very expensive wisdom.

Cheers

Phil Hobbs

My central AC won't restart immediately after a dropout. It has a delay time to allow the pressure to drop.

Bill

That's certainly comforting, but isn't universal, at least in smaller units. The thing I'd be worried about is a short-that-isnt-a-short--as in a shorted rectifier in an old-time transformer/rectifier/filter supply. The current isn't enough to blow the mains breaker but is quite sufficient to make the transformer catch fire.

I lost a very nice Krohn-Hite dual channel filter that way--a 'computer grade' capacitor's clamp had gotten loose over the years, and it slipped down and shorted out to the box, resulting in clouds of transformer smoke. It was a good thing that I was in the lab at the time. Didn't even blow the fuse in the unit. (A bit of fish paper would have been a nice touch.)

When nobody's around, we keep everything turned off at the power bar to prevent that sort of thing--industrial-type Tripplites, natch.

Cheers

Phil Hobbs

You are correct - This controller has a built in time delay and won't allow me to turn the compressor on and off at will. Commercial (large) AC's monitor the back pressure before allowing the compressors to run, and even cheap consumer products like refrigerators have an "overload relay" that over heats (because the compressor motor is stalled and eating a lot of amps) then the bi-metallic relay cools off and eventually gives it another go.

I have a wall-switch that disconnects the mains from the AC outlet. I don't trust leaving it on and unattended when I'm away.

I am curious about how they do the time delay though.... If the AC power has been off for a time (several minutes) and I apply power the compressor will run right away. Yet if I switch the mains off and on quickly it goes into it's time delay.

I figure that they must be looking at the charge on a cap that gradually bleeds off when power is removed - and prevents a re-start and goes into it's timing cycle instead. Easy to implement with a micro controller chip...

I called my power company to complain about the high voltage and they said it was within spec. The voltage at my place is 250 minimum with occasional spikes to 260. The spikes are transient but long enough in duration to be read with a digital voltmeter. And long enough for the CNC lathe's spindle drive to alarm out. Eric

It is within spec at 250. (if only just)

Remember when it was 110/220 volts nominal? I suspect as time goes on it will creep up. Most recent equipment is sophisticated enough to adapt. I'm impressed by how consistent it is since their upgrade. There are three houses that share one transformer, and the lowest I've seen it is 247 and highest is 252, but most days it is spot-on 250.

My house and the others on this tranny are at the end of the HT line for this street.

i Would sayt you need to get them back out there and move a Tap on the service transformer..

The voltage is too high..

Eric could you please give me directions to on-line info? I'm looking at dropping the voltage to a transformer so that I get lower secondaries out of it inexpensively. Single phase. My Google Fu isn't very strong on this one. I remember Big Clive doing similar in one of his videos a while back but have been unable to find that again.

Cheers,

Search for buck/boost transformer. Here's a link:

See:

Explains "the proper way" to wire a buck boost. Both of the methods shown work, one is just slightly more efficient.

My AC uses 7-8 amps so my 24 VCT transformer is rated at 10 amps or