It's right around 246 vac today. It's a beautiful Fall day in NE.. No AC needed.

Of course the new Gree wants 208 to 230vac..:o (see pic)..

The AC to DC part of a M/S unit, is a simple Unregulated DC Power Supply.
A higher AC voltage into a rectifier bridge gives a DC voltage that is dependent on the peak voltage of the AC grid, and power that
(high-current capable) DC voltage delivers to motor loads etc can not be controlled by lowering the DC voltage,(not economically) but only the timing of the pulses.

So, those extra high voltage pulses are going to be hammering the M/S compressor motor..
That means the controller has to be smart enough to shorten the pulse width, when the line voltage is causing extra high DC voltage into the motor controller's switching devices..

Sounds like high speed decisions have to be made, if the voltage suddenly goes up or down (from the norm)..

I'm thinking back to the snowy day when my Den Sanyo main board got zapped..
The grid fail was so short, it was hardly noticed. My PC display went black.
The PC kept on running.. The stove clock displayed 'PF', all the cable boxes on the street re-booted..
But, the den Sanyo noticed.. In a major way..
Perhaps it attempted to compensate for the drop, and stretched the next pulse a Bridge too Far..
Flooding the switching devices and the bootstrap parts, with way too much power.?.(in the form of higher voltage).
I think the defrost cycle was running, and power use was around 2KW? when the PF hit..
I know any surge (4+ KW?) was too short to register on the TED.
At least it died a quick death.. It was only I that lingered, wondering. :(

Much of the " normal size " HVAC equipment is rated 230 VAC . I always figured it was OK for + - 10% voltage variation . Which gives 253 volts to 207 volts .

Now , it is common for utility line voltage to vary with season . In our area , max load is during A/C season . Voltage will drop in the hottest part of the summer , each day , in the afternoon when everyone's A/C is maxed , Mom is home doing laundry & cooking ( electric ranges ) and every one has their electronics turned on .

Gas heat is our most common form of home space heating . So , in the winter , A/C load is at its minimum and electric heat is not creating near as much load as summer A/C .

Much less voltage drop on the electrical system , so line voltage rises .

If you have mild summers and severe winters , with a large amount resistance space heating , the cycle may be reversed ?

Could you use an under / over voltage relay to shut down the HVAC equipment when your power was out of specification ?

Maybe # D65VAKPA2 on page 23 of the pdf ? These can be had , adjustable , with time delays .

God bless
Wyr

Industrial equipment is designed to withstand wide voltage fluctuations because industrial customers won't tolerate anything less. I have a PLC on my desk that is rated at 90-264VAC line input. The 480V VFD's in our production line ran fine between 430-500VAC and shut down outside this range. We fought the power company every spring and fall over high voltage issues but the drives never failed.

Virtually all 3PH induction motors in the 200V class now run 208V or 240V without changing wire taps. The obvious downside is lower efficiency at either end but at least they run.

Residential products don't have this durability because the manufacturer can always blame failures on what insurance companies call "acts of God." They know components are going to fail and are counting on it. I have seen numerous HVAC boards with empty holes where an avalanche suppressor was supposed to go. Leaving this twenty cent part out was a marketing decision. It had nothing to do with production cost.

Finally, I had a line engineer from the power company tell me they run voltages at the upper limits because the region has surplus generating capacity. Higher voltages mean higher electric bills. It is as simple as that.

Doug

"Finally, I had a line engineer from the power company tell me they run voltages at the upper limits because the region has surplus generating capacity. Higher voltages mean higher electric bills. It is as simple as that."..

So, buying the LED lighting for the house, means they power company is going to be trying to destroy them.
(And our expensive Mini-Splits).. One of life's little ironic twists..

I guess there is something to be said for going off-grid..

Fun thing about conservation .

Conserve a little , you are golden . Conserve too much & they start raising prices and other ways of ways of poking us with the sharp end of the stick .

God bless
Wyr

Very literally true! We have a usage cost adjustment that is negative above 900 KWH and positive below 900 KWH. We cut our power consumption this summer by blocking some windows with XPS and are now paying a premium for our efforts.

Doug

Do you pay a minimum charge + a charge for what you use ?

God bless
Wyr

No minimum charge is shown on the bill. It might be hidden in the so-called adjustments.

My latest bill is for 1284 KWH and we are still paying the premium, so there isn't a break point at 900KWH. I now remember the co-op person telling me everyone pays the summer up-charge. He said the premium was to get extra money out of customers that use natural gas for heating in the winter.

I think it would look better if they showed it as a winter discount instead of a summer premium. Those with access to natural gas might disagree.

Doug

All energy providers have done this historically...
 

From the viewpoint of conservation, this statement sways me even more in favor of it. If I am saving 20 percent on my bill, they can do whatever they want to try to raise my bill. It just adds to my return on the dollars invested. It has the effect of me perceiving an even higher bill (at least part of the year) that I would have had to pay, had I not done the conservation measure. Let me explain.

Let's say I had a $100 average bill before installing a heat pump to replace the old energy hog. My power bill immediately lowers to $80 a month on average. The power company notices this change, and starts charging me 3 percent extra during the summer. My usage does not change substantially during the winter, so I don't pay a "natural gas" premium. In my eyes, the power utility just sped up their normal rate increases on me, maybe a year. Yes, I did pay an extra 2 dollars this month, but they would have increased their rates past his point in a year or two anyway. The fact that this increase happened early in the first place, to me, is a sign of weakness on the power utility. They are reacting to the pain of an arm twisting. That alone would have justified the conservation measure in my eyes, and would push me towards more aggressive measures to shave even more dollars from my bill.

Sometimes the spreadsheets and balance sheets don't tell the whole story. Events like this are not all about the bottom line capitalism. There are large scale political movements happening behind what is showing up on our power bills. The tycoons on top of these massive public utilities are paying WAY more attention to those of us who conserve than we are to them. In their positions, they HAVE TO make money every quarter OR ELSE. Their livelihoods and careers depend on it. I for one am not trying to keep them rich and powerful forever.