Does a higher voltage lead to a higher power consumption? - Page 1
Forum section: electronics / beginners

author: Saco
author_rank: Contributor
timestamp: January 30, 2018, 12:23:14 pm
content: Ok, I know this is a seemingly googlable question, but it was a random showerthought that I had and the scenario is a bit convoluted so I didn't know exactly how to phrase it on google.I live in 220V-land but the average voltage on my power outlets is 240-250 (yes, sometimes some things burn and yes, as the word average implies, I often have above 250) which means 10-15% more voltage than supposed.Now, assuming all the devices draw the same current regardless of the voltage applied, I would be paying around 10-15% more on my electricity bill than I should.At first I thought the AC/DC converters which each appliance has to have somewhere would make up for the voltage difference, but then I remembered stuff sometimes burns, which indicates the extra voltage is just being converted into heat.I understand it is virtually impossible to have 220V on every point along the grid especially here, in the middle of nowhere, but is my electricity provider ripping me off by supplying too much voltage? And is there any practical way to mitigate this effect?My monthly electricity bill is on the ~200€ range (~1kWh) so 10-15% really adds up at the end of the year.

author: DougSpindler
author_rank: Super Contributor
timestamp: January 30, 2018, 12:59:25 pm
content: Quote from: Saco on January 30, 2018, 12:23:14 pmGreat question. It's Physics time. You are asking about work which is measured in Joules or Watts. I live in the state where we are 120v but some appliances can operate at 120 or 220v. Following your logic a motor which would run at 120 or 220 v would cost a lot more to operate at 220 volts than 120. Not quite.Remember that guy Watt? And P=I*E. The amount of work say a pump is doing for you is the same at 220V or 250v. (Right?) It's a constant. This means as V increases, I decreases. My 120/220 motor says current at 120 volts is twice that of 220 v. So now your power company is not ripping you off. You are getting what you are using.Now in reality the motors run slightly more efficient at 220 volts that 120. Why? At 120 volts twice the current is needed. Increase current = more heat which is caused by the resistance in the wire. So actually you power company would be saving you ab insignificantly small amount of money by raising your supply voltage to 250. If only it wasn't causing more heat and reducing the life of your appliances..

author: wraper
author_rank: Unknown
timestamp: January 30, 2018, 01:23:52 pm
content: For devices with SMPS, power consumption will be around the same as they drop current with voltage increase. Electric kettle or water heater will consume more power but in the end consume around the same amount of energy as it will heat up and switch off faster. If the device does not have SMPS, it depends on type of device and how it operates.QuoteThis assumption is as far as it gets from what happens in reality. I device has SMPS, current drops with voltage increase. If it does not regulate current in any way like heater or electric motor current increases with voltage rise. Don't forget that I = U/R.

author: Zero999
author_rank: Super Contributor
timestamp: January 30, 2018, 01:31:49 pm
content: For purely resistive loads, the power dissipation increases to the square of voltage, so for the same resistance, 240V will dissipate 2402/1202more power, than it would on 120V.To transmit the same power, through the same cable, the resistive losses are cut by a quarter, every time the voltage is doubled. This means higher voltages are more efficient for electricity distribution.As mentioned above, switched mode power supplies uselessmorecurrent, as the voltage is reduced, but the efficiency may drop, as the losses increase, due to the higher current draw, resulting in increased I2R losses.

author: wraper
author_rank: Unknown
timestamp: January 30, 2018, 01:41:57 pm
content: Quote from: Hero999 on January 30, 2018, 01:31:49 pmFor devices with PFC, like any modern computer PSU, usually efficiency slightly increases with voltage increase.

author: Zero999
author_rank: Super Contributor
timestamp: January 30, 2018, 01:45:21 pm
content: Quote from: wraper on January 30, 2018, 01:41:57 pmYes, I meant to say that SMPSes use more current, as the voltage is reduced, not less. Post edited.

author: paulca
author_rank: Super Contributor
timestamp: January 30, 2018, 01:55:36 pm
content: For devices that draw a fixed amount of power it will draw lower amps at high voltage: Electronics, switch mode PSUs, TVs, etc.For devices that will draw a varied amount of power depending on voltage they will draw more power at higher voltage. Example: motors, light bulbs, heaters.In reference to the OP's cost concerns it will be the high power devices such as heating, lighting and washing machines etc, which will potentially draw more power at higher voltage. Although they will also do more work. More light, more heat, more speed... less lifetime.

author: Saco
author_rank: Contributor
timestamp: January 30, 2018, 02:12:34 pm
content: Quote from: DougSpindler on January 30, 2018, 12:59:25 pmPresent me: I know you guys answered in the meanwhile but I already had this all written up so I will leave it anyway so you can correct my train of thought if it is flawed.Past me: Speaking of the Watt guy, what about the Ohm guy?If P = VV/R and the R is always the same since the circuits don't change, I does not actually decrease. It's P that increases (right?).This is kind of what brought me to my shower thought.In the case of motors they would just spin faster so I'd be paying more but also pumping (or whatever the motor is doing) more.In the case of heating/cooling devices they would heat/cool faster and therefore be more time on cooldown, so it would average off.But what happens to the excess AC voltage on AC/DC adapters?Present me: As almost all of you said, the answer is that the adapters will actually draw variable current.Thanks everyone, it was very informative.EDIT: So all things considered, the only thing I could eventually adapt is lights. I could use lower power lamps, which assuming lighting in every room is perfect, I probably already am.

author: paulca
author_rank: Super Contributor
timestamp: January 30, 2018, 03:03:38 pm
content: If they are AC motors I believe they will turn at a factor of the main frequency and no other speed.

author: tpowell1830
author_rank: Frequent Contributor
timestamp: January 30, 2018, 03:52:34 pm
content: Saco, for devices that are setup for 220 volts, such as inductive motors, they don't run faster at higher voltages. One can't take a 120 volt inductive motor and plug into 220 volts, bad things will happen. The coils in the motor are specifically wound for a voltage/current and can't be interchanged. The speed of inductor motors is dependent on the frequency of the incoming mains, probably 50 hz. in your area. However, every device that has resistive loads are also designed to run at the designated mains voltage for best efficiency. For instance, a tea kettle with a resistive heating element that is designed for 120 volts would draw twice the current if plugged into 240 volts, which is very bad and would cause many problems, including increasing your electric bill. Again, bad things would happen if this was done. But, if you had a tea kettle that was designed to run on 220 volts and you plugged it into 120 volts, the current would be significantly less (almost half) as if you plugged it into 220 volts. This would save on your power biil, but, unfortunately, probably wouldn't boil water.I hope this helps...

author: schmitt trigger
author_rank: Super Contributor
timestamp: January 30, 2018, 04:16:00 pm
content: Quote from: paulca on January 30, 2018, 03:03:38 pmSynchronous motors:absolutely. But they are rare in household/commercial environments, they are mostly found in sizes exceeding hundred horsepower.Induction motors: yes, minus the slip. Most common type of motor.Universal motors:speed varies with voltage and mechanical load. Because they are very compact for the power output, they are used in vacuum cleaners, blowers, blenders.

author: DougSpindler
author_rank: Super Contributor
timestamp: January 30, 2018, 05:55:53 pm
content: We can’t give you a simple yes/no answer can we.So we’ve covered the theory. If you want to measure and see for yourself get a Kill-o-watt meter.

author: Saco
author_rank: Contributor
timestamp: January 30, 2018, 06:25:03 pm
content: Quote from: DougSpindler on January 30, 2018, 05:55:53 pmIn fact I did use a chinese Kill-a-watt type of device and on things like heater, toaster, soldering iron, lamps and other devices that I judged to use constant current and all the readings were about 10-15% off as well.At first I thought it was just device inaccuracy, it being chinese and all. I knew the Voltage readings were more or less ok by comparing with my UPS, but I had no way to verify the Current readings especially at high values because I didn't want to burn my cheap multimeter.It was the sudden realization that both Power and Voltage were off by about the same % that sparked the whole showerthought.Now that we are reaching peak electricity usage time in Portugal and the outlet voltages are much closer to 220V, I did another run and confirmed that indeed, on this kind of devices, the power usage is much closer to the expected value.

author: Brumby
author_rank: Unknown
timestamp: January 31, 2018, 04:10:19 am
content: Quote from: Saco on January 30, 2018, 06:25:03 pmChinese products aren't all bad - well, not these days. A lot of things that aren't "good" will suffer in build quality, safety or durability, but accuracy - not so much.QuoteLooks like you have taken the first step in understanding voltage and power -in a small sample of devices. There are many factors that go into a fuller understanding of a wider range of devices - and a number of them have been touched upon above.There is much to learn.

author: timelessbeing
author_rank: Frequent Contributor
timestamp: January 31, 2018, 05:12:53 am
content: Quote from: DougSpindler on January 30, 2018, 12:59:25 pmA Watt is a unit of Power, not Work.Power=Work / Time1 Watt = 1 Joule per second.

author: DougSpindler
author_rank: Super Contributor
timestamp: January 31, 2018, 06:43:34 pm
content: Quote from: timelessbeing on January 31, 2018, 05:12:53 amNot our universe of Physics. Let me share my reality and compare it with yours.Work and energy are measured in the same unit, the joule (J). When an object is moved by a force, energy is transferred and work is done. But work is not a form of energy - it is one of the ways in which energy can be transferred.The SI unit of work is the joule (J), which is defined as the work expended by a force of one newton through a displacement of one metre.The joule (/?d?u?l/), symbol J, is a derived unit of energy in the International System of Units. It is equal to the energy transferred (or work done) to an object when a force of one newton acts on that object in the direction of its motion through a distance of one metre (1 newton metre or N.Do you now share my reality?

author: DougSpindler
author_rank: Super Contributor
timestamp: January 31, 2018, 06:57:27 pm
content: Quote from: Brumby on January 31, 2018, 04:10:19 amI live in the United States, soo Candians and Mexicans you are Americans too. But not be the US defination. Would I buy American? Cars - Possibly. TV/Electronics/appliacnes - Nope Computers - absolutely not. Tools - Not so much any more. I guess I'm buying American food, nope most of it grown in other counties and shipped here. Heck I don't event think American Cheese is made in America. Healthcare - Only because I have to.This post remined me of this song.

author: timelessbeing
author_rank: Frequent Contributor
timestamp: January 31, 2018, 07:00:46 pm
content: Quote from: timelessbeing on January 31, 2018, 05:12:53 am

author: bson
author_rank: Unknown
timestamp: January 31, 2018, 08:47:12 pm
content: Quote from: DougSpindler on January 31, 2018, 06:57:27 pmNo, by the English meaning of the word which differs from the Spanish.The continent is either North America, South America, or The Americas if you want to sound quaint.When Spanish speakers speak English they use the English meaning. If they think of it in the Spanish meaning they're just not very good English speakers.When English speakers speak Spanish they use the Spanish meaning. They think of it in the English meaning they're just not very good Spanish speakers.

author: Brumby
author_rank: Unknown
timestamp: January 31, 2018, 10:45:50 pm
content: Quote from: DougSpindler on January 31, 2018, 06:43:34 pmNot sure about anyone else - but I don't.My reality acknowledges time.

author: CharlieEcho
author_rank: Regular Contributor
timestamp: January 31, 2018, 10:50:39 pm
content: Joules keep on slippin' into my wattage.I want to zap like a Coulomb on Fe. Zap like a Coulomb, let the field carry me.

author: paulca
author_rank: Super Contributor
timestamp: February 01, 2018, 12:58:47 pm
content: Quote from: DougSpindler on January 31, 2018, 06:43:34 pm... and if you take 1 second to do that work it will require 1 watt of power.What's the problem here?