Convert 240v to 220v to save money?

Hi
I work at a large residential site (imagine a hospital, but that's not quite it), and our maintenance guy has been to a conference where he saw a product which apparently down-converts incoming 240v supply to the site to 220v. On the basis that most equipment these days can operate at 220-240 anyway, we are being told that that is fine to do. They are selling the "device" that does this as a means of saving energy / money.
Can this possibly work?
I'm no engineer, but I'd have thought that for examply boiling a kettle would draw the same amount of power whether it is fed 220 or 240v, its just that the current that would be drawn would be higher in the 220v scenario. Similarly for any device that uses "power" at a specific rate, reducing the voltage would just increase the current draw.
I can see perhaps how normal incadescent light bulbs might not use as much power, but they would simply burn slightly less brightly, wouldn't they?
Does the device and its claims sound credible?
Thanks!
Matt
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Wrong. If the voltage is lower the current will be lower and the power lower. The *energy* consumed to boil the kettle *will* be the same (of course). This means it will take longer to boil (by a factor 240**2/220**2 ) - you will save nothing anywhere where a certain amount of energy is required.

Yes. Whether you would notice in practice is another matter.

Well yes but you would achieve bigger savings by changing lightbulbs to energy saving ones (or lower wattage ones of the same type) and save the money on the device.
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Bob Mannix
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snipped-for-privacy@gmail.com wrote:

Sounds like a complete scam to me.
to boil a kettle you would need the same amount of energy.
Watts is the thing, so a lower voltage would either have a higher current draw for the same power output (same energy usage) or, where current was limited then it would not work as well e.g. your incandescent bulb would glow with less light output.
To save money look at _real_ techniques rather than rip-off gimmicks.
CHeers Pete
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On May 9, 3:25 pm, snipped-for-privacy@gmail.com wrote:

No. A kettle element is just a resistor designed to get hot. At lower voltage, a *lower* current will pass through it. You need the same energy input to boil the water so it will take longer. reduce the voltage too much and it will never boil due to the heat loss being greater than the input.

Something with say a switch mode power supply will take a greater current at the lower voltage to supply a given power output.

Similar mechanism to the kettle example.
So, the only case where you save is by reducing light levels. Try suggesting that to the surgical teams, or equivalent in your not quite a hospital.
Why not go the hole hog and use candles, perhaps made from fat rendered down from victims of the obesity epidemic.
MBQ
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Not for a kettle, its resistive so the power will drop as the voltage drops. It will take longer to boil so someone will spend longer waiting around being paid to do nothing. It will lose more heat to the air over that longer time and so take more energy to boil so waste more money.

Yes, but not many "domestic" devices draw constant power.

Yes, but how many don't use fluorescent tubes?

No, it sounds like it could cost you cash. You would have to analyze things carefully to decide but I would say its snake oil.
If they guarantee to save money in writing and to refund any costs incurred as a result of it failing to do so then go for it.

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snipped-for-privacy@gmail.com wrote on 09/05/2008 :

The kettle would draw less current on the lower voltage, but still use the same Kwh to boil the same amount of water. Same principle applies to water heaters and space heaters.

Incandescent lamps work at best efficiency at their rated voltage. Reduce the voltage and less light is output, plus a greater proportion of the wattage consumed will be turned into heat. Each lamp will consume less, but more lamps will be needed to achieve the same lighting levels.

No!
Snake oil, like so many of these gadgets. Initially with the unit first installed, power will be saved on lamps but nothing else. Soon larger wattage/more lamps will then need to be fitted to compensate for their being so dim and because they will be less efficient, the net result will be higher consumption.
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wrote:

Thanks to all that replied - my gut instinct that this was snake oil seems borne out.
The device was on display at some green energy show (or something similar) - if I get any specific details I'll post back so you can see.
Cheers!
Matt
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snipped-for-privacy@gmail.com wrote:

These tend to be called transformers....

Well sort of...
Lightbulbs will use less power and be noticeably dimmer. If you can cope with that then fine, but if you switch more on or use more powerful bulbs to compensate then no nett saving.
Some other things may well still work ok at reduced perfomance.

What you say would only be true for some inductive loads - e.g. certain types of motor. Any resistive load will simply draw less current.

Yup
In short, no.
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Cheers,

John.

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On Sat, 10 May 2008 00:37:37 +0100, John Rumm wrote:
<snip>

<snip>
Not quite. To raise water from room temp up to boiling requires the input of a certain amount of energy (kW). Some of the energy will be lost. Now, you can use a lot of energy for a short time or less energy for a longer time, but the energy*time (kWh) will be about the same (with more lost as the time becomes longer). So a water heater will draw less current but take longer to reach the same temperature and waste more power in the process.
Reducing voltage to a site from 240 to 220 isn't going to make much difference (remember that the "standard" for the UK is now 230, not 240). You'll get less torque from all induction motors (e.g. fans in particular will take longer to get up to speed). EFLs and many other flourescent light fillings will have the same light output and run a bit cooler. Incandescent lights will be dimmer and change colour (slightly more red/ orange). Electric heaters will be slightly cooler. Electronic stuff in general won't see any difference at all.
There will be some losses in the conversion too! That thing had better be a perfect transformer and be *really* cheap or it could take centuries to repay its cost... IMHO you'ld probably get most gain in office installations (provided that the air conditioning is happy at 220v).
--
Mick (Working in a M$-free zone!)
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wrote:

Just out of interest, I guess there must also be an upper limit to this heat transfer rate (re efficiency)?
Assuming the element was so hot it boiled the water local to the element instantly, would that waste energy as the general heat transfer (convection?) throughout the kettle wouldn't be as good?
Maybe this new 'super kettle' would need a finned element to extend the surface area?
All the best ..
T i m
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They do that.. that's what makes the noise near boiling and is cavitation when the steam bubbles collapse.

I like the Tefal fast cup, nice and hot and on tap.
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mick wrote: <snip>

Any decently sized aircon system will be running on its thermostats (or equivalent) so if the output is reduced it will turn itself on for longer. And use the same energy.
Andy
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mick wrote:

I don't think anyone was suggesting otherwise - I certainly wasn't. There are some appliances - say a vacuum cleaner where it will still work and _may_ use slightly less energy overall if he performance is not unduly affected by the reduced suction.

The standard is 230V (+/- a tolerance) , however the voltage is still 240V (which is within the tolerance).

There is another slightly more problematic issue here - in that some motors will draw more current and hence dissipate more heat in their windings. This could reduce the motor life. In extreme under voltage situations it can cause fairly rapid motor failure. Fridge compressor motors being a common victim. The worst case obviously being when a motor stalls due to reduced startup torque and sits their quietly cooking itself.

It's possible that what the gizmo is actually doing is power factor correction rather than voltage reduction. For customers on commercial supply tariffs based on VA loading rather than straight kWhs consumed, a corrector can result in reduced bills.
--
Cheers,

John.

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snipped-for-privacy@gmail.com wrote:

The trouble with asking these sort of questions here is this is not an electronic engineering group, and you get as much noise as signal. One of the sci.electronics ngs could explain more.
UK nominal voltage is still 240v, but it can also be described as 230v, and now regularly is. Its a complex and political story, but IRL your light bulbs see 240. http://www.wiki.diyfaq.org.uk/index.php?title=Electricity_Basics
Running filament lamps on 220 will make them less energy efficient, not more. If you want better efficiency yet insist on filament lighting, increasing the lighting circuit voltage can achieve that, albeit with issues. http://www.wiki.diyfaq.org.uk/index.php?title=Filament_Lamps
CFL or fluorescent on 220 will simply reduce output a bit. You can achieve the same result by choosing slightly lower total lighting power. It would not affect life expectancy much. Linear fl can be improved in efficiency by overdriving if required.
Voltages can be altered using transformers http://www.wiki.diyfaq.org.uk/index.php?title=Droppers
On a large site you've got lots of appliances, all of which are specced to run on 240v happily. A lot will also run on 220v, but all? Sometimes all will, sometimes not. Many will work but not quite meet specs (eg most motors). Compressors should work but may stall at times, sometimes leading to overheating. Sometimes this causes premature failure (eg fridges).
On any large site, appliances working correctly and within spec matters. To toss that away for the sake of a possible minute saving on some goods is hard to imagine being a good move. Yes it can be done in some cases, but as a site-wide blanket measure, no, its a mess of an idea.
NT
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snipped-for-privacy@care2.com wrote:

In the context of this discussion, that statement is somewhat misleading. It is true in the sense that you will be getting fewer lumens per watt from the bulbs. However they *will* also consume fewer kWh. The reduced efficiency will translate into a lower light output that will be reduced by a greater factor than the power consumption.
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Cheers,

John.

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John Rumm wrote:

I think thats an unrealistic comparison though. Changing from 240 to 220 will have a big impact on light output, around 30%. End users choose their bulb wattages based on desire for a comfortable lighting level, so with reduced voltage will change some of the bulbs to higher wattage ones. The end result is definitely more energy use, not less. IRL you dont reduce energy consumption by choosing lower efficiency lighting.
NT
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Putting numbers to John's post: Reducing 240 to 220 means an incandescent light bulb will consume only 87% of the power, but will only output 74% of the light.
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