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Topic: Voltage optimisation? (Read 1 time)previous topic - next topic

cowjam

Nov 08, 2010, 07:10 pmLast Edit: Nov 08, 2010, 07:12 pm by cowjam Reason: 1
Hello,
Today I happened across voltage optimisation for buildings.

British mains voltage used to be 250v.  It is now standardised across europe to 220v =/- 10%.  I think the British mains now runs at about 240v.

"Voltage optimisation" is where you put a box on your mains circuit to drop the voltage to a steady 220v.  It's meant to save you vast amounts of money.

Is this a load of crap or sound science?

Edit: particularly when it comes to PCs and devices with transformers.

Groove

#1
Nov 08, 2010, 07:29 pm
Why would a lower voltage save money?
Power is the same, slightly higher current requires heavier wiring.
I think to domestic appliances shoukd run at at least 1kV, which would save huge amounts of copper.  ;-)

Senso

#2
Nov 08, 2010, 07:56 pm
Dropping voltage equals wasting energy, so it would be some sort of transformer or in the worst case resistors, so it will increase your energy consumption and no reduce it.

cowjam

#3
Nov 08, 2010, 08:01 pm
Thanks Grove, that's what I was thinking.

retrolefty

#4
Nov 08, 2010, 08:31 pm
Quote
Why would a lower voltage save money?
Power is the same, slightly higher current requires heavier wiring.

Well of course dropping your mains input voltage would save you money. You pay by the kilowatt hour consumed. Watts is equal to voltage X current, lower voltage = lower watts. If an appliance draws 1kw at 240volts if will consume 4.166 amps, as a 57.6 ohm load. The same load supplied with 220volts will draw 3.819 amps or 840 watts. That is 16% reduction in power consumed.

Now if the appliance will work as well at 840 watts Vs 1000 watts is another story altogther. Lights would be a little less bright for sure.

Lefty

mowcius

#5
Nov 08, 2010, 08:45 pm
UK mains is 230v, was 240...

Ran Talbott

#6
Nov 08, 2010, 08:53 pm
Quote
Is this a load of crap or sound science?

Yes

There are a few "sound science" cases where lower voltage would eliminate some waste.  But probably not enough to pay for an "optimiser" anytime soon.  And the "optimiser", itself, might turn out to be another energy waster.

But for PCs and other electronics with switching power supplies,  it would make zero difference.

Electronics with linear DC supplies would benefit,  but the question of the efficiency of the "optimiser" remains.

You need to look a little closer at what technology they're using,  and at what independent labs (not ones owned by/associated with the promoters) have to say.

cowjam

#7
Nov 08, 2010, 09:39 pm
Thanks for the correction mowcius.

Thanks also to retrolefty and ran talbott. I've just been playing with some equations.

I think the idea is that since all standard mains connected devices must be capable of operating with an input voltage of as low as 207v then you can safely drop the voltage to 220.

westfw

#8
Nov 09, 2010, 01:39 am
Reminds me of the 130V lightbulbs sometimes sold as "consuming less power" (in the US, with 110V mains.)

Sure, they consume less power.  But you don't get the rated wattage of light output either.  In fact, you probably move the bulb into the range where you get fewer lumens per watt, for overall less efficiency.

You can divide most power-consuming devices into two classes: ones with smart power supplies that consume essentially constant power regardless of input voltage (most electronics), and ones that consume less power with lower voltage but also  produce less output (light bulbs, heaters, motors, etc.)  Most of the latter with still need to do fixed amounts of work, so your heater will need to run longer to keep your house warm when operating at a lower voltage.

Combined with the fact that a voltage-converting device will have its own inefficiencies, I vote: Snake Oil!

retrolefty

#9
Nov 09, 2010, 01:40 am
Quote
I think the idea is that since all standard mains connected devices must be capable of operating with an input voltage of as low as 207v then you can safely drop the voltage to 220.

Safety is important and as you stated probably not an issue in itself. However performance of appliances and other devices might be, it really depends on the device. And it won't always save money. A cloth dryer might be one example. It will still take the same energy to dry a given load, at reduced voltage it will just take more time to dry thus not saving any energy at all. Lights as I said may be less bright and that may or may not be a issue. A vacuum cleaner may not pick up as well and it's never nice to piss off the person that runs the vacuum.

Lefty

cmiyc

#10
Nov 09, 2010, 02:30 am
Quote
Most of the latter with still need to do fixed amounts of work, so your heater will need to run longer to keep your house warm when operating at a lower voltage.

You said exactly what I was thinking, but I couldn't find a succient way to say it.
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