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Author Topic: step down transformer for mains ?  (Read 5315 times)
ads_b
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« on: December 26, 2010, 11:34:14 PM »

I recently saw a tv program where they fitted what I believe to be a step down transformer on the mains power supply.
this box dropped power from the supplied consumer voltage down to 220v which meant a % saving.
Has anyone any information about this as it really appeared good sence.  Has anybody seen these devices and is there any advice ?
Thanks in advance.
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docka
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« Reply #1 on: December 26, 2010, 11:58:30 PM »

Vphase make one, i assume it's a voltage regulator ie capicitors and inductors etc, about 225. Seem to make good sense to me too.
(No connection to manufacturer!)
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Stuart
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« Reply #2 on: December 27, 2010, 12:59:06 AM »

the conversion isn't 100% efficient so you may not get any benefit
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tony.
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« Reply #3 on: December 27, 2010, 08:20:38 AM »

Dont waste your money.

For exqmple  the voltage may be reduced, so a heater consumes less power, but it will take longer for that heater to heat a specific room, so will now have to be on for longer.

Best just to turn your stats on heaters down

Ps i think it only works up to 20 amps so your fuseboard will ned to be re jigged

Tony
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HalcyonRichard
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« Reply #4 on: December 27, 2010, 09:15:34 AM »

Hi,
    Reducing the mains voltage has a very limited scope for energy saving. Modern TV's,fridges,computers use switch mode power supplies. These will take the power required to run a device. If you lower the voltage they will take more current to compensate. Thus taking the same power. Older equipment used linear power supplies and in certain circumstances these may benefit from this device. Replacing older equipment with newer more efficient kit is likely to be cheaper and save more energy/money. If you have 200+ to spend look at the kit you use already. My new energy efficient T.V. cost 300. It will save this in energy consumption in 5 years. After that it's money in the bank and energy consumption way down.

Regards Richard
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« Reply #5 on: December 27, 2010, 09:21:43 AM »

These things surface every once in a while, and are generally viewed as being firmly in the "sounds good, but don't actually work" category for the reasons delineated above - save your money AND the earth's resources that are wasted on such things! Wink
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aloha
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« Reply #6 on: December 27, 2010, 02:34:45 PM »

These will take the power required to run a device. If you lower the voltage they will take more current to compensate. Thus taking the same power.

At the device.  Of course, the increased current in the wiring to the device will result in greater I^2 x R losses (as heat), so you are back to square one again, if not square -3

For least power loss, voltage generally wants to be high, not low.  As correctly stated above, higher voltage into a linear load, will result in greater power consumption, but the work will be done quicker.  If you were using an immersion heater, irrespective of the voltage / current, the heater itself will consume exactly the same energy to raise the water from the starting temperature to the end temperature.  With a higher voltage, it will do it quicker though, and lose less energy in the wiring from the meter to the heater.

Why then, would anyone want to make their immersion heater slower, and their wiring less efficient, by spending money on a transformer that also introduces inefficiencies?  Wink
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docka
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« Reply #7 on: December 27, 2010, 03:02:42 PM »

Indeed, very good points. But depending on your local voltage (ie it could be as much as 249v rurally) and what appliances you may have could it not still save energy? For motors optimised for 220 volts say or would they contain regulators within them? Plus if you have PV feeding a grid tied inverter would it incur less lossage?
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aloha
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« Reply #8 on: December 27, 2010, 04:16:33 PM »

Its unlikely you would ever save any energy.  Energy is a measurable quantity.  You always need a certain amount of energy to do a given amount of work.  Power meanwhile is the rate of doing work.

Negating losses, a motor of 1 kW power output, working for 1 hour, will convert 1 kWh of energy.  Meanwhile, a motor with 2 kW output working for 30 minutes will also convert 1 kWh of energy. 

So if your increased voltage results in increased power, but does so for less time, then at the device (motor say), the amount of energy converted has not changed.  But, between the meter and the device, the current has decreased (because the voltage has increased), so there is less thermal losses in the wiring.

Energy is only saved by reducing voltage (and thus generally power) if time stays constant.  If time increases to compensate for lower power, then energy remains the same.  As utility meters measure energy, not power, if energy stays the same, then cost stays the same.

Regards the PV inverter, if voltage is higher, then efficiency will generally be higher, as currents will be lower.  Most inefficiency is a result of heat dissipation.  Heat loss in an electrical circuit is generally a function of current squared x impedance.  A little bit more current therefore produces a lot more loss.
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docka
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« Reply #9 on: December 27, 2010, 04:42:25 PM »

That makes perfect sense, thanks for putting me right, I'm new to the science of electricity!
Cheers.
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ads_b
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« Reply #10 on: December 28, 2010, 04:29:17 PM »

Thank you to all who have cleared this one up - your answers make total sence and appreciate the information.
Sounds like this box is somthing to stay well away from  ! 
Many thanks again.
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SnaxMuppet
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« Reply #11 on: December 28, 2010, 04:40:24 PM »

We investigated VPhase. We decided not to get it. The benefits are not for all circuits in the house and theose benefits are very limited. It required a reconfiguration of our consumer unit and for us that would also mean a new CU. All in all we couldn't see that the benefit was worth the expense.

We decided just to make sure we replace older equipment to reduce the amount we waste of what we use.
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