Last nights DIY SOS

[stef]

afternoon chaps,

has anyone seen last night's DIY SOS, the episode with the eco house? They used a mains step down unit
to lower the power consumption (by lowering the supply voltage) to 220 V. This unit seemed to me very light
weight so it can't be a step down transformer so I assume it must be a MOS FET stack which is triggered
by a sine signal. A switch mode PSU would be inappropriate for a mains supply.
Has anyone any experience with such a unit? (efficiency, price, noise, heat)

TA

 

[Adam W]

No the whole point of them is that the supply voltage could be around 250v but the appliances are rated and will work perfectly well on 225v.

Think of halogen downlighters - yes a 12v one will need a higher current between the transformer and the bulb, but simply replacing the 12v bulb for a 230v one won't suddenly mean you need less current, what will happen is the bulb will be dimmer. Likewise using a 12v bulb without a transformer (230v) won't just mean it draws less current, it'll blow the bulb, because it's not designed to work on 230v.

Same with appliances - yes if you reduce the supply voltage to, say, 110v and replace all your appliances for 110v appliances the cables will need to be able to take more current, but keeping all the same appliances and reducing the voltage to the lower range of what they will work on will not.