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I got an idea while thinking about transformers (which I lately do a lot), and It occurred to me that you can sum or subtract the voltages from the primary and the secondary like an autotransformer and get multiple output voltage levels. Furthermore, with this you can get much higher output powers than with a normal transformer, because you're only adding/subtracting a portion of the output voltage. For instance if you've got a 1kW load, the transformer only needs to add/subtract 12Veff to the output at the given current rating of 4.3Aeff. That means that for an output of 1kW, the transformer only needs to be rated at 50-60VA. So, If you use a moderate power 200VA transformer you should be able to drive loads of up to 3.5kW. Different secondary taps will change the maximum load, as the transformation ratio changes!!! Anyway, the idea is that if you use the add/subtract feature of the transformer and add some control networks, you can get a pretty tight mains regulation of ±5%. If you have more than one secondary on a given transformer, you can add up relays to control the voltage for more severe voltage drops/spikes. I haven't done the math, but I bet that you can get at least a 10% regulation from a 30% unregulated mains (that is 160V-300V). In rural areas this is a great problem (at least in Bulgaria), so a handy device like this could be used to regulate the mains voltage. I've done some measurements in my country house, and even though we're the closest house to the village transformer, at winters where the whole village turns up the heating, the voltage drops at times down to 180V (-20%)!! This is just a concept, but if you rewind an old welder transformer, add 3-4 secondary windings with different tap points, and make a complex control network (Arduino based maybe?), you can power your entire rural house with a decent regulation.
Some improvements this devics may need:
- Several switching points for different voltage levels. Will require multiple secondary windings. Added advantage - tighter regulation. Disadvantage - many relays, and a complex control network (if not using Microprocessor control)
- Welder transformer should get your entire house powered up, as they are already working at 3-4kW. Even a transformation ratio of 1:5 would give you more than 15kW of available power.
- Microprocessor based control network. This is too sensitive to be controlled with an analog comparator. Bad shit may happen if the relays don't engage correctly - you may end up with a summed voltage of more than 300V (depending on how many secondary windings you have).
- At the power levels I'm thinking about, the relays need to be quenched. Either zero crossing detection is needed, at which point the relays should be driven, or some other kind of arc quenching. Otherwise the relays will wear out pretty quickly.
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