Thanks for the posts, chaps.
I've already got a small inverter (300w) for 12v to 230v and a stepdown chassis transformer to 24v, which I will hook up and test out tomorrow, so thanks to BrokenYugo for that observation.
I was hoping to construct something smaller and dedicated to this specific purpose, so I am still interested in Zero999's circuit diagram. I'd not heard of an H-bridge, so bear with me... As I understand it, it can switch the output polarity from a dc input, and I assume this can be fast, e.g. 50x per sec.
A couple of questions, please:
The input voltage is at V1 (?), but I can't see where the output is*.
Also, I'm not familiar with the downward pointing triangle symbols are, as shown connected to the emitters of the npn transistors (*is that the output?) and the V1 input. I'm supposing it can't be common, earth or chassis? What is it, please?
Thanks for the tips!
Much appreciated.