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Coping with wide mains voltage variations

In the same issue as your helpful auto-transformer voltage bucking project (Mains Moderator, SILICON CHIP, March 2011) you comment on a related letter on page 104 by suggesting that while ferro-resonant AC voltage regulators are best, you are unsure whether they are still available.

Where the mains voltage is fairly constant but is the wrong value, your auto-transformer project naturally is the best economic solution and provided its ratings are not exceeded nothing will be more reliable. However, for someone with very variable voltage, say a household a few miles down the long country line you instance, a better solution than a ferro-resonant transformer might be an on-line or no-break “sinewave” UPS.

From time to time they can be bought secondhand on eBay for relatively modest sums, even up to a kVA or two. They are quiet, fairly efficient and apart from the gel cells, tend to be quite reliable. However, as long as no hold-up is demanded of them, no or only a very modest battery will be needed.

Nevertheless you will be pleased to know the ferro-resonant regulators are indeed still manufactured. In addition to Asian sources, the firm that was perhaps the most well-known of the traditional suppliers, Sola of the USA, lists models which are more or less unchanged from 20 years ago, right down to the catalog numbers.

You are right that they are pretty expensive new. They are also unavoidably noisy due to the high degree of saturation in the core and for the same reason are pretty lossy and run hot; full load efficiency would not exceed 85% and no load losses are around 8-10% of nameplate rating, which is a significant factor these days if they are run for extended periods.

Ratings tended be quite modest. For example whereas units of say 100-500VA were plentiful, a 1kVA unit was large, heavy and in my experience not too common.

At our home on a rural NZ road fed by the proverbial “piece of wet string”, the nominal 230V mains is set high at around 245V on light load and regularly varies between about 210V and 250V. On occasion it gets as low as 190V. I successfully deploy both small vintage “ferros” and a Variac servo regulator to supply my vintage test gear and receivers. We just accept the short household lamp (globe) life though.

John Reid,
Tauranga, NZ.

Film-to-DVD conversion tricks

I’m sorry that the article on transferring movies to DVD (April 2011) was not around five years ago when I needed it. I struggled with all sorts of electronic magic for timing but I suggest that your readers use DVD Infinity at North Sydney for easy and excellent results on mini-cassettes or DVDs.

But this is the only the start of the problems. Older film has a nasty way of twisting, distorting and shrinking. If you look along it, it appears curved crosswise. This means that as it crosses “the gate” in the projector, the centre is out of focus with the edges or vice-versa.

I suggest your readers contact “The Redcliffe Picture Palace” in Queensland for advice on their “Liquid Film Plasticiser”. This treatment may take 12 or more weeks but with it you will be able to get consistent focus. Then I suggest you send it off to DVD Infinity and you will be thrilled with the results. I got great results from a 1948 standard 8mm film that had been badly warped.

Robert Armstrong,
Toronto, NSW.

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