As I think I've reported before, I came across one potentially-lethal exception to that back in the 60s - a TV with model number "TV1" (I forget the make), in a floor-standing mahogany cabinet, which had a mains-driven EHT supply for the CRT (rather than the usual voltage tripler fed from the line output transformer, which has very low current-supplying ability).
You could only directly calculate the required number of turns for the secondary if you knew the number of turns in the original secondary (and the voltage the transformer was designed to produce - which may well be marked on it) - if, for example, the present secondary had 1000 turns to produce a 2000V output, you would need about 12 turns to get a 24V output. However, since you would almost certainly have to totally destroy the present secondary to get it out, you're unlikely to be able to count the turns (even if you were very patient!).
With the small number of turns you're likely to need, it should not be a problem - I would think the main problem would be in removing the present secondary without damaging anything else (like the primary!) - some of the on-line descriptions talk about using an angle grinder to remove the secondary!! If you Google "rewind microwave transformer" (without the quotes) you will find lots of stories, and some videos, of people who have done more-or-less what you want to do, often to create transformers for welders
That could be an issue, but the on-line articles and photos/videos seem to suggest that it's usually possible. The material BAS linked to suggests that there are only about 4 different manufacturers of such trannys in the world, so they are probably all very similar.
You're welcome.
You would need to dump the existing high voltage rectifier and capacitor and replace them with some suitable high current low-voltage rectifier (probably a bridge rectifier) and a high value (lower voltage!) capacitor. As for regulation etc., that depends upon what you want - battery charger regulators can be quite sophisticated these days, but might be almost non-existent - those interesting in welding etc. obviously don't have much interest in regulation!! A 24V RMS output from the transformer would theoretically give you something approach 34V 'raw DC', off load, from the rectifier/capacitor to feed to a regulator. How much voltage you needed would depend entirely on the regulation arrangements. If you were going to have little regulation, you'd probably want a lot less than 24V coming from the tranny. You would need a fair bit of knowledge to design an appropriate regulator
Indeed - as I said, everything depends upon what sort of regulation etc. he requires. I suspect, however, that he is talking about "plain old lead acid", since he would probably have to be too rich to be even thinking about re-winding transformers if we were talking about any of the other types of battery that needed 40A charging current!
Indeed - as I wrote ....
Kind Regards, John
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