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  • There were two white parts. The first was the basic wire insulation, and the second was a protective sleeve for the leads where they come out.

    Old time transformers which that resembles, had cloth, or threads wound around the wire. That wire may be like that. It is effective, and absorbs varnish, becming good insulation.

    Yes, varnish insulation is more space efficient. And, real varnishing is done by vacuum; dunk, pull a vacuum, let the air bubble out, then let the pressure back in to force the varnish into all the spaces. For that, the varnish is usually a heat-cured varnish that does not rely on a solvent evaporating. it's more like bakelite.

    It's pretty obvious that neither space, nor efficiency is very important to them. Cheap chargers for low-profit shops. Like cheap wrenches for the same shops. It gets people working, and money moving, which is the basis of an economy.

    You can't really fault it, although the wages are likely to be very low except for the most expert workers.
    CNC machines only go through the motions

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    • Agree'd their just doing the best with what they have,,, but wow what it takes to wrap all that wire in some kinda sheathing, and you know their not "hammering out" their own copper wire at that "factory"

      Just an observation as to why they can't get varnish insulated wire to begin with... nothing to do with dipping it themselves --- just buying it in bulk like everyone else - their already buying the copper that way...

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      • I don't think the wrap their own wire... the orange stuff was regular plastic insulated wire. The coil wire may be varnish insulated and then with a top wrap to make it less easy to damage in handling and winding. "Magnet wire" used to be available like that here in the US.

        The sleeving for protection is pretty normal, even a higher quality feature. What the cores are made of is a question... "Random steel" varies in it's magnetic characteristics. But that is apparently secondary to their main goal of making transformers for their product. And we have no clue what ANY of these factories are using as far as composition of steel. Scrap can be anything from CRS to transformer steel, to some form of tool steel or specialized alloy. It all "looks" the same.

        My suspicion is that they have some clue what they have. The various casting operations seem to select their melt material in various proportions from piles. I'd bet they bought the scrap with a good idea of what it was. Pakistan has some good engineers, and the rest of the population are not 100% rubes.
        CNC machines only go through the motions

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        • I must admit I have not seen cotton covered wire in recent years, not even in some of the junk I get to dismantle. The machine that applies the cotton is probably a hundred years old and of course the cotton may be locally produced and the windings are varnish(?) dunked so not too bad by old time standards.

          They do close the core after all the windings are in place.

          The half wave system seems odd as a diode bridge cannot be that expensive. Likewise, why do some units have three windings?

          The plug leads adjust the output voltage? Why are there two? Is one of those windings used as a choke to reduce current?

          Rusty steel in the core laminations and of course rust is a poor conductor so maybe that will reduce eddy current losses!

          Yea, ancient transformer construction and quite a few shortcuts in the construction but I could be lead to believe the circuit design is actually smarter than it at first appears.

          The cabinets have a nice choice of colours and some appear to be designed to stand straight on a dirt floor!

          All in all, I would like to have a nice hulking battery charger for the range of batteries we have at the aviation museum and I am sure that these ones will not spit the dummy if connect to a 'too flat' battery. I wonder how much they cost but the freight to NZ would be the killer.





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          • I'd bet the two sets of plug connections are to adjust the voltage in finer steps.

            The half wave messes up the transformer, but is as cheap as it gets, using one plug for adjustment. That used to be done back when tubes were used for rectification, and it worked "ok". If they used a two diode full wave, they would need a different adjustment method. A full wave bridge would be extra expense.
            CNC machines only go through the motions

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            • The adjustment steps are (presumably) taps on the transformer secondary and the principle would be exactly the same for half or full wave rectification.

              Considerations of core saturation et al aside the choice of half wave is likely due to some old wives' tale that the 'rough' DC is better for battery charging.

              Ten coarse steps of coarse voltage adjustment plus ten steps of fine would give a total of 100 voltage steps!

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              • Originally posted by The Artful Bodger View Post
                The adjustment steps are (presumably) taps on the transformer secondary and the principle would be exactly the same for half or full wave rectification.

                Considerations of core saturation et al aside the choice of half wave is likely due to some old wives' tale that the 'rough' DC is better for battery charging.

                Ten coarse steps of coarse voltage adjustment plus ten steps of fine would give a total of 100 voltage steps!
                yes, the principle is the same.

                But, if you use two diodes (the minimum for full wave) you need a center tapped winding, and the "steps" become more complicated. If you use a full wave bridge, then the same single plug system works, but you have to use, and mount, connect, etc, 4 diodes.

                The largest package full wave bridges are about 35A Their meter seems to go to 10 A. They are using a large stud mount diode, probably because they want something that will stand the inevitable short circuiting by folks who are not any too clear on dealing with electricity. The "test" does not pop the fuse, although it "pegs" the meter with a bang, so................. presumably it is large enough to not be particularly effective at protecting a rectifier. They just want to have a product that is fairly fool-proof for use out in the sticks; cheap, and not prone to popping fuses often.
                CNC machines only go through the motions

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