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A follow-up to What are the ratings of vintage Selenium Rectifier B20/16-2,4?

The photograph linked shows, in the red-box, a spiral wire on the transformer bodyspiral wire on the transformer body. What is the purpose of this?

p.s. I vaguely recall a similar (pardon my language!) contraption on top of a sub-station transformer - think it may have been at a Railway yard.

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  • \$\begingroup\$ I think I fail to see the transformer .. can you zoom out a bit? \$\endgroup\$
    – jippie
    Commented Feb 9, 2014 at 19:23
  • \$\begingroup\$ This is the top of the transformer. I'll get another photo, and post it. \$\endgroup\$
    – Everyone
    Commented Feb 10, 2014 at 3:49

3 Answers 3

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It's probably a hand-wound inrush/current limiting resistor.

Basically, it's a big, low-resistance power resistor used to limit the inrush current when the device is plugged in.

Since this is part of a battery charger, and not a device with significant internal capacitors, it's probably more to protect the rectifier in the case of an output short then limit inrush current.

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It could be a home-made power resistor (made from something like Nichrome).

enter image description here

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It shows like an "equipotential connection" for earth (PE). May there is some similar connection in the chassis or case.

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