1 transistor negative resistance circuit Now working Attention Winfield Hill :-)

There's mil spec gear out there that can run on anything from 5vdc to 240v ac on the same input. It's certainly doable, just a question of resources & efficiency.

If V drop weren't critical I might look at current limiting with thermal shutdown for a cheap & simple option.

NT

Re mains frequency transformer types: A minority have short-proof transformers. Most have a fuse or thermal fuse.

NT

• ALL transformer-based wallwarts that i have seen have ZERO protection; that would raise the cost of manufacture...

Some are "impedance limited" which means they are wound with such thin wire that they can't deliver much current. That *reduces* the cost!

A schottky wouldn't hurt either.

On a sunny day (Wed, 10 Jul 2019 13:08:04 -0800) it happened Robert Baer wrote in :

Watch closely, there may be a thermal fuse mounted under the transformer, or even wound in it.

Maybe I was lucky, I have some transformer based going back to the eighties in use 24/7 to power an antenna pre-amp. And an other to power a MP3 player, and an other to power a camera ?

In any case in relation to using the SCR crowbar as overvoltage protection, a series fuse will not always blow when powered from a wallwart, it should be there though. And in that case you will depend on that thermal protection. And I use fuses with wires, like these:

Sure, by 23 cents?

OK, you got a point, I do not have any recent transformer based wallwarts from China. Are those still made? From China all switchers here, mostly big 12V several amps LED strip supplies, usefull for many things.

OTOH they drop so much in action that they need to be rated for more VA. Hence only done for tiny transformers.

NT

It's common for doorbell transformers that can legally be wired directly to the AC line without fusing. They may use some inductive current limiting too... less core materials is cheaper too!

A lot of domestic electric fans are "impedance protected", i.e. they won't catch fire if the rotor seizes up.

Cheers

Phil Hobbs

(Who has one of those in the kitchen that needs to be overhauled again.)

Usually the cheap bronze bearings gunk up. Often a solvent clean and moly re-lube fixes them for a few years.

Shaded-pole motors usually don't mind being stalled.

I'm reading a Tesla book. Stuff that seems perfectly obvious to us now, like making a rotating magnetic field, wasn't.

Yup. This one is mounted in an 8-inch long by 10 inch diameter duct, right over the cooktop, and has been in use since 1960. I last overhauled it ten years or so ago, and there's been a lot of bacon grease through there since. ;)

Well, they come with a shorted turn, no extra charge. ;)

You and Niki are homeys. I find him a bit like Mary Queen of Scots--interesting character, but no surprises in the story at this point, and way too many books written.

Maybe he's tapping into the Great Oz--there are superficial similarities there too.

Cheers

Phil Hobbs

He had some good instincts and not much in the way of theory or quantitative judgement. I sure hope I don't get crazy in later life like he did.

This book includes some history, Westinghouse and Edison and GE and Siemens and Niagra Falls and such. And fat cats with money.