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I offer an even worse thing... (rare) Austrian railway stuff: fluorescents run directly off 16.7 Hz... Now THAT flickers awfully!

Just thinking about that gives me a migraine... I can notice computer monitors and LEDs around 70Hz... 16Hz would probably look like a rave to me.

Ah, like U.S. pints vs. Imperial pints!

On the frequency issue, my mother always used to say that she could notice the flickering sometimes on fluorescents, even on our normal 50Hz supplies.

The 25Hz is still big in the steel industry I am told because it has less zero crossovers. Supposedly that is better for melting steel.

Aren't arc furnaces DC?

Wasn't the choice of 25Hz made for the use in slow speed motors that are used in the rollers & conveyers?

Ya as far as I know 25Hz is still used in at least 2 of the major steel mills here in "Steeltown", and yes its for slow speed motor applications only..

On another note I just finished cleaning out my boss' storage barn and found a pile of old fixtures with similar ballasts inside, only difference was there was a screw to set frequency instead of that "plug" like the ballast I posted had.. Also in the pile of spare parts I came across an old oil burner and attached to the housing was a metal tag that said " This unit has been converted for 60 Hz operation".. Can tell that thing was around from the days of 25Hz power originally!

A.D

I don't work in a steel plant. That is just what someone told me.

most arc furnaces are AC ..and are used by the "mini-mills" rather than the large mills who still make steel using blast and basic oxygen furnaces

iron from the blast furnace is converted to steel by pumping huge quantities of oxygen into the molten iron
which coincidentally release large quanities of carbon monoxide....which is why we have to wear CO monitors when playing around most things in the BOF or above the blast furnace

I do recall seeing 25 Hz stuff but all the newer equipment uses VFDs or DC drives

I'm kinda surprised that this ballast is still alive.

But the older stuff was almost always built to last anyways (It's called conservative design, folks. )

But there is one major safety flaw that no one's mentioned yet...lack of thermal protection built in. (Not "P" rated.)

There are not too many smells as rank and putrid as a burning ballast. Think stinky tennis shoes, mouldy fish and hot tar and it'll be close.

And in a few cases such ballasts have caused serious fires.

I have seen a few "P" rated ballasts still get hot enough to expel the tar-like potting compound inside, though.