"Magnetic ballast" as power choke?

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geezertron

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Joined 2015
#1
So called "magnetic ballasts" for old florescent light fixtures, and I mean specifically the kind that use traditional coil and core construction and look identical to a ordinary choke, are far cheaper than power chokes (in fact free if you are willing to dumpster dive 🙂. Also they are commonly rated at 277V, which is high enough for a lot of tube power supplies. But they aren't spec'ed for DC current or inductance.

Has anyone ever characterized them or tested them as a PS choke?
 
#4
JonSnell Electronic said:
DC chokes have an air gap, AC chokes do not.
Click to expand...
It has nothing to do with AC or DC: the choke is completely agnostic about it, all that matters is the instantaneous current it senses.
Some DC chokes may have no gap, some AC ones may have it, it just depends on the use, inductance, peak current, etc.
In addition, ballasts have hugely elongated sections of iron acting as high reluctance sections, playing the same role as lumped airgaps.

Note that you are not alone in your mistaken views: a learned participant in the quoted threads has been caught in the same trap.
 
#5
Teardown of a very common 18W 240V flourescent choke - note the central square-section laminated steel core, and the four long airgaps between the central core and the outer C section laminations - the 'cut' was made at one end, just before the winding loop around - the single winding is very compactly wound:

Flourescent%20choke%20teardown.JPG


Supporting measurements of that type of choke:

http://dalmura.com.au/projects/Choke%20measurement.pdf
 
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