Must say don't think I've seen this type of ballast before. Can't find a voltage listed either.


https://www.ebay.com/itm/NEW-175W-Outdoor-Dusk-to-Dawn-Security-Road-Street-Parking-Lot-Light-Luminaire/310372615814?epid=1400265806&hash=item4843a64686:g:f6gAAOSwBPNXSFJU

 That  type of Ballasr is for regulated 6.6 amp series street lighting circuit.  that reason why voltage is not
listed. It basically a step up transformer that is regulated
output to the lamp.   6.6 amps at 175 watts is 26.5 volts
this reason why wires are thick and heavy cause it due
to high voltage.  this steet lght is design to replace
a old Incandescent 6.6 series street lighting fixture.

You'll need one of these to run that street-light as is.

https://www.lighting-gallery.net/gallery/displayimage.php?pos=-139630
https://www.lighting-gallery.net/gallery/displayimage.php?pos=-80602

Never knew you could do that with MV. What happens when the bulb fails though? Id imagine the ballast impedance gets very high, beyond what constant current can compensate for?

I imagine that the ballast will rise the voltage, both across the primary and secondary, until it's magnetizing current reaches 6.6A. At this point the ballast will probably be in deep saturation

I can't imagine this being a good thing to the ballast... Current transformers get destroyed immediately from open circuit secondary due to isolation breakdown. If not for the isolation breakdown, they overheat from the saturation. I would imagine that this ballast won't blow up immediately due to hot restrike of a lamp after a line glitch, but it very possibly gets very hot during such events

I'd say your spot on Ash. Saturation would be inevitable as the voltage rises uncontrollably.


After seeing this, I wonder if a transformer ballast is practice or physically possible. 120 volt primary and a 240 volt secondary. The impedance so high that secondary short circuit current would be limited to that of a standard ballast. Basically a CWI ballast without a capacitor. 

Transformers with high leakage inductance do this. They have a magnetic shunt like most transformer ballasts (HX, CWA, Microwave oven transformers) but the primary and secondary are isolated

You can get the same effect by using an isolation transformer in series with a choke (the choke can be on either side of the transformer, but for a transformer that isn't 1:1, the choke will act as a chokes of different values when placed on one side or the other, according to the transformer's turns ratio squared)

What do you mean by magnetic shunt? To me low impedance power transformers look the same as CWA ballasts, but as we know aren't so.

In all transformers the primary creates magnetic flux through the core, and the secondary picks it up. The magnetic flux will go through magnetic materials - the Steel lamination core where possible, and not through air

In power (Low X) transformers, the primary and secondary are simply wound on the same core - side by side or one on top of the other. Flux that goes through the core must go through both windings

In High X transformers, there is an additional block of Steel lamination, placed so that some of the primary flux can go through it, without going through the secondary. This block is called a magnetic shunt

The shunt does have some minimal gap between it and the core, so that it won't be the preferred path by default. In addition, the part of the core that goes under the seconrary have a window in it, that restricts the flux that can go to the secondary, before the thin areas (the sides of the window) saturate. Once they saturate, the air gap of the window is way bigger than the gap to the shunt, and then the rest of the flux from the primary will go through the shunt without getting to the secondary

The current limiting of the secondary depends on the design of the window in the core (how much flux the thinned area will take before it saturates) and the shunt