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#127871 02/24/02 12:59 PM
Joined: Feb 2002
Posts: 840
Can someone here explain the difference between the types of HID ballasts, such as the reactor type and an autotransformer? I know how an autotransformer works but now how it relates to HID lighting. Also, I know the reactor is more effecient? Why?
I understand technical terms so use as much "techno jargon" as you need. Thanks! [Linked Image]

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#127872 02/24/02 07:37 PM
Joined: Oct 2000
Posts: 2,723
Likes: 1
Broom Pusher and

Ask and thee shall receive [Linked Image]

Most basic consept, to if a Straight Reactor core or an Autotransformer-Reactor arrangement will be used, is in regards to the available Voltage and the Lamp's normal Operating Voltage. If these levels are within 15% +/- of each other, then the Lamp can run from a simple Reactor core.

When Lamps are "Simple", the above guidelines are sufficient.

To drive Lamps with any complexity, a simple Reactor needs to be supplimented - thus the usage of CWA [Constant Wattage Autotransformer] and HX [High Reactance Autotransformer] arrangements are used.

Another basic item for Straight Reactor cores and Autotransformer-Reactor cores is they have an inherently poor Power Factor of 50% [Nominal PF]. Using a Capacitor with these Reactors can improve the PF from 80% to 95% [High PF] - depending on designs.

Some Autotransformer-Reactor setups use the Capacitor for PF correction and Lamp Regulation / Tweeking.

If you would like more info, please let me know with a reply in this thread.
Also, do you want any information on the other types of Ballasts? {CWI [Isolation Type], Reg.Lag [Regulated Lag], etc.}.

Here are links to HID Ballast Schematics for references:

HID Reactor Ballast

HID CWA Ballast

HID HX Ballast

HID CW / Reg. Lag Ballasts

HID CW 1 and 2 lamp Ballasts

Scott SET

Scott SET

Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
#127873 02/25/02 04:16 PM
Joined: Feb 2002
Posts: 840
Scott- Thanks for the info. The diagrams are very helfpful.
A few questions: What are some examples of complex and simple lamp types?
I guess Im confused about the term "reactor." Does "reactor core" simply mean the transformer itself? Is a reactor an autotransformer or an isolation type transformer? (I would guess that its an autotransformer).

My inquiry comes from some Ruud lighting literature stating that the 277 volt reactor was more effecient that the multi tap auto. I was wondering why.

Yes, I would like more info on the other types of ballasts. Thanks. [Linked Image]

#127874 03/03/02 12:44 AM
Joined: Oct 2000
Posts: 2,723
Likes: 1
Broom Pusher and

I'll throw some basic stuff out right now, then come back later for more indepth details [if I don't have to go back up north next week!]

The Reactor is simply a coil of wire wrapped around a laminated Silicon Steel core. It's very similar to an Inductor.
The term "Choke" applies to Reactors. They are Inductive Reactance devices which simply "Choke" the current, and the results are a limited level of current which can flow in the complete circuit.

The Reactor is the basis of any Ballast. Ballasts are used with Discharge Lamps simply to limit the amount of current [in Amperes] that can flow through the lamp.
Without a Ballast to limit the current, the Discharge Lamp will draw as much current as is available from the Power source, to the point where the Lamp self-destructs!
This situation is known as "Negative Resistance / Negative Impedance".
Once a Plasma [thick Arc] is established between the Electrodes [Cathodes] of a Discharge Lamp, the lamp's initially high Impedance is now gone.
The Plasma flowing across the lamp is increased when the level of current flowing is also increased.
The larger the Plasma, the easier it is for current to flow. The higher the current, the larger the Plasma becomes.

So, in order to keep things from becoming extreme, a Ballast is incorporated in series with Discharge Lamps.

Reactors control current levels by "Working Against Increasing Levels Of Amperage".
They work very much different than the way a typical Isolation Transformer would, only in the way the "Choking" effect is produced.

An Isolated Transformer would limit the Primary Current per the drawn load on the Secondary.
The Reactor would limit the Input Current per the drawn load of Output Current.

Both will do this via the Magnetic Flow in the Core.

As to simple and complex type HID Lamps, very simply a 150 Watt HPS using the Medium Base type lamp [55 Volt Lamp] is a simple type of lamp, and if the AC supply is at 120 VAC, only a simple Reactor core is needed to drive this type of lamp.

A complex type HID lamp would be a 35 watt Metal Halide lamp. It's output characteristics would benifit from a Ballast design that is more complex than a simple Reactor core - even if the lamp's operating voltage is close to the available AC supply voltage [like the S55 lamp described above].

Starting certain HID Lamps [not the ones that use High Voltage Pulse Ignitors] will need various Ballast designs.

An example of one Starting design is with Mercury Vapor lamps. They use internal Starting assistance components, which will have variable starting - thru - warmup load levels.
These lamps will draw a higher starting amperage, which tapers off to a fixed operating level when the lamp becomes stable and is running at full output.
When input voltages change, or the lamp's temperature changes, so will the load amperage.

If the Ballast cannot "Adjust" for these load changes, the Plasma will become too thin, which will decrease the load amperes, which continues to reduce the Plasma to the point where the Plasma [arc] can no longer be sustained...thus the lamp "Drops Out" and must be restarted.

Also, after 40% of the lamps operable life has evolved, things inside the arc tube begin to change. When lamps come close to the end of their useful lifespan, the arctube becomes darkened, which retains too much heat.
This causes the pressure within the arctube to become excessive, thus requires a higher voltage to push current through the arctube.

When the arctube is operating and the internal pressure is at the designed level, there's a "Happy Medium" between the size of the Plasma and the Voltage required to push current across the lamp and keep that Plasma stable.
With a stable Plasma and current flow, the lamp voltage might drop to as low as 10 volts. Once things are flowing, it doesn't take much to keep them going!
After the lamp ages, the internal pressures and reduction of conductive surfaces result in an increased lamp voltage to sustain the Plasma. Now a voltage of 100 volts to 200 volts is needed to keep the lamp operating.

When the restrictions within the arctube exceed what the available lamp voltage can overcome, the Plasma stops and the lamp must restart.

Starting involves an initial arc across the arctube and between the Electrodes [between the points of different Potential]. If the arc can be sustained, it will become a Plasma. If not, it will extinguish and the whole process is repeated again.

The temperature of the arctube will need to be reduced, so the internal pressure will also be reduced. When this becomes low enough, the arc will create the needed Plasma.

That's the reason for end of life lamp cycling [on and off] behavior for HID lamps.

Scott SET

Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
#127875 03/03/02 01:31 AM
Joined: Feb 2002
Posts: 33
Scott....Does the increase in voltage to sustain the plasma in the old HID bulbs cause a significant difference in watts used? Enough say, see a difference in electric bill, on larger scale like with a building with many HID lights. Dose leaving old lamps burn kill ballasts?

#127876 03/03/02 12:12 PM
Joined: Feb 2002
Posts: 840
Thanks for the answers. Everything I learned in AC Circuits class is beginning to make sense now! If I'm not mistaken, what you described about the reactor is a real life example of Lenz's Law. Correct?

A few more questions: What voltage do sodium lamps operate at? Is is approximately line voltage?


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