A Guide to Fluorescent lighting with magnetic ballasts


This article is a quick intro to wiring fluorescent lighting systems using external magnetic ballasts. Magnetic systems are very easy, as there are only three components. The Ballast, the Lamp and the starter. Due to the nature of magnetic fluorescent systems, the circuit needs a starter. This type of system is called a "pre-heat" system. The lamps filaments are first turned on for a pre-set time, then the system attempts to strike an arc. If the resistance is low enough it will ignite, if not it will flash, and the cycle will repeat. This is why some lamps flicker as they start.

For a much more thorough explanation,  my inspiration for these pages and where I learned everything I know about fluorescent lighting, I will redirect you to my local mirror of a site. This site gives an amazing explanation of the system, but seems to have gone off the net since 2005 (a damn shame, it was a great resource). The local mirror is here.

For those of you not keen on a detailed lecture on the system, here is a quick overview.

                                        [ STARTER ]
                                        [         ]
                                        [   o/    ]
                                        [   /     ]
                                        [ +/  o-+ ]
                                        [ | ~~~ | ]
                     |                  [   ~~~   ]                  |
                     |                                               |
                     |                                               |
                     |   +---------------------------------------+   |
                     +--=|--                                   --|=--+
                         |  )        FLUORESCENT LAMP         (  |
                     +--=|--                                   --|=--+
                     |   +---------------------------------------+   |
                     |                                               |
                     |                                               |
                     |                                               |
LINE   --NEUTRAL--<>-+ (WHITE)       +---------------+               |
 AC                                  |               |               |
MAINS  --HOT------<>-----------------|    BALLAST    |---------------+
                                     |               |            


This is the schematic of the automatic pre-heat system. When you first apply power, the resistance of the gas inside the lamp is too high for any current to flow. Instead the current flows through the gas in the starter bulb (which has a lower resistance), heating the bi-metal strip inside until it bends and contacts the other side. This pushes a lot of current through the lamp and attempts to ignite it. If the gas is hot enough it will arc through, further lowering the resistance. Now at this point the resistance of the lamp is lower than that of the starter bulb. As such no more current flows through the bulb, causing it to cool and break the contact. Now all the current is going through the lamp, and the sequence is finished. If the lamp fails to light not then we start the whole cycle again until successful.

On industrial/commercial fixtures, the starter and the lamp are seperate. This can be seen by the fact that the lamp has 4 pins. Now the 2-pin systems are very often seen on CFL systems. This is because many CFLs have a starter built in. The schematic for this system looks like this:

            .                                                                 .
            .                           [ STARTER ]                           .
            .                           [         ]                           .
            .                           [   o/    ]                           .
            .                           [   /     ]                           .
            .                           [ +/  o-+ ]                           .
            .                           [ | ~~~ | ]                           .
            .        +---------------<>=[-+)~~~(+-]=<>---------------+        .
            .        |                  [   ~~~   ]                  |        .
            .        |                                               |        .
            .        |                                               |        .
            .        |   +---------------------------------------+   |        .
            .        +--=|--                                   --|=--+        .
            .            |  )        FLUORESCENT LAMP         (  |            .
            .        +--=|--                                   --|=--+        .
            .        |   +---------------------------------------+   |        .
                PIN1 +                                          PIN2 +
                     |                                               |
| |
| |
LINE --NEUTRAL--<>-+ (WHITE) +---------------+ | AC | | | MAINS --HOT------<>-----------------| BALLAST |---------------+ | | +---------------+ 

In this set up the CFL has only two pins, the other two are already wired to the starter, which is usually built into the base. Below is a picture of a 2D CFL with the front cover removed, showing the starter and it's connections to the filaments:

I also have a film showing the startup sequence of the 2D lamp, which will hopefully help with understanding the system behind the ignition:



An example project

An example of this system in use is this little example project. My living room uses 3*100W lamps as the main lights. They are attached to a dimmer so I can't use energy saving bulbs, and as I rent the place, so I'm not allowed to make any changes to the wiring. As such I decided to make use of a lot of lamps wired to the sockets.

This project will be the creation of a dual 11W CFL lamp that will sit on the top shelf and provide one of two main lighting systems in the living room.

First thing I did was measure out the free space I had on the shelf. Next thing I did was cut out some MDF from an old door someone thrown out and put two protruding point on it to mount the 2D CFLs. I use 2D CFLs because they give out a uniform light and I like them (they are the thing that got me interested in CFL's all those years ago). Anyway once done the MDF looks like this:

Next thing I did was mount the magentic ballasts onto the MDF, as so:

and the same for the other side. After this we attach cables between the ballasts and the the lamp. I found that the perfect fit for CFLs is in fact Molex connectors, as in those that are part of computer PSU's (as shown):

We took out four of the pins, in my case I picked four black ones:

The Ballast is wired in seried along with the lamp, and is tested out from a computer power cord (see below). The lamps are rated for 16W but the ballast is rated at max 11W. This results in the ballast running hotter than usual (due to higher current) but it still works fine:

Here is a picture of both sides wired up, running in order to help with the drying of the glue:

and the final product, both off and on: