What is a ballast?

[billybob]

I have a Home Depot (ballast) at home which outputs high voltage for a fluorescent lamp, but apparently there is another ballast, the kind for a Tesla coil. There are probably more definitions for a ballast. What is a ballast’s purpose in a Tesla coil and can I build one out of microwave oven caps like styropyro did on his Tesla coil?
Thank you,
Ben

 

[MaxHeadRoom78]

Ballast: To limit and stabilize.
In electrical circuits it generally does just that.
Particularly in the older florescent's that have a heavy wound ballast unit.
Max.

 

[MacIntoshCZ]

I have a Home Depot (ballast) at home which outputs high voltage for a fluorescent lamp, but apparently there is another ballast, the kind for a Tesla coil. There are probably more definitions for a ballast. What is a ballast’s purpose in a Tesla coil and can I build one out of microwave oven caps like styropyro did on his Tesla coil?
Thank you,
Ben

I would reccomend you for begining to stay under 50V DC on primary. After some experience you can play with mains.

 

[billybob]

I would reccomend you for begining to stay under 50V DC on primary. After some experience you can play with mains.

What do you mean? What does a ballast do?

 

[MacIntoshCZ]

What do you mean? What does a ballast do?

it wasnt to topic; sorry
Ballast contains inductor. Purpose of ballast is to make gas inside fluorescent lamp conducting.

 

[Diver300]

The ballast in a fluorescent lamp has two jobs. One is to limit the current once the lamp turns on. The lamp's impedance at that point is quite low so an impedance in series is needed to limit the current.

The second job is to provide a high voltage pulse to ionise mercury vapour to turn the lamp on. The starter will short out when the lamp is turned on, and a current flows, limited by the ballast. When the starter goes open circuit, in about 1 seconds after turn-on, there is a voltage surge produced by the ballast and the rate of change of current. That voltage surge is what ionises the mercury vapour.

 

[billybob]

So I came back to this thread to reread the advice on ballasts. How does impedance in series to a load limit current? Is it acting like a resistor? Don‘t resistors draw more current?
Sorry still not getting it,
Ben

 

[KeepItSimpleStupid]

The ballast is generally a very lossy transformer. So, you have this gas inside of a tube A florescent light contains some inert gas and a bit of mercury. The mercury heats up and creates mercury vapor. The phosforus on the lamp gives off white light normlly
The neon sign is another example is like the neon lamp, but the sign requires a ballast.

The open circuit voltage of the ballast might be 3000 Vac or so. Means no load. That voltage is sufficient to ionize th gas creating a orange plasma. Now, you have a circuit that looks like a short. The ballast goes into current regulating mode. I never really wanted to measure the operating voltage of the neon transformer.

I did, however, since this was a 254 nm source, look at the light output over time with a conditioned sensor and scope. It peaks and decays. It's not sinusoidal..

A 1000 W arc lamp I had the pleasure of maintaining had about 900 hours of life. Actually it's spectrum became unusabel after about 900 hours. The lamp operated at about 22V and 44A, I think. To start the lamp, the voltage was upped to 80 VDC and then a 40 kV start pulse was added. Once the lamp started, it actually had feedback to control the intensity. The current has to be limited.


This http://www.hammondmfg.com/ba.htm transformer couls almost be considered a ballast. You can short the secondary and nothiing catastrophic happens.

A florescent lamp has another little problem. It needs a source of electrons from a heated filament just to start the lamp.

 

[Diver300]

So I came back to this thread to reread the advice on ballasts. How does impedance in series to a load limit current? Is it acting like a resistor? Don‘t resistors draw more current?
Sorry still not getting it,
Ben

Any impedance, whether it is a resistor, inductor or capacitor in series will almost always reduce the current.

A resistor will take current from a supply. An electric heater is a resistor, and if I plug in more heaters, more current is taken, but that is putting the heaters/resistors in parallel, not series.

When a resistor is in series with a load, the current will be reduced. Cars have heater fans that have variable speeds, and the fans are often made to run slower than full speed by putting resistors in series with the motor. The more resistance, the less the current, and the slower the fan runs. The control just connects different resistors for different speeds.

The ballast has inductance, so when connected to ac mains, that has an impedance. If the inductor were connected directly to the mains supply, the current flowing would be the mains voltage divided by the impedance, and the designer can chose the inductance to give however much current is required.

If the fluorescent lamp is in series, the current will be a bit, but not much, less than that, and the amount of current is mainly controlled by the design of the ballast, the mains voltage and the mains frequency.