View Full Version : Fluorescent light TL Ballast

19-05-2014, 06:21 AM
What's the actual power consumption of a complete TL fixture of 36W connected to a ballast with a power factor of 0.8?
Is the lamp itselves 36W rated and then add additionally some power for the ballast? Or is the complete setup 36 W?
What's the heat generated by the ballast and heat generated by the lamp?
I'm confused and I don't find the right information via Google.

19-05-2014, 07:44 AM
G'day Peter. a while back i measured a working 36 Watt fluro to be consuming around 55 Watts.
Ballasts run at 70+ degrees. Seen a bank of ballasts run over 100 degrees C in a commercial case that wasn't ventilated. Needless to say, they didn't last long.

19-06-2014, 12:29 AM
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I see the question is quite old but I can give a little information for you. The best is to use a clamp ammeter to actually measure the current then multiply by the supply voltage to get power. You can't work backward very well from the power of the tube to the total energy consumption because firstly as you point out PF is an issue, also harmonic distortion which is sometimes given as THD number on the ballast. Secondly the ballast is not 100% efficient, the efficiency is sometimes given and it will be a figure that is less than 1. Finally manufactures are liars, their numbers that they publish are made under ideal testing conditions and they often find ways to bend them when it suits them and they think they can get away with it.

The life expectancy or MTBF for an ballast will be inversely proportional to it's running temperature once you get above around 50C, with some devices after a certain threshold every 1 degree C rise in temperature can half the life span. Rule for thumb with the newer generation electronic ballasts I'd expect them to consume the wattage of the tube plus 60%, for older wire wound inductive ballasts I'd expect them to use double the wattage of the tube or more and this could increase considerable as the tube ages. After tube failure to strike the ballast power consumption could be 4 times the tube wattage. Old fluorescent fittings were a fire hazard because of the heat that was produced by the ballast when the tubes failed. This was until they started building in safety system to disconnect the ballast.

Ballasts are often designed to be mounted hard against a metal surface or the metal body of the fitting which helps with dissipating the heat. With many ballasts together there should be a space between each one also to allow for cooling and the enclosure should be venntilated. There are formulas for working out how many devices you can mount inside an enclosure with a certain surface area depending on ambient temperatures also. If the enclosure is too small for the calculated heat load then forced ventilation or a small air conditioner must be used.