Understanding the specs of an electronic ballast (UV-Tubes)

Question

I got lost on the topic of selecting the right electronic ballast for 4 UV-tubes (Cosmolux S pink 15W). I have learned about magnetic ballasts and starters, about electronic ballasts and connecting them in series or parallel (or not).

Currently I am using an electronic ballast suitable for 4 tubes (4x15W) which I would like to replace by a new electronic ballast.

The datasheet of the tubes says:

• Supply Voltage = 230V +/- 0.2%
• Ballast = 15W /230V
• Lamp wattage = 13W +/- 5W
• Lamp current = 395 mA
• Lamp voltage = 40V +/- 10V This voltage and current rating would indicate 0.395A * 40V = 15.8W. Not exactly 13W, but within range.

The driver I have connected says:

• U-OUT = 300V
• Iout = 0.5A

I have several questions:

1. How can this setup work (because it is connected and it works). 300V as U-OUT is not even close to 40V, yet it does not damage the tubes. What is this 300V meaning?
2. At what inputs of the tubes should I be able to measure the 40V? Because, when ON, the voltage I measure is really low, talking about tens of mV's. (Measured over outputs 10&7 and over outputs 10&9).
3. I read that a series connection of tubes is possible for magnetic ballasts. Then the required power should be doubled and an extra starter should be added. Is such a series configuration at all possible with an electronic ballast?
4. The current that is supposed to flow (395mA), is it transported through the tubes from the one end to the other?
5. The electronic ballast says 4x15W = 60W. What causes this spec, because multiplying 300V by 0.5A would result in 150W -which is unlikely, so I must be thinking wrongly-.

The sources I used to get a better understanding are:

• https://www.youtube.com/watch?v=qLaD11LITbQ
• Multiple forum questions about wiring an electronic ballast.

Answer 1

1. Uout would be the (max) striking voltage, not running.
2. Pin 9-10 would only see the preheat voltage during starting, after that zero. 10-7 should see the running voltage, but you need an oscilloscope to measure it or a high end DMM which can measure in the high tens of kHz. Most DMMs have low pass filter (intended or just from parasitics) and will have more and more attenuation on measured voltage the higher in frequency you go above 50/60 Hz.
3. For some yes, others no. Check the datasheet. Yours is made for series connected tubes for instance.
4. Yes.
5. See 1.

Answer 2

The current on the ballast does relate to the lamps(s) it's compatible with. Lamp voltage and current don't work out to precisely 15W, but 400 * (0.395) is close. The voltage and current can vary with temperature and age, but the spec allows a knowledgeable person to be able to decide what lamps are compatible. For safety, the industry prefers people simply obey the label instructions and not use mix lamps, ballasts, and series/parallel configurations that are not intended. For liability, reliability, etc.