# Fluorescent tubes in series?

Is it possible to use fluorescent tubes wired in series, provided that the ballast can supply a high enough voltage and power?

## Problem description

F28T5 are too long (4ft) for me, so instead I plan to use pairs of F14T5 side by side, which are 2ft long. The problem is this would require more ballasts. Typically, one ballast can power one or two lamps, like so

But I would like to use the ballast like this

My theory is that 2 x F14T5 would be electrically equivalent to one F28T5, if wired in series. The ballast will provide the appropriate current, which would be almost the same. Is this correct? or would the plasma have very different characteristics with an intermediate electrode?

## Starting issues?

Another potential problem is starting the lamp. My understanding is that the plasma in the tube must first be ionized, typically by heating a filament at both ends. But with lamps in series, the middle two filaments would be cold since they are not connected to the ballast.

Would this prevent the lamp from starting? or does it only need to be heated from one end? (Note that with two lamps in series, each lamp has one heated filament. But with three or more, the middle lamps will be cold. Would it also work with three or more lamps?) Would using a different type of ballast (instant start) that uses a high voltage to induce breakdown avoid this problem?

The lights are gas discharge tubes, so have a struck voltage usually between 60-80 V. So on 110 V mains you won't have enough to keep them alight in series, but at 220-240 V you would have enough voltage. If you have a simple inductor/choke limiter, and glow starters this may be your solution:

With electronic ballasts it will depend on the connection complexity they support, but there are plenty that support 2, 3 and 4 tubes with heater activation and no starters. Here's a pointer to a 2 tube electronic ballast.

• This circuit seems to correspond to the 2 parallel lamps configuration. The series circuit I'm asking about would look more like this: i.stack.imgur.com/BSYVC.png I haven't found any documentation that supports this configuration, though I believe it should be possible. – goweon Dec 29 '16 at 19:14
• @goweon. Both are series connected. Your circuit with one starter will not work unless you can guarantee a very large start pulse since this does not use any of the heaters at all. The circuit I showed has two starters so each tube can be started separately and both heaters are used. I don't know what to tell you if you don't recognize this as tubes in series. – Jack Creasey Dec 29 '16 at 20:39
• Is the power factor correction capacitor required for the discharge tubes to turn on ? I have a display panel which got broken. Replaced everything (starters, ballast and tubes) except capacitor and it's still not working. – tigrou Jun 22 '18 at 20:07
• @tigrou The power factor capacitor has no impact on the discharge tube circuit. – Jack Creasey Jun 22 '18 at 21:18
• I made the circuit Jack Creasey posted with a magnetic ballast without the capacitor (because I can't find how many micro farads it needs) and it didn't work. – Nathan May 15 '19 at 2:32

Very common commercially. Normal 36 watt bsllast. Two 18 w tubes. Two s2 stsrters. Note, do not use universal starters.

• It's not clear what you are saying. Please use grammatically complete sentences. A schematic would be good too. There's a schematic button on the editor toolbar. – Transistor Jun 14 '20 at 10:18