Can I use CFL's ballast to power fluorescent lamp/tube ?

[BravoV]

Just bought 2 cheap UV tubes rated 10 watts each (label printed at the lamp), and currently I don't have any ballast handy to power them, but I have many of those CFL electronic ballast circuits that are still working but died because of their broken/darken tubes.

Most of them are salvaged ranging from 10 to 20 watts CFL bulbs, which one is more suitable ? The one closer to 10 watt ? or use higher one like 20 watter is even better ? 

PS : Yes, I'm aware of the dangerous since this circuit is working with high AC voltage from mains power lines.

[westfw]

I pretty sure you can.  A typical CFL is just like a linear tube, only curled up.  And the driver is essentially a constant current driver (for AC!), so using a 9W CFL ballast on a 10W tube should work fine, with slightly reduced brightness.  (I wouldn't use a 13W CFL ballast, though.)

I have actually used 3W battery-operated CCFL drivers to drive CFL and linear fluorescent tubes, and that works just fine.

[BravoV]

Thanks for replying, also I didn't know those ballast are AC "constant" current driven. 

I guess I have to find harder, currently all my ballasts starting from 15 watt up to 25 watt.  Will 15 watt ballast toast the 10 watt tube ?

Also at higher wattage tube driven by lower wattage driver even with reduced light, will have longer tube's life right ?

[westfw]

I didn't know those ballast are AC "constant" current driven

That's sort of an approximation.  A gas discharge, like an LED, will conduct a relative arbitrary current, and the ballast limits that to desired levels.  Filaments and starting are other issues.  An old-style magnetic ballast is a big whopping inductor that limits current at the 60Hz mains frequency (I =V/Z, where Z is the complex impedance, which is frequency dependent (j*w*L for a perfect inductor).)  CFLs step up the frequency and so can use a much smaller inductor.

Will 15 watt ballast toast the 10 watt tube ?

I don't know.  They're pretty thin-wall tubes, and that's 50% over...

longer tube's life

I don't know that either.  The reduced power=longer life thing is largely related to filaments burning out, which is separate than the fluorescent wattage.  And fluorescents have other failure modes as well.

[BravoV]

Will 15 watt ballast toast the 10 watt tube ?

I don't know.  They're pretty thin-wall tubes, and that's 50% over...

Damn , just searched my house, the smallest CFL is still 15 watt, I guess I have to buy those el-cheapo 8 watters new CFLs just to yank out their ballast.   

[SeanB]

Use the 15W units, it will not affect the life of the small tube that much, and as it will only be running for a half hour at most at a time it is likely to last a few years. Just replace the capacitor in the ballast ( if 220V unit, a 110V unit will have either 1 or 2) if it is looking sick ( most are going to be either bulging or be dark brown from heat) and it will work well there. 10W tubes are pretty forgiving, I have seen them run for months with a 40W ballast ( junky fish tank light) before failing.

[BravoV]

Use the 15W units, it will not affect the life of the small tube that much, and as it will only be running for a half hour at most at a time it is likely to last a few years. Just replace the capacitor in the ballast ( if 220V unit, a 110V unit will have either 1 or 2) if it is looking sick ( most are going to be either bulging or be dark brown from heat) and it will work well there. 10W tubes are pretty forgiving, I have seen them run for months with a 40W ballast ( junky fish tank light) before failing.

Yeah, you're right, these will be used only for exposing the pcb using photoresist film purpose, probably much less than 30 minutes and its not like I'm going to produce high volume pcbs anyway.

Thanks SeanB. 

[steve30]

I'm building a UV exposure box with two 10W UV tubes.

I don't really use CFLs so didn't have any spare, so I went down to Wilkinson's (Poundland will probably be suitable as well) and got some GE CFLs to pinch the ballasts from. I think they are 11W. They power the UV tubes fine.

[BravoV]

Steve, thanks for the confirmation.

[steve30]

Just had a thought... Maybe I'll get some (CFL) Ballasts of different powers and try some them with some tubes of the wrong rating.

Would be cool to see what happens.

[SeanB]

Nothing much, the tubes are constant voltage devices and are capable of quite severe overloads. I have seen them run with a 9W tube on a 65W ballast, and aside from a very shortened life they ran, though they were a lot brighter, but not linearly so, just about 3 times as much. Massive overdrive just blows out the heaters and then nothing. Massive overvoltage can burn the leadout wires out and break the vacuum seal.

[BravoV]

Cool, thanks everyone, this means I'm not going spare those tubes anymore, few watts higher will be fine, also they're dirt cheap here.

Just fyi for those curious what is this all about, related to this topic, made a thread here -> Are these the right UV tubes for pcb dry film photoresist exposure ?