Compact fluorescent ballast for 4' tube?

BatteryCharger · #1 03-07-2005, 08:46 PM

I happen to have a 4' shoplight with a bad ballast, as well as a 25 watt compact fluorescent bulb with a broken tube. I already took apart the broken CF light, because I was bored. [img]/ubbthreads/images/graemlins/grin.gif[/img] If I wired the ballast from the CF light to a 4' 25 watt tube, might it work? [img]/ubbthreads/images/graemlins/ooo.gif[/img]

Lynx_Arc · #2 03-07-2005, 10:20 PM

don't most 4 foot shoplights use 40 watt tubes? If so you will probably be underdriving the tube if it works at all.

BatteryCharger · #3 03-07-2005, 11:22 PM

No...most shop lights are 25 watt.

jtr1962 · #4 03-08-2005, 12:31 PM

I've tried this already. A ballast for a 28W CFL works just fine on a standard 40W, 4' tube. The tube even seems as bright as on a normal ballast. Just because a ballast is made for a 25W CFL doesn't mean that it will pump 25W into every tube connected to it. Rather, the actual power pumped into a given tube will depend upon its characteristics. In acutality, most ballasts are constant current circuits to a first approximation, and will pump their design current into almost any tube connected to them. For a 40W tube I think the current rating is 430mA. A 25W or 28W spiral CFL may actually have a similar current rating, but less of a voltage drop. This explains to me why my 28W CFL ballast works just fine with a 40W tube (measured power draw is about 36W).

Zelandeth · #5 03-08-2005, 03:08 PM

Simple answer: Yes, it should work.

Will the tube last as long as it would on its original ballast? No idea. Depends on the characteristics of the tube compared to that the ballast was made for.

Connect it up, see what happens!

I've had a F15T8BLB tube here running for a good few months off a 15W CFL ballast now, still seems to be working fine.

snakebite · #6 03-08-2005, 04:48 PM

as long as it can produce enough voltage to reliably strike the tube from cold it will work.
but with the cheap crap these things are made of who knows for how long?
better enclose it in a fireproof box in case of flameout.

Lynx_Arc · #7 03-08-2005, 05:13 PM

I think most of my shop lights are F40T12 4 foot tubes which are 40 watts. I would think if a lower wattage rated ballast could drive a higher output tube at spec it may have less safety margin... overheating could be a possibility.

brickbat · #8 03-09-2005, 08:01 PM

It probably will work. It may work even better if you buy a "T8" lamp. A 4 footer is rated at 32 Watts and is designed to operate on high frequency electronic ballasts. I'd take the flameproof box suggestion pretty seriously. Most shop lights have metal housings, which should be fine. But if it has a plastic housing, I would not risk operating it in my house...

yuandrew · #9 03-21-2005, 05:29 PM

Hey, I've done it too. GE F20T12 CHROMA-50 on a Chinese Made 20 Watt CFL Ballast in an old ultility fixture.

I've talked about this a few times before but I've just got a new camera so here are some pictures

The fourth picture from the top shows the old ballast and starter bulb that was originally in the light. Look at how everything neatly fits in. In case you're wondering; yes, the fixture is plastic.