Author Topic: Fluorescent tubes and ballasts...  (Read 1068 times)

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Offline westfw

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Fluorescent tubes and ballasts...
« on: December 25, 2017, 09:34:19 am »
So...  My gut understanding is that fluorescent bulbs are all essentially the same, whether they are linear tubes, circline rings, or CFL spirals.   And that a ballast is essentially a current-limiting circuit, so that about the only bad thing that will happen if you connect a 40W tube to a 20W ballast is that you'll only get 20W worth of output.   So that means, at least in theory, that I could tear apart an 18W CFL and use its ballast to power a 22W circline bulb?   Yes?

The reason I ask is that I pulled one of these lovely magnifier lamps http://www.ocwhite.com/magnifiers/magniliter-7-5-big-eyetm-round-magnifier-43-reach-screw-down-base.html out of a dumpster.  It has no bulb; the bulb it wants seems to be relatively rare, and costs about $50!  And I'm not sure that this lamp actually works - I've plugged in another circline bulb with matching connector (but doesn't fit in the lamp), and it didn't do anything at all.  I'm not enthusiastic about spending $50 for a bulb that might not work, but I'm more willing to think of re-wiring the whole thing with a more-standard bulb and a CFL ballast, if that's likely to work...
 

Offline mikerj

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Re: Fluorescent tubes and ballasts...
« Reply #1 on: December 25, 2017, 10:05:37 am »
Why not convert to LED's and avoid any tube related problems?

The working voltage and starting voltage of fluorescent tubes is greater with higher powered devices,  and the heater resistances can vary.  However with such a small power difference in this case I think it has a good chance of working.
 

Offline IanMacdonald

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Re: Fluorescent tubes and ballasts...
« Reply #2 on: December 25, 2017, 10:27:44 am »
All fluorescent tubes are not equal. The voltage drop can differ. Fitting an incorrect replacement can cause excessive current flow, and the ballast choke burning out. Or, reduced light output (which is tolerable) This can be an issue even where the replacement has the same connectors and will physically fit.
 

Offline TassiloH

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Re: Fluorescent tubes and ballasts...
« Reply #3 on: December 25, 2017, 12:09:48 pm »
A long time (12y) ago my dad did this with a smaller magnifying lamp which had a 12W circular fluorescent tube and a manual starter switch (press for one second, release) that burned out. He fitted the electronics from a mechanically broken CFL of approximately the same power into the base where the ballast inductor used to be (and re-wired the lamp with 4-conductor cable from there to the fluorescent tube). The lamp isn't being used that frequently, but still works. I don't think the 22W/18W will cause problems in your case.
 

Offline SeanB

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Re: Fluorescent tubes and ballasts...
« Reply #4 on: December 26, 2017, 09:06:05 am »
On the low power end ( under 13W) you find iron core choke ballasts that are multi rated 7,9,10,11,13W which will work fine with all lamps in that power range, and a nominal 20w ballast works with 18W tubes as well, and with 16W low power tubes as well, though there the efficiency comes at a cost of needing an electronic starter to limit the restrikes at EOL and also provide a longer preheat time.

however in the US with 120VAC your choke ballast is not so generously rated, and most likely has failed open circuit if choke type, or has a broken connection on the terminals ( pretty common). If electronic then rather than buy a new one simply look for an "angel eye' circle of LEDs online, and a small 12V power brick to power it. Sold as car light rinds in assorted sizes, and a lot lighter than the circline tube and ballast, though you probably want to leave the existing choke ballast in the base to keep the light base heavy.
 

Offline westfw

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Re: Fluorescent tubes and ballasts...
« Reply #5 on: December 27, 2017, 10:56:16 am »
Quote
Why not convert to LED?

LED would be swell, but ~200mm to 250mm diameter LED ring-shaped LED lights seem to be pretty rare.
I guess that's probably big enough to go piecewise-linear...
 

Offline stj

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Re: Fluorescent tubes and ballasts...
« Reply #6 on: December 27, 2017, 12:56:14 pm »
actually the chinese sell led rings to replace tubes in fittings!
big clive reviewed a couple.
 

Offline SeanB

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Re: Fluorescent tubes and ballasts...
« Reply #7 on: December 27, 2017, 01:29:35 pm »
If you just buy some LED strips you can piecewise approximate a round lamp out of them easily enough, or just use some flexible tape onto the steel backing, putting a strip on the side near the inside and another on the strip to the outside of the channel, and connect to the power supply. will give more light than the original tube as well with 2 strips of tape.
 


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