Author Topic: BANG !!!  (Read 3794 times)
Powell
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BANG !!! « on: December 07, 2011, 12:32:16 AM » Author: Powell
I went to rewire my old 14 watt desk lamp and somehow I got wires wrong.  So the first time I hit the switch I tripped the breaker and I had made a dead short. So second try I blew up the bulb. GRRRR!  I took apart another 14 watt fixture where I could trace wires, and when I plugged it in the ends lit. I could hit the black button and it would turn off until I released it, and the ends lit. I pulled one of the wires off going to the red button and stuck a starter socket in series and it is happy but you can't turn it off. I may have shorted the start part, though it doesn't look like it.  It's now a plug in only device, unless I can find another switch that has the screw in the middle. The ends light rather brightly and the ballast has gotten fairly warm over an hour or so.  But this fixture appears not to have been used recently. The lamp appears to be rather bright also.  Not something I want to leave on 24/7 right now.  I am not sure if it will be easy to fit a new ballast in as this one is small, chrome-ish looking with no writing on it.

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funkybulb
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Re: BANG !!! « Reply #1 on: December 07, 2011, 09:10:35 AM » Author: funkybulb
that sucks. you can add a normally close switch in series with the main so when you press the button it break the circuit. and that manual press start switch can start up again when you press it. then tbe other switch breaks it.
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Re: BANG !!! « Reply #2 on: December 07, 2011, 10:12:39 AM » Author: Powell
Yeah, but I don't want to put holes in the lamp that wasn't there.  Changing the ballast will be a chore.  The ballast is riveted in. I can break the rivet and put screws in the place of it.

I will be using the lamp  for short periods to see if this running hot will abate. I expect the fixture was not used much. It's a chrome colored potted ballast with no writing on it. 


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Re: BANG !!! « Reply #3 on: December 07, 2011, 12:37:44 PM » Author: paintballer22
@Powell I have see those buttons on eBay
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Re: BANG !!! « Reply #4 on: December 07, 2011, 12:47:48 PM » Author: Powell
Thanks.  I wil have to replace the ballast.  About 45 minutes and the ballast is extremely hot and you can smell tar.  I think, IF I am careful I can get the ballast out.


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Ash
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Re: BANG !!! « Reply #5 on: December 07, 2011, 05:36:40 PM » Author: Ash
If the start switch contacts afre welded, i think most vintage switches can be disassembled and the welded contacts separated with a screwdriver

What type of ballast it uses ? If preheat, is it autotransformer or just inductor ?
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funkybulb
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Re: BANG !!! « Reply #6 on: December 07, 2011, 07:33:03 PM » Author: funkybulb
at Ash those flourescent desk lamp are choke ballast like you would see on your F40 switch starts in your country. inductor ballast work from F14 to F20 T8 and T12. but it can be pain finding the right ballast to fit in desk lamp somtimes.
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Re: BANG !!! « Reply #7 on: December 08, 2011, 10:50:46 AM » Author: Powell
First, the switch is very cheap, but that is no problem. Also, the lamp is preheat, and the trigger start ballast is just a fraction too large. I have plenty of preheat / switch start ballasts that will work.  I may, if I am very careful, be able to remove the metal on the "rivet" on the end holding the ballast in place. I will have to carefully bend the 2 ends of the curved metal that holds the "rivet" in place. If I break it I will have to find a screw I can use.
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Re: BANG !!! « Reply #8 on: December 08, 2011, 11:31:54 AM » Author: paintballer22
You can drill out the rivits using a small drill bit it's easier than prying/bending them out.
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Powell
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Re: BANG !!! « Reply #9 on: December 08, 2011, 01:43:08 PM » Author: Powell
It's not exactly a rivet, but that's the best word I could think of. I will attempt to fix this tonight.
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Re: BANG !!! « Reply #10 on: December 08, 2011, 08:35:34 PM » Author: Powell
Ballast is changed. I used some Needle Nosed pliers and got the "thing" holding the ballast down on one side loose enough to slip the ballast out.  I used one of my black non potted Robertson ballasts that came from a scrapped 4 lamp 20 watt fixture I should not have gutted. ANYway the old ballast is a Stratfield Company ballast. There is a mounting plate on the bottom to mate it to the holes in the top of the base for mounting. It should have been mounted on the bottom, and the plate for mounting is non standard. IF the bottom screwed on I would just use the single lamp trigger start ballast.....

The "new' ballast powers the new bulb not nearly as bright...... DUH !!

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Re: BANG !!! « Reply #11 on: December 23, 2011, 10:10:03 AM » Author: Nevada Willis
You may have had some insulation break down in the windings of the original ballast that was involved in the dead short situation.  That could cause both excessive heat and overvoltage to the tube and could explain the difference in brightness.  It's best that the tube is now running at its not-so-bright proper voltage.

I think you learned the age old lesson - check your wiring twice before applying power!

It's nice you got it running again.
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Re: BANG !!! « Reply #12 on: January 16, 2012, 11:57:18 PM » Author: SeberHusky
Not meaning to sidetrack the topic here, but is it normal for a fluorescent bulb to blow out  in a big flash like a normal light bulb?
I have a little 4 watt bulb that I did not know it's lifespan, but it had some small blackness on the side. I plugged it in, and it did not light. Plugged it in again after spinning the bulb slowly in place to get a better connection, and it immediately exploded like a camera flashbulb, or when an incandescent bulb goes out. I have not bought a new bulb yet to re-test.
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Re: BANG !!! « Reply #13 on: January 17, 2012, 02:16:42 AM » Author: Medved
Not meaning to sidetrack the topic here, but is it normal for a fluorescent bulb to blow out  in a big flash like a normal light bulb?

Not at all, simply the ballast is not able to deliver enough peak power for such flash (the incandescent lightbulb may draw 100x..1000x the rated power from the mains during the flash, as there is no power limitation in the circuit).

So that behavior mean then the ballast is defective (shorted), so it does not limit the current delivered to the lamp. Note, then with the discharge lamps the lamp take any current the power supply is capable to feed (at least for a brief period, then the lamp may get destroyed by that), so it is the ballast task to "dose" the correct current into the lamp (e.g. 0.17A for the F4T5). So when ballast stop limiting the current, up to the mains short circuit current (high 100's til few 1000's A) could flow into the lamp, obviously destroying it with loud BANG...
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Re: BANG !!! « Reply #14 on: January 17, 2012, 05:25:37 PM » Author: Powell
MY Bang was caused by me accidentally getting 120 volts across filaments.....    :'(
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