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Testing CCFLs
dynomo:
--- Quote from: FIXITNOW on February 07, 2013,02:37:51 ---try ebay
400349118892
--- End quote ---
Looks exactly the same as the ones used in pc's to light cold cathode tubes. Only they added a 12 volt transformer to run it off the mains and made some leads with croc clips. Not sure if they would be any use to run larger tubes. Like Keith suggests Ok for 20 inches and under i expect.
OldLes:
Hi guys, thanks for replies. I told my pal last night, and he sent me a link to a you tube video.
http://www.youtube.com/watch?v=CK7rlLRHO3U
I have drawn out the circuit (below, subject to a recheck, and not sure about the transformer, but maybe almost any off a board will do).
After reading Kieth's Ebay link, I somehow don't think the Utube one would work off a PP3.
If I build it, I will probably add a milliameter (or a voltmeter across a resistor). Maybe different voltages for different length CCFLs.
Please comment.
OldLes.
fix2003:
i run my tster from my 12 v bench power unit this way i can check the current (using its built in display)of each ccfl as i have had them come on but using a lot more current
OldLes:
I have just been looking at CCFL specs. Approx values as follows:--
500mm tube length. Striking voltage 1,000. Running voltage 850 at 6mA current
900mm tube length. Striking voltage 1,500. Running voltage 1,300 at 6mA current.
Having regard to the points Kieth makes earlier regarding colour, current and start up time, it seems that a suitable tester should at least have a short/long length switch.
Looking at inverter boards, it seems that typically the HV secondary is centre tapped. Perhaps use one half only for short, end to end output for long lamps?
Any comments? Any suggestions for the best inverter unit to bodge, and how to over-ride the protection circuits etc.
It seems 40-60Khz is optimum frequency for operation. Would it matter for testing? I wonder what frequency that circuit I posted yesterday runs at? Probably less than 1000Hz? I built something similar 40 years ago to power a car radio when the vibrator "inverter" packed in, but I think that only ran at about 30Hz. Obviously the transformer will be important for frequency determination.
Les.
Edit. A quick calculation suggests that with 100% efficiency, a variable supply of 6-12v and adjustable from 0.5 to 1amp would be needed, rather than the PP3 of that earlier circuit. Les.
OldLes:
Maybe it was a mistake starting the Samsung inverter thread separately, time to bring it back together, but I will be referring to the circuit posted there.
With 12 v applied (-ive to 1,3,5,6,8 and 9. +ive to 10, 11 and 12) application of the +ive to pin 4 via 10K fires up the inverter for about 2 to 3 seconds. I have not found any effect of using pin 2 via a resistor to anywhere. (Above ref Nos. all CN1)
Using a 100:1 probe, measurement across CN2 yields 2,700vpp, equiv to 950V rms.
Using two probes in add mode, from output at blue capacitor end of CN2 to same point off CN3 yields 7,800vpp, or 2,760v rms. (Not sure that makes total sense, but it does suggest one output pair OK for 20" CCFLs, and possibly the two "hot" outputs of CN3/CN4 will drive the 42" ones).
Hopefully I will test it out on some CCFLs tomorrow, and if OK, I can look again at my Sharp LC-42DH77E mentioned in its own thread.
More input welcomed.
Les.
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