measuring CFL voltage - Page 1
Forum section: electronics / beginners

author: Pirateguy
author_rank: Regular Contributor
timestamp: September 10, 2018, 08:33:39 am
content: so i took the circuit out of a cfl bulb and tried to measure the voltage it outs outto the tube, but i can't get a steady reading on it.all i get is either 0.5v-ish and with only 1 probe attached i get 1.5v-ish (both unstable)so i looked around and what i read is that they usually put out around 60 volts.i tried several of these circuits and several meters, all results are the same.why can't i measure this?

author: Pirateguy
author_rank: Regular Contributor
timestamp: September 10, 2018, 08:44:57 am
content: ugh, nevermind.follwing youtube tutorials verbatim had me using the wrong pin :S

author: ultrarunner2018
author_rank: Contributor
timestamp: September 11, 2018, 12:45:58 am
content: You won't get the correct voltage unless there is a CFL bulb connected to the output. The circuits are designed specifically for that type of load, which is not constant. Also, the frequency of AC (or pulsating DC) applied to the bulb is not 60Hz. It is usually much higher.

author: Pirateguy
author_rank: Regular Contributor
timestamp: September 19, 2018, 11:09:39 am
content: i see.i will do some measuring with a load, thanks for the tip!

author: wraper
author_rank: Unknown
timestamp: September 19, 2018, 11:15:12 am
content: Nice way how to kill your multimeter.

author: Pirateguy
author_rank: Regular Contributor
timestamp: September 19, 2018, 11:40:21 am
content: why would that destroy my meter?

author: wraper
author_rank: Unknown
timestamp: September 19, 2018, 12:35:38 pm
content: because of overvoltage.

author: Pirateguy
author_rank: Regular Contributor
timestamp: September 19, 2018, 12:53:31 pm
content: i thought these were supposed to put out something in the 50-100v range?

author: wraper
author_rank: Unknown
timestamp: September 19, 2018, 12:59:48 pm
content: Quote from: Pirateguy on September 19, 2018, 12:53:31 pmMultiply that by 10-20 times. When bulb is lit, it drops to a few hundred volts but during ignition or with open circuit, peak voltage can be huge.

author: Pirateguy
author_rank: Regular Contributor
timestamp: September 19, 2018, 01:52:33 pm
content: could i use one of these circuits to power a small tesla coil?

author: schmitt trigger
author_rank: Super Contributor
timestamp: September 19, 2018, 01:58:12 pm
content: Remeber, CFL power supplies are high frequency. Used to be 27 to 30 Khz but that caused interference with TV remotes, so the frequency nowadays is higher than 40 Khz.I doubt that most common multimeters would be able to read the voltage at that frequency accurately.Additionally, the voltage may have an unusual crest factor.I would read the voltage with a scope. Use a 10X probe and start with the highest volt/div setting. As others have mentioned, the open circuit voltage is significantly higher than the operating voltage.

author: Pirateguy
author_rank: Regular Contributor
timestamp: September 19, 2018, 02:34:39 pm
content: as luck would have it i am about to invest in my first proper scopei wonder, in this context, would a plasma arc be considered a load?and what about coils? could i wirelessly measure the frequency?

author: wraper
author_rank: Unknown
timestamp: September 19, 2018, 03:06:28 pm
content: Quote from: schmitt trigger on September 19, 2018, 01:58:12 pmAre you crazy suggesting this? It's a killer for probes and oscilloscopes, way more dangerous than for multimeters. Not only scope inputs are not isolated, they and their probes usually are rated for around 300V peak only. It's not even sufficient to measure 230V RMS because peak voltage exceeds 300V. Not to say CFL ballast output where you could often see one kilovolt or sometimes even more. There are already plenty of people with destroyed oscilloscopes, probes and multimeters.Don't ever touch CFL ballast with oscilloscope unless you have high voltage isolated probe.

author: drussell
author_rank: Super Contributor
timestamp: September 19, 2018, 03:09:13 pm
content: Quote from: schmitt trigger on September 19, 2018, 01:58:12 pmUmmmm, i don't think probing a couple thousand volts with a X10 oscilloscope probe is a very good idea.Edit:Likewrapersaid, in the post above...

author: Pirateguy
author_rank: Regular Contributor
timestamp: September 19, 2018, 03:24:25 pm
content: would a diy high voltage probe work?(the ones where u multiply the internal resistance of the meter)

author: schmitt trigger
author_rank: Super Contributor
timestamp: September 19, 2018, 04:02:21 pm
content: Guys, guys ,guys.Take a deep breath and slow down.I actually worked for several years for an electronic ballast manufacturer. Universal Lightning Technologies, if you ask. I KNOW WHAT I AM TALKING ABOUT.Very high startup voltages are only found ininstant startballasts. For a long, 75 watt, 8 feet tube, the starting voltage was at its highest 800 volts.For preheat tubes, and specifically, for short length tubes, the startup voltage is far lower.For a preheat, 4 feet, T12 tube the open circuit voltage was around 250 volts.We were in the process of starting to build CFLs when I left the company so I did not have much experience with them, but they were always preheat. I have opened up many CFLs during these last years, and with the exception of some piss-poor Chinese ones, all the CFLs I have seen are not instant start but preheat ones.What you are correct though, is that you have to use good probeswhich are rated for the correct voltage.

author: schmitt trigger
author_rank: Super Contributor
timestamp: September 19, 2018, 04:13:30 pm
content: I found this information, for an instant start ballast. Please note these are 72 inch and 96 inch tubes. Long, long tubes.

author: Gyro
author_rank: Super Contributor
timestamp: September 19, 2018, 05:40:34 pm
content: The great Jim Williams was a master of these sort of measurements. Go and look at LT AN65 and scroll to Appendix C.http://www.analog.com/media/en/technical-documentation/application-notes/an65fa.pdfListen to the master:Quote

author: edavid
author_rank: Super Contributor
timestamp: September 19, 2018, 06:47:01 pm
content: Quote from: Gyro on September 19, 2018, 05:40:34 pmCCFL backlight tubes and inverters are very different from CFL light bulbs. This app note and warnings are not relevant to OP's question.

author: wraper
author_rank: Unknown
timestamp: September 19, 2018, 06:47:48 pm
content: Quote from: schmitt trigger on September 19, 2018, 04:13:30 pmThis is not maximum that can be there and especially with bulb removed or damaged.QuoteSomething you did not mention. Therefore I criticized your suggestion. Don't forget this is aBeginner threadand op had no clue about voltages.

author: Gyro
author_rank: Super Contributor
timestamp: September 19, 2018, 06:52:16 pm
content: Quote from: edavid on September 19, 2018, 06:47:01 pmDoh, I misread and missed the absence of the extra 'C'.

author: wraper
author_rank: Unknown
timestamp: September 19, 2018, 06:59:07 pm
content: Quote from: edavid on September 19, 2018, 06:47:01 pmIf you read it, that app note does mention hot cathode fluorescent lamps. Also as I previously said when there is no lamp or lamp is damaged, peak voltage can go up a lot.

author: Pirateguy
author_rank: Regular Contributor
timestamp: September 19, 2018, 08:49:54 pm
content: speaking of beginner threads, i would really appreciate it if you guys could stop comparing penis size for 2 secondsand maybe answer 1 or 2 of my questions?QuoteQuoteQuoteQuote

author: TheNewLab
author_rank: Frequent Contributor
timestamp: September 20, 2018, 05:59:07 am
content: interesting.1.) regarding a tesla coil, I would look at info on DIYing a tesla coil first. I suspect Tesla coils use much higher frequency.2.) I know nothing about plasma arc..duck duck DIY plasma arc? or DIY plasma arc? or what's the frequency of plasma arc?3.) coils, like clamp meters and hall effect are designed for measuring high currents - I would look into TV repair methods that have KV levels of voltage.4.) DIY HV probes are a mixed bag. I am sure plenty of people. likely much more experienced than I would say nothing except a quality built HV prove. However, I have seen instructions on how to make two types of DIY HV probes from Delton Horn repair bookHow to Repair Almost AnythingIt's old..Homer Davidson was big on HV probes for TV repair too.For me...it is all about keeping a distance...say 3 or 4 foot long pole on the probe, in case the DIY probe flashes over.Please, note that I am a hobbyist, not a pro.. I am sharing how I would approach it...listen to anyone more knowledgeable than me FIRST!.Thanks for posting this question

author: Pirateguy
author_rank: Regular Contributor
timestamp: September 20, 2018, 07:35:35 am
content: thanks for the reply1: i did look around and played with this java calculator. turns out small coils like the one i had in mind 300-600 turnswill run at hundreds of khz, but a larger size coil with more windings will resonated at a lower frequency.2: with plasma arc i just mean the spark u can make with high voltage. like a jacob's ladder, would that act as a load andmake the voltage drop?3: i was thinking only of measuring frequency this way. if i just rig up 2 coils, one to transmit and one as an antenna, i'd imaginei can get some sort of signal, and the frequency at least should not be effected by reception quality.4: well i suppose i can just test it out with a cheap meter. i wasn't planning on measuring high current anyway.based on some tutorial videos i watched, i measured the internal resistance of several meters and all are 1 meg andso a 99meg resistor array should give me a 100x factor. should be enough for the cfl circuit, but i suppose i could rig up a spark gapfor extra safety.