Flourescent lamp -Wasting Power?

Could they use ferroresonant xfrmrs instead of chokes?

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You can do it with an oscilloscope and a resistive shunt to measure
the current.  Display voltage on one channel, current on the other,
determine the phase angle between them and then P = IE cos(phi).

You could also do it with a current transformer once you've determined
its primary-to-secondary phase shift.

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So is getting up in the morning.

You guys are correct, I didn't take the phase angle into into account, I just wired a 25 ohm wirewound resistor in series with the lamp and measured almost 2 volts ac across it (lamp switched off) with my olde Simpson 260 VOM. I can't properly relate the temperature my fingers felt to the real power being dissipated by that electronic ballast. The board was mounted in liberally slotted flimsy plastic cage in the center of the two nested circline flourescent bulbs in the lamp's bowl. There was good convection cooling through those slots, but who knows, maybe it was only 2 watts, that wasn't my point 'yknow.

But, thanks for accepting that even in retirement I could probably drag my two channel scope off the shelf, hit the "hellbox" for parts and kludge up a setup to measure the real power - without frying myself.

But, I'm reminded of the words of the MIT prof who tought a course in "rotating machinery". He was a Brit, and while we guys were hacking around with a bunch of 240v 3 phase apparatus with big exposed knife switches, motors without guards over their live parts, and stuff like that, he proclaimed, "You boys will never become real engineers until you learn to 'take' a shock". (Thanks for the mammaries.)

I was obviously overly incensed by what I percieved as a wasteful and stupid design that I just multiplied current times voltage in my head and was probably wishing for a high number to further justify my angst.

Nonetheless, the principle is the same, and I'm still wondering if there was any reason other than saving a few pennies to design those damn lamps that way.

The two other "two tube" flourescent torchier lamps we have in the house have two separate skinny electronic ballasts hidden inside the pole, controlled by a single pole four position rotary switch which sequences like the one in a "3-way" incandescent lamp, except it controls the power to the inputs of the two ballasts rather than to the filaments of a 3-way bulb. (This I know because I've had to replace a switch in one of them when it got lazy had to be teased to get it to work.)

Happy Holidays guys,

Jeff

--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

"As long as there are final exams, there will be prayer in public
schools"

Jeeze guys, I didn't forsee my OP turning into this.

But when I wrote "Thanks for the mammaries" in my response to Fred Bloggs, maybe I should have included this link to one of my web pages:

Happy Holidays,

Jeff

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Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

"As long as there are final exams, there will be prayer in public
schools"

Designs like this, that expose electronics to line voltage, continuously, and with no load, are subject to destruction by line surges, a lot more than electronics that is only connected to the line when the device is actually in use.

I just fixed my DVD player (blown rectifier and fuse) that got damaged in a storm even though the unit was switched off. The switch was between the rectifier and the rest of the power supply. Idiotic design, if you ask me.

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John Popelish

If the lamps would use 9W they would be *very* hot, I suspect the most current is not "real" in phase with the voltage, but imaginary as some capacitive or inductive load. I would guess 1-2W as you descibe it, much like the small low voltage xformers when idle. You cannot measure the power consumption with an amperemeter, even if it is true rms, but you need a dedicated power meter for it with 3connections at least.

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ciao Ban
Bordighera, Italy

John, what you suggest is potentially lethal, as you will have to connect a power line directly to the case and earth, hopefully tripping only the earth leakage circuit breaker. You will need two transformers, which are isolated on the secondary, or you could use an isolation transformer in the power line. But all this is *not* appropriate for an unskilled hobbyist.

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ciao Ban
Bordighera, Italy

The OP is an MIT EE grad...note his signature file- he is definitely "old school"- very hands on:)

I read in sci.electronics.design that John Fields wrote (in ) about 'Flourescent lamp -Wasting Power?', on Sun, 19 Dec 2004:

Well, he does call himself 'Ban'. (;-)

-- Regards, John Woodgate, OOO - Own Opinions Only. The good news is that nothing is compulsory. The bad news is that everything is prohibited.

Also see

Nope. Build a box, with a power resistor in series with the neutral.

Add a couple of dividers from each end to ground, say 20:1, with an output impedance of maybe 100K, and 100K from there to the output (strapped with a couple of 20V zeners each before the output resistor).

(the output resistors should be composed of two resistors each capable of constant working at the nominal mains voltage)

Fairly safe, even if the outlet is miswired. You connect the scope to the outputs, in differential mode, and use "line mode" triggering.

I read in sci.electronics.design that Ian Stirling wrote (in ) about 'Flourescent lamp -Wasting Power?', on Sun, 19 Dec 2004:

How can you measure the phase angle between voltage and current with that set-up?

--
Regards, John Woodgate, OOO - Own Opinions Only. 
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

Oops, I forgot, a third divider to live.

You connect the scope to that, set the mains trigger to zero crossing, setup the timebase so it shows a positive going half cycle (or whatever), then stick the scope in differential mode, and do the current measurment.

Just a guess, but does it take any longer to come to full brightness when you plug it in/power it up with the switch on (as when the socked is controlled by a wall switch) than when you turn the switch on with it pligged in? In other words, does this thing being powered up save any "warmup" time?

I have a 1967-model Heathkit B/W TV that has an "Instant On" feature - when off, the filament winding of the power transformer is half-wave rectified and fed to the CRT filament, keeping it warmed up enough that when the set is turned on (a double throw switch shorts out the rectifier as well as turning on power to the rest of the set), the picture appears instantly, if not exactly at full brightness. I understand this feature was outlawed (this is second-hand info, I have no idea what the law might say) during the energy crisis of the

1970's (under Presidents Ford and Carter). One can see where products such as microwave ovens and VCR's might take a small amount of power all the time, as this would enable some useful features, but many other things take power when off as well, just so the power switching circuitry (specifically the on-off button) can be low-voltage/low power. And then there's that lamp. I can only guess the law has changed, is no longer enforced, or only covers TV's and not lamps (because who would have ever thought a lamp would pull power when turned off?).

Have you written your congressional representative about this?

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I am reminded of some circuits used to measure Microwave power ! Basically it measures the temperature rise of a Dummy Load, and is calibrated by comparing it to a easily measured DC voltage ie. P=E squared /R where R is the 50 ohm Dummy Load. In plain language, if it get warm (hot) it is drawing power, and we really don't care about Power Factor or Phase angle. This is what the Power company is billing us for ! So if the fixures are warm, they are drawing power from the Mains. Fingers, a Manual Watt-meter ?? Good for

1~25 Watts, above this range, testing cycles must includes days to weeks downtime for healing !

Yukio YANO

Sure - You can also pop down the shop and buy a Power Meter which plugs into the socket and the appliance on the other side - like one of those timer watches. If you program the kWh price into it, it will calculate the Daily, Weekly & Annual costs of running the appliance when left there long enough to get capture the use pattern.

They cost about USD 20 - much less than an hour of my time!

And have the added fun of being several hundred percent out on some loads.

If it's as accurate as his electric company's power meter, he's probably going to be happy! :-)

Even the mechanical ones have pretty decent specs (fractional percent accuray). As you'd expect from something that involves money changing hands. Check out the GE datasheets.

Best regards, Spehro Pefhany

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