# Thread: Florescent lights and ammeters

1. ## Florescent lights and ammeters

Do i need a SCOPE to determine the power consumption from a compact florescent bulb?

i use an ammeter, and sombody said that it will not work because its not in "unity" i assume he means pulses.

now i know you cant read PWM with a normal ammeter, and need a scope or one really fast good quality ammeter.

which brings up the question of, if the ammeter is not correct, what is the sofisticated ammeter they are metering my power using ,,, a Scope :-)

can anybody toss a few compact florescent on a scope and tell me what they read?

2. ## Re: Florescent lights and ammeters

Pulses would be one problem. He might mean that there is a phase shift between the voltage and the current.

Power is the product of volts and amps, but using a different instrument to measure each would give the wrong result when measuring AC unless the current and voltage were in phase. And to measure AC accurately I guess you need meters that measure RMS voltages.

To measure power directly you need an instrument that measures the product of current and voltage. Apparently the power meters used by the electric power companies do this.
http://www.britannica.com/eb/article...att-hour-meter

3. ## Re: Florescent lights and ammeters

Compact florescent lights have a strange current wave form when I run a 13W through a 1 ohm resistor and measure the voltage across the resistor with a o scope to see the current drawn. The wave form looks like one very large short spike at the peek of each AC sign wave. I have a P3 Kill-A-Watt meter and it can accurately measure even the strangest loads like these types of lights. It is an invaluable piece of equipment that I would recommend to anyone.

4. ## Re: Florescent lights and ammeters

Compact florescent lights have a strange current wave form when I run a 13W through a 1 ohm resistor and measure the voltage across the resistor with a o scope to see the current drawn.
Where are you measuring this waveform - between the line (wall socket) and ballast or between the ballast and tube?

5. ## Re: Florescent lights and ammeters

Between the wall socket and the Ballast.

6. ## Re: Florescent lights and ammeters

Originally Posted by Brlux
Compact florescent lights have a strange current wave form when I run a 13W through a 1 ohm resistor and measure the voltage across the resistor with a o scope to see the current drawn. The wave form looks like one very large short spike at the peek of each AC sign wave. I have a P3 Kill-A-Watt meter and it can accurately measure even the strangest loads like these types of lights. It is an invaluable piece of equipment that I would recommend to anyone.
so if there was a Pulsing of sorts, you show it occuring at the same rate as the sinewave itself. i was thinking about a pulseing that would be at 1K or whatever rate the bulb actually operates in.

what IS the cycle rate of the bulbs themselveS?

7. ## Re: Florescent lights and ammeters

I don't know about what any internal oscilation rate of the driver inside the bulb or what frequency it would be but when measuring the current through the few bulbs I have it was a large spike for a small duty cycle at the peeks of the sine waves.

8. ## Re: Florescent lights and ammeters

There is a fairly interesting thread on usenet - alt.binaries.schematics.electronic, entitled "CFL current draw" dated 2/22/07 thru 2/25/07. Quite a few knowledgeable fellows over there discussing the rather nasty waveform these lamps are kicking out (scope traces shown).
Rob

9. ## Re: Florescent lights and ammeters

I have a small 150W Samlex Sine wave inverter and when I try to run even a small 13W CF bulb on it the inverter makes and awful buzzing noise which makes me think it is dying. I have not had a problem running several CF bulbs on even a small modified sine wave inverter other than the bulbs dying very prematurely and some times catastrophically.

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