Effect of voltage drop on power of fluorescent lamp w/ magentic ballast

Status
Not open for further replies.
E

energymv

Member
How does voltage variation typically affect power of a fluorescent lamp with magnetic ballast? Note that fluorescent lamp ballasts and lamps behave like inductive appliances, rather than incandescent (resistive) appliances.

I am looking for something more than P = V^2/R here...

I would prefer to hear from people with experience in this calculation. I would also like to see links to find some publications on this topic on Google.
 
080912-1038 EST

energymv:

Here is a partial answer to your question. This is not power input but current because I do not have a wattmeter here. Later I will setup a wattmeter.

Voltage adjusted with a Powerstat (Variac). Current measured with a Fluke Hall clamp-on probe and a 27 meter.

Code: 
[FONT="Courier New"] Volts    Amps
  130     0.97
  120     0.98
  110     1.01
  100     1.03
   90     1.05
   80     1.08
   70     1.09
   60     0.96[/FONT]
Close to a constant current load. Only a slight variation in light intensity.

.
 
080913-0837 EST

energymv:

Continuation of my above experiment. This time with a wattmeter and a true RMS current measurement. Still the same Fluke Hall current probe, but using a Fluke 87 true RMS in place of the Fluke 27 average reading meter. Note the power factor difference between the two fixtures. The RMS current does not look as constant as did the average, but it still varies at a slower rate than voltage.

I suggest you do some of your own experiments and see if you get comparable results. Also try the experiments on an electronic ballast.

Code: 
The fixture has two 60 W Philips 8' bulbs, magnetic ballast,
This fixture may include a noise filter.

Voltage  Current  VoltAmp   Wattmeter    PF
           RMS

  134     0.94       126       114      0.90
  125     0.96       120       110      0.92
  114     0.99       113       105      0.93
  104     1.03       107       100      0.93
   94     1.07       101        94      0.93
   83     1.12        93        86      0.92
   72     1.15        83        77      0.93
   61     1.12        68        64      0.94
       61  is basically at failure point


An older unit with same type bulbs but more aged.
Does not have a noise filter.
         
Voltage  Current  VoltAmp   Wattmeter    PF
           RMS

  134     0.72        96        76      0.70
  125     0.69        86        69      0.80
  114     0.78        89        76      0.85
  104     0.85        88        71      0.81
   94     0.93        87        71      0.82
   83     1.02        85        67      0.78
   72     0.99        83        60      0.72
   61     fails above this point
Code: 
Moved the newer bulbs into the older fixture and a one 
point test.

Voltage  Current  VoltAmp   Wattmeter    PF
           RMS

  125     0.76        95        76      0.80

Somewhat more power into the lamps, but comparable 
results for the older ballast. Still shows 0.8 PF.
.
 
Last edited:
Thank you... Based on the results of your experiment, RMS current may increase as voltage decreases. Now that is counter-intuitive, not what I expected to find for a magnetic ballast / fluorescent bulb. Are you surprised with your results?

The lamps you used are fluorescent lamps with magnetic ballasts? Are you sure it is not a newer "universal voltage" or "voltage compensating" electronic ballast? Just checking...

I was curious whether or not your results would agree with this study:
http://www.itee.uq.edu.au/~aupec/aupec04/papers/PaperID77.pdf which says that
"...The fluorescent lamp faired worse than the incandescent in its power changes with a rise of 22% in active power for a 10% rise in voltage. The total power measured showed and increase in 38% for the same voltage rise. Fluorescent lights have the same problem as the inductive devices i.e. the increase in reactive power with over voltage. As the voltage is increased the fluorescent lamps power factor decreases."
 
080913-1849 EST

energymv:

Yes both are definitely magnetic ballasts. The older one is probably 45 to 50 years old, and the ballast may have never been replaced. The newer one is maybe 35 to 40 years old, but may have a new magnetic ballast. I have no fluorescents with an electronic ballast. The older unit showed little intensity variation until the voltage was quite low.

Not really counter intuitive. The bulb is essentially a constant voltage device, and if the current remains near constant as shown by the average meter, then load power is constant and as input voltage goes down, then input RMS current may be expected to go up over some range.

Do run some of your own experiments. This is sort of like an induction or synchronous motor with a constant mechanical load as voltage is reduced.

.
 
Status
Not open for further replies.
Top