Delamping; less bulbs = more power??!

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RayS

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Question was, if 2 of 4 flourescent lamps are removed, do you save 50% of lamp wattage, or more, or less? I said more than 50%, because of ballast losses, and have read that cooler operation helps efficiency.

I tried 1 fixture, removing the outer lamps actually increased current draw- about 40% as I recall. Removing inner 2 lamps did reduce current 56%. I am at a loss to explain this.
Why would it increase removing the outer lamps?
Why would it be different for the inner lamps?

notes: 4 Tube t8 fixture, sylvania ballast, true RMS clamp on meter
 
RayS said:
Question was, if 2 of 4 flourescent lamps are removed, do you save 50% of lamp wattage, or more, or less? I said more than 50%, because of ballast losses, and have read that cooler operation helps efficiency.

notes: 4 Tube t8 fixture, sylvania ballast, true RMS clamp on meter
Click to expand...

without ever checking it, I had generally told customers there was no way they could save money by removing half of their lamps, b/c every time I touched a ballast (lamped or not) it was still kicking off a lot of heat. My assumption was based in general on experiences with magnetic ballasts. I usually got a good service call for changing over to T8's with electronic ballasts, and they increased their efficiency and the lumens in their office/shop/wherever.

I am impressed that you thought you'd check it on a meter. My next question would be: even if you can achieve a reduction in current by removing lamps, will this affect the operation of the ballast and the remaining two lamps, shortening their operational life?
 
Some flourescent lamp circuits use a capacitor in series with one lamp or one pair of lamps, the other lamp or pair of lamps being connected to the line via an inductance only.

This results in the lamp/pair of lamps connected via the capacitor having a leading (capacitive) power factor, and the other lamp/pair of lamps having a lagging (inductive) power factor.
This provides an acceptable overall power factor for the fixture.

Removal of one lamp or pair of lamps, removes the effect of the leading and lagging power factors cancelling each other out, and can result in an increase in current, as noted by the O/P.

The wattage however will be about halved by removing half the lamps, this is unavoidable, no way is the ballast going to consume as much power as would otherwise be used by the lamp(s), it would catch fire.

The exact reduction in total watts from removing lamps will vary according to the type of ballast, it will however allways be ROUGHLY equal to the wattage of the removed lamps.

If lamps are removed from a transformer type ballast, then the winding will still use use some power, as may be determined by the fact thast it will still get warm.
If lamps are removed from a switch start type ballast, then the ballast will absorb no power at all, and will remain at room temperature.

In order to determine the watts used by a fixture you will need a wattmeter, the watts can not be determined by a current meter since the power factor is not only unknown but also likely to vary according to how many/which lamps are in use.
 
benaround said:
Ray,

Some 4 tube ballasts are also used for different combinations, such as 3 tubes.
Click to expand...

Yes, I've installed those, too, now that you mention it. It appears
Broadgage answered most or all of the questions you presented, and any that I had too. Thanks to Ray for OP
 
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question..if the ballast draws .89 amps to run any number of given scenarios. say a 4 bulb t8 running 3 f40 t8's, whether it runs 4 or 3 it is going to draw .89 amps if you took the bulbs out and turn on the fixture is it going to draw .89 amps?? I thought regardless of whether it has a load or not it is going to draw .89 amps??

The amp number may not be accurate i was using a number just as a number for questions sake.
 
cschmid said:
question..if the ballast draws .89 amps to run any number of given scenarios. say a 4 bulb t8 running 3 f40 t8's, whether it runs 4 or 3 it is going to draw .89 amps if you took the bulbs out and turn on the fixture is it going to draw .89 amps?? I thought regardless of whether it has a load or not it is going to draw .89 amps??

The amp number may not be accurate i was using a number just as a number for questions sake.
Click to expand...

As Frank, post 3, mentioned there are those electronic ballasts for T8s which will run three or four lamps. The current draw listed on the ballast is less for the three lamp configuration than for the four, if I'm not mistaken, and I'm not looking at one right now. and couldn't find any info. w/ a quick google.
 
cschmid said:
question..if the ballast draws .89 amps to run any number of given scenarios. say a 4 bulb t8 running 3 f40 t8's, whether it runs 4 or 3 it is going to draw .89 amps if you took the bulbs out and turn on the fixture is it going to draw .89 amps?? I thought regardless of whether it has a load or not it is going to draw .89 amps??

The amp number may not be accurate i was using a number just as a number for questions sake.
Click to expand...
Just from a common sense point, I say no. There is less energy leaving the system (light) so the system drops the energy input needs.
 
Thanks for the help. Broadgage seems to be onto the solution- I didn't do actual power or power factor readings, just current. It was just hard for me to believe even a simple reading would not show a reduction in all cases.

I have been looking at various electronic ballast info,many are actually rated for different numbers of lamps, ie 2-3 or 3-4, some have only 1 rating- this is probably the type Broadgage mentioned has the capacitors on some tubes. I guess I will have to check each type of ballast. The building has a poor power factor already, sometimes reaching .65, so I do not want to worsen it. PF correction is already planned to be implemented with a switched cap. bank.
 
Looking at a 4-lamp, 4 ft with "I" for active lamps and "X" for removed lamps:

IIII: W=82.7, pf=0.58, VA=142.59, A=1.2, A/L=0.29, W/L=20.68
IXII: W=69.0, pf=0.56, VA=123.21, A=1.0, A/L=0.34, W/L=23.00
XIII: W=68.3, pf=0.56, VA=121.96, A=1.0, A/L=0.34, W/L=22.77
IXXI: W=51.2, pf=0.53, VA= 96.60, A=0.8, A/L=0.40, W/L=25.60

IIII: W=82.9, pf=0.58, VA=142.93, A=1.2, A/L=0.30, W/L=20.73
IIXI: W=67.6, pf=0.57, VA=118.60, A=1.0, A/L=0.33, W/L=22.53
IIIX: W=68.1, pf=0.56, VA=121.61, A=1.0, A/L=0.34, W/L=22.70
XIIX: W=51.2, pf=0.54, VA= 94.81, A=0.8, A/L=0.39, W/L=25.60
 
cschmid said:
mivey those are good figures and I like how you listed them. are those purely math or actual readings.
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The W & pf were direct readings. I got VA by VA = W/pf.

The amps were not directly measured. I was trying hurry the procedure because of lamp/ballast stabilization, plus my wife was not amused with holding lamps while I played on the ladder. I took a few voltage readings and they were 121 +/- a few tenths. I used 121.0 to find the A = VA/121.0 for all the readings.

The A/L & W/L was just A & W divided by the # of remaining lamps.
 
sweet a man who does things just out of curiosity. I would like to know if they were t-12's or t-8's? Do you think a magnetic ballast and electronic ballasts are affected the same?
 
cschmid said:
sweet a man who does things just out of curiosity. I would like to know if they were t-12's or t-8's? Do you think a magnetic ballast and electronic ballasts are affected the same?
Click to expand...
F40T12s & one electronic ballast. FWIW, F40's were not listed on the ballast.

I don't expect a magnetic to react exactly the same. I don't have a magnetic handy to test, but I seem to recall that removing one causes the other to go out (or at least flicker). When I removed one of mine, the other three stayed lit.
 
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