5-9 watt PL CFL adaptor

[JohnR]

I'm wondering if the power drawn really would vary between a 5, 7, or 9 watt
tube used with one (plain reactor type) since they are universal in that
size. Of course, the 13 watt bulbs are keyed not to fit. It would seem the 5
watt tube should actually draw more power since the arc is shorter and the
inductor has no active regulation.

John

 

[Andrew Gabriel]

I'm wondering if the power drawn really would vary between a 5, 7, or 9 watt
tube used with one (plain reactor type) since they are universal in that
size. Of course, the 13 watt bulbs are keyed not to fit. It would seem the 5
watt tube should actually draw more power since the arc is shorter and the
inductor has no active regulation.

The inductor sets the current, which is the same for all those tubes.
The tube sets the voltage, which (ignoring cathode drop) is proportional
to the length of the lamp. Hence the power is proportional to the tube
length.

The voltage across the inductor is going to change slightly with the
different tube voltages and constant mains voltage. However, as most
of the voltage drop is across the inductor and not the lamp (at least
on 240V supplies here), this effect is tiny and will only have a tiny
effect on the lamp current.

 

[JohnR]

The inductor sets the current, which is the same for all those tubes.
The tube sets the voltage, which (ignoring cathode drop) is proportional
to the length of the lamp. Hence the power is proportional to the tube
length.

The voltage across the inductor is going to change slightly with the
different tube voltages and constant mains voltage. However, as most
of the voltage drop is across the inductor and not the lamp (at least
on 240V supplies here), this effect is tiny and will only have a tiny
effect on the lamp current.

On 120v AC supply, the 5 watt tube draws 200ma, two 9 watt tubes draw 150ma
(old) and 166ma (new). I let the tubes run for a few minutes to stabilize
before taking readings with a true RMS multimeter. I guess power factor
could have some effect as the loads change.

At any rate, I'm drawing more VA with the lower wattage tube!
John

 

[Victor Roberts]

On 120v AC supply, the 5 watt tube draws 200ma, two 9 watt tubes draw 150ma
(old) and 166ma (new). I let the tubes run for a few minutes to stabilize
before taking readings with a true RMS multimeter. I guess power factor
could have some effect as the loads change.

At any rate, I'm drawing more VA with the lower wattage tube!
John

A simple series inductor-lamp system has a very poor power factor, and
the higher power lamp will produce a better power factor because it
has a higher resistance. You need to measure or calculate power in
watts instead of VA.

--
Vic Roberts
http://www.RobertsResearchInc.com
To reply via e-mail:
replace xxx with vdr in the Reply to: address
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[JohnR]

A simple series inductor-lamp system has a very poor power factor, and
the higher power lamp will produce a better power factor because it
has a higher resistance. You need to measure or calculate power in
watts instead of VA.

--
Vic Roberts
http://www.RobertsResearchInc.com
To reply via e-mail:
replace xxx with vdr in the Reply to: address
or use e-mail address listed at the Web site.

I added 2 uf of correction. This brought the current down to 90ma with the 9
watt tube and 125ma with the 5 watt tube.
Next I checked with 3 uf. still 90ma with the 9watt tube and about the same
(95ma) with the 5 watt tube. So, yes, the current is constant with the
different tubes. As a matter a fact, shorting the tube socket, current only
rose to 105 ma. Without correction, current rose to 250ma when shorting.

John