Power factor of a retrofitted LED unit in a fluorescent fitting

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Discussion Overview

The discussion revolves around the power factor and energy consumption of retrofitted LED tubes in fluorescent fittings. Participants explore the implications of using LED tubes designed to replace traditional fluorescent lights, particularly focusing on the discrepancies between the expected and measured power consumption, as well as the effects of existing ballasts and capacitors in the circuit.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant reports that their LED tubes, rated at 24W, are consuming 80W as measured by a clamp meter, raising questions about the accuracy of power ratings and the influence of the existing ballast and capacitor.
  • Another participant explains that the inductors in the original setup were intended to maintain current flow over a greater angle, while the capacitor was meant to improve power factor by neutralizing inductance.
  • Concerns are raised about the potential for the clamp meter to measure reactive current, which could lead to higher apparent power readings without corresponding real power charges.
  • One participant mentions that removing the inductors and capacitors could reduce reactive current and potentially lower energy bills, though the extent of this reduction is uncertain.
  • Measurements from a participant's desk lamp with an LED replacement show a power factor of 0.64 and a phase angle of 50°, suggesting a significant difference from purely resistive loads.
  • There is speculation about whether the ballast in use is electronic or magnetic, with one participant leaning towards a magnetic ballast based on the age and characteristics of the setup.

Areas of Agreement / Disagreement

Participants express differing views on the implications of the power factor and the necessity of modifying the existing setup. There is no consensus on whether the current configuration is optimal or if changes would yield significant benefits.

Contextual Notes

Participants note that the power factor of the LED tubes must be at least 0.5, and discussions include assumptions about the nature of the loads and the effects of existing components in the circuit. The complexity of the situation is acknowledged, with various factors influencing the measurements and potential outcomes.

Guineafowl
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TL;DR
How does leaving the ballast and capacitor in circuit affect power factor of LED lights?
A poster on another forum has fitted a large number of 230V 50Hz 24W nominal LED tubes, apparently designed to be plugged straight into the old fluorescent fittings.

He has found, by clamp meter measurement, that the new LED lights appear to be consuming 80W, not the claimed 24W.

A number of us pointed out the difference between apparent power as measured by the clamp meter, and real power as charged by the power company, and the possible effects of leaving the ballast and capacitor in circuit.

An engineer from the supplier has visited, and merely measured the consumption by clamp meter again. I would be very interested in the input from members on here.

May I link the thread here?: https://www.mig-welding.co.uk/forum...florescent-led-replacement-efficiency.128634/

edit: I should add that this class of LED tube must have a minimum power factor of 0.5. In my scribblings, I have (for now) modelled them as 24W resistive loads. It might be more meaningful to assume a 0.5 (leading?) PF and calculate the complex impedance of the tubes as such.
 
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The inductors were there to keep current flowing through the tubes for a greater angle, not just at the peak of the voltage cycle.
The capacitor was there to neutralise the inductance, to partly restore the PF.

The clamp current being measured now is the reactive capacitor current. That will be of the same magnitude as the original tube current through the inductor. That explains why the clamp current shows the VA of the original tubes. Depending on the type of metering used and tariff, they may actually be paying for the reactive current.

Removing both the inductor and the capacitor will reduce the reactive current, and the circulating energy. It will minimise the bill for lighting, by an unknown amount, depending on the metering.
 
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Thanks. The OP is, I believe, on a domestic three phase tariff, meaning only real power is charged. This may change in the future.

The height of the ceiling means that removing the inductors/caps would be a significant upheaval. Given that the ‘extra’ current is not being charged for, it looks like the job would not be worth it.

May I quote, or at least link to your post?
 
Guineafowl said:
May I quote, or at least link to your post?
Feel free.
 
I have a magnifier/desk lamp at my work station with an 8 inch Circ-line LED lamp in it. The LED lamp is a plug-in replacement for the original fluorescent tube, the ballast is still in the circuit.

I plugged it in to a KIL A WATT meter and here are the numbers with the LED:
V = 118.5
A = 0.42
W = 32.1
VA= 49.8
PF= 0.64

If I did the math right, that shows a phase angle of 50°.

Cheers,
Tom
 
Tom.G said:
I have a magnifier/desk lamp at my work station with an 8 inch Circ-line LED lamp in it. The LED lamp is a plug-in replacement for the original fluorescent tube, the ballast is still in the circuit.

I plugged it in to a KIL A WATT meter and here are the numbers with the LED:
V = 118.5
A = 0.42
W = 32.1
VA= 49.8
PF= 0.64

If I did the math right, that shows a phase angle of 50°.

Cheers,
Tom
Would that be an electronic ballast?
 
Guineafowl said:
Would that be an electronic ballast?
I haven't taken it apart, but:
It used a conventional starter for the original lamp.
The housing size where the ballast seems to be is 3 x 3.5 x 2.5 inches in size.
It is about 12 to 15 years old.

I vote for a magnetic (transformer) ballast.
 
Tom.G said:
I haven't taken it apart, but:
It used a conventional starter for the original lamp.
The housing size where the ballast seems to be is 3 x 3.5 x 2.5 inches in size.
It is about 12 to 15 years old.

I vote for a magnetic (transformer) ballast.
…and when can we expect the stripdown and analysis? :wink:
 
'Fraid not, the steel case, presumably with the ballast, is crimped together.
 

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