On Fri, 26 Jun 2015 22:30:18 +0000, Andrew Gabriel wrote:

In article ,
Fredxxx writes:
On 26/06/2015 21:00, Brian-Gaff wrote:
Less flicker with the hf, but more radio interference probably.
Brian

Given that even electronic ballasts are driven by 50Hz mains, why would
they produce less flicker?

There is no energy storage as such in electronic ballasts.

Yes there is - first thing they do is rectify mains to 340VDC, and use a
storage capacitor.

Secondly, the high frequency driving circuit does not care about having
some ripple on the DC supply, since it's driving the tubes at constant
current. If the capacitor significantly fails, you can get 100Hz ripple
creeping through - you can't see that, but the light output will be
noticably reduced. It's rare though.

Thirdly, you don't get 50Hz flicker which you can with magnetic ballasts
(due to the tube partially rectifying near end of life, and from tube
ends sometimes too). The tube runs at 20-50kHz instead, which apart from
not being visible, actually means the tube won't extinguish as the
current passes through the zero point, because that's a shorter duration
than the mercury ion decay time (which is of the order 1/10000th of a
second).

Which is the very reason why using 10 to 20 KHz ac current instead of 50
or 60Hz gives something like a 10% or so boost in lamp efficacy. IIRC,
large department stores were one of the early adopters of using a
dedicated high frequency lighting supply feed to modified luminaries.

They didn't go to the extreme of 10KHz but, afaicr, chose a common 3KHz
supply generated by a Thyristor based frequency converter[1] which
allowed the use of lighter more efficient inductive ballast chokes in
each luminary. Nevertheless, the higher frequency supply did improve the
efficacy of the tubes, reducing running costs sufficiently to justify the
capital investment in the system.

[1] The Thyristor based frequency conversion technology used by such
department stores required the use of a three phase supply afaicr. I
suppose the less than ideal choice of 3KHz was a compromise over
conversion and distribution losses that would have otherwise been
incurred with a 10KHz supply.

--
Johnny B Good

In article ,
Johnny B Good writes:
On Fri, 26 Jun 2015 22:30:18 +0000, Andrew Gabriel wrote:

In article ,
Fredxxx writes:
On 26/06/2015 21:00, Brian-Gaff wrote:
Less flicker with the hf, but more radio interference probably.
Brian

Given that even electronic ballasts are driven by 50Hz mains, why would
they produce less flicker?

There is no energy storage as such in electronic ballasts.

Yes there is - first thing they do is rectify mains to 340VDC, and use a
storage capacitor.

Secondly, the high frequency driving circuit does not care about having
some ripple on the DC supply, since it's driving the tubes at constant
current. If the capacitor significantly fails, you can get 100Hz ripple
creeping through - you can't see that, but the light output will be
noticably reduced. It's rare though.

Thirdly, you don't get 50Hz flicker which you can with magnetic ballasts
(due to the tube partially rectifying near end of life, and from tube
ends sometimes too). The tube runs at 20-50kHz instead, which apart from
not being visible, actually means the tube won't extinguish as the
current passes through the zero point, because that's a shorter duration
than the mercury ion decay time (which is of the order 1/10000th of a
second).

Which is the very reason why using 10 to 20 KHz ac current instead of 50
or 60Hz gives something like a 10% or so boost in lamp efficacy. IIRC,
large department stores were one of the early adopters of using a
dedicated high frequency lighting supply feed to modified luminaries.

They didn't go to the extreme of 10KHz but, afaicr, chose a common 3KHz
supply generated by a Thyristor based frequency converter[1] which
allowed the use of lighter more efficient inductive ballast chokes in
each luminary. Nevertheless, the higher frequency supply did improve the
efficacy of the tubes, reducing running costs sufficiently to justify the
capital investment in the system.

[1] The Thyristor based frequency conversion technology used by such
department stores required the use of a three phase supply afaicr. I
suppose the less than ideal choice of 3KHz was a compromise over
conversion and distribution losses that would have otherwise been
incurred with a 10KHz supply.

Probably the RFI too. The full boost in efficiency is normally quoted
as occuring at 5kHz. Note that in the EU, you won't get any more light
from an electronic ballast because EU rules now require them to all
underrun the tubes by the same amount for energy efficiency reasons.
If your ballast is marked EEI=AA1 or AA2, then it underruns its tubes,
and if it isn't marked with one of these efficiency ratings, it's
illegal to import or manufacture in the EU.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

In article ,
Fredxxx wrote:
On 26/06/2015 21:00, Brian-Gaff wrote:
Less flicker with the hf, but more radio interference probably.
Brian

Given that even electronic ballasts are driven by 50Hz mains, why would
they produce less flicker?

The clue is in the name - HF ballast. Stands for high frequency.
Transformers are smaller and cheaper to make for HF.

There is no energy storage as such in electronic ballasts.

--
*If at first you don't succeed, destroy all evidence that you tried *

Dave Plowman London SW
To e-mail, change noise into sound.

On 27/06/2015 01:05, Dave Plowman (News) wrote:
In article ,
Fredxxx wrote:
On 26/06/2015 21:00, Brian-Gaff wrote:
Less flicker with the hf, but more radio interference probably.
Brian

Given that even electronic ballasts are driven by 50Hz mains, why would
they produce less flicker?

The clue is in the name - HF ballast. Stands for high frequency.
Transformers are smaller and cheaper to make for HF.

HF is the drive to the tube, where as you say inductors are smaller and
cheaper.

On the other hand capacitors are expensive. If someone asked me to make
a HF ballast, the first thing I would do is eliminate such a component
that is both costly and unreliable; and allow the HF to be modulated at
100Hz. Hell, I could even design a unit to have near perfect Power Factor.

After looking at circuits, I do see that most have a ~33uF 400V cap to
provide a "smoothed" nominal 325V DC supply. I'm just surprised.

There is no energy storage as such in electronic ballasts.

Interesting that for what I'd call a normal florry with say a 5ft or so
tube, neither LedHut or TLC sell replacement LED tubes for. Wonder why
that is?

--
*The older you get, the better you realize you were.

Dave Plowman London SW
To e-mail, change noise into sound.

In message , "Dave Plowman (News)"
writes
Interesting that for what I'd call a normal florry with say a 5ft or so
tube, neither LedHut or TLC sell replacement LED tubes for. Wonder why
that is?

LEDhut do:

http://www.ledhut.co.uk/led-strip-li...ight-1500mm-5f
t.html
--
Chris French

On Sun, 28 Jun 2015 01:16:42 +0100, Chris French wrote:

In message , "Dave Plowman (News)"
writes
Interesting that for what I'd call a normal florry with say a 5ft or so
tube, neither LedHut or TLC sell replacement LED tubes for. Wonder why
that is?

LEDhut do:

http://www.ledhut.co.uk/led-strip-li...-24w-led-tube-
light-1500mm-5f
t.html

I note that it has a 90L/W efficiency and the need to slightly modify
the wiring in the luminary (a common requirement for many such 'drop in'
tube replacements).

At ten or more times the price of a regular tube, I do wonder at the
point of such an exercise right now. In my view, it makes more sense to
wait for the 200 to 300 lumens per watt LEDs to finally materialise in
the stores sometime in the next 12 months or so according the the
promises being made by the likes of Cree and Philips Lighting Technology.
One more replacement fluorescent tube aught see you through till then.

--
Johnny B Good

在 2015年6月26日星期五 UTC+8下�3:40:59，Corporal Jones写�：
Need a new Fluorescent light fitting for the kitchen as the old one has
given up, what are the pros and cons between a standard ballast and a
high frequency one, looking to get one from Wickes.

Barry

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