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PostPosted: Fri Oct 20, 2017 10:59 am 
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I want to convert an old twin-tube fluorescent light from 2 x 100 Watt T12 (8 foot) tube to 2 x 125 Watt. Some time ago I acquired a small stock of 125 Watt T12 tubes at a reasonable price. New 100 Watt ones are a ridiculous price. I tried one of the 125 Watt tubes in one side of the luminaire. It started and lit, but went on and off, meaning, I think, that the Crompton choke was imposing too much reactance to the current flow for a 125 Watt load.

I tried to buy 125 Watt ballasts, but none seem to be available. So I have bought two new ballasts (switch-start chokes). These are Helvar/Tamlite L100 TE8 240 Volts. The seller claimed that they are also suitable for 125 Watt tubes, but did not mention that they are not a straightforward exchange!

I say that because there is a very minimal circuit diagram printed on the case showing just the choke and the tube and L and N supplies. The wiring for a 100 Watt tube is as original, but, for a 125 Watt tube, there is a capacitor in SERIES with the choke.

This capacitor is specified below the diagram as 7.2 microFarads/440 Volt.

There is already a capacitor in each of the two original circuits - across the supply, to suppress EMI. The original capacitors are 8.4 mF.

These are my questions:-

1. Do you consider that fitting a 7.2 mF capacitor in series with a Tamlite L100 choke will allow the choke to run a 125 Watt tube normally?

2. What do I do about EMI? Will the series capacitor suppress this, as well as altering the reactance of the choke? Do I leave the original 8.4 mF capacitor in its original place across the supply, or what?

I am not a qualified electrical engineer, but am knowledgeable electrically (pre-2005 I could have rewired a house, legally. I could still do this, but am no longer allowed to!).


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PostPosted: Fri Oct 20, 2017 1:02 pm 
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I would take the 8.4 mF capacitor out, since the new "choke" does not require it, but it does require a 7.2 mF capacitor (You say it does, I do not know)


As for will it work, its not ideal, but while you are waiting for some one who has actually done it,* you could have tried it your self.



* TBH 8 foot lights are no longer available / becoming rare, I would change them for 2 x 4foot lights and save the hassle, but then its not my money.

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PostPosted: Fri Oct 20, 2017 1:32 pm 
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imho change the fitting, fittings and tubes have come a long way there more power efficient for a start, why a 125w T12 ? when was the last time you purchased tubes ? 100w T12 (8ft) £15 each for Sylvania/Crompton less discount, that price inc the recycling fee your charged on new tubes that not expensive (Its the diy sheds that hike up the prices)

https://www.tlc-direct.co.uk/Products/LAFL100.html

https://www.tlc-direct.co.uk/Products/LAFL125.html

100/125w will give you a nice tan :lol:


iirc 8ft T12 got banned along with incandescent bulbs hence the lack of ballasts and new fittings 6ft twins and modern hf fittings will be more efficient and put out more light I have 4x 6ft twins (diffused) in my 14 x 14 work shop and that's waaaaaay over kill


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PostPosted: Sat Oct 21, 2017 9:05 am 
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Why not retro wire and fit led tubes ?

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PostPosted: Sat Oct 21, 2017 11:04 am 
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multiman wrote:
Why not retro wire and fit led tubes ?

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8ft led tubes that's why, do they even make them in T12


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PostPosted: Sat Oct 21, 2017 11:16 am 
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flash22 wrote:
multiman wrote:
Why not retro wire and fit led tubes ?

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8ft led tubes that's why, do they even make them in T12
You would not need led tubes to be 8ft also fitting two led light fittings would still use less energy and provide more lighting

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PostPosted: Sat Oct 21, 2017 11:53 am 
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Thanks very much for the responses. I just need advice on the question raised by the skeletal wiring diagram on the Tamlite chokes, and appreciate that the only realistic answer to this may well be "S--k it and see"!

My difficulty there is that I could not return the two capacitors (£14.98 including carriage and VAT) if the modified wiring does not run the tube normally. At least one of them will be judged to have been used. I could probably return the two ballasts, but also at my own expense.

So I am still hoping that someone has enough experience of these circuits to know definitely whether to be optimistic or otherwise about the prospect of an inline 7.2 mF capacitor effectively transforming a 100 Watt choke into a 125 Watt one.

As regards non-fluorescent-tube options, I have already considered them. I would not go for LED arrays because I read that there are different types, with and without external "drivers" etc, and who knows if whatever type I bought would be replaceable without further complications a few years hence. That doubt is underlined by the fact that LED lighting is already out of date. Metal Halide discharge lamps currently seem to be the way forward. However, this technology, like the LED, is poor on power factor, so who knows what the legislators will decide to plump for, and for how long whatever this may be will last as "flavour of the month"

My fall back position if I can't keep my lovely 35-year old 2 x 8 foot T12 Crompton unit going would probably be two four-foot twin-tube units end on, using T8 tubes and with HF ballasts, of course. But, excluding the cost of the tubes, this would be a lot more expensive than £38.96 for the two Tamlite ballasts plus two 7.2 mF capacitors. So I l still live in hope!


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PostPosted: Sat Oct 21, 2017 5:18 pm 
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I would be concerned about putting a band aid cap in circuit, also not knowing the stress implications on the ballasts (I assume there magnetic and not electronic ?)

do you have the part numbers for the ballast and caps ?

edit. just found the tech info on L100 TE8 - there rated for 125w but only for T8, basically not enough current to drive a T12

Attachment:
L100 TE8.pdf [698.98 KiB]
Downloaded 11 times



Edit 2. The diagrams show the cap for the 125w across the incoming supply


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PostPosted: Sat Oct 21, 2017 6:06 pm 
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Carl Haworth, looking at it from a financial POV I would say that in todays age its not worth anyone going to all the effort you are, as you pointed out, you "acquired a small stock of 125 Watt T12 tubes at a reasonable price." so unless some one also has a collection similar there is no financial gain so there is no one than can help you. On the flip side, if it works you can post your findings on here.
Some times you have to move on with technology, now is one of those times and you have to let your " lovely 35-year old 2 x 8 foot T12 Crompton units" go.

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Take it easy, a forum is only a collection of opinions. Above, are mine.

Which is correct? Metre or Meter? Click the link. to find out more.

No such thing as "Thou shalt put this wire here, Thou shalt put that wire there" .............Take a picture BEFORE you do the job.

If gloom had a voice, it would be me. :mrgreen:

:idea1: How to post a picture on this forum Click here



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PostPosted: Sun Oct 22, 2017 9:18 am 
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flash22 wrote:
multiman wrote:
Why not retro wire and fit led tubes ?

Sent from my LG-K100 using Tapatalk


8ft led tubes that's why, do they even make them in T12


Well you can get 8ft LED tubes. But they will not look like T12s, they will look like T8s,

T is a reference to the OD of the tube and although they are similar in operation T8s and T12 are different. The OP's real problem is that the T12 contains more mercury than the T8 and so needs a different ballast to strike the lamp.

The capacitor across the mains terminals that he refers to is there for power factor correction and not for EMI suppression.



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PostPosted: Sun Oct 22, 2017 10:11 am 
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I have done my fair amount of tube changes, and I know the sizing of tubes and how they work, the cap across the incoming supply is for suppression of any mains spikes is also acts as decoupling device to reduce noise in the ac wave form before it enters the equipment, a cap has very little to do with PCF especially with a magnetic inductor based Ballast

As you rightly state its the dimension of tube or it T valve, knowing that your aware a T8 tube will no fit in a T12 fitting so that point is mute

Technically you could put a ignitor inline with the tube and use a T8 Ballast so there is enough current to strike the T12 tube but your in to yet more money

At the end of the day (comes night), replacing the fitting with a modern item means less hassle and the extra cost will be offset in the long term as there more efficient reducing consumption

iKN.



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PostPosted: Sun Oct 22, 2017 2:37 pm 
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A T8 tube will fit a T12 fitting. Same pin fitting and same length of tube.

And the capacitor is there for PFC reasons.



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PostPosted: Sun Oct 22, 2017 3:14 pm 
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Many, MANY thanks to all who have taken the time and effort to help me!

I am sure that Flash22 is right. I have downloaded his copy of the datasheet which includes the high wattage T8 ballasts which are presumably now obsolete. The wiring diagram/capacitor placing as shown on the ballast is correct, but, as Flash22 points out, this is for a 125 Watt T8 tube. I have never come across such a high wattage in T8 and, in any case, the T8 is limited in length to 1,800 mm ("6 feet") so could not be fitted into my "lovely old" (sorry about that!) Crompton luminaire.

I shall try and return the ballasts for a refund, as the order confirmation from the firm concerned stated "Helvar L100 TE61 ballasts for 125 Watt T12 tube". There is little or no difference between this ballast and the Tamlite L100 TE8 ones that they sent. And both/all are for T8 tubes.

Obviously, I shan't now order the caps!

As for the 125 Watt tubes, these cost me very little, and will just have to go to the tip!!

I am immensely grateful especially to Flash22 for allowing me to see this obsolete datasheet. The information on this confirms that the tube application is T8, whereas there is no such information on the ballasts (as normal, I think).

My plan now is, in order of preference:-

1. To try to get a small stock of 100 Watt T12 (8 ft) tubes;

2. Replace the Crompton unit and replace by two 4 foot twin-tube T8 fluorescent unit, to be fitted end-on in the space currently occupied by the twin-tube 8 foot unit. I really don't want to go for LED arrays at presen. I can buy 4 ft T8 tubes at my local trade counter.

If (1) grinds to a halt, please have you any suggestions about the best 4 foot dual tube luminaires to buy, and from where?


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PostPosted: Sun Oct 22, 2017 3:55 pm 
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iirc mine are Philips or GE, does your application need them to be ip rated ? don't forget you can now get different K or Kalvin rated tubes 4200-4800K is as white as a bright summers day, 5200k you a more blue-ish tinge and 3000k is a warm white

In a domestic environment, The PCF will be minuscule, it terms 70 odd mF is like urinating in the Atlantic, on the other hand, on an industrial scale you could make some savings but that all depends on how the incoming supply is metered either by true (real) or apparent means, but that's its own thread, not to hijack this one with :roll: :wink:


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PostPosted: Sun Oct 22, 2017 5:15 pm 
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No ip rating. They're for my indoor home workshop, so a colour temperature of 4200 to 4800 Kelvin would be good - better than 3000 to 3500 K. Yes, the very high K values are indeed rather "blue" - not good in a workshop!

What do you suggest? Are there twin-tube luminaires for 1,200 mm T8 tubes? What's the maximum normally available wattage of these tubes?

I don't personally worry about power factor. I'm a domestic consumer so we're billed by the kWh with no calculation of PF (1968 meter, anyway!). I mentioned it only because it is likely to become an increasing concern*, especially if we leave Euratom when (?) we leave the EU. So I imagine that PF will be scrutinised along with efficiency (lumens per Watt) when reviews are carried out nationally of which types of lighting should be encouraged, and which discouraged/banned.

LED GLS lamps seem to run at little better than 0.5, which means that a 6 Watt lamp draws 12 VA but actually uses only 6 Watts. This is very poor compared with the PF 1 of the banned tungsten-argon lamp, but has to be set in the context that the latter works at a small fraction of the efficiency of an LED lamp of equivalent light output, so the equivalent t-a lamp may draw and run on 60 Watts/60 VA. However, both the current "flavour of the month" LED lamp and the even more efficient metal halide tube have poor power factor, so who knows how the politicians will jump? (That sounds rather energetic!)

* If PF over the whole of the national electrical grid was, say, 0.67, then, on average, if all power stationsweare of equal output, we would have three power stations for every two that we would need if national PF was 1. All the cables would need 50% more capacity than at a national PF of 1 (think the arithmetic is more or less right, but I'm prepared to stand corrected!).


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