Thorn 6ft twin ballast wiring

[RichThompson]

Hi,

I'm looking for some advice from someone who is familiar with magnetic ballasts being wired in series with one another for vintage thorn strip lights, ie 8ft but specifically the 6ft twin batten.

I've bought some 70/75w spl and helvar ballasts off ebay to have installed by a professional electrician at my local church to fix some faulty battens. In each case one tube works and the other doesnt but on the one which doesnt you can hear the starter going mental. You get the odd flash but generally the tube is unlit and the ends do not glow. New tubes and starters haven't solved the issue so there is a problem inside the batten. I'm not a qualified electrician so I haven't removed the cover off the battens to look inside, but i assumed it would be two ballasts, two capacitors and 2 starter sockets. Thing is looking on ebay I've seen some 6ft twin thorn battens for sale which have 3 ballasts inside and only 1 capacitor. They are 2xG69428.4 ballasts in series for 1x75w 1800mm tube and a G69392.4 ballast presumably not in series which can take a 1500mm or 1800mm tube. The capacitor is rated at 5 micro farad.

This has made me question if I've bought the correct ballasts to fix these fixtures. If one of the series ballasts has failed I dont imagine it could be replaced by a non series type? And if both series ballasts were replaced by one I've bought I'm guessing the capacitor rating would then be incorrect?

Has anyone any thoughts on this old thorn battens and how they work? Or even better a wiring diagram...

I was hoping to do the church a favour by prolonging the life of their old lights while they raise funds for new crappy leds.

Thanks for reading,

Rich

 

[fluorescence]

These battens will almost certainly have what's known as lead & lag circuit. The tube which still works will be the lag circuit. The lead circuit has a capacitor in series with the ballast, this will be what has failed. You can simply bypass this capacitor and fit the new ballast you have, or what I would do is replace the capacitor. You will need a 440v rated capacitor and it will most likely be 5 micro farad, but you will need to check

FYI if the ballasts are the older Thorn type they are some of the best ballasts ever made and will do hundreds of thousands of hours with no issues.

If these lights are used irregularly as I imagine they are, 'upgrading' to LED will be a waste of money imo.

 

[RichThompson]

Thanks for that quick reply! Much appreciated.
Which ballast is the capacitor in series with? (series one or the non series). I'd probably want it to be a like for like replacement and not bypass anything.
They've already fitted leds to some rooms in the church and a few are playing up already. Long live fluorescent I say.

 

[fluorescence]

There will only be two ballasts in the fitting, one for each side/tube. Here's a wiring diagram I've just cobbled together, you'll need to trace the wires to see which ballast has the capacitor in series.

Don't get me started on nasty LED replacements that are supposed to be saving the planet but are in fact doing the complete opposite. I've had to take working 40+ year old fittings down at work and throw them away in favour of LED battens that sometimes fail within a couple of years. Sad times imo.

 

[333rocky333]

how do you know the ebay ones have 3 ballasts inside.
Not seen it with 6ft but 8ft sometimes used 2 half chokes per lamp
The main reason for the cap was to prevent strobing in sync when lights were fitted in machine workshops.

 

[RichThompson]

I queried with the seller as the picture showed the fitting had 3 ballasts, 2 are labeled as series types as I've seen on a YouTube video for an 8ft batten. He acknowledged it was unusual. My initial question to him was was it an srs fitting as I'd love to own one but it's a switch start fitting.

 

[333rocky333]

Can we see the picture
Also
Why do you want a Srs fitting

 

[RichThompson]

Thank you for the schematic it's a great help. I'll have to take a look inside the fitting and see what's what.
Look out for some ballasts going back on Ebay shortly

 

[333rocky333]

By the way what lamps are you fitting, i find 6ft the most troublesome size going, just using 70w tubes can be a nightmare in older 75w fittings.

 

[RichThompson]

I like the way srs fittings start and the way the tubes fail (memories from school).

I cant copy the picture but if you search for Vintage Thorn 6ft Twin Fluorescent Fittings on Ebay there is a picture.

 

[333rocky333]

Post pic of the Helver ballasts you have bought, they wont need the capacitor to work and will likely do the job, in a church strobing is not likely a problem..
The big size cap is not for PF correction, though there may be one for that also in the fitting across the supply.

 

[RF Lighting]

I pay around £40 inc vat for an led fitting which will out perform and outlast your current fluorescent fittings.

I’ve installed loads which are in use every day for prolonged periods, and have never had one fail yet.

 

[RichThompson]

They use 70w greenstock shatterproof tubes. I have a 6ft t12 which didnt work either.

 

[333rocky333]

I like the way srs fittings start and the way the tubes fail (memories from school).

I cant copy the picture but if you search for Vintage Thorn 6ft Twin Fluorescent Fittings on Ebay there is a picture.

If you fit electronic starters like a BG EFS600 they have a slight delay then on, no annoying flicker,

 

[RichThompson]

Here you are