Considerations for UV light box ballasts and tombstones, timer?

I'm planning to build a UV light box for cyanotypes using eight F15T8/BL fluorescent tubes I already own.

Do you have specific recommendations for the type of ballasts to use? Does it make much difference whether I go with four 2-lamp ballasts vs two 4-lamp ballasts? Any particular brand?

I'm considering 2 of these or similar: https://smile.amazon.com/dp/B00H4HNN6K/
This one seems rated above the needs of four 15w tubes so I assume it will be fine, see attached spec sheet.

I'm confused about selection of tombstones- according to the diagram, these require the shunted type?

Also, can you post a current link for an inexpensive timer to use with this setup?

Thanks,
Keith

i can't help with the electronics but i would include a cooling fan and an off/on switch. I have a light box from Bostick and Sullivan and leave the lights on for the entire printing session. You can find countdown timers for under $20 although it won't be connected to your unit. My understanding is that the bulbs should warm up for about 5 minutes before exposing your pape so off and on ie a test print may not be the best way to go.r. I don't do cyanotypes i do pt/pd. My light box has 8 bulbs and handles a printing frame for 11x14's.

http://www.jeffreyglasser.com/

http://www.sculptureandphotography.com/

keithostertag said:

I'm confused about selection of tombstones- according to the diagram, these require the shunted type?

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Here is something that can help you decide regarding the tombstone. I think shunted look right for you given the number of leads you have on the ballast.

https://insights.regencylighting.com/shunted-vs.-non-shunted-sockets-tombstones-lampholders

I bought a similar kit (8 tubes + 2 ballasts + 16 shunted tombstones) but yet to make the box except making sure my circuit/tubes worked. Will be curious how you progress with yours.

:Niranjan.

keithostertag said:

using eight F15T8/BL fluorescent tubes I already own.

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For a new exposure system, I would not recommend to use tubes anymore. Product choices have become more limited, and while you now have some tubes, in case you break any, it will become more and more difficult to find appropriate replacements. The alternative, LEDs, is just much simpler these days to implement with easily available electronics. Ready-made LED power supplies are omnipresent and LED strips or COB leds are easy to get also for UV, in varying wavelengths (esp. COB leds).

There's a real difference between today's market and that of, say, 5 years ago.

Having said that - yeah, those ballasts will likely work but I'd prefer to look for some that are explicitly aimed at powering 15W tubes. With ballasts it is NOT a case of 'rated for more power than I will use is probably a good thing'. Tube ballasts need to actually fit the power of the tubes used.

I could not find if your bug light tubes actually allow for rapid cycling; I suspect they don't. If that is the case, I would NOT recommend using them for an UV exposure box at all. You'd be designing a compromised solution right from the start; a waste of time and money IMO.

koraks said:

Having said that - yeah, those ballasts will likely work but I'd prefer to look for some that are explicitly aimed at powering 15W tubes. With ballasts it is NOT a case of 'rated for more power than I will use is probably a good thing'. Tube ballasts need to actually fit the power of the tubes used.

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This is something I have wondered about- could you elaborate?

keithostertag said:

This is something I have wondered about- could you elaborate?

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Well, it depends - but take the simplest, old-fashioned magnetic ballast, which is basically an LC (inductor - capacitor) circuit. Its dimensioning (i.e. the value of the inductor L and the capacitor C) is chosen for the output current needed and fits the input voltage and AC frequency. I.e., a magnetic (LC) ballast will *only* work properly for a tube that has the power rating the ballast was designed for.
Electronic ballasts can be somewhat more flexible, but in the end in the engineering of those assumptions need to be made as well as to the output current because of ultimately the same kind of reasons that were true in old fashioned magnetic ballasts.

Think of it as getting tires for your car. You might reason "let's get a bigger tire than the original ones, those will be certain to survive whatever abuse I can throw at them with this car", but of course there are things like rim diameter, clearances etc. - in the end, a tire should not be either too small or too big to work properly with your car. It's perhaps a slightly far-fetched analogy, but in the end it works out quite the same for ballast and tubes. There is *some* leeway, but it's limited.

Thanks for replying. I don't know how the new electronic ballasts work, so I need to look that up. Actually, I have never understood how older magnetic ballasts are different from simple transformers, so I guess I am pretty far behind the curve on this.

Anyway, I did order the above named ballasts for my F15T8/BL fluorescent tubes I already own and built the light box- seems to work fine but of course I won't know until I've run some tests. If the bulbs don't last very long... well, my bad for not researching better beforehand. I am out-of-town for awhile, but will followup in a few weeks.

keithostertag said:

I have never understood how older magnetic ballasts are different from simple transformers

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I get what you're saying; well, just consider they're completely different animals. The only thing the have in common is that induction plays a major role, but that's about it. They're about as similar as a bicycle and a wheelbarrow. There's a minimum of one wheel on each; apart from that, they're not very similar.

keithostertag said:

built the light box- seems to work fine

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Good job! I'm sure it'll work. Like I said, it's not the approach I would have chosen at this point, but I can get behind the sentiment of 'I got those tubes anyway; why not put them to good use.'