Me and my friend are designing a USB powered F4T5 programmed start driver, if anyone could provide me with the filament heating voltage for one that would be great!

Darn I have an F4T5 tube+ballast but it's at home so I can't measure right now. I would assume it's the same 8 or whatever volts that most preheats are but I have no idea, wouldn't be surprised if it was a lot lower.

I am not sure if this full voltage is used in program start ballasts, I don't know enough about them. Next time I am home I will measure for you if nobody has the answer by then.

To be safe I would assume no more than 6 to 9 volts. It wouldn’t take much, anytime I’ve messed around with lamps if I do more than 10 I’ve blown filaments before.

Yeah often when you get above a certain voltage an arc will strike across the tungsten filament. Not a problem with a current limited supply like a preheat choke, but depending on your circuit it could be essentially an unballasted arc. Needless to say the lamp doesn't like that lol.

Also pretty cool they are designing usb ballast. If I had the smarts or money and time I would try to manufacture some of my own branded ballasts and fixtures. (Properly, not cheaply)

Me and my friend are designing a USB powered F4T5 programmed start ballast, if anyone could provide me with the filament heating voltage for one that would be great!

to answer the direct question asked, for an ANSI specification 4W T5 the cathode heating voltage is nominally about 8V, you can read more about the exact details and allowable ranges/tolerances in the C78.81 standard for fluorescent tubes

https://www.nema.org/docs/default-source/about-us-document-library/ansi-c78.81-2016-(r2022)_aspublished.pdf


but are you looking to design a program start that preheats the cathodes for a fixed amount of time and then fires the tube or a continuously heated cathode rapid start ballast?


different design criteria exist with regards to cathode heating voltage/currents so the distinction is fairly important


for a program start ballast you will want to implement a fixed constant-current based preheating method rather than a fixed constant voltage method

@LightBulbFun I was thinking it heats them constantly, but also fires the tube after a specific amount of time. Due to USB current limits (and there will be three F4T5s running), they will have to be underdriven a bit.

Thank yall for the help! Hopefully this can help my friend come up with like what the driver needs

Good luck! If you guys are able to get it working or somewhere give me some more details, maybe I could try and make some of my own wattages or units. Not the best at designing but I love soldering.