Absolutely! The difference between operating and inrush-current is a leading cause of burnout. If you recall, incandescent room lights generally fail when you turn them on. It's the same mechanism.
If you dont plan on power-cycling the filaments very often, you can just leave it as is and replace tubes every few years. You will probably have phosphor degradation before the filaments burn-out. If you like doing reliable designs, you can limit the inrush current with a series resistor, and driving from a higher voltage. Or you could use a triac to control the filament transformer, and gradually increase the proportion of the AC-cycle to soft-start the filaments. Here's a table of filament resistance vs current, once temperature had stabilized, from a BA0000P31 NIMO tube: [image: ScreenHunter_28 Jul. 15 07.16.jpg] ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- I faced a similar issue when designing my NIMO -tube clock. NIMO tubes are very rare, so every means must be incorporated to protect them. I chose to drive the filaments from a higher supply voltage and some series resistance. In my case, I was able to reduce the peak current from 400mA to 250mA, while keeping the operating current at 180mA. The datasheet specifies 200mA. In addition, I have a 250mA fuse for each tube, and hardware+software to check each filament, fuse, and dropping resistor. The last part is what algorithm should I use for shutting-down the filaments ? Leaving them on continuously will eventually lead to burnout, but turning them on/off too frequently will also cause wearout. Right now I'm using a 30-hour timeout on my IR motion sensor, so if nobody enters the room for just over a day, they shut down. Furthermore, it takes a bit of extra movement to turn them on so if you tiptoe into the room, they stay off. On Wednesday, July 15, 2020 at 6:20:16 AM UTC-7 Jasper C. wrote: > I'm working on a project using some IV-17 tubes, and I cam across > something I need advice on. The datasheets I've found say that the > filament current is 47 mA at 2.4 Vac, so an effective resistance of about > 51 Ohms. But on 3 tubes I've measured, they're all about 20 Ohms. Does > the filament resistance change when hot? Because that seems like a huge > difference... > -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/cc559484-d502-4866-81f0-88566758d52dn%40googlegroups.com.
