Or, you can just deal with the AC mains directly. I have 6 clocks of 3 different designs that run hot on the AC line to varying degrees, but in all cases the nixie anode supply is not isolated. Most have been running for 6 years now, with no issues. All told, there's almost 30 years of runtime (250,000 hours) with zero circuit issues.
If you are going to go this route, it is absolutely essential that you provide redundant fuses, have good surge-protection, proper PCB trace-width and separation, and noise-filtering. And yes, be sure to use an isolation transformer during testing/debug. Being extra careful will go a long way; it's been more than 30 years since I've been shocked, had something smoke/overheat, or explode. There's nothing inherently "bad" about the AC mains; the real issue is that they are typically protected by a 20amp circuit breaker, so it takes a lot of power to trip the breaker. When all of that power is running thru your gizmo, it will cause a lot of damage. In other words, NEVER rely on the circuit breaker in your house to provide safety for your project. For starters, use a UL-listed (or equivalent) power-entry module. They have a socket for an IEC power cord, a fuse, and a power switch, all in one nice compact unit. So no matter what happens with your gizmo, a *properly-sized* fuse in the power entry module will blow before damage occurs. I suggest the smallest slow-blow fuse that is rated for your typical operating current. That way, any power-on transients to charge power-supply filter caps will not blow your fuse. If you are extra diligent, run a simulation of the peak AC line current during power-on, and use the fuse-manufacturers datasheet curve to see if it will withstand the transient. If you're lucky, a fast-blow fuse might even work. Next, when your AC power comes onto your PC board, have *both* legs (hot and neutral) run thru their own fuses; PCB-mounted fuses are inexpensive. Now you technically have triple-redundant fusing; if any of the 3 fuses (power-entry, hot-lead, neutral lead) blows, you will not have a complete circuit for the AC line. After the fuses, add a varistor for surge protection; a nasty surge will blow a fuse though the rest of your gizmo should survive. Then place a 0.01uF 1kV cap across the varistor to absorb fast transients. If you run SPICE simulations on your gizmo, you can compute the RMS current, and use that to select your fuses. Otherwise, use a 'Kill-a-watt' device to measure the actual current consumption. -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- In case you wondered, it's pretty easy to find out what time it is in my house....total of 61 nixies are on-the-job, and I've only had 2 fail (both were Burroughs 6091) -- 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 post to this group, send an email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/7baf9174-309d-4f91-91b4-19149369a792%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
