robert.c.baruchPower! Surely 80 Nixie tubes will require lots of power?
According to the datasheet, a digit takes a maximum of 2mA while the dot takes 0.3mA. Call that 2.3mA, assuming that all places have a digit and the dot lit. Times 80 is 184mA. At 170VDC, this is about 32W.
My plan is to provide 170VDC by rectifying wall voltage (120VAC where I am). The "120" in 120VAC is not peak-to-peak, but root mean squared, meaning that peak-to-peak voltage is 1.4x RMS voltage, or 168V, close enough.
Now, suppose I don't want to drop below 160VDC in the 1/120 seconds it takes for the rectified voltage to go from peak to peak. I = C dV/dt, and let's just approximate that by I = C ∆V/∆t. For 184mA and ∆V/∆t = 960V/s, we get C = 192μF. Also, such a capacitor needs a working voltage of at least 200V.
There are a lot of approximations here. For example, the Nixies, when on, aren't going to sink a constant current when the voltage changes. But this is close enough for good operation.
Also, let's assume 92mA flowing through each recifier diode (since each conducts for only half the cycle). I'm using the KBP206G diode bridge, which looks like it has a drop of 0.7V at 100mA. So two diode drops at 92mA (average) is 130mW, which is nothing compared to the 32W needed.
Finally, I'd like to use an AC wall-wart to power the calculator so that I don't have to touch the mains. At Digikey, I found a 24VAC adapter at 43W (Triad Magnetics WAU24-1800) which seems like it should more than power the display plus all the other electronics. Then I can just use a transformer to convert 24VAC back up to 120VAC, rectify, and I'm done.
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The power consumption is a bit on the pessimistic side. I bought a used 16 segments 20 characters multiplexed Nixie made by Cherry that was from a pinball machines. I designed a replacement DC-DC high voltage supply and it only needs 3-4W at the 12V input and it is very bright even for a worn out display. So factoring the inefficiency of the supply say 75%, that's about 3W at the high voltage side. Scaling my display to 80 characters would only require 12W nominal.
If the display really requires 36W, you'll also have to worry cooling issues.
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This is true, I don't actually need to go up to the max spec.
The brightness is proportional to the current, so it's just a question of what looks good without exceeding the max spec of 2mA. With 1mA, the digits are fuzzy. 1.75mA looks okay. I also chose the digit requiring the most current: 1.61mA for the "1" and 1.75mA for the "8". Interestingly, adding the dot to the "8" only brings up the current to 1.80mA. Times 80 is 24.5W instead of 32W. So there's definitely some savings there.
I hadn't thought about cooling. I thought that since the tubes would stick out of the housing, they'd be cooled just by being outside. But then there are the current-limiting resistors. I measured 79mW dissipation, times 80 is about 6.4W. I don't know if that would need fan cooling.
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