Danger Danger! High Voltage!

I've been wanting to experiment with vacuum tubes for quite a long time, but there was always the problem of proper power supplies, especially for the high voltage side. Not anymore!

At work, we throw out a bunch of SAFT LS-series "AA" 3.6 volt Lithium thionyl chloride cells that are used in crash data recorders for six months at a time. When they come back, the cells still carry 80% of their useful charge. Wasteful, I know, but that's the price of reliability. Anyway, now that the demand for the units the cells are installed in has increased so much, there are more and more cells to dispose of. True to my treehugger nature, I don't want to see Lithium enter a landfill or go to a recycler in a dangerous form. While these same cells were one commonly used for clock backup in computers, this is now rare so it's low-volume.

So what do I do with the 300 cells I already have? Use them.

The advantage with Lithium cells is they have a relatively flat discharge curve, dropping like a rock at the very end of their life. This is a good thing since a consistent supply is always helpful.

Radio Shack, and other such dealers, sell holders for 8 AA size cells at a cost of about $2 each. While normal AA cells in such a holder would result in 12VDC at the terminals, Lithiums give 28.8VDC. My plan is to build a few different supplies. The first will use four banks (32 cells total) for 115VDC output while others will be built for up to 400 volts (14 banks or 112 cells). All of these supplies will be housed in insulated cases with isolated keyswitch interlocks and .063A fuses to guard against shorts. I'm only likely to be pulling a maximum of 30mA current anyway, and that's with a lot of tubes running. Most of the time, I'll be seeing a maximum of 10mA. The cells are rated for a maximum pulse current of 270mA. Continuous drain carries a 70mA rating. I'm sure the internal resistance of so many cells in series is going to limit that.