Ok, so something using a couple of AA cells might well be appropriate.
How long is this in use on one trip?
2 AA cells would be excellent, but probably a little lacking in the
actual amount of power they can deliver. At 25 percent overall
efficiency, the total power drawn from the batteries is about 60
milliwatts. If I could power it directly from batteries, I would only
need 12 milliwatts because they are nearly lossless. Hence my interest
in batteries:>:
It might have to run for 2 days, only in total darkness, so that's
probably less than 10 hours of actual operation. Each time the tube is
turned off, it needs 30 minutes to warm up. Worst case would be 12
hours of total operation.
Also, you seem to be equating efficiancy with 'goodness'.
You don't care about this, just that it lasts long enough, is small
enough, and doesn't cost too much.
and/or it's light enough.
Surface mount batteries are available, but not in the way that you mean,
they are relatively large button cells, and they are quite expensive.
What sort of current/voltage do the various dynodes need?
The load is somewhat complex.
I present 2 scenarios:
------------------------------------
#1)
Tube is operated at high gain, each dynode needs 125v and the gain of
each dynode is 5. Starting at 125 volts, each successive stage needs
125v more, but draws 5 times less current. The max current the tube
can draw is 100 ua. Since the tube is looking at a light source, the
tube draws 100 ua at the lower dynode. Under these conditions, the
tube needs:
125v @ 100 ua, 250v @ 20 ua, 375 volts @ 4 ua, 500v @ 8 ua.
------------------------------------
#2)
Tube is dark sky, each dynode needs 125v and the gain of each dynode
is still 5. Starting at 125 volts, each successive stage needs 125v
more, but draws 5 times less current. Since the tube is looking at
relatively dark sky, it is only drawing 1 ua at the lower dynode.
Under these conditions, the tube needs:
125v @ 1 ua, 250v @ 200 na, 375 volts @ 40 na 500v @ 8 na.
------------------------------------
We can get these stepped voltages by using a voltage divider string of
resistors, but this wastes a lot of power. 12 volt supplies using this
method often draw 150 ma from the battery, even if the tube is in
complete darkness.
Another lower power alternative is to get these stepped voltages is
with a cockcroft-walton multiplier using a small transformer based
free running oscillator for step up. Since the only dc load is the
actual dynodes (no resistive divider string is used), the tube only
draws as much current as it actually needs based on the illumination
of the tube by a light source. A dim light causes the tube to use less
power. These types of supplies draw 10 to 12 ma from a 12 source at
low light settings and about 25 ma when the tube sees a bright light
source.
My hope was to use small batteries and connect them directly to the
dynodes themselves. The lower dynodes would need larger capacity
batteries since the lower stages draw more current. This would be the
ultimate in efficiency and be very simple. It would waste very little
power. The higher dynodes use pico to femto amps, so the actual power
requirements for the upper dynodes is very small-hence my interest in
small (ultra-miniature) batteries.
------------------------------------
Are these small batteries available???
Thanks,
AB
