Small rechargable batteries?

hobby and specialty primary.

lots of interesting voltages.

Ok, so something using a couple of AA cells might well be appropriate. How long is this in use on one trip? 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. 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?

--
http://inquisitor.i.am/    |  mailto:inquisitor@i.am |             Ian Stirling.
---------------------------+-------------------------+--------------------------
My inner child can beat up your inner child.                   - Alex Greenbank

OK, thanks very much-I'll have a look.

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.

and/or it's light enough.

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

2 2200mAh AA NiMH cells will provide around 4 watt-hours.

Call it 20 hours, that's 200mw, or around 80ma draw you have to get below.

For a total of around 12.5+5+2+1mw = ~20mw.

So, efficency needed is around 25%, to run from a couple of AA cells.

A properly sized CW multiplier can be relatively efficient, as long as you don't try to skimp on capacitor size, run it at too high a speed, or too many stages.

I'd start out with one of maxims chips to run a boost converter from the

2 AA cells to 20V. Then a H bridge to convert it to +-20V, and a CW converter from there.

No, you don't get much smaller than 1.3mm*6mm dia, which are 8mAh.

And they are relatively expensive.

Looking at the cheapest way to buy volts at

(nearest bulk catalog I have to hand) gives 50*GP27 for around $20. These are 12V batteries, and around the same height as a N cell, but thinner. (18mah) Make up a pack for 10 of these, and you can swap them around between dynodes using them evenly, and they'll last around 150 hours.

These are not rechargable.

--
http://inquisitor.i.am/    |  mailto:inquisitor@i.am |             Ian Stirling.
---------------------------+-------------------------+--------------------------
If it can't be expressed in figures, it is not science, it is opinion.
                                                         -- Robert A Heinlein.

[] []

----------------- Liar.

-Steve

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-Steve Walz  rstevew@armory.com   ftp://ftp.armory.com/pub/user/rstevew
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Y'know, Frank, posting the same nonsense three times in a row doesn't make it any shorter OR any more sensible.

"EER" is, simply put, ridiculous.

Bob M.