Small rechargable batteries?

[AB]

On Wed, 10 Sep 2003 13:44:46 -0500, "Dave VanHorn"
<dvanhorn@cedar.net> wrote:

If I could power all th edynodes directly from batteries, that would
be awesome!

batteries plus still carries 510v photoflash batteries.
they are simply stacks and stacks of 1.5v cells.

OK, thanks for the tip.

I assume you mean batteriesplus.com. I went there and looked and
looked. Couldn't find it in various categories and there is no search
engine! I thought I'd find it under photo aps, but it was not there.
I'm not sure if the 510v photoflash battery is a solution for me, but
I'd like to check it out.

Can you give me a category or a direct url to it??

Thanks,

Art

 

[Dave VanHorn]

I assume you mean batteriesplus.com. I went there and looked and
looked. Couldn't find it in various categories and there is no search
engine! I thought I'd find it under photo aps, but it was not there.
I'm not sure if the 510v photoflash battery is a solution for me, but
I'd like to check it out.

Can you give me a category or a direct url to it??
http://www.batteriesplus.com/Product/specialtyp.html

hobby and specialty primary.

lots of interesting voltages.

 

[Ian Stirling]

In sci.electronics.misc AB <artky1k@uninets.net> wrote:

Can you come up with an actual mass, volume and life spec, rather than
just saying "small" ?


OK, this is complicated and there is no simple answer.

It has to be the right combination of cost, weight, bulk and life
spec. If it's cheap, it can be soemwhat heavier/bulky. If it's very
small, I can live with some extra initial cost. If it's expensive, it
needs to be reusable (battery power that can be recharged).
snip
For example how large is the PM tube?

The pm tube is a 3/4 inch head on tube, 3/4 inch diameter (not
including shielding) and about 4 inches long.

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

 

[AB]

On Wed, 10 Sep 2003 21:00:33 -0500, "Dave VanHorn"
<dvanhorn@cedar.net> wrote:



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

Can you give me a category or a direct url to it??
http://www.batteriesplus.com/Product/specialtyp.html

hobby and specialty primary.

lots of interesting voltages.

 

[AB]

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

 

[Ian Stirling]

In sci.electronics.misc AB <artky1k@uninets.net> wrote:

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:>:
snip
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.

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.
<snip>

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
snip
125v @ 100 ua, 250v @ 20 ua, 375 volts @ 4 ua, 500v @ 8 ua.

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.

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???

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 http://www.cpc.co.uk/
(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.