Small rechargable batteries?

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I'm looking for some small rechargable batteries. I only need 10 or 20
ma/hours, but they have to be small and stackable so I can get higher
voltages.

I found 1/2 N cells, they are still a little larger than I'd like.

Any other candidates?

Thanks,

Art

Re: Small rechargable batteries?
Depends how small. My current  ;@} favourite is an Li-Poly, 3.6V, wafer
thin, and about stamp sized. But high current, and fast charge.
21x28x4mm and 150mAh. I use a sot-23 300mA switcher to boost the voltage.

Al

AB wrote:

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Re: Small rechargable batteries?

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Hi Al,

I googled for '3.6' 'Li-Poly' and did not get any hits, not even a
vendor.

Can you give me a vendor or model number please.

Many Thanks,

Art



Re: Small rechargable batteries?

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4.2 and li-poly turned up:

http://www.robotcombat.com/marketplace_lipoly.html

For R/C plane use. They claim > 1 amp though that is out of OEM spec as
they say.

I guess better suppliers exist. Hard to find retail because of 'boy
scout proof' issues.

Li-ion is not much worse I think.

BTW I searched for 4.2 because that is the usual maximum charge voltage
these days. But check your manufacturer.

Also check out sci.chem.electrochem.battery for everything battery
related. Very quiet group, but with the right people (excluding me...)
and excellent info.


Thomas


Re: Small rechargable batteries?

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I googled for Li-Poly, 3.6V

and got a hobby site with a link to:

http://www.bktsi.com/powerflite/batteries.htm

which has "Polymer PowerBar" batteries, which are sub 1" and 3.6V @135mAh.

Rather than guess at which battery you need, I suggest you try looking again
because these batteries really do exist.





Re: Small rechargable batteries?

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A supercap might work for you, or one of the vanadium pentoxide rechargeable
lithiums.



Re: Small rechargable batteries?
Thanks for the info. I was able to locate Panasonic and found the
specs.

The VL621 through the VL3032 look great, but it appears they will only
supply .2 ma.

I need occasional (but for short periods) 2 to 3 ma capability.

Also, the supercaps leak, I'd have to charge them every day, whether I
used them ofr not.

Any more ideas??

Thanks

Art


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Re: Small rechargable batteries?
snipped-for-privacy@uninets.net mentioned...
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They say they have very low leakage, and stay charged for a long time.  
But I've never confirmed that experimentally.

Just a hunch, but I think you won't find any rechargeable cells that
are really small because the labor or assembly costs for a small cell
are not much cheaper than a large cell.  And since you can buy throw-
away button cells for next to nothing, it's just not economical to use
rechargeable cells.

Has anyone noticed this?  If you look at the prices of batteries, you
see that they are cheapest in the AA and AAA sizes, and as they get
smaller the price goes up, especially if you look at it from a cost
per mAh.  The justification for using the smaller cells is for use in
small sized equipment, so they can sell them for more per mAh.  Of
course there is less demand for cells smaller than AA or AAA, so the
economies of scale are less.  In any case, it will probably be cheaper
to use two or three rechargeable cells and a V boost circuit to get
the voltage you need.

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Re: Small rechargable batteries?

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That is definitely true. Distribution cost plays a role as well. Keeping
all this stuff in stock may be more expensive that making it in the
first place - as is demonstrated by the availability of packaging with
10 or so different watch batteries for 1 euro, where a single one will
set you back more.

Also don't forget the gouge factor. "Oh, mr. Device wants to have his
expensive gadget working again, that'll be 7,49 then!" - and the supply
chain adjusts to that.


Thomas


Re: Small rechargable batteries?
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I belive I've seen 1/3 AAAA NiCd cells, but have mislaid my bookmark.

However, one solution might be use one 1/2N cell, and boost the voltage
with a small inverter.

Can you point me to the 1/2N cells?

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Re: Small rechargable batteries?

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Yes indeed, that would be marvelous Ian!

How does one build an ultralow power inverter? Circuit complexity and
expense (within limits) isn't a big factor, but efficiency and light
weight are. I can tollerate high ripple as long as the oscillation
frequency is relatively stable and is >10 kHz.

I need 80 to 120 vdc variable and regulated (or stiff enough so that
regulation is not necessary). Note that my load will draw 100
microamps (worst case) and will be as low as 100 nA (or less).

My idea was to use a small stack of batteries, which would not have
inefficiencies at low load currents.

If you can give me a boost circuit that won't waste a lot of power
when the load current is in the pA range, I'd be a happy camper.

Maxim has an ap note on this, although they only make 75 volts.
Despite their low power expertise, they do not have anything that is
anywhere near the efficiency I need. I am happy to send you the Maxim
ap note outlining their best effort to make an efficient supply.

Hence, my inquiry about batteries:>: Batteries do not suffer low
efficiency at low load currents.

Suggestions???

Thanks,

AB


Re: Small rechargable batteries?
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Ok, that's an utterly reasonable, and totally impractical solution
(in many cases) reliability will suck, as a hundred cells in series
only needs one to fail.

Why do you want this?
Some numbers on your proposed solution.
Call it 90 1/2N cells.
That's 10mm or so diameter by 14mm * 90, or about 10mm diameter by
a meter.
Call it 100cc, and I'll guess 800g, probably a kilo of battery pack,
and it'll store maybe 10Wh.
You say you want efficiancy down to picoamps, which is under a microwatt.
The batteries will typically self-discharge by at least a percent a week,
or 100mWh/week, or about .59mw, so around 5ua.
There generally isn't much point in going below 2-3ua.

You need 100ua *150V, or say 15mw.

Not a really big number, you might concievably get it from one cell.

If weight is a big concern, I'd probably be looking hard at using a
Li-ion cell (mobile phone battery) that are light, availble nearly free,
and have very good self-discharge rates.
They also have a reasonable voltage, whereas Ni* get a bit low on one
cell at the low end.

I'd look at maxims low power chips that have low battery cutoff (li-ion
hate being deep discharged) with a transformer on the output inductor.
You probably want a very low frequency, perhaps 10Khz.
Also perhaps an external FET rather than an internal one.

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Re: Small rechargable batteries?

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Photomultiplier power supply.


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Actually, that's YOUR proposed solution I think:>:

1/2 N cells are too large.

The supplies for the upper dynodes need less current still.

I'm not sure there are batteries appropriate for this, which is why I
asked on usenet.

I heard that some battery fabrication using semiconductor processing
techniques were just developed, but I can't find the source of them.
They will certainly be small and cheap, since they don't need sealed
metal packages.

Any other ideas for small rechargable batteries?


Art

Re: Small rechargable batteries?
    Most photomultipliers I have seen use a 1.5 to 3 volt supply and step it up
through a voltage multiplier.  This is so simple to do that I am astounded that
any piece of equipment would not do this.
    Now you have a single cell or a pair of cells and they can run the equipment
for a very long period of time, and are very cheap and easy to replace.
    You may want to look into voltage multipliers.

Cheers!

Chip Shults
My robotics, space and CGI web page - http://home.cfl.rr.com/aichip



Re: Small rechargable batteries?
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Well, it was the one you implied by saying you wanted a simple battery,
I was just doing the numbers.
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Perhaps, but you won't get that much smaller.
I have some 6mm dia *4mm NiMh cells (the maker no longer makes them) but
even with those it's quite bulky.
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While you probably could do this with really small rechargables, you
almost certainly don't want to.
It'll be expensive, and time consuming, especially when a cell fails, and
you need to hunt through the pile.

Multiplying the voltage up using a small transformer and driver from
a small battery/cell giving several volts is simply the right way to go.
Do you really need rechargable?
One Lithium AA cell could last a very long time.
Even ordinary alkaline would.

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Re: Small rechargable batteries?
Charles and Ian,

I have looked into multipliers. A multiplier is how I hope to get my
100 volts boosted up to 1000v (so I can run the PM tube).

Driving a multiplier is not trivial, it takes real power to charge and
discharge those caps on each transition of the input signal.

I might be able to start with 20 volts (from 3  X  7.2 volt transistor
batteries), and multiply that up to 100 volts though.

This would mean I'd have 2 cockcroft-walton voltage multipliers.

I tend to think that the efficiency of a transformer goes to heck fast
at the higher turns ratios, maybe a dual cw multiplier chain is the
answer.

Maxim has an ap note using a multiplier and one of it's low power
chips. The single inductor method works poorly. The transformer step
up method works better, but they end up with 30 percent efficiency at
best (they only made 75 volts output, I need 125 volts). Even with
Maxim's low power chips, the overhead of sensing the output (for
regulation) and driving the switching transistors takes a big toll on
battery power.

My hope was that a battery solution would be direct, quick, clean and
more practical. I'm not necessarily looking for 1.2 volt cells
either!! If someone made a 100 volt cell, I'd be happy as a clam with
it.

Regards,

AB




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Re: Small rechargable batteries?
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Can you come up with an actual mass, volume and life spec, rather than
just saying "small" ?
For example how large is the PM tube?

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Re: Small rechargable batteries?

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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).

Above all, it has to be reasonably dependable as it will be backpacked
to the hilltop and used outdoors, Radio Shack will be very distant:>:


If I could power all th edynodes directly from batteries, that would
be awesome! For the upper stages where current is nanoamps and
picoamps, a surface mount string of batteries would be great! That's
surface mount as in the size of surface mount electronic components.
Not sure if any battery technology is available for microminiature
batteries.

For the lower dynodes, I'm guessing that a string of hearing aid sized
batteries would do the job.

Are there any battery chemistry that produce higher voltage per cell
than 1.2, 1.5 or 3.6????

I wish I could give a better definition of 'small', 'service life',
'cost' and 'volume'. But, they interact as specified above.

Is this hopeless??

Thanks,

AB


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




Re: Small rechargable batteries?

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



Re: Small rechargable batteries?
On Wed, 10 Sep 2003 13:44:46 -0500, "Dave VanHorn"

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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





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