Hi,

I am trying to find the best power source for a tiny spy wireless camera.
The camera operates at 9V, 200-300mah.
I have a serious weight problem with the configuration. The whole
configuration must not exceed 30 grams. Camera weight is 10 grams.
The best power source I was able to find was three coin batteries
(CR2025 or similar models) joined serially. Each battery has a weight
of 3-4 grams, which is within the system limitations, but I am not
sure how well the camera will operate.

If someone has a better idea how to operate this, please answer.
Any tips from someone who tried to build such a configuration is also welcome.

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Clarification of Question by shohayon-ga on 01 Oct 2005 00:15 PDT

Hi,
Sorry, I meant ma, and not mah.

Here is the camera specification....
Video Camera Parts: 1/3, 1/4 image sensors 
System: PAL/CCIR NTSC/ELA 
Effective Pixel: PAL:628x582 NTSC:510x492 
Image area: PAL:5.78x4.19mm NTSC:4.69x3.45mm 
Horizontal definition: 380 Lines 
Scanning Frequency: PAL/CCIR:50HZ NTSC/ELA;60HZ 
 Minimum Illumination: 3Lux 
Sensitivity: +18DB-AGL ON-OFF 
Output Electrical Level: 50 MW 
Output Frequency: 0.9G/1.2G 
Transmission Signal: Video 
Linear Transmission distance: 50-100 M 
Voltage: DC +9V 
Current: 300mA 
Power Dissipation:<640MW

A good spec on coin batteries can be found at :
http://www.panasonic.com/industrial/battery/oem/chem/lith/coin1.htm

Shay

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Clarification of Question by shohayon-ga on 01 Oct 2005 00:16 PDT

Hi,
Sorry, I meant MW, and not mah.

Here is the camera specification....
Video Camera Parts: 1/3, 1/4 image sensors 
System: PAL/CCIR NTSC/ELA 
Effective Pixel: PAL:628x582 NTSC:510x492 
Image area: PAL:5.78x4.19mm NTSC:4.69x3.45mm 
Horizontal definition: 380 Lines 
Scanning Frequency: PAL/CCIR:50HZ NTSC/ELA;60HZ 
 Minimum Illumination: 3Lux 
Sensitivity: +18DB-AGL ON-OFF 
Output Electrical Level: 50 MW 
Output Frequency: 0.9G/1.2G 
Transmission Signal: Video 
Linear Transmission distance: 50-100 M 
Voltage: DC +9V 
Current: 300mA 
Power Dissipation:<640MW

A good spec on coin batteries can be found at :
http://www.panasonic.com/industrial/battery/oem/chem/lith/coin1.htm

Shay

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Clarification of Question by shohayon-ga on 01 Oct 2005 06:08 PDT

Weight is most important. Shape & size are less important.

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Clarification of Question by shohayon-ga on 01 Oct 2005 06:08 PDT

Weight is most important. Shape & size are less important.
Camera should operate for at least 1/2 hour. a full Hour is even better

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Clarification of Question by shohayon-ga on 08 Oct 2005 08:48 PDT

Hi,

Last answer seems like an interesting configuration.
I am still waiting for the camera to arrive, so I can't measure the
minimal voltage. But, in the meanwhile, I found that this might be a
good option:
http://www.panasonic.com/industrial/battery/oem/images/pdf/Panasonic_LIthium_CR2412_CR2450.pdf

They have 620mah and weighs only 6.2 gram.

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Clarification of Question by shohayon-ga on 29 Oct 2005 10:05 PDT

Hi again, Here is an update:

I finally got the camera and did some tests.
Although the specification says 9V 300mA, I got the following:
the 9V is regulated down to both 5V and 8V. The camera gets 5V and uses 30mA.
The transmitter gets 8V and uses 70mA.

So, the bottleneck here is actually the transmitter, which must operate at 8V. 
I guess the best option would be to search for a tiny transmitter,
which operates at 5V, and weighs approx 10gram.

I found the following options:

http://www.spystuff.com/SHOP/index.html
http://www.blackwidowav.com/bwav240200components.html
http://www.hicam.com.au/pro_x2.htm
http://www.abacom-tech.com/transmitters.htm (weights is not specfied)

But I'm still searching...
Any comments ?

Many thanks,

Shay Ohayon

This is impossible to answer without two more pieces of information:
    - what current does the camera draw
    - how long do you want the batteries to last?

Is the "9V, 200-300mah" spec for the camera?  That sounds like the
spec for a battery, since "mah" is how batteries are specified
(milliamp-hours).

Other helpful things would be:
    - what is the minimum operating voltage of the camera?  Odds are
the 9V input is regulated down to some lower voltage, so it can
probably go lower
    - Does size matter, or just weight?

Posting the camera model number so we could look up the specs would be
helpful.  If you don't what the current drain is, posting how long the
camera runs on the 9V battery would help - it could be estimated from
that.

Here's a handy table of different battery types, including their Wh/kg values:
http://www.madkatz.com/ev/batteryTechnologyComparison.html

In general, lithium batteries have the highest energy density in terms
of energy per unit mass.  Zinc-air batteries (small button cells used
in hearing aids) may be slightly better than commonly available
lithium types, but they have the disadvantage that they expire within
a few weeks of opening them.

That helps, but we still need one thing -
   how long do you want the camera to run on one set of batteries?

640mW is a lot of power for CR type batteries.  I've tried to do
something with a similar current drain, but for a flashlight, not a
camera.  To get that kind of power output, you have to series a lot of
them, which means you have too much voltage.  That requires some
electronics to convert the voltage down to 9V.

Your best bet might be a rechargeable lithium ion battery (that's what
I ended up with).  Do you care about battery shape or volume, or just
mass?

One important spec is what's the minimum voltage the camera will
operata at?  You may have to find out by experiment, but usually it's
lower than the nominal voltage.  For instance, the 9V input may be
re-regulated down to 5V, in which case it might run with an input as
low as 5 or 6V.

Lithium coins cells- coin cells cannot generate the power you need
without putting many in series (at least 10 or 20).  Although they
have a high capacity, they cannot provide much power (i.e. they are
designed for low discharge rate).

Lithium AAA battery - This is your best option.  This battery is
pretty new (just a few months old).
Here's the datasheet: http://data.energizer.com/PDFs/l92.pdf
A single 7.6g cell holds 4500J, which is almost all you need. 
Realistically you'd need two, giving you 3V (2V at discharge) with
9000J, and a 1.5A max dicharge rate.  You'd need some electronics to
boost the 3V to the minimum needed by the camera (hopefully you could
get away with 6V, but you could boost it to 9V).

Camera power requirements:
   9V, 300mA, 30 minute run time = 2700 mW, 4860 Joules
Battery pack:
   2 AAA lithium batteries in a single pack
   3V nominal output (2V at discharge)
   weight = 15.2g
   capacity = 1250mAh
   energy = 2V x 1.250 x 3600 = 9108J
   max power = 1.5A x 2V = 3000 mW

So, the battery pack has the energy and power capability to do it. 
You could get even better runtime by using three batteries, but that
would put you just over your 20g limit.  You still need a switching
power supply to boost the voltage to 9V.  This could be a very small
piece that wouldn't add much to the weight (a few grams).  Efficiency
would easily be 85% with light-weight parts, and 90% wouldn't be that
hard to achieve.  Getting above that would add some to the weight. 
Before doing that it would be worth investigating the camera input to
see what the minimum voltage really is.

A step-up circuit could be made with a chip like the MAX771:
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1534/ln/
or the LT1302:
http://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1003,C1042,C1031,C1061,P1029,D3678

Without any custom electronics, your only hope is a 9V NiMH battery:
The nominal output is not actually 9V, but it might be enough for the
camera.  Here's a datasheet:
http://www.gpbatteries.com.hk/pic/GP17R7H_DS.pdf
Note that the discharge curve graph doesn't show a 2C rate - that's
pretty high for this battery, but it might be barely OK.  I doubt
you'd get a full 30 minutes, though.  Realistically, you might get
10-15 minutes, depending on how fresh the battery was.  Battery weight
is 28g, which is above your limit.

You can't get more than a few milliamps out of any of those coin-cell
batteries for more than a few seconds.  They're designed for low
current drain, and long battery life (years).  You're trying to
discharge the battery in 30-60 minutes, and that high rate requires
batteries designed for that.

You can experiment without the camera.  At 9V, a 300 mA load is 9/0.3
= 30 ohms.  The power is 9^2/30 = 2.7W.  So, if you had a 30 ohm, 3W
resistor, that would simulate the camera load, enabling you to do
battery tests without the camera.  You can get some 8 ohm power
resistors at Radio Shack, series four of them to get 32 ohms.  Then
pick up a few coin cells at a local drug store or Wal-Mart, and see
how long they last, using a voltmeter.