>-----Original Message-----
>From: Jesse Lackey [mailto:jesse@CELESTIALAUDIO.COM]
>Sent: 16 February 2004 05:42
>To: PICLIST@MITVMA.MIT.EDU
>Subject: [EE:] Using two 9V in parallel for greater capacity... ok?
>
>
>Hello all,
>
>I have a project that involves blinking LEDs that the client
>would like to have run for 2 months per battery or battery set.
>
>2 9V wired in parallel would do it and is preferable to 4 AA.
>
>Is this a reasonable thing to do?  Is it dangerous at all if
>both are fresh of the same kind?  How about if not?  Would a
>5ohm resistor in series with each before being wired in
>parallel alleviate any dangers from users who don't follow
>directions?  (its a consumer product).  The current is pretty
>low so the loss due to a small resistor is not a problem.
>

Out of interest why would 2x PP3 style batteries be preffered to the AA's?
An alkaline PP3 has a capacity of around 550mAh, an akaline AA cell has a
capacity of 2500mAh.

If you need 9v for whatever reason a simple, low cost voltage doubler (e.g.
MAX1044) could be used to provide 9v from just three AA cells and still
provide more capacity than 2x9v batteries.

Regards

Mike




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