CR1632 (3v) vs. Two AA's

Discussion in 'The Projects Forum' started by wolfrado, Apr 5, 2015.

  1. wolfrado

    Thread Starter New Member

    Apr 5, 2015
    3
    0
    Hey,

    Kind of a newbie at this, so forgive me if this is a stupid question. I've disassembled a small lifeline alert pendant transmitter that normally runs on a CR1632, can I replace it with two AA's? Are there any disadvantages? Do CR batteries last longer, have more capacity than AA's, etc.?

    On a separate note, if I want to replace the batteries with a power supply, can I use a 5v USB supply or would I have to look for a 3v supply?

    Thanks,
    Ward
     
  2. RichardO

    Well-Known Member

    May 4, 2013
    1,228
    382
    General note:
    Doing any modification to a safety device is generally a very bad idea. Having said this here are the answers to your questions:

    Maybe. The AA batteries you would use will likely be alkaline and the CR1632 is lithium. The two AA's are a lot bigger than a CR1632. The CR1632's have a very long shelf life compared to AA's.

    The CR1632 cells have a capacity of about 130 maH and a pair of AA batteries have a capacity of something like 2 amp hours. The discharge characteristics are different in that the CR1632 has a flat discharge compared to the AA cells. This means that your circuit may quit working or work erratically as the AA cells discharge.

    I would not recommend doing this without a voltage regulator. In the worst case the too-high voltage could cause damage. Even if no damage is done, the transmitter is going to output a lot more power than it is designed for and could cause illegal interference. You should usse a low dropout type of linear regulator to reduce switching noise from the USB power supply.
     
  3. Roderick Young

    Member

    Feb 22, 2015
    408
    168
    If the device is being powered by a 1632, it probably draws less than a couple milliamps, maybe far less. The AA batteries would give incredibly long life, but by making the pendant clumsy and possibly unusable. The 5V USB power supply would give infinite life, but then the device would be tethered to one place. If using the USB supply, I'd probably put 270 ohms or so in series with it, and use a zener diode of 3.3 volts to limit the voltage.

    Are you planning to use the life alert for its original purpose? If you are, I think the 1632 batteries are probably optimal. Do know that you can get them in quantity from places like precisionproducts.us for less than $1 for a card of 5, if expense is a concern. Personally, I wouldn't mess around if it was the health of a loved one at stake.

    Or are you hacking it for another purpose?
     
  4. wolfrado

    Thread Starter New Member

    Apr 5, 2015
    3
    0
    Sorry, I should have clarified. The pendant is no longer being warn. It is being triggered by a relay. Since it no longer has to be portable, I figured I would look at some alternate methods of powering it. Are there any off-the-shelf 3.3v power supplies anyone can recommend?

    Would something like this work?

    SMAKN® DC 3.3V 1A Switching Power Supply Adapter 100-240 AC https://www.amazon.com/dp/B00OZDY950/ref=cm_sw_r_awd_iSEivb08B6WEB

    thanks
     
  5. wolfrado

    Thread Starter New Member

    Apr 5, 2015
    3
    0
  6. GopherT

    AAC Fanatic!

    Nov 23, 2012
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