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Battery Pack Newbie HELP

  1. Jan 17, 2008 #1
    I work at a local entertainment venue and wanted to experiment by building my own pack for current laser tag vests. The manuf charge us a FORTUNE!

    So the specs are 6 NiMh 3800mah 1.2V 4/3 Panasonic 370a's wired in a block series

    there is a small resistor (i think) on the lead but I cannot make out what its specs are..this is where i need some help. What do you guys think it might be?
     
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  3. Jan 17, 2008 #2

    mgb_phys

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    It's unlikely to be a resistor that would just waste heat, it's more likely to be a fuse which is a good idea if you are strapping the batteries to your body.
     
    Last edited: Jan 18, 2008
  4. Jan 18, 2008 #3
    k

    quite possible...... looked like it might have had bands like a resistor though.....

    its not on the lead to the connector so to say.. there is a wire (small) soldered to the first positive cap in the series drops down next to the battery and is then connected to the middle lead of the three lead series

    [​IMG]
     

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    Last edited: Jan 18, 2008
  5. Jan 18, 2008 #4

    mgb_phys

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    In that case it's probably a thermistor to monitor temperature of the battery while charging.
    A common way to charge NiCd/NiMH is to turn up the charging current until it starts to get hot and then back off a little.
    If you aren't worrried about charging speed it is better/safer to just charge for 10-12 hours at 10% of the battery capacity.
     
  6. Jan 18, 2008 #5
    is there any specifications that one would need to replace such a part?
     
  7. Jan 18, 2008 #6

    mgb_phys

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    You would need to know it's cold resistance which you can measure with a meter, you could estimate the temperature coefficent by putting in warm water and then measuring it's resistance again.
    But like I said, it's easier/safer to just trickle charge the batteries, quick charging home made battery packs is a bit dangerous to the battery and you!
     
  8. Jan 18, 2008 #7
    It is exactly a thermistor! Im actually duplicating an existing pack. What would be the downfalls of hooking in the wrong thermistor? I have an existing intelligent charger that is being used as well. Is there anyway to estimate what thermistor should be used?
     
  9. Jan 18, 2008 #8

    NoTime

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    You might want to try some electonic supply houses.
    For instance, Radio Shack sell a 6 cell nicad pack for RC cars with charger for about $20.
    They also sell connector adaptors.
     
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