How do I reduce amps??

Discussion in 'Modding Forum' started by BJ43, Dec 13, 2011.

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  1. BJ43

    BJ43 Vaping Master Verified Member

    Supporting member
    Need some help from electronic friends, I know how to reduce voltage with resistors, what do I use to reduce amps? I want to branch off my 12v 5 amp source with a 12 v 300 mA for battery charging. I google it and the results are always that the source amps doesn't matter as the item draws what it needs except for battery charging. They mention a current limiter but I don't know what this is.
     
  2. Str8V8ping

    Str8V8ping Vaping Master Verified Member

    Resistorssss
     
  3. BJ43

    BJ43 Vaping Master Verified Member

    Supporting member
    I don't want to reduce voltage..
     
  4. jrm850

    jrm850 Senior Member

  5. jrm850

    jrm850 Senior Member

  6. BJ43

    BJ43 Vaping Master Verified Member

    Supporting member
    I can't connect Ohms law to my mod. I want to reduce my source from 12v 5amp to 12v 300 mA to charge my batteries, if I put 5amps to my Li-Po they will explode. My battery is a 11.1v Li-Po.
     
  7. VpnDrgn

    VpnDrgn Ultra Member

    If you where trying to apply juice directly to your batt, they would be destroyed from the fact that you
    where putting 12V through a presumed 3.7V batt. The charger will regulate amps regardless of the source,
    but you need to step down the voltage to 5v's if it is an USB charger. An AC adapter would presumably
    step down voltage and regulate amps, but it sounds like you're using a 12V batt? Or, maybe a PC
    power supply?

    Think about it, the 5V 2amp wall adapter that most of us use for PT's and charging instead of
    risking our PC's does not apply 2 amps to batt. The charger that you plug into it regulates that.

    Duh!! I just seen where you said batt was 11.1V's, is 12V's what is required to charge that batt?
    I would still think that a charger will regulate the amps, and on a side note, it seems to me
    300ma's would take FOREVER to charge a batt that big. :ohmy:
     
  8. BJ43

    BJ43 Vaping Master Verified Member

    Supporting member
    No one is answering my question. How do I reduce 12v 5amp source to 12v 300 mA. Forget why I want to do it. And yes all I use for vaping is stepped down 11.1 v Li-Po batteries so all this abought 5v and 3.7v is irrelevant.
    I thank you all for your suggestions but still haven't found the answer.
     
  9. BJ43

    BJ43 Vaping Master Verified Member

    Supporting member
  10. northhar

    northhar Super Member

    Maybe this will help..

    I understand that you want to limit the current possibly to slow charge a battery.
    I found this it says you can adjust the current by changing R2.

    An Add-On Current Limiter For Your Power Supply
    Ahh more studying..:p
     
  11. jrm850

    jrm850 Senior Member

    Yor question was answered in post #5. Wait for the App to load and you will see exactly what you seek. Put a 40ohm resistor is series and you will have your 300ma. Make sure your resistor can handle the watts.
     
  12. nicotime

    nicotime Ultra Member

    Shunt resistor comes to mind...but I dunno.
     
  13. pailpoe

    pailpoe Moved On

    What do you want ? 12v ( constant voltage) or 300ma ( constant curent).
     
  14. BJ43

    BJ43 Vaping Master Verified Member

    Supporting member
    Thanks, my Java plugin wasn't opening the simulation.
     
  15. BJ43

    BJ43 Vaping Master Verified Member

    Supporting member
    I want to reduce my 12v 5 amp source to 12v 300ma to charge a 11.1v Li-Po
     
  16. pailpoe

    pailpoe Moved On

    You want to charge a 11,1v lipo pack .
    3 cells 3,7v = 11,1v --> you need 4,2v/elements = 12,6v max voltage during charging with a constant voltage first (12,6v) and constant current after (depend of your lipo pack capacity).
    What do you use for charging ? I power supply with just current/voltage limitation is not sufficient :facepalm:
     
  17. BJ43

    BJ43 Vaping Master Verified Member

    Supporting member
    Pailpo my source is 12.6v 5amp, I have been in the RC hobby for many years and understand multicell Li-Po charging and balancing and have many expensive battery chargers to do that It was more a curiosity of how to reduce amps.
     
  18. jhonutz

    jhonutz Super Member

    you need a current regulator.At that moment i don`t have ideea for a IC but try to find at maxim,TI or other sites

    look out at http://www.ti.com/product/bq24450 have adjusting output, and regulat both voltage and current
     
  19. pailpoe

    pailpoe Moved On

    A easy way to build a current regulation (linear). Use a LM317 in current source , not voltage.
    [​IMG]
     
  20. pailpoe

    pailpoe Moved On

    or a transistor with resistance :toast:
     
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