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Powering my project with a 7.4v battery

Discussion in 'Power Electronics' started by smau, Jul 10, 2017.

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  1. smau

    smau

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    Jul 10, 2017
    I've been looking to do a handheld intel compute stick for a while now but have been held back on how the hell im going to power the thing.
    From my research and friends who hooked up oscilloscopes to the m5 compute stick, it needs 5v 3.5A to comfortably power it. This, plus an LCD screen, USB hub, etc. puts any 3a battery bank out of the equation.
    So, I decided to use a 7.4v internal battery. I then found a step down regulator (https://www.pololu.com/product/2865), a charging circuit (http://m.ebay.com/itm/TP5100-2-cell...er-Module-2A-18650-Charging-PCB-/181687643612), and a protection circuit (http://m.ebay.com/itm/2S-8A-7-4V-8-...tery-18650-Protection-PCB-Board-/192110391518).

    The problem is that I have no idea how to wire these up as I have only used boards that output power to the project and charge the battery on one circuit. Also, how do I power all the other components in the build like the teensy board and lcd from the regulator? If there are any easier ways of doing this please let me know.
    Thanks.
     
  2. BobK

    BobK

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    Jan 5, 2010
    Can you post a link to the device? 17.5W seems like a lot of power for a hand-held device, except maybe for a hand warmer.

    Bob
     
  3. smau

    smau

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    Jul 10, 2017
  4. kellys_eye

    kellys_eye

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    Jun 25, 2010
    The protection board connects to the two cells as per the drawing shown on the advert..

    There are two pads on that board (P- and P+) and these connect to the output of the charging board (TR5100) where it says 'lithium battery + and lithium battery -. You MUST solder a short on the link where it says 'short connect 8.4V charging'

    The power INPUT to the TP5100 board connects to your charging supply - a supply anywhere from +5V to +18V apparently.

    Power the input of your Pololu 6A step down regulator from the B+ and B- pads on the protection board.

    Take the output of the Pololu regulator to whatever you want to power.
     
    smau likes this.
  5. Audioguru

    Audioguru

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    Sep 24, 2016
    7.4V is the average voltage of two half-discharged lithium rechargeable battery cells in series that produce 8.4V when fully charged and the voltage drops as they discharge until they produce about 6V when they should have their load disconnected.

    The voltage regulator will produce an output of 5V at 3.5A or more with the input as low as 6V.

    The charger comes pre-set for charging only one cell and cannot do balanced charging for 2 cells.

    The protection circuit allows conditions that will cause a fire or explosion.
     
  6. smau

    smau

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    Jul 10, 2017
    Here is where I got the components, he is using two 3.7v batteries and hasn't had any problems so far:
    http://www.sudomod.com/forum/viewtopic.php?f=13&t=3331
     
  7. smau

    smau

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    Jul 10, 2017
    What if I want to use one lithium ion 7.4v battery?
     
  8. Bluejets

    Bluejets

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    Oct 5, 2014
    One battery (7.4v) is made from 2 cells (3.7v each) as shown.
     
  9. smau

    smau

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    Jul 10, 2017
  10. Audioguru

    Audioguru

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    Sep 24, 2016
    That battery is huge.

    Ali is a Chinese company with horrible Engrish. In the first part of their specifications they say the wrong over discharge protect voltage and say an impossibly low temperature rating.

    Later in the ad they have a correct over discharge voltage but later they say that you are supposed to turn off the energy to avoid over-discharge (because it doesn't work?).

    The protection circuit is not a charger circuit.
     
  11. smau

    smau

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    Jul 10, 2017
    Say the battery is safe and legit, would I be able to use that instead of 2x 3.7v batteries? How would it connect to the protection board or does it not need one?
     
  12. Audioguru

    Audioguru

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    Sep 24, 2016
    The 20,000mAh 7.4V Li-PO battery has a protection circuit. Then all you need is a Li-Po battery charger circuit for it.
     
  13. Bluejets

    Bluejets

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    1,048
    Oct 5, 2014
    If you want to go that way, (MASSIVE) then why not just buy the battery in a case with the charger that suits and all the bells and whistles included. Called a power pack I believe. Probably cost about the same. Just looked it up .... power bank
     
  14. smau

    smau

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    Jul 10, 2017
    Can I use the one I already linked?
     
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