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How to set amps to charge lipo batteries

Discussion in 'Power Electronics' started by Shockie44, Jan 15, 2017.

  1. Shockie44

    Shockie44

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    Jan 15, 2017
    Hello, I am new as new can get. I want to start flying drones. NOW. I bought a charger that plugs into my computer to charge one battery. These batteries are 3.7 volts and 720amh. I am supposed to charge it at .72 amps. I bought a harness that I can plug in to the usb port. and it has leads so that I can charge up to five batteries at a time. Hooked in parallel. But I can't change the amps. so how is that supposed to work. thank you for your help.
     
  2. Arouse1973

    Arouse1973 Adam

    5,164
    1,078
    Dec 18, 2013
    Hello
    From memory, USB 2.0 ports can only supply 0.5 Amps each. So you are not going to be able to charge a battery at 0.72 Amps from one USB connector let alone connecting five batteries. Can you post a link or upload a picture of this charger and charging harness. The charger may be able to share current from the USB port say 100 mA each battery, but that would take a while to charge them.

    Thanks
    Adam
     
  3. Shockie44

    Shockie44

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    Jan 15, 2017
    I also bought one similar to this. Except it has a usb plug on one end, and Losi connectors on the other to fit my batteries.

    [​IMG] I bought this along with the five way charger. But I guess I can't use this or the five way charger on my computer. So, I bought the charger that was recommended. I sure hope this makes sense because I my self am confused. I am very very thankful for any and all help I can get." Another thought." I have an I max B 5 that I bought many years ago and never used. If I had a power supply. Maybe I could use that to charge the batteries.? thanks again
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Don't play around with charging of lipo batteries. If you charge them to too high a voltage or at too high a current (or lots of other things) they can catch fire or even explode.
     
    Shockie44 likes this.
  5. Shockie44

    Shockie44

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    Jan 15, 2017
    That is why I am going to the better charger. I want to be able to adjust the volts and amps. thank you for the warning.
     
  6. Audioguru

    Audioguru

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    Sep 24, 2016
    Do Not adjust the volts and amps of a Li-Po charger circuit. The charger circuit is supposed to do it. Buy a charger that is made for your battery.
    Do Not use a cell phone "charger" that is simply a power supply for the charger circuit inside the phone.

    It is wrong to charge Lithium batteries in parallel. The moment you connect them together if one has more charge than another one then a massive current will cause them to explode.
    If you succeed to connect a few in parallel but if one reaches a full charge first then the others will cause the charger circuit to over-charge that first one that might cause an explosion.
     
  7. Shockie44

    Shockie44

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    Jan 15, 2017
    Wow, now I am confused. It sounds like you are telling me. That I can only charge one battery at a time. I can do that if that is all that works. Does any one out there. Charge their lipos in parallel.? Has any one had a problem by doing that.? thanks again for all the help.
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    The are problems charging batteries in either series or parallel.

    If charging in parallel, the batteries must have the same state of charge initially. This may be because they are permanently connected in parallel, because you measured them and find they have the same voltage (for lipo), or some other method.

    If charging in series, the batteries also need to be in the same state of charge (assuming they are of equal capacity). Balancing chargers allow you to bend this rule somewhat.

    The safest way to charge multiple cells is in their normal configuration, so if the cells are in parallel when in use, charge them that way.

    If charging multiple cells in series, use balancing charger.
     
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  9. Audioguru

    Audioguru

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    Sep 24, 2016
    I have a Lithium battery from an old cell phone. It has two cells permanently welded together on parallel since the battery was made. There is never one cell with some charge and the other cell with less charge which will cause an explosion if they are connected together. The two cells are exactly the same so that there is not a weak one and a stronger one to cause one to overcharge.

    Look on the internet at fires and explosions caused by Lithium batteries. Some people are lucky paralleling them and other people are not.
     
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  10. BitHead

    BitHead

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    Mar 2, 2012
    I've been designing a charger/protector and playing with LiPo batteries for a few months - and I have discovered that it's not that scary/difficult for parallel configurations. The safe rule is to simply 'charge all of them together at a rate that is OK for one of them'. No - you aren't going to satisfy your impatience, but the job will eventually get done. The most-discharged battery gets most of the current until it charges up to the voltage of the next-most-discharged battery, where is begins to share more equally, and so on until they all get to 4.2V. However, I don't do as I say - I charge at twice the current that's OK for one . It seems that in the 'real world' the batteries discharge rather equally and the condition of one battery being 'way more discharged' than the others doesn't happen.
     
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  11. Shockie44

    Shockie44

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    Jan 15, 2017
    That makes a lot of sense. What you are saying is : If I am going to charge four 720mah 3.7 volt batteries. I should charge them at .72 amps and 3.7 volts. Do I have that correct? thank you
     
  12. BitHead

    BitHead

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    Mar 2, 2012
    Well, LiPo chargers will charge to 4.2V - that's the 'I'm full' voltage - and a proper LiPo-using device/circuit should have an auto-off circuit to keep them from going below 2.7V or so. The '3.7V' is the generic label they're given because that's the 'middle 80% of the curve' voltage. Here's a picture... https://static.rcgroups.net/forums/...-pro-power-40c-cell-discharge-curve-graph.jpg
    Me... I'd probably turn the knob up to 1 Amp and check on it in 2 hours.
     
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  13. Shockie44

    Shockie44

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    Jan 15, 2017
    Thank you, thank you, thank you. I have learned some thing today.
     
  14. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Don't set your voltage above 4.2V.

    As the batteries charge, the current will reduce
     
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  15. Shockie44

    Shockie44

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    Jan 15, 2017
    Got it. thanks. I have notes all over the place. I better get them in order.
     
  16. Audioguru

    Audioguru

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    Sep 24, 2016
    No, when the voltage reaches 4.20V the battery is still charging and is about 85% fully charged. The remaining 15% of charging takes a fairly long time because then the charging current drawn by the cell keeps reducing The cell is fully charged when the 4.20V charging current is about 3% of the mAh rating of the cell and it must be detected so that the charger can shut off.
     
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  17. Shockie44

    Shockie44

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    Jan 15, 2017
    Thanks guys, I did get some very good and very important information. Just getting started and it is not easy. But it is fun.
     
  18. JunaidShahid

    JunaidShahid

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    Jan 17, 2017
    Thanks for the solution :)
     
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  19. Shockie44

    Shockie44

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    Jan 15, 2017
    I would like to thank every one for their input. It is great to hear different ideas from people who know. thanks again
     
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