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Battery Charging Setup

Discussion in 'Pro/Adv Discussion' started by Morkster, Dec 10, 2015.

  1. Morkster

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    Ok, I did a bit of research on the charger setup for the P3. The charger itself is just a 3,3amp power supply. The batteries actually contain the charging circuitry. I have been in the electronics hobby for 40 years and have a general understanding of they setup. The P3A has a 17.3v, 3.3a charger with a output of 57w. My plan is to connect a battery charging bank, capable of charging 4 P3 batteries at once. This will be supplied by a 17.3v, 7a small bench supply I just completed. This will give me 121w of charging power. Has anyone else did this sort of thing and what has been your experience with it.
     
  2. kenwhite

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    Without knowing how the internal charging circuitry works, I would just charge them sequentially, one at a time, and save yourself from some possible safety/damage issues.

    The reason for my response is the input impedance of the batteries will not be the same for each battery so charging them in parallel could cause one to be severely over charged while the other receives a low charge.

    This could be dangerous
     
    #2 kenwhite, Dec 10, 2015
    Last edited: Dec 10, 2015
  3. tcope

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    Sequential chargers can be bought on ebay for $10. I don't know much about electronics but those charges have a circuit board and a good amount of circuits on them. I'd guess, for Example good reason. If nothing else they would need to only allow the charge in one direction. Perhaps you'd be better of just spending the $10 and getting something that has been well tested.
     
  4. TheRealNick

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    If you are correct that the batteries control the charging then you should be able to supply them with 17.3V (my charger says 17.5V) and they will charge until complete with no risk. The batteries can not tell other batteries are connected, as long as all the batteries do not pull the voltage down. The key is that you are correct about how the battery charges. I would want to check measuring current and voltage...
     
  5. kenwhite

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    Since the same batteries are used in both the P/A and S, with the only difference being the size of the supplied chargers, my guess is the brick actually provides the voltage/current regulation part and the battery contains the smart controls for just the monitor/discharge.

    LiPo batteries are quite dangerous if not charged/discharged correctly, so I would err on the safe side.
     
  6. bobmyers

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    The Smart Batteries control the charge voltage going into the batteries--not the charger-- the charge is balanced thru the Smart Battery Circuitry-- any power supply putting out 17.5 to 18 volts will work. There are battery charging sticks available on Ebay and other places that there batteries can be plugged into and charged by simply providing direct voltage to the charging strip.
     
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  7. Scozz76

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    The internal circuitry of the battery pack would control the charging current etc.

    If you can supply enough amperage to avoid the voltage from being pulled down, you will be ok.
     
  8. alokbhargava

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    Not correct. Battery internal resistance will not have any effect on charging as terminal voltage will be the same for both the packs. Setup as proposed by Morkster will work.
     
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  9. kenwhite

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    Interesting...

    So how does the same battery get charged faster by the 100W brick versus the 57W brick if its regulator is internal?
     
  10. kenwhite

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  11. N017RW

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    While not taking sides, and sans any physical damage or trauma... charging is where the most LiPo 'accidents' [fires] occur.

    Patience is a virtue.
     
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  12. kenwhite

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    I agree and that was really my point in the whole discussion - safety...

    :)
     
  13. TheRealNick

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    I think if you check the voltage is slightly higher with the higher wattage charger, my 100 W says 17.5V, what does the 57W one say? Also, the charging unit may limit the current the battery can draw. I also find it interesting that most of the chargers, including the aftermarket ones, also charge sequentially. It could be to lower the required wattage or for another reason. I found one on amazon that basically said it may change them sequentially or all at once, or alternating, which to me is concerning. I think since the battery only connects on 2 terminals that it appears the charging circuit is internal to the battery, otherwise there is no way to balance the cells...all that said, I would probably not try it myself...
     
  14. Scozz76

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    The battery is 4480mAh. The 100w charger can supply enough current to charge at 1C, the 57w charger is just over half that.
    That is why the charging times vary.
     
  15. Scozz76

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    According to the DJI website both chargers should be at approx. 17.4v
    So according to my calculations, the 100w should deliver 5.7amps and the 57w should deliver 3.3amps
     
  16. alokbhargava

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    100W charger can supply more charging current.
     
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  17. kenwhite

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    Exactly, so how does the same battery with a supposed internal charge regulator now decide to draw more current?

    I really don't want to argue the point, but the smart battery system manages the discharge cycle - connects a load between the terminals, LED voltage level response, and terminal disconnect when fully charged.

    Not the regulated charge cycle since both bricks charge the same battery at different rates...

    LiPo batteries are very finicky and I would not parallel them, but if you guys want to, its your choice.

    Have a happy holiday season.

    :)
     
  18. Scozz76

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  19. bobmyers

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    I have various sizes lipos for my rc airplanes from 6 cell to 3 cell and have been parallel charging them for years on parallel charging boards. You do have to parallel charge the same cell counts and mAH sizes, but they can safely be charged in parallel. The only difference being is that the charger balances those batteries thru a balance board whereas the Smart Batteries are balanced thru the battery circuitry with a the 17.5 to 18V direct power feed to the battery.

    Knock on wood-- I have never experienced anything even close to a battery fire or heat up while charging or discharging my standard airplane lipos. I am always in the same room or close by when they are charging so if there were an issue I could address it immediately. Parallel charging is common practice for the rc model industry. It is not new technology.
     
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  20. Mork007

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    Which is my intention. I am surprised that the 57W charger that comes with the P3A is so small that it is rated at 3.3amps.