Setting up CS8 with 2 batteries

Discussion in 'Cinestar Misc' started by Will Good, Mar 31, 2014.

  1. Will Good

    Will Good New Member

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    Hey guys!

    We've been flying our cinestar 8 with 10,000 mah batteries successfully for the past month and have decided to expand and try out a dual battery set up with 2 6200mah batteries.

    My question is in understanding how the two batteries will work together and how our TX will understand it. If we're flying 2 - 6200mah 5s batteries is that the same as flying a single 12400 10s?

    When we plugged in the batteries to our copter, the Grauper MX20 immediately told us low voltage even though we know they were charged, should we disregard and fly anyways? Is there a way to change 'battery profiles' in the TX?

    Thanks in advance for your knowledge!
    Will
     
  2. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    The two LiPo's should be connected in parallel -- that is the two red (positive) wires from the two batteries go to the red wire of the Cinestar -- and the two black wires from the two batteries go to the black wire of the Cinestar.

    The two LiPos are now wired "in parallel." They should be charged together (many chargers allow "synchronized" charging of two batteries) so that they are charged to within about 0.1 volts of each other, and flown together -- the goal is to avoid the two batteries having different voltages (which would result in one battery charging the other!)

    When you wire batteries in parallel, the voltage does not increase, but the apparent "capacity" of the "battery" (it's actually two batteries) has been doubled.

    Thus if you're were flying two 6,200 mAH 5s batteries, you're effectively flying "one" battery of 12,400 mAH 5S.

    Are you sure that you are really flying a 5S battery, though. Most folks either fly 4S or 6S. What does a single LiPo's voltage read when it's fully charged?

    Note: The above only applies to LiPo's connected in parallel (red to red, black to black). You *can*, if want, connect the batteries in series, but I'll not address that until I really understand what battery types you're using.

    Andy.
     
  3. Will Good

    Will Good New Member

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    Hey Andy! Appreciate the quick response. Yep it's a 5s (here is the link to the specific battery - http://www.quadrocopter.com/QuadroPower-6200mAh-5S-Lipo-Battery_p_541.html)

    If I'm understanding correctly the two 6200's become the 12,400mah with 18.5v and the same C of 25.

    At what voltage should I bring the copter down? 3.5 volts per cell, same as the 10,000 mah?

    Again, really appreciate your help!
     
  4. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    OK...good....I'm glad you confirmed that. Thought it might be a typo as a lot of folks using 6,200 4S.

    When wired in parallel, yes, the battery becomes double the capacity, but the voltage stays the same.

    C is a slightly more complicated thing...it represents the capacity of the battery in Amp Hours -- so divide 6,200 by a thousand and you get 6.2.

    Vendors use C to tell you how to charge *single* LiPo batteries -- which is usually either 1 x C or 2 x C. Meaning, "You can charge this battery at 2C = 2 x 6.2 = 12.4 Amps." (Or to tell you how much current the LiPo can supply. Your battery is 25C, meaning 155 Amps.)

    That said, you'll find you get more charge into a LiPo if you charge it at 1C -- in this case 6.2 Amps -- although, of course, it takes longer to do the charging. You'll also find the batteries last longer. But, if you're a hurry, the specifications for this battery say 5C -- which means you can charge it at 31 Amps -- but that's a cruel and unusual thing to to do it and it will respond in kind! Also the risk of a LiPo fire increases when you start stuffing in lots of current.....(do a Google search for Lipo fire).

    The best way to deal with LiPo voltages is to recall what the "5S" really means -- 5 cells in Series.

    A fully charged Lithium Polymer cell is 4.2 volts. The "don't go below" voltage is 3.0 Volts without any load. (If you do go below this voltage you'll find you can recharge up the LiPo but it will not hold its charge.)

    A typical storage voltage is the mid-point = 4.2 - 3.0 / 2. Or 3.6 volts.
    Now we can answer the questions for a 5S LiPo:
    1. Fully charged 4.2 x 5 = 21.0 volts.
    2. Storage charge = 3.6 x 5 = 18 volts.
    3. Do not go below voltage = 15 volts (no load).

    If you have a fully charged LiPo that you're not going to use for more than a couple of days, take it down to storage charge, or wait a few weeks and get your credit card out so you can buy a replacement. Many chargers have a "Storage" setting that will charge or discharge LiPo's to their appropriate storage voltage, otherwise you'll end up using car light bulbs as a dummy load to discharge the battery.

    As to your question when do you bring the copter into land: 3.6 volts -- bear in mind this is an "under load" voltage. For a 5S that will be 18 volts. You'll find that when you stop the motors, the battery voltage will rebound a volt....don't be fooled....that's an effect of removing the load.

    Can you keep flying below 3.6 volts / 18 volts? Sure. If there is risk to someone if you don't keep flying then keep flying and be prepared to trash the battery...how long can you keep flying....just as long as the props are turning fast enough.... ;)

    Hope this helps.
    Andy.
     
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