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Understanding Lithium Polymer batteries

Discussion in 'Beginners Drone Forum' started by Bartman, Jul 31, 2013.

  1. gtranquilla

    gtranquilla RadioActive

    Posted by gtranquilla, Sep 11, 2014 #141
    IMHO - I would avoid using an C rating below 35C for VTOL type aircraft...... and 12C is way too low.
    And here is why......see attached. http://www.maac.ca/docs/2013/lipo_b...e_max_current_draw_true_crating__rev3_toc.pdf


     
  2. Bartman

    Bartman Welcome to MultiRotorForums.com!!

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    Posted by Bartman, Sep 11, 2014 #142
    at your normal flying weight how many amps does your helicopter draw? if you can't say then look at the specs for the motors given the props you're running....you may be able to use table data to get a rough estimate for your application.

    if you're running eight motors drawing 5 amps each hovering and 9 amps max then that is 40amps of draw hovering or 72 amps max. with a 12C battery, it's 12 times capacity as its max amps discharge capability. It would have to be at least 72/12 or 6 amps-hour, also known as 6000mah for it to be suitable but even then it's borderline. If you have two in parallel then it would be fine as they'd each be supplying half of the amps but if you lost a battery the second would be working hard to keep the helicopter flying.

    Bart
     
  3. polylawman

    polylawman Member

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    Posted by polylawman, Oct 5, 2014 #143
    Here's my question. I fly stock F550. At first I used a 3S 5200Mah 45C lipo and was getting about 7 1/2 minutes flight time. I purchased a 4S 5000Mah 50C lipo and got over 15 minutes flight time. During the last flight with the 5000Mah lipo, I notice that as the lipo voltages dropped, it seemed to take more throttle to keep the copter in the air. It flew with a little pep in the beginning of the flight, but that pep went away as the flight progressed.
    So to keep the throttle/power constant throughout the whole flight would you chose a lower C rated battery, like a 20 to 25C?
    I hope my question makes sense.
    I don't want to zip through the air doing tricks, just a normal smooth flight, hovering to take some videos and pics.


    Sent from my iPad using Tapatalk
     
  4. Motopreserve

    Motopreserve Drone Enthusiast

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    Posted by Motopreserve, Oct 5, 2014 #144
    Actually, if anything, you might want more C rating to be able to discharge more. The higher the C rating. the more current it is capable of discharging. Of course, the higher the C rating, the heavier the pack, so that fights against/for how the MR will react. That being said, it seems that there is always going to be some lack of power towards the end of a pack, regardless of the C rating. How low was the pack when you began to notice a difference?

     
  5. Posted by Roger Ramjet, Oct 5, 2014 #145
    The first thing you want to check is the prop you are using! You may very well fly a 10X5 prop with a 3S but you may have to reduce the prop i.e 9X5 or something along this line if you go with a 4S battery. It is all a matter of how much amps you motors and ESC can take. By going to a more powerful source of energy (4S vs 3S) your motors are going to develop more thrust but will also consume more current (amps).

    The stock 920 KV DJI are certainly overworked with a 10X5 AND a 4S battery pack! I myself run the Sunnysky 800 KV with 4S 35C on my loaded 550 (3 Kg) and I use 10 X 3.8 props. Keep an eye on your motor temp upon landing, if you can not keep your hand on it it is likely running too hot. You have to reduce either the pitch and/or the span of your propellers to allow your motors to operate in the normal operating temperature range. An electric motor that gets too hot is far less efficient and the extra heat on the bearings isn't great either... Hope it helps!
     
  6. Motopreserve

    Motopreserve Drone Enthusiast

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    Posted by Motopreserve, Oct 5, 2014 #146
    Roger is absolutely right. Sorry, I was taking for granted that the props matched the motors, and could be appropriate for the give batteries.

    Thanks Roger!
     
  7. polylawman

    polylawman Member

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    Posted by polylawman, Oct 5, 2014 #147
    I really don't remember how low the pack was, but will pay attention next time.
    Thanks everyone for the helpful info.


    Sent from my iPad using Tapatalk
     
  8. polylawman

    polylawman Member

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    Posted by polylawman, Oct 5, 2014 #148
    What are your average flight times with your setup?


    Sent from my iPad using Tapatalk
     
  9. Posted by Roger Ramjet, Oct 5, 2014 #149
    As previously stated, I use a 6000 mAh 4S on a fully loaded F-550 that weighs in at 3.0 Kg. It is basically a video Platform that features a Gopro camera and a DJI H3 3D gimball using AVL58 for video downlink. Add the landing gear, few strobes light, a Spot Trace Locator and a small battery for the video transmitter and you are inevitably approaching the 3 Kg mark. My flight time is a solid 10 minutes with a 20% reserve upon landing (80-20% rule). I feel that I could fly for 13+ mins if I was flying the frame naked, still landing with a decent reserve.

    I much prefer doing 6 X 10 mins flights than 3 X 15 mins when in video capture mode. Quite demanding to fly and monitor what is being shot at the same time. Maybe I am getting old... Ha! Ha!
     
  10. johnsonsten

    johnsonsten Johnsonsten

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    Posted by johnsonsten, Oct 7, 2014 #150
    very helpfull and information rich
     
  11. patrickwin

    patrickwin New Member

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    Posted by patrickwin, Oct 7, 2014 #151
    A very good post

    Hey, you have done a good job, very good post, you must be hardworking. I have one question, what do you think of Tattu battery?
     
  12. AK1990

    AK1990 Member

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    Posted by AK1990, Nov 1, 2014 #152
    Great Post Bartman! That was very informative and helpful. Thanks for sharing.
     
  13. Ian

    Ian New Pilot

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    Posted by Ian, Jan 14, 2015 #153
    I have a question or two

    Can you calculate how much capacity you have used from how much the battery takes to reach full charge ? is there any losses in capacity it takes to recharge ?

    secondly the 3v per cell lower limit, does this include under load ? battery voltage can recover have a volt after resting
     
  14. Bartman

    Bartman Welcome to MultiRotorForums.com!!

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    Posted by Bartman, Jan 14, 2015 #154
    I suppose if a cell has a high internal resistance then the MAH going in (as measured in the charger) would actually be higher than the actual MAH absorbed by the battery in the charging process since some is being lost to the heat generated by the higher than normal internal resistance. But the programming in a charger could be factoring in some loss to internal resistance so it's hard to say exactly what is happening. If a cell is rated at 6000 mah and the charger says it's putting back in 5000 mah after a normal flight, you can say with a reasonable amount of accuracy you replaced 83% of the capacity and this is a worthwhile strategy to know what you're using so as to not damage your batteries.

    it's usually 3.3 and yes it would be under load as measured while flying. the voltage recovery you see after landing isn't really factored in. when you reach 3.3 volts while under normal flying loads it is recommended that you land to prevent damage to your packs.
     
  15. Kratos

    Kratos Member

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    Posted by Kratos, Jan 15, 2015 #155

    Heh this is my problem too...
    Is there any other type of battery that have similar specification like this LIPO? Why is this so important compared to others? Is there more simple batteries to plug and play? Like phone Li ion or Gopro or some other ? I really don't like this Time Fire Bomb in my appartment... I Dont want to go outside on work or a meeting and think subconsciousness about batteries are they going to get fire... Also how to store them.. Use mother flowerpot on balcony LOL and install sprinklers in my appartment..., also in my country winters are cold -20 was for new year how does that affect battery and multirotor (isnt better to be more cold like superconductors)? I dont like these batteries so much that now I dont want to assemble my quadricopter...
    For all fire comrades here is old hit from highschool



    Fire starts on 2:34 or 2:07 depending on what you like more :D

    Dont get me wrong I am beginner ;)
     
  16. Motopreserve

    Motopreserve Drone Enthusiast

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    Posted by Motopreserve, Jan 15, 2015 #156
    Keep in mind that most issues happen during incorrect discharge or charging (too much or too little is not a good thing).

    For storage safety, keeping them in an ammo box (can be purchased for under $20) is a decent option.
     
  17. Kratos

    Kratos Member

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    Posted by Kratos, Jan 15, 2015 #157
    aaa my brain hurts because lipos :(
    How can you charge too much ? why it doesnt stop automatical? And you have led indicator is it full or not... Dont get it, is it because human impatience and inattention ? Man this lipos, I wont sleep because of them, this is like bad nightmare :D
     
  18. Motopreserve

    Motopreserve Drone Enthusiast

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    Posted by Motopreserve, Jan 15, 2015 #158
    Take a deep breath... :)

    Your charger should have an automatic shut-off at the set voltage. But many you have to set up correctly. Most will have a safeguard so you don't get nightmares.

    Discharging is where it gets dicey. People push the envelope too far which can create issues.

    You should try to follow the 80% rule - meaning do not use (discharge) the battery more than 80% (leaving 20% in reserve). You can calculate that based on voltage (4.2v cell multiplied by .8 gives you 3.36v) so that you don't dip too low. Very inexpensive alarms are available to tell you you've hit a set voltage under load. Most people will only fly down to 3.6v or 3.7v to be safest.

    Then when you get to charging, keep track of the mAh put back to the battery. It should not be more than 80%.

    If you have to put back more than 80% mAh or your voltage sags under 3.36 in flight, you're probably pushing it. Best to play it safe.

    Following this rule should keep you as safe as can be....

    Keeping the lipos in special storage bags or the ammo boxes I mentioned is for peace of mind.
     
    3 people like this.
  19. Kratos

    Kratos Member

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    Posted by Kratos, Jan 16, 2015 #159

    What about plug and play bateries, why this lipos are so important?
     
  20. Motopreserve

    Motopreserve Drone Enthusiast

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    Posted by Motopreserve, Jan 16, 2015 #160
    I'm not sure what you mean by plug and play, but these lipos come ready to go other than charging. You may need to swap plugs if your MR has a different type to the onboard power.

    I'm no expert, but I think the advantage to the lipos is that they provide a high discharge rate capable of handling the power draw that these MRs require.
     
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