batteries dilemma, 2x 5s 10 000mah vs 4x 5s 5000mah

Discussion in 'Batteries & Power' started by Jay Pearl, May 22, 2015.

  1. Jay Pearl

    Jay Pearl New Member

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    Hi Everyone .I have cinestar 8 with WKM and I'm using 5s 10 000mah lipos , KW8 motors and 14x6 xoars props. My lipo packs geting old so I'm thinking about options for new ones.I know that kw8 are happy with 5s lipos and If i would like to upgrade to 6s i need to use 13x6 props so I'm not sure if its the best idea.I come with this idea to use 4x 5000mah s5 batteries connected in parallel Y and then pairs again Y if you know what i mean.What do you think guys? Pros are that overall smaller lipo packs are cheaper and weight of 2x 5000mah is almost same as one 5s 10000mah. Other pros what i can come with is If one battery fail,rest should take care on safe flight?
    Is it good idea to go that way?
     
  2. Steve Maller

    Steve Maller UAV Grief Counselor

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    Using 4 batteries dramatically increases the possibility that one of the batteries or one of the many connectors will go bad. Are you certain that the overall weight of four small batteries is less then two larger ones? I would really be surprised if that was the case.

    Unfortunately you do not have many choices when it comes to 5S batteries. Very few people use that size.
     
  3. Jay Pearl

    Jay Pearl New Member

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    I weighted one 10 000mah battery and after 2x 5000mah and weight is very close +/- 10g .Only thing which add more weight is 2x y connector but still it is not much difference.My only worry is how system will work if one battery or pair fail? other option is to try 6s and 13inch props instead of 14inch but I am not sure if it's good idea.
    thanks for answer Steve:)
     
  4. Steve Maller

    Steve Maller UAV Grief Counselor

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    Why would you use smaller props with the larger LiPos? that doesn't make sense. The extra power of the 6S system should allow you to use larger props, or at least the same size.

    And the odds of a battery failure in flight are extremely low, especially if you take care of your batteries. I've never experienced this, and the consensus is that if you retire batteries when they start to show their age, you're highly unlikely to have them fail. Most, if not all, of the failures I've analyzed have been caused by something other than a battery failure. The closest I've seen is a few cases where the battery connectors failed.
     
  5. Jay Pearl

    Jay Pearl New Member

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  6. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    I have the MK electronics set to give me a low voltage alarm at 3.6 (14.4V 4S, 21.6 6S). That seems to provide for enough time to come home and land -- with reserve power for a "missed approach" if some hazard appears in the landing zone.

    What threshold voltage do you use Steve?

    Andy.
     
  7. Steve Maller

    Steve Maller UAV Grief Counselor

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    I've traditionally used 3.5V for warning, but I closely monitor my voltage in flight, so I don't typically run into this limit. Truth be told most of my flights with my big copter are well short of its max flight time. My copter (ex-copter now...it's off to the highlands of Colorado with its new family) was theoretically capable of 16+ minute flight times, but I rarely flew it more than 8-10 minutes. I also found with high-end batteries (I prefer Tattu) the voltage sag was minimal, and I could fly for a long time at 3.7V or so.
     
  8. James Adkins

    James Adkins Member

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    I disagree. There are several good reasons to run 4 batteries over 2.

    - it is possible to keep the individual packs below to 100Wh TSA limit
    - having more packs increases reliability through redundancy, just like having more motors/props. If one of two packs fails, bad news. One of four fails, not as bad.
    - in 10 years I have only had one connector fail (bad solder joint)
    - more packs allows for higher current flow and lower resistive heating by lowering overall internal resistance of the battery system. Battery temps after a hard flight are lower with four than for two which proves this fact. Four is more efficient in power delivery than two.

    There are people who will make custom batteries to any size you want also.
     
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