Featured Lipo parallel questions.

Discussion in 'Gun Building, Modifications & Repairs' started by Jimps, Sep 16, 2021.

  1. Jimps

    Jimps Active Member

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    I see a lot of mixed views on this topic. I guess there is a right and wrong though. I hear people say to parallel, the batteries need to be the same. Then I see people running a 1500mah and a 2200mah battery in parallel. From what I have seen, that seems to be okay. The batteries will always drain to the same voltage no matter the capacity of each, it is how batteries work apparently. The bigger battery will pick up the slack from the smaller battery. From what I read, just make sure the voltages are the same when connecting, and charge them separately with balanced chargers. Hard to know when I read so many different statements. What if you had a 30 amp draw and wanted to parallel a 20 amp capable battery with a 10 amp capable battery. Together that makes 30 amps. Does it matter that neither one alone can produce enough? This might be a dumb question, IDK. I've seen a guy with a 1000mah, 800mah, and 1200mah paralleled inside his stock. Ill never parallel lipos anyway. I was just curious about it after I saw what that guy did. If anyone could explain dos and don'ts with a little science to back it, that would be great. Everyone talks about upgrading, gears, springs, motors, ETUs/Mosfets...... I then see people go 12:1 SP120 and 16TPA motor, puts a 1100mah 15C lipo in his PDW stock because it is the only thing that will fit. Then wonders why his lipo is hot or puffed up. You got the con artists at Titan battery selling crap batteries for airsoft to people. Batteries seem to be the most uninformed area in airsoft.
     
  2. Guges Mk3

    Guges Mk3 Administrator Staff Member Administrator Supporting Member Lifetime Supporter

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    Not just batteries.

    Green Gas
    CO2
    Proper Lubrication and Silicone Oil/Siloxanes.
    High Polish BBs

    You can run any battery in parallel and the drain is based on discharge capability of the pack. Case in point is you have a small battery with a high discharge rate (GENS Ace LIPO) and a large battery with a low discharge rate (Titan LION). Most of the power will come from the LIPO and NOT the LION.

    It's going to take power from the channel of least resistance.
     

  3. Jimps

    Jimps Active Member

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    Augusta
    Yea Green gas seems to be a scam. I got a extended 30 pound propane tank I take to the field. Made an adapter to fill mags directly from it. I charge people $3 to fill all day. Cost like $13 here to get it filled.

    Never thought about polish on bbs though. Is the Idea they have less grip to apply backspin consistently? Is too much polish on bbs kind of like having oil on them, too slick to grip? Not sure.

    Titan have great marketing I guess. People will believe anything they hear a youtuber says that is getting paid to say it. They have people thinking lipo batteries are not safe. Well they are not safe if you use them wrong, and ion batteries in airsoft are almost always wrong. You can use lipo batteries safely in airsoft, pretty hard to use ions correctly in airsoft.
     
  4. Ben3721

    Ben3721 Well-Known Member

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    That maybe the cheapest and easiest way to make cash I've ever heard of lol

    You just need to make it automated, put in a quarter for 5 seconds of gas fill lol
     
  5. aotsukisho

    aotsukisho Well-Known Member

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    Matched batteries in parallel work best for a multitude of reasons, but mix and matching is not recommended. If you have to, I would place significant overhead for amp delivery and you are only doing a shallow DOD (depth of discharge, ie. few minutes of testing not going into a game with it).

    The voltages will equalize at rest, but that does not take into account what happens when the batteries are delivering power. Unless each battery has equal effective impedence (battery internal resistance, wire resistance, connector resistance) one will have a heavier load placed on it and it will discharge unevenly. There is also something regarding matching impedence of the source (battery) and load (motor) for maximum power transfer, I am assuming hooking up multiple source IR to a single load IR will have varying efficiencies but it's been awhile since I took that class
    https://en.wikipedia.org/wiki/Current_divider

    Battery IR fluctuates during discharge, varying both with DOD and amp draw/temperature. If the voltages of each battery differ, then in the process of attempting to equalize it will generate heat. If a huge load current spike drains the smaller battery voltage down significantly more than the larger battery, the stronger will charge the weaker - this unregulated current flow will generate heat, potentially enough to damage one or both.

    Also don't forget minimum voltage considerations, under heavy enough draw the weakest pack may dip below 2.5v/cell which may cause permanent damage to them.

    As packs age their IR tends to rise and mAh tends to drop, making the ability to match packs even more difficult. Even two cells next to each other on the production line will never be 100% equivalent. Matching cells in an Xs1p pack for capacity and IR is difficult and costly enough, and the measurement equipment used to do so are expensive for the average hobbyist.

    Because of the above-mentioned unbalanced IR problem, you need to heavily over-rate each lipo because it may end up pulling most of the slack so to speak. If I match lipos together for higher amp delivery, I personally over-rate 50%. This means if I needed 40A of current flow, I need a combined output of 60A continuous with two batteries for peace of mind. Compare 2000mAh 20C single battery setup to a parallel 2x 1000mAh 30C dual battery setup (ie to balance Crane-style stocks).

    Purposefully mismatching packs in an extended use role, I would over-rate the battery even more if I had no way to use any other setup.

    Real-life example: my 8s lipo 1:8 scale Traxxas E-Revo RC truck uses 2x 4s 14.8v 4500mAh packs as its power source, in both 8s1p and 4s2p configuration to power a brushless motor rated at 120A. Original packs were 20C rated (112.5A) so in 8s configuration I connected a huge capacitor bank in order to smooth surge under hard acceleration which worked. Running in 4s configuration I had double that amount on paper (225A) but I always ran it with the balance taps connected to each other to minimize the possibility of over-discharging any cell in either battery.

    Very much so, and as you just mentioned it is exploited mercilessly.

    Most of the output power yes, but there is still current flowing inside the battery packs as they attempt to equalize. You run the risk of them overheating, and not just from the load current draw.
     
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  6. Guges Mk3

    Guges Mk3 Administrator Staff Member Administrator Supporting Member Lifetime Supporter

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    See...I know just enough to get a C. Need to show my work...
     
    OutlawAirsoft and aotsukisho like this.
  7. OutlawAirsoft

    OutlawAirsoft Active Member

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    Hamilton
  8. aotsukisho

    aotsukisho Well-Known Member

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    DoD = Depth of Discharge

    https://www.solarips.com/blog/2021/january/battery-storage-101-what-is-depth-of-discharge-/