How To Choose A LiPo Battery (Tutorial)

Discussion in 'Electronics' started by LukeWarm, Jan 20, 2012.

  1. LukeWarm

    LukeWarm Top Gun

    Posts:
    3,827
    Likes:
    941
    Points:
    133
    [​IMG]
    [​IMG]
    Above are two pictures that can be saved for future reference or to print as a chart.
    Print one on one side of the page, and the other on the back side.
    It was up-dated on 8/14/2012 to be much more beginner friendly. Enjoy

    The battery has a storage capacity rating in mah, that is mah (milli amps per hour). 2200mah is the same as 2.2 ah (amp hours).
     
    Whonoze, RobDavis, hubman56 and 5 others like this.
  2. Learning

    Learning Rookie

    Posts:
    86
    Likes:
    1
    Points:
    0
    Nice work a great quick reference chart.
     
  3. Argonath

    Argonath Top Gun

    Posts:
    7,418
    Likes:
    772
    Points:
    133
    Great chart Luke.
     
  4. LukeWarm

    LukeWarm Top Gun

    Posts:
    3,827
    Likes:
    941
    Points:
    133
    THANKS!!
    I made the chart and the instuctions into a picture, that way you can save it as a resource.
    To save it:
    1) right click on it with your mouse.
    2) in the menue, select "save as picture"
    3) choose a location to store it
    3) select save
    I have a file on my storage drive called RC Stuff, I save things like this there.

    If you print it , it will print the same as you see it.
     
    RobDavis and rcfoamfly like this.
  5. Argonath

    Argonath Top Gun

    Posts:
    7,418
    Likes:
    772
    Points:
    133
    I have a portable drive I keep all this stuff on and I also have a 32Gb USB key that has it as well. I've pretty much always got access to my stuff anywhere I go because my Laptop goes with me everywhere.

    I started working on a Web based tool that would allow me to store it all on a DVD and auto-run it but I haven't had much time to finish it...
     
  6. oostevew

    oostevew Rookie

    Posts:
    8
    Likes:
    2
    Points:
    3
    SO a Grayson Super Mega Jet V2 COMBO will run on a 2200 11.1V (3s) 30C / 40C Li-Po? I'm also concerned with the ESC in that combo kit. It's not "over-kill" in the fashion of "10-20amps beyond what I think I'll ever need", are these baseless fears?
     
  7. LukeWarm

    LukeWarm Top Gun

    Posts:
    3,827
    Likes:
    941
    Points:
    133
    They are baseless fears but I think you are dancing with the wolves a little. Many pilots skirt the edge of danger to save on weight or money. There is a sweet spot;
    1) Above it, your plane weighs more but will not overheat. I like to have 5 to 10 amps above what I think I will ever use.
    2) On it, you dances in the sky; you enjoy great performance with some management.
    3) Below it; you try to save weight or money and you risk danger. When done wrong, starvation is hard on electronics; It limits performance, increases heat and kills equipment.

    Some times there is a way around a limitation. By taking the heat shrink off of the ESC and cooling it well, you can safely get 5 or 10 more amps out of it. It is lighter, but it can more easily get damaged.

    A battery with a lower C-rating cost less, and weighs less.

    A 30 amp ESC for that motor is marginal. IF you know the risk and are willing to take the chance, go for it, but be smart about it!!!
     
  8. Learning

    Learning Rookie

    Posts:
    86
    Likes:
    1
    Points:
    0
    From experience 'which was expensive' I totally agree that a higher rated ESC by say 10 or 20 amps is a safer way to go. They do not get hot and you can use them on various sized motors. Cost a little more and weight a little more but when you lose complete control of your plane because the ESC has just burnt out and it glides beautify into a pond. Cost me ESC, battery and receiver and a broken plane.

    Learn from my lesson give yourself headroom. Getting a higher rated ESC doesn't mean spending lots of money a cheap one is good enough.

    40A.JPG

    I recommend a Tower Pro 40A bit heavy but runs very cool and has a durable heatsink not that rubbish heat shrink.
     
  9. LukeWarm

    LukeWarm Top Gun

    Posts:
    3,827
    Likes:
    941
    Points:
    133
    I have added this information and more, to post #1, now post #1 is more beginner friendly.

    Lets look at a "3s, 25c, 2200mAh" battery

    The s rating: 3s, 2s, 4s --same as 3 cell, 2 cell, 4 cell
    Each cell puts out 3.7volts DC, so a 3s is 11.1volts DC

    The c rating: The 20c, 25c, 30c rating needs to be used with the "mah" rating to calculate the allowable amp load.
    The number of cells does not matter.
    2200mAh x 25C = 55,000mA or 2.2Ah x 25C = 55Amps) so Ah x C = Amps.
    55 amps is the maximum safe current a motor can draw from this battery.

    The mAh rating: 2200mAh is 2200 milliamp hours or 2.2 amp hours. That is the amount of energy the battery can hold. This battery will give 2.2 amps of current for one hour. Or 4.4 amps for half an hour, or 8.8 amps for 15 minutes.
     
  10. LukeWarm

    LukeWarm Top Gun

    Posts:
    3,827
    Likes:
    941
    Points:
    133
    2200mah battery - 3 cell - weight 237 grams
    Your plane will be Heavier and will sustain more damage in a crash, but the motor will have longer run times.

    1000mah battery - 3 cell -weight 107 grams
    A lighter battery will give your plane better performance because your plane will have a better power to weight ratio. The motor will be more punchy, and your plane will go faster

    1000mah battery - 2 cell -weight 67 grams
    A 2 cell is even lighter. With not having that extra cell, the decrease in performance will be somewhat offset by battery weighing less.
     
    RobDavis likes this.
  11. graham96

    graham96 Cadet

    Posts:
    68
    Likes:
    0
    Points:
    6
    Thanks alot! I now know exactly what battery to get for future motors! To know I am understanding this right. The microjet has 8-15 amps of "max efficiency current" and 20amps for 60sec. of "max current" it also has a 20amp esc. So, I bought a 20c (must be 1000Mah because thats the minimum for a 20amp motor) 1300 Mah battery, Thats right, Right? But I only have 7 amps of "give" because of the 20 amp ESC. But thats OK right?

    Thanks again for the chart!
     
  12. LukeWarm

    LukeWarm Top Gun

    Posts:
    3,827
    Likes:
    941
    Points:
    133
    By George, I think you got it !!!!!
    Interpretation: Everything you said is at least close.

    The load that is placed on the motor is what determines its amp draw.
    An AC motor ESC or battery should never restrict amp draw; if it does, you need a better one.
    If the ESC or battery is being ask to give more than it can, it will overheat.
     
    RobDavis likes this.
  13. graham96

    graham96 Cadet

    Posts:
    68
    Likes:
    0
    Points:
    6
    Thanks, I got confused on where the "give" was (ie between the max amps that the battery can give and the max amps the motor will be able to handle) I think I got it now. Is there a way I can save this whole thread on my profile or something? I already saved the chart.
     
  14. LukeWarm

    LukeWarm Top Gun

    Posts:
    3,827
    Likes:
    941
    Points:
    133
    1) HyperSnap will save a whole page.
    2) you can cut and paste into MS Word, one post at a time.
    3) you can also "print Screen" and put the pages together in "MS Paint" and save them.
     
  15. LukeWarm

    LukeWarm Top Gun

    Posts:
    3,827
    Likes:
    941
    Points:
    133
    Let’s look at a "3s, 25c, 2200mAh" battery

    The s rating: 3s, 2s, 4s -- same as 3 cell, 2 cell, 4 cell
    Each cell puts out 3.7volts DC, so a 3s is 11.1volts DC.
    The voltage rating: The number of cells times 3.7volts is the voltage rating of the battery.
    1s = 1cell = 3.7volts * 2s = 2cell = 7.4volts * 3s = 3cell = 11.1volts * 4s = 4cell = 14.8volts * 5s = 5cell = 18.5volts
    The c rating: The 20c, 25c, 30c rating needs to be used with the "mah" rating to calculate the allowable amp draw. The number of cells does not matter.
    2200mah/1000 x 25C = 55A; so >> mah/1000 x C = Amps.
    55 amps is the maximum safe current a motor can draw from this battery.
    The mah rating: 2200mAh is 2200 milliamp hours or 2.2 amp hours. That is the amount of energy the battery can hold. This battery will give 2.2 amps of current for one hour. Or 4.4 amps for 1/2 hour, or 8.8 amps for 15 minutes. Motors consume current.
    The charge rate: The charge time depends on the amount of unused energy that is left in the battery, the available energy capacity (mah) that is left to fill, and how fast you charge the battery. 2.2 amps is the maximum rate that a 2200mAh battery should ever be charged at. A cheap 2200mAh will puff at a 2.2 amp charge, .2amps lower is much safer. Lower is safer, but too low waste time.
    A 2200mah battery maximum charge rate is 2.2 amps, but it should be charged between 2.0 amps, and 1.1 amps.
    A 1800mah battery maximum charge rate is 1.8 amps, but it should be charged between 1.6 amps, and .9 amps.
    The first number is max, the second number is .2 below max, and the third number is half max.
    To calculate a batteries discharge rate: The milliamp hours divided by 1000, times the C rating, equals the maximum continuous discharge amperage the battery is capable of sustaining.
    That's >> mah/1000 x C = Amps. So >> 2200mah/1000 x 25C = 55Amps
    Amp draw problems: The motor and the load that is placed on it is what determines the amp draw from the ESC and the battery. Nether the ESC nor the battery should never restrict amp draw; if it does, you need a better one.
    If the ESC or battery is being ask to give more than it can, it will overheat.
    Motor Load: The dynamics of the aircraft deals with friction and momentum; it is information like the weight, Air flow obstructions and the aerodynamics of the air frame. Anything less than perfect puts more of a load on the motor. Anytime you’re flying and you hear the motor working harder, it’s because the plane turned hard, the plane accelerated , the motor is WOT (wide open throttle), or the plane is climbing fast; these things all put more of a load on the motor. Increasing the load on the motor creates more heat for the motor’s self-cooling to deal with. The more load, the more heat. The motor’s self-cooling can only dissipate so much heat. Anything beyond that point, the motor will overheat. During flight, When you have to control the aircraft in a certain way by doing less things that place an extra load on the motor, this is called “flight control management”. This is a great way to control the heat and keep the electronics from overheating.
    Weight: A 25c 2000mah LiPo battery can weigh from 170 grams to 270grams depending on the brand and model number. When you look to buy a battery, weight should be one of the things you look at. Some 1600mah batteries weigh as much as some 2200mah batteries. A batteries weight has a huge effect on the planes power to weight ratio, Two extra ounces will make a big difference in your planes performance. Jets need a better than 1 to 1 power (thrust) to weight ratio to perform like a jet.
    Averages weights per capacity is:
    1000mah - 141grams
    1300mah - 176grams
    1600mah - 195grams
    1800mah - 216grams
    2200mah - 225grams

    You find more information in the RC course about batteries in module #7.
     
  16. Jbirky

    Jbirky Ace Pilot

    Posts:
    1,449
    Likes:
    25
    Points:
    48
    This is a very nice chart; thanks. Unfortunatly, I really don't think the 45C batteries are even close to 45C; I think it's a lie.
     
  17. phoenix_md

    phoenix_md Airman

    Posts:
    539
    Likes:
    221
    Points:
    43
    Where is the chart? I don't see it.
     
  18. LukeWarm

    LukeWarm Top Gun

    Posts:
    3,827
    Likes:
    941
    Points:
    133
    Post #1, at the top of the page.

    Your right, but if you really need a 45C battery you can trust, go with a reputable company.
     
  19. LukeWarm

    LukeWarm Top Gun

    Posts:
    3,827
    Likes:
    941
    Points:
    133
    How to connect two batteries in our planes
    [​IMG]
    On a Parallel Battery Connection:
    Warning: Before a parallel connection, fully charge both pack. The voltages need to be the same in each pack. When you first make the parallel connection, the battery packs will quickly equalize to the same voltage. When you first connect them, If their voltages are too far apart, the packs will over heat. Feel their heat when you plug them together. Warm is OK, hot is not. Disconnect them if it gets hot and check the voltages. This rule is for anytime you make a parallel connection of any batteries, matched or not.

    If you have identical battery packs:
    Two 20C, 3s, 1000mah, 20 amp, batteries in parallel. Gives you one 20C, 3s, 2000mah, 40 amp, battery. Only the storage capacity (mah) and amperage output will double (to 40 amps). The C rating and cell count will stay the same. The C rating does not change because it is tied to the storage capacity (mah).

    If you have a Different number of Cells in each pack (different voltage):
    Do not do this. the voltage and cell number for each battery has to be the exactly same. Warning: Ignoring this will cost you. They will equalize when you connect them. During this, one or both batteries might exceed their charge or discharge amperage limit. One of them will over charge. This will ruin one or both of them.

    If you have a Different C rating or mah rating in each pack:
    After connected, each pack will equalize to the same voltage and stay that way. One pack cannot discharge faster than the other one. Theoretically, If both batteries have a perfectly linier discharge, each battery would be responsible for their percentage share of the load. The research I did shows a perfectly linier discharge, but I would not completely depend on it. I personally would use batteries that went over their needed rating by a ways.
    With matched batteries:
    and a 50 amp load, each would be responsible for 50% of the load, so that would be 25 amps each.
    With unmatched batteries:
    With a 2200mah and a 1300 mah being 3500mah when added together and sharing a 50 amp load,
    2200 x 100/3500 = 62.9%, then 50 amps x 62.9%/100 = 31.5 amps; the 2200's share of a 50 amp load is 31.5 amps
    1300 x 100/3500 = 37.1%, then 50 amps x 37.1%/100 = 18.6 amps; the 1300's share of a 50 amp load is 18.6 amps.
    .

    On a Series Battery Connection:
    A series battery pack combo is only as good as its weakest cell.

    If you have identical battery packs:
    Two 20C, 3s 1000mah batteries in Series. Gives you one 20C, 6s 1000mah battery. Only the “cell” count will double.

    If you have a Different number of Cells in each pack (different voltage):
    It’s not a problem, the “cells” will add. A 2s pack in series with a 4s pack gives us a 6s pack.

    If you have a Different C rating in each pack (different amperage out-put):
    A series combo is only as good as its weakest cell. Figure the amperage out-put of the weakest pack, and use that as your base line for the available amperage.

    If you have a Different mah rating in each pack (different storage capacity):
    I would not do this, use only identical capacities. Warning: The first pack to empty will continue to discharge. Continued use after the first battery empties will cause that battery to discharge below its 3.1 volts per cell minimum voltage limit. This will ruin the battery.
     
    EvilTessmacher likes this.
  20. FatherAndSons

    FatherAndSons Top Gun

    Posts:
    1,120
    Likes:
    738
    Points:
    113
    Great power system summaries Luke warm. Thanks!

    Sent from my SAMSUNG-SGH-I897 using Tapatalk 2
     
Similar Threads
Forum Title Date
Electronics Lipo 'issue'' HELP! Aug 20, 2018
Electronics Smart Lipo Nov 28, 2017
Electronics Lipo Fire Nov 20, 2017
Electronics Hyperion LiHV G7 Graphene Lipo's - The Power you were looking for? Feb 1, 2017
Electronics Pulse lipos Apr 10, 2016
Electronics HobbyKing Graphene Lipo test! Mar 10, 2016

Share This Page

string(1) "1"