Battery 3s 2200 plane
05-27-2018, 04:16 PM
#1
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Battery 3s 2200 plane
new to the rc airplane hobby. Have 4 new 2200 mah 3s venom batteries with about 5 cycles on each or so. Right now I have been flying for 5:30 min and landing and replacing batteries. I have noticed when charging them I am only putting about 800 to 1100 mah back into them. Voltage is usually about 11.5v when I go to charge them.
The question i have is how much longer could I push these batteries in the air? Seems like I have a lot of charge left r am I mistaken?
The question i have is how much longer could I push these batteries in the air? Seems like I have a lot of charge left r am I mistaken?
05-27-2018, 06:04 PM
#2
Hobby King sell a small battery monitor.
https://hobbyking.com/en_us/hobbykin...ker-2s-8s.html
You can safely fly until the cell Voltage reaches 3.2 Volts. Then the alarm sounds.
You should be able to land using the 1.2 Volts left in reserve.
Cheers
Max
https://hobbyking.com/en_us/hobbykin...ker-2s-8s.html
You can safely fly until the cell Voltage reaches 3.2 Volts. Then the alarm sounds.
You should be able to land using the 1.2 Volts left in reserve.
Cheers
Max
07-04-2018, 05:59 AM
#5
Moderator
Your batteries will be just fine if you go to around 10% charge left. The number on your charger isn't exact, because some of that energy is being used to heat up your battery. If you get to the point of seeing 2000 mah being put back in, it's safe to say you are probably using 1800-1900 mah.
However,
That assumes your batteries are delivering their full capacity and have a low internal resistance. The above advice should be fine for new batteries, but as they age things change. The real number you should care about is the loaded voltage. 3v per cell, so 9v for the whole pack, is fully discharged on a battery in good condition. Try not to ever go that low as you will be endangering your plane. The above mentioned 3.2v per cell, which works out to 9.6v for the whole pack, is safe. If you have telemetry on your radio you can set an alert at that point, or you can just monitor your flight times to stay somewhere near that number. If you use flight time to do it, get an average of you batteries' voltage from multiple flights instead of just one. Aim for 10v as your landing voltage to allow for more aggressive flying or changes to density altitude affecting your amp draw. And if you change props, you'll need to recalculate all of this.
Or you could do what I do, and just land when you notice the power is starting to drop noticeably. That will be around the 10v mark anyway, still safely within the battery's capacity and having gotten pretty much all the fun there is to get from it anyway.
However,
That assumes your batteries are delivering their full capacity and have a low internal resistance. The above advice should be fine for new batteries, but as they age things change. The real number you should care about is the loaded voltage. 3v per cell, so 9v for the whole pack, is fully discharged on a battery in good condition. Try not to ever go that low as you will be endangering your plane. The above mentioned 3.2v per cell, which works out to 9.6v for the whole pack, is safe. If you have telemetry on your radio you can set an alert at that point, or you can just monitor your flight times to stay somewhere near that number. If you use flight time to do it, get an average of you batteries' voltage from multiple flights instead of just one. Aim for 10v as your landing voltage to allow for more aggressive flying or changes to density altitude affecting your amp draw. And if you change props, you'll need to recalculate all of this.
Or you could do what I do, and just land when you notice the power is starting to drop noticeably. That will be around the 10v mark anyway, still safely within the battery's capacity and having gotten pretty much all the fun there is to get from it anyway.
07-04-2018, 08:28 AM
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Calculate Flying Time and Battery Use
Wrestled with flying times and battery voltage as well so devised a simple system and spreadsheet to create good estimates, though still estimates. First, determine max. amps and watts pulled with wattmeter for each setup (use watts for determining if setup adequate for quality flying and takeoff). That includes motor, esc, battery and prop size. I found actual quite different from just using motor specs. Props also change amps and watts significantly. Then put that information into a formula and calculate minutes of flying time based on 50%, 70% and 100% throttle use. Gives me a good range to use and some level of reserve. Generally, try to keep battery voltage above 10.8. My batteries last 3-5+ years.
Formula: ((mAh/1000 x 80%)/(amps x est%throttle usage)) x 60.
So, if using 2200 mAh battery pulling 21.1A at 50% throttle then:
2200/1000=2.2 x .80=1.76. That is divided by 21.1x .50=10.55 or .17 multiplied by 60 or about 10 minutes. At 70% you would have approximately 7 minutes. The 80% mAh is recommended max. depletion.
For the above had 214 watts using 10 x 5 prop. Plane flying weight is 2.5# or 85 watts per pound - adequate for this plane that is high wing and no dihedral.
Overall, typically fly 5-6 minutes before starting into landing pattern. As I am older that is about my maximum focus time, so with 6-8 batteries and a recharge ability at field of 3 1800-2200’s, get in 8-10 or so flights if desired. For me that is plenty. If I fly using 4s batteries then maybe 1 flight less.
While sounds complicated and time consuming it isn’t that bad and provides me a comfort level.
Formula: ((mAh/1000 x 80%)/(amps x est%throttle usage)) x 60.
So, if using 2200 mAh battery pulling 21.1A at 50% throttle then:
2200/1000=2.2 x .80=1.76. That is divided by 21.1x .50=10.55 or .17 multiplied by 60 or about 10 minutes. At 70% you would have approximately 7 minutes. The 80% mAh is recommended max. depletion.
For the above had 214 watts using 10 x 5 prop. Plane flying weight is 2.5# or 85 watts per pound - adequate for this plane that is high wing and no dihedral.
Overall, typically fly 5-6 minutes before starting into landing pattern. As I am older that is about my maximum focus time, so with 6-8 batteries and a recharge ability at field of 3 1800-2200’s, get in 8-10 or so flights if desired. For me that is plenty. If I fly using 4s batteries then maybe 1 flight less.
While sounds complicated and time consuming it isn’t that bad and provides me a comfort level.
07-05-2018, 07:00 AM
#7
Moderator
That's not a bad way to go, but I can't help but point out there is an issue with the math there, sosterhaus. Amp draw is not linear as you increase the throttle. The faster an object is going through the air, the less aerodynamically efficient it becomes. So 1/2 throttle doesn't have 1/2 the amp draw of full throttle. It's more like 1/3, maybe even 1/4 with a particularly inefficient prop or a high speed motor. Now if your routine works for you that's fine, but I wouldn't want someone to be surprised that their full throttle run didn't last as long as they thought it would.
One other misconception is that a measured watt usage on the ground is an indicator of flight power. The truth is electric systems pull more wattage on the ground because you are holding the plane back from moving away from the high pressure air being made on the back of the prop. The difference varies, with big props on fast planes having the biggest difference and small props a bit less. 3D planes won't be different enough to really matter, although the difference is measurable. Based on this, I've generally tried to start with a prop that puts me in the top of the range for wattage that I need and see how it flies. Of course, the real test is how the plane performs in the air as there is no substitute for choosing components based on performance.
One other misconception is that a measured watt usage on the ground is an indicator of flight power. The truth is electric systems pull more wattage on the ground because you are holding the plane back from moving away from the high pressure air being made on the back of the prop. The difference varies, with big props on fast planes having the biggest difference and small props a bit less. 3D planes won't be different enough to really matter, although the difference is measurable. Based on this, I've generally tried to start with a prop that puts me in the top of the range for wattage that I need and see how it flies. Of course, the real test is how the plane performs in the air as there is no substitute for choosing components based on performance.
07-05-2018, 08:37 AM
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Flying time
You are correct jester, but as I noted this an estimate that one can work from. Everyone’s flying style, wind and other unknown variables together with non lineal throttle will affect it. One could have a far more complex formula, but unknowns make that imperfect. My use is to get some idea of time and after a few flights and checking voltages it is pretty accurate. Start with the 100% or maybe use 85% as a starting point and go from there.
As for watts, my thought is use the “industry” recommendations as to watts necessary to get airborne and get solid flights for initial flights. May require different motor, prop or even more volts, but again is starting point for type of plane one is flying. Do not rely on specs or other testing of an even identical set up - use a watt meter as I have found significant differences due to age of motor or battery condition.
As I have learned (and have a long way to go), know your numbers as under power can result in surprise stalls or insufficient lift; over power and you may not have the skill to handle. But, that is what makes RC electric fun and and an ever changing challenge.
As for watts, my thought is use the “industry” recommendations as to watts necessary to get airborne and get solid flights for initial flights. May require different motor, prop or even more volts, but again is starting point for type of plane one is flying. Do not rely on specs or other testing of an even identical set up - use a watt meter as I have found significant differences due to age of motor or battery condition.
As I have learned (and have a long way to go), know your numbers as under power can result in surprise stalls or insufficient lift; over power and you may not have the skill to handle. But, that is what makes RC electric fun and and an ever changing challenge.
