I would be interested to share what others are using and how they have their power systems set up and what they find does and doesn't work. .
I am using a 3300mAh 4S 35-75C Turnigy battery and I'm in the dark about what to expect from this considering it might even be to small for my X8 Quad (880kv motors 30amp ESC)I have done a number of 2 min flights and haven't really pushed them past this. But what happens if it is under powered during flight?
I ready just recently that for the health of the battery it should not be allowed to run below 80%.
See this interesting page on batteries http://www.rchelicopterfun.com/rc-lipo-batteries.html
I'm a bit confused on this. Does it mean its ok to draw 80% out of the battery and not below this or does it mean draw 20% out of the battery and leave 80%.
What voltage levels are others letting the battery drop before it is regarded as time to land?
I use one of these: http://www.hobbyking.com/hobbyking/store/__7225__Hobby_King_Battery...
As the battery gets down, it gives a beep or two (loudly), then more rapidly and when the battery is done, it beeps like crazy. It also has an LED that gives an idea of battery status.
They mean you can use 80% of capacity, leaving 20% in the battery.
Is 3300mAh light on? Could be. Depends on the load you'll be carrying. This calculator can give you an idea of run time: http://www.ecalc.ch/xcoptercalc_e.htm
Thanks Dave. Ive tried that calculator but the Jdrones motors aren't listed and I was told by Jdrones there isn't a motor on the list the same.
I also have one of those gadgets for the battery and it give the red LED critical warning at 9.9v which isn't 80% but I assume then from this that about no lower than 10v is acceptable? .
What I'm a little confused about on that article is if I run the battery down by 80% then 14.8v battery would have 2.96v left, but this cant be right I'm sure. So likely it means the amps used up are run down by 80%. (Ive probably answered my own question here)
Now that I installed a battery sensor chip and I get a reading on Mission Planner I can now watch the battery levels there. The percentage reading though shows amount left not used so I assume this percentage is reading the Amps... or Voltage?. (I have both selected in MP setup).
I'm mostly trying to figure out where is a safe level to let it get to and also for getting the best life out of the batteries.
My rig weight is about 2.5kgs and I'm running 8x880Kv motors 12x4.5 props so like to much for a 3300mAh battery. I have tww of these so I might connect then in parallel and use them both together.
So have you measured your batteries after flight and what were the readings?
If you can get the raw data for the motor, you can enter a custom setup in the calculator.
From the voltages you are quoting, it sounds like you have the 3S version of the battery monitor, but you have a 4S battery. 9.9V is way too low for a 4S and will seriously damage the battery. The 4S monitor should go crazy beeping at 12V which is the lowest you should go.
The 80% refers to the mAh capacity of the battery. For ease of calculation, say your Quad draws 33A average, then a full 3300mAh battery will give you 1/10 hour flight time, or 6 minutes. However, limiting it to 80% (some say 90% is OK) gives you 288 seconds running.
The battery voltage will stay fairly constant until just at the end of the charge where it takes a dive.
I have a 3S battery and monitor. I haven't measured the under-load voltage at the end of a flight. However, when I connect the battery to the charger (Accucell 6), it is normally around 11.0 V and takes about 90% of capacity to recharge it.
That info has made it much clearer and thanks again Dave. I made a mistake, I was looking at the 3S on the monitors data sheet and not the 4S and you are correct there. I do have the 4S monitor and sheet shows 13.2v as critical level.
How would I go about getting the raw data from the motor? And how can I find out what my quad is drawing in Amps?
Are these your motors: http://store.jdrones.com/product_p/ac2836358.htm
If so, a very similar Turnigy motor is listed in the calculator. Results below.
You might want to try a run with a Custom motor with the same settings but Limit reduced to 210W as per the jdrones specs.
Yes those are the motors. But Jdrones said theirs are wound differently compared to the Turnigy motors and it was my feeling he wasn't really willing to revel what on the list was a close comparison anyway.
I did some testing on my rack today and seems some differences from the voltage reading on Mission Planner compared the the multimeter reading. Start of the test Multimeter reading was 16.75v. MP was 15.95
After 3 min running then the multimeter reading was 15.68v and MP was 14.89v
I did as advised on the battery sensor instructions to subtract 0.3v from the power supply which on mine is a 5v/3amp switching regulator. I set this to 4.7v.
I assume this is to compensate the difference in the draw off power from the APM? Any idea why there is nearly 1 volt difference from the multimeter and the MP reading?
If you're using the onboard sensing and APM1, in the setup notes, as well as what you've already set, it also says:
Then with the multimeter measure the output voltage of your battery, from those balancing-port cable wires. Enter that in the "Measured battery voltage" field.
So, in theory, the APM and your multimeter should give the same readings if you're measuring at the same point in the same conditions (e.g. motors not running).
The quote is from the Wiki: http://code.google.com/p/arducopter/wiki/AC2_Current
Yes, for the other field, you'd measure the output of your regulator and subtract 0.3V from that.
Could others please advise what battery reading use off the Mission Planner to gauge when to stop flying. What voltage level and percentage is it at when it is time to RTL?
For LiPo batteries you should stop flying when each cell reaches 3.2 volts. For a 3-cell LiPo that is 9.6 volts. You will want to set your alarm higher than 9.6 volts to give you some time to RTL.