Not understanding NEW LiPo battery behavior

[Gary Seven]

Hey everyone. I'd like to get some feedback on what I'm missing here in terms of my understanding of LiPo batteries, especially brand new ones and how they behave. Some background:

Completed my first quadcopter build (F450 with DJI E300) a couple of weeks ago. In anticipation, I bought two Turnigy MulitStar 4000 mAh 3S 11.1V 10C and two Zippy Flightmax 4000 mAh 3S 11.1V 20C.

With the two Mulitstars I decided (mistakenly) to just use them in the just shipped state (ie, I guess about 60% charged) to do my first preliminary power tests in my yard. Nothing strenuous or fancy, mostly hovering and a little easy climbing. I ran the batteries down to around 3.5V/cell and put them on my Imax B6 charger. I was stunned to see that each battery took 4000mA on the recharge. So once charged, I attached my little "LiPo battery voltage tester/alarm", set the alarm for 3.6V, and again proceeded to do some easy flight testing, both in GPS and and ATTi modes. When the alarm starting beeping continuously (ie, even when I wasn't putting heavy loading on the motors), I brought the craft down. After allowing for about a 1/2 hour battery cool-down, I measure them and see the cells over 3.6V (around, 3.65 to 3.7V). Go to the charger, and they again take in what I consider a lot of mA....about 3800 to 3850.

Am I doing this wrong? Should I set my alarm for say, 3.7V? Do new LiPo's show this behavior until they "degrade" down to their nominal, stated mAh numbers?

Just ran my fully charged Flightmax battery today (for the first time) doing a lot of flying and lot's of vertical acceleration. I set the voltage alarm at 3.6V, and when it went off I immediately landed. After 20 min. or so I took a reading and each cell was at around 3.7 to 3.73 volts. Put it on the charger and it took 4200 mA!! Again folks, what am I missing here?

TIA to everyone who can throw some pearls of wisdom my way. ;-)

 

[Carapau]

3.7v is where you want to stop which should equate to 80% of battery capacity. For your next flight, fully charge the battery, fly for lets say 2 mins and then recharge the battery noting how many mAh go back in- divide this by 2 to get mAh/min and then divide this into 80% of your battery capacity and that will give you the amount of time you should fly for. What you are seeing at the moment is not wrong its just that you are flying your batteries to a point beyond that which is optimum.

 

[Bartman]

it depends on the combination of motors/props also. how hard are the motors working to keep the helicopter flying? the harder the motors are working the greater the chance that when you goose the throttle you'll cause the voltage to sag and the monitors to beep. I'm using 3.3v per cell for my alarms and even then when I'm done flying they recover to 3.65 to 3.7 volts per cell. putting more in mah back in than the packs are rated for though, that's just weird but the alarms and knowing what you're getting vs. putting back in should dictate how you run them.

bart

 

[Gary Seven]

3.7v is where you want to stop which should equate to 80% of battery capacity. For your next flight, fully charge the battery, fly for lets say 2 mins and then recharge the battery noting how many mAh go back in- divide this by 2 to get mAh/min and then divide this into 80% of your battery capacity and that will give you the amount of time you should fly for. What you are seeing at the moment is not wrong its just that you are flying your batteries to a point beyond that which is optimum.

Well ok. That's an interesting approach and one I never thought of. I'll give it a go.

 

[Gary Seven]

it depends on the combination of motors/props also. how hard are the motors working to keep the helicopter flying? the harder the motors are working the greater the chance that when you goose the throttle you'll cause the voltage to sag and the monitors to beep. I'm using 3.3v per cell for my alarms and even then when I'm done flying they recover to 3.65 to 3.7 volts per cell. putting more in mah back in than the packs are rated for though, that's just weird but the alarms and knowing what you're getting vs. putting back in should dictate how you run them.

bart

Bart, yeah thanks...I get the part about voltage sag (wished I had used that word in my OP). I mean, my setup is a DJI Flamewheel F450 with the E300 propulsion system. That is, it's supposed to be "tuned" for the first time clueless dolts like myself. All I did was put this thing together with the parts supplied (a shout out to Marionvillemodels.com for their super professional service and of course [MENTION=1]Bartman[/MENTION]; for his super helpful videos), tune it up in the Naza Assistant, and off I went. The vehicle has NO camera and no landing gear...just the frame, motors, ESC's, etc. It really doesn't weigh much and it can't possibly be working very hard.

I originally set my alarms at 3.4V and was stunned at how much mA I put back in. Then I set the alarm to 3.5V and still, I was putting back in nearly 4000 mA. Then I set the alarm to 3.6V and with the Flightmax at least, put back in almost 4200 mA in a 4000 mAh battery! How is this possible??

Again, I understand voltage sag and recovery. I understand that when my alarm goes off it is going off under load. I also understand why the voltage "recovers" after I wait 10 or 20 minutes before taking a reading. It just confuses the hell out of me that after waiting 20 or 30 minutes to hook my battery up to the charger that, even with a per cell reading of 3.60 - 3.65V, I am putting back 4000 mA (or more) into a 4000 mAh rated battery. I don't get it!

My theory is that brand spanking new batteries will give you much more than the advertised or rated values, until "x" amount of charge/discharge cycles. They will then "degrade" down to their nominal advertised rated values and hold at least for a while assuming they are treated correctly.

Please...anyone...correct me if I am wrong.

 

[Bartman]

hmmm....unless they're conditioning the batteries by cycling them before delivery (which I doubt), batteries are usually going to have less capacity the first few times you use and charge them. it's possible that the packs are using higher capacity cells and downgrading them with the label but why they'd do that is what I'd call a "mystery"

short of an exact lab analysis of your packs i'd just say to use the voltage monitors, keep track of the mah you're putting back into them and keep an eye on the cells to make sure they aren't puffing. if the cells stay tight and compact then you're generally going to be fine with how you're using them.

Bart

 

[min0nim]

My understanding is that the mah rating is a minimum too.

Also I think that some chargers accurately measure mah, while some don't. The first charger I had would show enormous mah numbers on a balance charge cycle.

I've given up on battery voodoo and now just monitor the voltage with telemetry. In a test flight I monitor where the voltage starts to drop off quickly (in my current batteries this is around 3.48v - way lower than what I used fly, but after load is removed they return to 3.65 instantly), and set my alarms to give me 30 seconds warning from 3.5v (or more, depending what I'm doing).

Just one more thing - if your batteries are getting hot enough to wait for them to cool on your E300 system, maybe consider getting a 4s battery to see if it makes a difference.

 

[synrg]

It is my understanding that charger mAh is never 100% accurate or efficient. Some output will always be lost while charging. Not all of the chargers output will be retained by the battery. To be on the conservative side and shoot for 20% reserve, setting your alarm at 3.6 would probably be prudent. However the low 10C rating on the Multistars under full throttle climb could temporarily cause your alarm to drop below 3.6 prematurely and then the batteries could quickly recover and still have a lot left. Telemetry and/or OSD could be more accurate. I'd also cycle your new packs on your charger a few times before your next flight. Hope this helps.

 

[Gary Seven]

Thank you all for your input. I'm beginning to suspect my Imax B6 charger is not being faithful with the mA's being reported. I feel so cheated (snicker). I see in another thread both [MENTION=1]Bartman[/MENTION]; and [MENTION=11354]Motopreserve[/MENTION], talking about an "iCharger." Guess I will have to research this a bit more.