I have a 2250mAh 11.1v 3 cell battery that I'm using for my 450 kit build, motors are 1000Kv motors. 

Using a Pixhawk with the PX4v1.3.3 flight stack, loaded via QGC.

And I'm using an Imax B6 charger for the battery. Battery is brand new.

This is the issue; I will plug the battery in, with the props off, as a system check. I can throttle it up all the way, no problem. QGC says batteries are at 100%. External voltage meter says all 12.1, no1 4.03, no2 4.03, no3 4.06. 

System check looks good, so I put the props on.

I get the UAV up and within seconds, QGC tells me that the battery has dropped to 33% and the Pixhawk battery alarms go off. The external voltage meter, that is set at 3.6, does not go off. 

I keep it up for a few more seconds and the battery level drops to 17% and the alarms go nuts. I set the UAV down, for a flight time of mere seconds. 

I will then unplug the UAV from the battery, wait a second, plug it back in and reboot. QGC will say the battery is still at 100%. External voltage meter hasn't changed. 

So with the props off I have no issue, but as soon as I put the props on, the battery can't seem to handle it.

What am I doing wrong?

Thanks you for any insight.

Cheers!

_M

Views: 1736

Reply to This

Replies to This Discussion

Have you tried load testing the battery? Even just connect a multimeter and tether the quad down, run it up and watch the voltage. Chances are it is a dud battery, the low 'fully charged' terminal voltage is pointing that way as well, it has either been over discharged below 3v/cell or is very old stock, or it's a zippy/fluoreon battery.

It's a 3 month old Turnigy Graphene battery.  But yes, shortly after I started having issues, I lost 1 of the 3 cells.  Seems like it may have been going South, which caused the false readings and red LED.  New battery coming Thursday, so I will see.  

If you wait two days, then flash PX4 developer build and download the latest QGC daily build. Then under Power you should see support for voltage and current calculators which allow you to calibrate the power module. The work for this is complete, it just needs to work it's way through the build systems which is taking a little while due to build provider problems.

Thanks for the heads up!  I will be on the lookout!

Mark,

Your battery charger should display the mAH added to the battery during charging.  If you keep a log of the energy added to the battery after each use then you will have an independent assessment of the energy used in each flight.  You can use this to help calibrate the PM.  The objective is to avoid discharging more than 80%, based on the mAH use, not necessarily voltage. 

Have you done an analysis of your system with Ecalc?  (Ecalc.ch)  Your battery might just be to small a capacity or not have a sufficient C rating.  The fact that you lost a cell suggests that you may have discharged over 80%, or the current draw (C rating) is more than the battery is rated for, causing damage that would not be apparent, but cause a significant permanent drop in capacity.

Another problem is, the energy put in, unfortunately is not what you get out, after subtracting resistive losses due to failing cells, or even healthy cells, there is always some loss. When the cell has plated off from over charge/discharge it struggles to deliver anywhere near normal current, but can still accept a majority of it's capacity in amp hours. The wasted energy is what heats the pack and usually causes puffing by liberating oxgen from poorly assembled cells usually containing too much water within the polymer electrolyte, but that's another story.. Another thing often overlooked is the temperature of the battery during charge, this has a major affect on terminal voltage, and the typical 4.23v/cell is only correct for 50-60 degC and yet at 10 deg C it should not exceed 4.0v/cell, above this and excess electrons will free lithium to bond with oxygen and make lithium oxide, and goodbye battery. Most chargers do not give you any option here, let alone being smart enough to calibrate their termination voltage to pack/ambient temperature, so the best thing to do is charge them in a warm place to maximise life within spec. I built a warmer for use in our low temperature climate, it regulates temp within a few degrees, compensating for pack heating during charge, but that's drifting off topic..

I didn't lose a cell, the other dude D Ohlarik lost the cell.

I did another test flight today, and I got the same results. I'll detail my steps in this thread in a few.

_M 

Okay!

To reiterate, I'm using a 2250mAh, 11.1v 3S1P battery on a 450 quad kit build with 1000KV motors with 30A ESC's, and I'm using the PX4v1.3.3 flight stack.

Attached are screenshots of my power and battery settings in QGC. From what I know, which is apparently nothing, those setting are correct.

And these are pix of my battery just after my failed test, with the readout from the voltage meter that reads ALL 12.2, with cell1 reading 4.04, cell2 4.03 and cell3 4.08

Though, I haven't been keeping a log of mHA use I have been sure to discharge the cells to at least 3.6v before I re-charge.

What am I missing? I'm a total noob at this, but with my extensive history of technical VFX work, I suspect my problem is a minor detail that I am completely unaware of.

Harry, I do have an ecalc account but the input fields are so detailed and I just don't know what to input. Again, I'm just a noob.

Alasdair, thank for the input, but it was way over my head. What I can tell you is that I've only charged and discharged the battery less than a dozen times. Also I live at 10,000 feet, so all my charging cycles have been in a cool environment.

Don, should I just wait for the new PX4 developer build and latest QGC daily build?

I'm trying really hard to figure this out on my own, before I bite the bullet and hire a drone tech, who's going to see my error immediately, I suspect.

I'll have a link to a video of my failed flight test up here soon, stay tuned.

Cheers everybody!

_M

Attachments:

Here's the vid.

and here's the direct link;

https://youtu.be/_CZJRHJ7AMU

If you can hear QGC, in the windy background, you'll hear the alarms go off immediately.

I bounced the landing and it rolled over onto the front rotors. I immediately disarmed, and set it upright. Then I moved in close to get a shot of the alarm lights.

Any ideas?

Cheers!

_M

I haven't used the QGC yet, only the Mission Planner, so I am not very familiar with it. But there has to be a setting in the QGC, where you can adjust the battery values or setting in general, have you had a look at that?

Francisco,

Yes I have. I posted those settings two post ago. Here are those screen shots in the body of this message, so you don't have to click. Again, as far as I know (not much) these settings are correct. Am I wrong?

This screen is missing two key parameters which are used to adjust things: 

BAT_V_DIV - Voltage divider you can adjust if voltage isn't reading correctly

BAT_A_PER_V - Amps per volt value you adjust if current isn't reading correctly

Both of these are currently available using the parameter editor.

Latest version of QGC (not yet available as daily build, hopefully by tomorrow) has these parameters exposed in the Power screen:

And there are calculators to adjust then. Here is the on for voltage:

Reply to Discussion

RSS

© 2019   Created by Chris Anderson.   Powered by

Badges  |  Report an Issue  |  Terms of Service