Tattu 16000 mAh flying time/minimum voltage

[Stratifier]

Hi,
Iam trying to find the limits of my Tattu 16000 powering a S900+GH4.
I have been reading about 18 mn... Is it really? I like to rely on the voltage indicator on the iOSD as well. At what voltage do you guys decide when it's time to land?
Thanks.
S

 

[Amerly]

I was told by guys from Revered Cinema not to go to much under 3.6V per cell (under load) for healthy long lasting Li-Po's... I stick to that... If you want to use the full ''charge cycle potential'' they can provide I suggest you do the same... Flight time depends also on temperature, altitude, wind speed or turbulence... For heli's you get lower flight time in stationary hovering since you create prop wash that tends to counteract the lift your blades produces... Not sure if this principle applies as much for multi's but it can be as high as 20% for heli's...

Cheers

 

[Mojave]

Have you read the thread here: http://www.multirotorforums.com/threads/understanding-lithium-polymer-batteries.12072/

One of the best parts of this forum is the reference material!

 

[Stratifier]

Yes I did, and learnt a lot, great job ! (Will help me in my quest to become a lipo Ninja...!), but I wanted to get personal experiences as well on the same kind of gear to refer to.

 

[Mojave]

Take a look here: http://www.multirotorforums.com/threads/lipo-voltages.19942/#post-177556

Hopefully others will chime in as well. I think one of the key points is knowing the limits of your system without taking the batteries to low and ruining them.

 

[Stratifier]

I receive the data as an average remaining voltage, so I assume that I should land when I read between 21.9 v and 22.2 v...

 

[Carapau]

Best thing to do is so a 5 min flight and then see how many mAh you put back in to the pack. You can then work out mAh per minute of flight and thus how many mins per 80% of your 16Ah. The key figure is not so much your in flight voltage as your voltage drop will vary on weight etc but on the amount of capacity used.

I land at 21.1-21.3v and this is bang on 80% but my rig is 20kg at take off


Sent from my iPhone using Tapatalk

 

[annagensace]

flight time also depends on the take off weight, and motor/ESC/propeller and system performance

 

[Dave_EP]

Best thing to do is so a 5 min flight and then see how many mAh you put back in to the pack. You can then work out mAh per minute of flight and thus how many mins per 80% of your 16Ah. The key figure is not so much your in flight voltage as your voltage drop will vary on weight etc but on the amount of capacity used.

I land at 21.1-21.3v and this is bang on 80% but my rig is 20kg at take off

Do you find it varies much from one battery to another?

 

[Bartman]

a LiPo is a LiPo and the rule of thumb is to stop when any one cell is at 3.3 volts.

if you use that for the whole pack then you land when

3S=9.9
4S=13.2
5S=16.5
6S=19.8

etc., etc., etc.

80% of the pack's capacity is another rule of thumb you can follow and what Carapau said is true if you're willing to do the work but for any given day's temps and altitude, duration will change making it harder to determine when you've hit 80% whereas 3.3 volts per cell will work regardless of the day's conditions provided you have a way to monitor voltages while flying.

when you're too far to hear an aural warning then telemetry on the radio or OSD is necessary. When you're close enough, the $3 battery monitor/alarms from hobbyking are an awesome and very lightweight way to keep the batteries safe. you can velcro them right to the battery packs and they plug into the balancing taps.

hope that helps!
bart

 

[Dave_EP]

3S=9.9
4S=13.2
5S=16.5
6S=17.8

Probably a typo but 6S should be 19.8 not 17.8

 

[Bartman]

yup, i'll fix that, thanks for the free proofreading services!

 

[Bartman]

and keep in mind that telemetry or an OSD voltage readout will mask a bad cell if you don't get to also see individual cell voltages. you might land with one cell at 2.7 and the others just above 3.3 so being able to look at individual cell voltages at some point in your activities (flying, charging, whenever) is critical (bold AND underlined! ) to making sure a bad pack doesn't crash your heli.

 

[Carapau]

If you have telemetry on your voltage that is the best way to gauge your 'fuel level'. For a 6s pack I land at about 21.1v under load and this works well for my aircraft. If you don't then the timing method I mentioned works well. Unless you change the payload I find this pretty accurate even with temperature and pressure changes, wind etc.

 

[Guernegor]

Hello everyone,

Brand new to the forum, I wanted to share my experience with the use of a Tattu 16000 mAh 4s 15C in order to avoid the same situation to others.
I made several flights not going under 3.8v per cell to train the battery.
Today, I wanted to see how much I could drain from this battery because at 3.8v, I used only 6400mAh.
So I setted my warning at 3.6 and decided to land at 3.5v, which I thought was safe (way over 3.3v).
When I reached 3.6v, I began my descent until about 10m. As soon as I heard 3.5v, I decided to land, but suddenly, after a few seconds, I heard 3.2v and the hexa crashed from 5m without any power left.
When I went back home, I checked the battery which was quite warm and saw that they were only 3.2v left per cell.
Why such a sudden voltage drop from 3.5v to 3.2v.
How can I find now my safe limit? Do I have to land at 3.6v?
The hexa is quite heavy (6.2kg)... Could it be a reason? Is the battery defective?

Many thanks in advance for your kind suggestion...