How far can I safely take my Lipo's?

[Spyrotechnics]

I am using Zippy Flightmax 5000mah 4s 20C Lipo';s on my F550. I have up to this point been very apprehensive about keeping the Hex in the air for too long for fear of damaging the batteries or the batteries failing. At the moment, as soon as the telemetry reads around 14.5v I prepare to bring it in to land. This usually gives me around 5/6 minutes of flight.

How low can I safely take the batteries before considering a landing?

Thanks in advance

(Oh and for how long do I need to keep typing the answers to silly pictographs and questions?!)

[Biffa]

80% of the packs capacity is what many people, myself included, go by.

So for your packs 4000mAh is 80%.

[andythilo]

Get one of these:

http://www.fast-lad.co.uk/store/fusion_smart_guard_digital_battery_checker_balancer_p-fs-bc05-p-17791.html

Then, set your timer for 5 minutes. Fully charged pack, go out and fly it round, mixture of hovering, gentle flying and hard flying. Then bring her in, plug the balance lead into the battery checker and it';ll give you a percentage, your looking for 20%, no less.

If it';s say 40%, then set your timer for 6 mins, fresh pack, repeat till you get 20% and set your timer accordingly.

[Spyrotechnics]

I have a voltage read out on the ground station screen (and on my Spektrum controller with vibrating alarm) is it not better just to keep an eye on the voltage on screen and head home once I reach a certain voltage? It';s the ';head home'; voltage I would like to know :)

[andythilo]

Well it';s up to you at the end of the day, but coming in at 20% is pretty commonplace. You don';t have to keep watching the voltage read out, as soon as your tx starts beeping/vibrating, bring her back and you know that you haven';t over discharged the batteries.

[Spyrotechnics]

No problem, I will set the alarm to go off when the batteries reach about 14.2v to be safe, gives me plenty of time to get down from 400ft (I never take it to far laterally).

Cheers

[mutley2]

I take my 4s packs down to 14.3V, this is around the 85% mark, and have always slow charged. I still have my original 3s packs from my Hornet micro heli which are now over 10yrs old and still in great condition. Keep um cool and store around the 50% mark If you';re not going to use them for a while.

[Biffa]

The problem with just relying on voltages is how a pack will sag. In the hover it may be fine, punch out and the voltage will sag and alarm goes off.

I haven';t bothered monitoring voltages for years but it';s important to remember that there is no hard and fast rule.

[kilby]

Hmm I have one of those battery checkers but its values don';t really line up with the charger says it is putting back into the Lipo when I charge it.

Problem is that I';m not 100% sure which is incorrect, though I have been sticking my values into a spreadsheet and I will eventually get around to working out if the disagreement is a constant figure.

Assuming that the charger is correct (or quite close) the battery checker a quick look at the figures implies somewhere 15 to 30% disagreement between the two devices (with the checker overestimating the % of charge used).


I don';t have to worry too much as the meter is giving a low remaining value so it won';t cause me to over discharge the battery, I will eventually get around to plugging the Fluke into a battery pack to confirm the values (as I know the Fluke will be right)

It';s best to check that the values are real

[flybywire]

Hi
I have a 550 also, so it';s likely to be a similar weight to yours, as i too use 5000 mah 4 cell lipo';s.  It';s only rule of thumb i know, but i fly for about 10 mins with this setup, which translates to about 80% discharge rate.  I could probably go another 2 mins in the air, but when u think about it, unless u want to drop out of the sky, you';ll need to come home with some to spare anyhow.
A thing to note here is that after a year or so';s use, lipo';s start to get exhausted, and although they still work ok, you';ll notice the voltage will drop quicker than when new.  I use an osd, in conjunction with the timer on my tx, which i set to 10 mins, just for belt and braces.
As i say, it';s not a science, but something one gets a ';feel'; for with experience.
My ezosd has added bonus of showing mah used, as well as current drain in real time, whereas my dji osd just gives voltage.
I generally run my lipo';s down to 14v, but a bit lower will do no harm

Andy

[nub]

ach for the price of batteries nowadays

personally i don';t monitor the battery voltages at all, i fly for 5 mins and see what i put back and try stick to the 80% discharge that people usually recommend, never usually works out like that though

ive been doing this with my batteries for years and never really had any problems with them.

[flybywire]

That';s what i said! 

[andythilo]

I still firmly believe that you should ';know'; how much you can safely take out of your batteries. It';s not hard to time flights and test what';s left.

Just bear in mind though, you won';t have the issue when you';re flying, it';s when you come to recharge your batteries that the quality of your pack treatment will show. And as Biffa said, you really shouldn';t rely on load voltage, it';s not accurate.

[esoarer]

It';s important to remember that it';s the individual cell voltage that really matters and that the total pack voltage can be OK and yet an individual cell can still be well below it';s safe minimum voltage. This is why I use adjustable Lipo alarms on all my models. The attached pic shows 2 because on this particular FY680 I';m running 2 x 6S Lipos - so I have 12 (TWELVE) individual cells to monitor. If just 1 cell drops below the 3.6 V setting I use, then the alarm goes off and I land. After some testing I know how long I can safely fly, but I still regularly bring the model back close enough to hear and/or see the voltage displays, just in case ! Setting to 3.6V means the alarm will go off under load (if the model is flying of course), and the individual cell voltages will then recover almost immediately once I';ve landed. (To 3.75 to 3.80V off load)

As an aside my new Taranis Tx & Rx arrives tomorrow and I understand that I can set up a data link to provide the same individual cell voltage information and relevant warnings (audible and visual) as the Lipo alarms on the model. I';m sure I';ll need some help with that setup mind you, but I';m sure the Taranis experts on here will be able to help!

[flybywire]

I never got on with those on-board alarms, they were always giving false readings.  Even if they worked, wouldn';t be much use half a mile or so away! 
I have come to rely on my own setup, a combination of science and suck-it-and-see!

P.S oh, I have also used AR1000 telemetry modules, but since using osd';s they have become rather obsolete/un-necessary weight/complication.
Andy

[Biffa]

I have come to rely on my own setup, a combination of science and suck-it-and-see!

My method exactly

[Amorgos]

I use a DJI iOSD which keeps a log of the data during flight time. One of which indicators is voltage. You can then look at the graph using the DJI Data Viewer app to see how the voltage drops during flight time then base your safety levels on the curve.

I don';t have an image of mine right now so the image below is from Google Images and is a very similar curve (but different voltage) to what I see on my batteries. My 4S (14.8V) starts at about 16.7V, drops quickly, then falls below 14V. I don';t have the exact safety values I use on me at the moment, but this is how I calculated mine.