When to land ...Lipo Question, please help my head hurts!

[Quinton]

Having just set up voltage telemetry on my machine has got me thinking a lot, about what is the best time to land.
As its probably one of the most important questions I need to ask.

I have read 100 posts on the internet and there seem to be 100 different answers.

I know the 20% rule, which basically says when you land and you check your lipos there should be at least 20% left.
However, I am trying to get my head around what is nominal voltage and what is completely killing a lipo.

Im taking 6s lipo as an example, as its what I'm using.
nominal voltage is 22.2V, what exactly does nominal voltage mean, 3.7V per cell I know its 4.2V fully charged, does that mean though that you have .5V between nominal and fully charged, and is 3.2V completely dead (0%)

I thought I knew how it worked until I started browsing for answers, and read things like never let a cell goto 3V??
Also when is the best time to land when you have 20% left while under load, or after you have landed, as I have seen 0.6/0.7 V difference between loaded on a full climb and landing.

Love having voltage telemetry, but it has opened up so many unanswered and Important questions to me. Please can anyone explain, and help me sleep tonight?
What is a completely dead cell, and whats the best time to land, 20% when loaded or when landed?

 

[Maverick]

There are sooo many theories as to when you should land.

The way I work it is, when I land, and the load is removed from the pack, after a few mins, the voltage will creep back up slightly from what it was at, immediately after landing, and I like this value to be 3.7v per cell. Work out what your line loss voltage is, between no load, and a hover, by using a lipo voltage checker, and hovering at about 6 or 7 feet off the ground. So, for example, if your line loss voltage is 0.7v over the 6 cells, then add say 0.3v to this, and then take that away from 22.2v. This value (21.2v LOADED) is what you should land at. In my case when full payload is on, I always like to be fairly close to 'HOME' as I reach 14.0v, 13.9v. Then by the time I actually am landing, my iOSD is reading 13.8v (3.45v/cell). Immediately after landing, it will shoot up to 14.4v, and then within 3 or 4 mins, it will be reading 'nominal voltage' - 14.8v.

Line loss voltage will vary depending on number of motors, size of props, payload, AUW. So, it will be trial and make note for each pack/payload, until you're familiar with your limits. Just make sure your pack isn't swelling or overheating when you land. Take note, when the pack reaches a critical level, the voltage will just plummet in seconds, and that's when the swelling/IR increase starts. When configured properly, the WooKong Assistant voltage alarm does an adequate job, at warning you, providing you heed the LED colours. I also back up with individual voltage checkers on each balance plug, in case there is a problem with an individual cell or my iOSD.

Some people like to spend more of their packs' capacity than this, and don't mind bringing their packs down to 3.6v/cell, UNLOADED! Personally I think that this will gradually shorten the life of the pack, and increase internal resistance. At the end of the day, you don't want to risk your very expensive machine, for an extra minute or so in the air.


P.S. The 20% rule refers to the pack's mAh capacity, not the voltage! So if you were flying 2 x 5000mAh packs, you would spend 4000mAh from each pack per flight, and during recharge, it should show around 4000 going back into each pack. Always allow at least 10 mins for pack cool down, before re-charging.

In general, ESCs are programmed to cut off at 3.3v cell to save the pack, but that's pushing it. 3.0v/cell would be a damaged pack.

 

[Quinton]

P.S. The 20% rule refers to the pack's mAh capacity, not the voltage! So if you were flying 2 x 5000mAh packs, you would spend 4000mAh from each pack per flight, and during recharge, it should show around 4000 going back into each pack. Always allow at least 10 mins for pack cool down, before re-charging.

In general, ESCs are programmed to cut off at 3.3v cell to save the pack, but that's pushing it. 3.0v/cell would be a damaged pack.

That P.S is probably the most important part.
I have been taking note of every flight, and seems I am putting back in between 3500 and 3900 mAh, so I am being quite conservative which isn't a bad thing (13 mins flight time).
I have 2x 6s 10400 mAh lipos coming tomorrow, will be really interesting to see how they compare.

Also have the Futaba FASSTest Telemetry GPS Sensor P-SBS-01G coming tomorrow too

Too much data, but so much fun learning

 

[jwk72]

There are always exceptions but one thing that is fairly standard is that anything below about 3.3v/cell will damage the battery. Sometimes if it is "close" or just slightly below that the battery may still charge but has likely sustained minor damage... too far below and it's toast... way too far and it's likely to puff or possibly catch fire.

 

[Quinton]

Getting back to this 20% rule, you say it doesn't apply to voltage, just the mAh capacity

Got my 10400mAh lipos today, and so far seems to be with them on it seems to be around 358 mAh/min being used up.
The 6200 mAh lipos so far are working out at around 292mAh / min normal flying.

So if you took that to the 80% rule, then really you can get about 17mins fly time with the 6200 lipos and 23 mins with the 10400 lipos (theoretically of course if you want to push the limits) (lipos x2)

No gimbal payload yet also.

 

[PeteDee]

Best to go buy one of the Hyperion Battery Sentry devices or a similar one from somewhere else, plug it on and it will give you a percentage readout of what is left in your pack.

 

[Maverick]

Getting back to this 20% rule, you say it doesn't apply to voltage, just the mAh capacity

Got my 10400mAh lipos today, and so far seems to be with them on it seems to be around 358 mAh/min being used up.
The 6200 mAh lipos so far are working out at around 292mAh / min normal flying.

So if you took that to the 80% rule, then really you can get about 17mins fly time with the 6200 lipos and 23 mins with the 10400 lipos (theoretically of course if you want to push the limits) (lipos x2)

No gimbal payload yet also.

In theory, yes, that analogy is correct! I take it your 10,400mAh is the combined capacity of the two, yea...?

 

[Quinton]

In theory, yes, that analogy is correct! I take it your 10,400mAh is the combined capacity of the two, yea...?

2x 10400 mAH 35c 6S2P.. SO 20800 mAh
The weight of 1 lipo is 1.591KG

Not much room if any to include a payload, but great for just flying around testing.
Saying that hover was still just less than half throttle, and motors ESCs all cool.

 

[Quinton]

Best to go buy one of the Hyperion Battery Sentry devices or a similar one from somewhere else, plug it on and it will give you a percentage readout of what is left in your pack.

Already have 1, but they are a bugger trying to get % when flying
I am liking telemetry Voltage a LOT
It actually saved my bacon yesterday, as my transmitter started alarming after just 4 mins, so I brought her down..
Would help if I plugged both lipos in at the same time!

 

[Maverick]

2x 10400 mAH 35c 6S2P.. SO 20800 mAh
The weight of 1 lipo is 1.591KG

Not much room if any to include a payload, but great for just flying around testing.
Saying that hover was still just less than half throttle, and motors ESCs all cool.

Well, if this is the case, then in theory, your analogy is wrong!

2 x 10400 = 20800
80% of 20800 = 16640mAh
16640 ➗(divided by) 358 = 46.48 mins flight time.

 

[Quinton]

Well, if this is the case, then in theory, your analogy is wrong!

2 x 10400 = 20800
80% of 20800 = 16640mAh
16640 ➗(divided by) 358 = 46.48 mins flight time.

My apologies, my working out was based on 1 lipo, was just looking at the charge time/lipo.
Will be really interesting to see though when I do get a bit of a load under her.
Can't belive how well its flying at the moment, its like its on rails, and every single part of latest Wokkong firmware 5.26 I am very impressed with.

Oh also learned a very valuable lesson tonight charging my new 10A lipos.
Dont try and charge 2 lipos at the same time, over 6.2 amps with 18AWG cables, as they will melt 18 AWG is only rated for 25A

 

[PeteDee]

Already have 1, but they are a bugger trying to get % when flying
I am liking telemetry Voltage a LOT
It actually saved my bacon yesterday, as my transmitter started alarming after just 4 mins, so I brought her down..
Would help if I plugged both lipos in at the same time!

You don't have to though, fly for one minute and see how many percent you use if it is ten percent then you will have around 8 minutes flight time, fly for seven minutes and see how close the calculation is, once you know how long you can fly for set the timer on your Tx and land when it goes off.

Pete

 

[Quinton]

You don't have to though, fly for one minute and see how many percent you use if it is ten percent then you will have around 8 minutes flight time, fly for seven minutes and see how close the calculation is, once you know how long you can fly for set the timer on your Tx and land when it goes off.

Pete

I understand what your saying, however I'm flying with 2 lipos and I have an alarm that goes off on my transmitter at a certain time, say 13 mins, also another one that goes off at 22V.
I forget to plug 1 of my lipos in, and you should be landing after 4-5 mins.
A timer is great, however having a real time voltage sent to your receiver, and a Timer, is a life saver, as I have already experienced.
I see you have the 14SG also, do you have the SBS-01G sensor, as today I only seem to have the altitude shown, so not sure what the problem is with the other ones yet.

 

[Maverick]

My apologies, my working out was based on 1 lipo, was just looking at the charge time/lipo.
Will be really interesting to see though when I do get a bit of a load under her.
Can't belive how well its flying at the moment, its like its on rails, and every single part of latest Wokkong firmware 5.26 I am very impressed with.

Oh also learned a very valuable lesson tonight charging my new 10A lipos.
Dont try and charge 2 lipos at the same time, over 6.2 amps with 18AWG cables, as they will melt 18 AWG is only rated for 25A

Congratulations! - This is what it's all about. Seeing all your effort and time actually work, gives you a great sense of achievement!

Remember however, all your gains will have to be adjusted again once you add the payload. She will actually fly better, when the weight is hanging under her.

Soon, all your pre-flight checks will become second nature to you, and it will be a wee routine that you go through each time, before you fly. It will be as normal as driving a car after a while - you won't even have to think about it!

 

[PeteDee]

I understand what your saying, however I'm flying with 2 lipos and I have an alarm that goes off on my transmitter at a certain time, say 13 mins, also another one that goes off at 22V.
I forget to plug 1 of my lipos in, and you should be landing after 4-5 mins.
A timer is great, however having a real time voltage sent to your receiver, and a Timer, is a life saver, as I have already experienced.
I see you have the 14SG also, do you have the SBS-01G sensor, as today I only seem to have the altitude shown, so not sure what the problem is with the other ones yet.

The audible alarm on the 14SG is pretty rubbish but I use it as a first check, I am flying FPV with on screen telemetry most of the time anyway but the alarm reminds me to look at the top of the screen and see how many mH's it has consumed. With the 14Sg you don't need a sensor you just have to plug you pack into your receiver if you have one that is suitable, at the moment I only have one 7008SB and the other 4 Rx's I have do not have this feature so I don't use it. If I am flying long range I don't use the Futaba Rx's so the onscreen telemetry will not work anyway.

I also have an audible alarm that I can plug into the balance lead, very loud and I can hear it from 100 metres away, you should have an idea that you have been flying for a while and should be heading closer to home.

Cheers

Pete