Newby to Lion RX Batteries

[Martyn G]

Hi All

Wondering what kind of flight times to expect using Overlander 2s 2200mah Li Ion cells on a glider with 6 king max servos.  Or another way, whats the minimum voltage it's safe to fly down to before landing?

What would a low voltage alarm be set to? Sorry, but it's my first foray into these batteries and I'm not sure!

[Brett]

They say don't ever discharge an 18650 battery below 3v per cell, so 6v for a 2s.

I have an alarm on my Tx set for 6.6v, so that leaves a little wriggle room of 3.3v per cell. ***EDIT: 6.8v, so 3.4v per cell***

Time is a bit of a guessing game. It depends on the flying style, servos used and how good the install is. Binding servos will draw more current. 

Best thing to do, set a timer to see exactly how much time you spend actually flying, then when you get home charge the battery and see how many mah you put back into it.

Edited November 14 by Brett
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[Redbird]

Youll probably have several hours flying time. 

[Martyn G]

Cool. That’s amazing, so for li ion 6.6 is well under their nominal voltage but that’s ok? I’m used to nimhs and nominal voltage being 4.8v, so I tend to land around the 5v mark, esp with crows sapping away at that voltage 

[MikeE]

You may find an alarm signalled when the model is under full crow and coming in with ballast or flying fast, loading the servos.

If you do, then modify your approach.

If your model is built well, you should use around 1000mah after a very good day's flying

I watch my transmitters display, and consider the batteries if it shows below around 7.2v

 

[Martyn G]

Hmm, quite a lot of difference between 7.2 and 6.6! Anyone else want to wade in here?!

[Brett]

Hi Martyn

The reason I set my alarm that low is because when you apply crow for example, the voltage will drop briefly as all 6 servos go under load. If I set it at 7.2v for example, it will set off the alarm prematurely.

I wont fly the battery to that level, sorry I should have explained that. Thats what Mike was saying above about you may get an alarm. Its just a personal preference so the alarm doesnt go off too early. 

Brett

[Brett]

I just checked my radio, sorry I got the voltage alarm wrong. I set it at 6.8v, so 3.4v per cell. 

You had me doubting myself.

[Martyn G]

Ok

Thanks for clarifying that Brett. That absolutely makes sense. The last thing you want is a pile of alarms going off on a hectic crow braked final…

So, what I’ve understood thus far; set your low voltage to around 6.8v on the tx, then keep an eye on things with the idea of landing around the 7.2 v mark. I can’t see me getting hours of flight time.. it comes off charge at under 8.4 , quickly drops down to 8.0, then there’s what’s left. I’m hoping for a nice surprise to my pessimist outlook lol!

[MikeE]

I don't recall were mine is set. I never do get an alarm. But with 2200mah batteries, and one eye on the transmitters telemetry displayed voltage, and a personal view that it's time to stop around 7.2v I managed without concern.

I always charge with a balance lead connected, as this allows me to see that each cell is charged and equal, and I monitor the level of mah added to ensure they are what I expect relative to how long I was flying for.

[satinet]

I find each cell has different levels it settles down to.  

So I wouldn't really rely to much on voltage. If you look at the discharge curve for an 18650 you will see it's pretty flat. The voltage doesn't drop off massively until it's really quite flat. 

For me it's more about getting to know the model through recharging it.  Different linkages make a difference as obviously does how you fly it.  I think you are looking at the range of 300 to 800 an hour in my experience. 

Aside from the actual servos the rx uses about 100 an hour these days. 

 

 

[rc-soar]

With my 2S packs I set the alarm to trigger if the voltage dips below 7.2V for more than 3 seconds, repeating every 5 seconds until/unless the voltage recovers. The first alert is usually with crow deployed.

[Martyn G]

Thanks everyone. That’s all really helpful/interesting stuff, far more informative than trying to dig it up on the web. I’ll try the suggestion of setting up the alarm on my tx that rc soar suggests too. Is charging a li ion in the glider a no no, I always balance charge and are always careful to double check settings b4 charging. I use the lipo settings on the charger btw

[rc-soar]

LiIon is safer then LiPo and it's fine to charge the cells in situ if they're kept in good nick. (That said, it's not a good idea to leave them completely unattended during charge, or to charge them overnight.) 

It's LiPo's that need particular care - they're normally used to power electric models. I would try and avoid using them just for rx/servo use unless for a special reason.

Edited November 14 by rc-soar

[Martyn G]

5 minutes ago, rc-soar said:

LiIon is safer then LiPo and it's fine to charge the cells in situ if they're kept in good nick. (That said, it's not a good idea to leave them completely unattended during charge, or to charge them overnight.) 

It's LiPo's that need particular care - they're normally used to power electric models. I would try and avoid using them just for rx/servo use unless for a special reason.

Very sound advice. Thanks