LIPO 3S low voltage cut off ????

[Joshcail]

Im programing my esc to run LIPO what is a safe low cut off voltage for my 11.1v LIPO 3s that wont harm it by draining to low but give me as much run time as i can get??????

 

[mikebecher]

Usually it's 3.0v per cell but you need to check the battery manufacturer's recommendation.

 

[k7zpj]

Im programing my esc to run LIPO what is a safe low cut off voltage for my 11.1v LIPO 3s that wont harm it by draining to low but give me as much run time as i can get??????

I wouldn't go below 3.2v per cell or 9.6V. I usually run my LVC at 3.4v per cell just to be safe in the case of one of the cells going out of balance and running a lower voltage.

Instead of running down to the LVC, it is better practice to know how much time it takes to get to the 80% discharged level. A good charger will either give a % charged or the MaH that it took the charge the battery. With a few runs you will get a good idea of how long you can run it and not exceed 80% discharged. (You still need the LVC set at 3.2 to 3.4v per cell)

 

[Olle P]

With the LVC set to 3.0V it will activate around 3.4V/cell, which is more than sufficient unless the cells are really different capacity or off balance.
The key issue is that no cell is allowed to go below 2.8V at rest. The voltage drops while the cell feeds current, and then goes back up a bit, so the admissible voltage while driving is actually a little lower.

If you want maximum run time and have batteries where the individual cells are properly balanced and pretty much the same capacity there's absolutely no danger to have LVC set at 2.8V/cell (or even slightly less). Running the batteries to below 2.95V/cell at rest will reduce their life span a little bit though.

 

[Joshcail]

Ok thanks its a brand new battery....i set it at 3.0v/cell

 

[TacoCrawler]

I set my lvc to 3.4v per cell also
better to error on the safe side ;-)

IMO... 3.0v lvc could be pushing one's luck
no justifiable reason for discharging a LiPo cell below 3.3v

the difference in run time, during discharge,
would likely be indistinguishable to most ;-)

 

[Joshcail]

Ok i dont want to risk doing any damage... default is 3.0v...ill bump it up to 3.4v better safe than sorry"thumbsup"

 

[Johnnysplits]

there's absolutely no danger to have LVC set at 2.8V/cell (or even slightly less)

Truth!

 

[Olle P]

I set my lvc to 3.4v per cell also better to error on the safe side...
the difference in run time, during discharge, would likely be indistinguishable to most ;-)

Another 60% runtime is "indisitinguishable"? :shock:

With LVC at 3.4V/cell it will kick in when about 50% of the energy is used.
With LVC at 2.8V/cell you can use some 80% of the energy. The cell voltage will stay at about 3.3V unless one cell is decidedly less capacity than the rest.

 

[Ohioskills]

I had a 3s batt that was at .5v and I took a 12v car batter charger to it. put it to jump start and very quickly use it as a defibrillator and it worked afterwords.

 

[TacoCrawler]

Another 60% runtime is "indisitinguishable"? :shock:

With LVC at 3.4V/cell it will kick in when about 50% of the energy is used.
With LVC at 2.8V/cell you can use some 80% of the energy. The cell voltage will stay at about 3.3V unless one cell is decidedly less capacity than the rest.

If a 3s LiPo is fully charged @ 4.20v/per cell, and then discharged to say 3.3v/per cell...
How do you come up with 60% more voltage - run time remaining ?

would be my guess... it's likely nearer 20% voltage remaining...
give or take.

If a LiPo's max consumable life (cycles) merit any value...
it would be smarter not to discharge below 3.0v ever
as it's better for the LiPo if it's not fully discharged.
Using an 3.3v lvc is basically insurance for a longer
LiPo consumable life/usage (cycles)

Discharging 80% of the voltage
and leaving 20% remaining...
is playing it safe, for the long haul.
Just a smart guide to follow...
if wanting a longer LiPo consumable life expectancy.

Overly charging/discharging LiPo's is simply more abusive...
and their consumable life (cycles) will be shortened.

Got puff !? :roll:

Granted... higher C rated batteries will handle more abuse (amps).
But I have no understanding as to why one might feel
that they need push their LiPo's lvc to their lowest limits ?

If one wants more run time... it's not the voltage that matters.
it's the LiPo's mah/capacity rating.

I would not utilize any LiPo that has become swollen.
As it's just a road flare fire waiting to happen.
So I prefer to avoid that issue from the start.

I say run NMih batteries...
if max voltage discharge is desired.

I had a 3s batt that was at .5v and I took a 12v car batter charger to it. put it to jump start and very quickly use it as a defibrillator and it worked afterwords.

Similar method can also be used to bring back a 1:1 glass mat 12v battery that was overly discharged.
Tho' generally a charger, stand alone, is not the correct procedure...
and instead a 2nd fully charged battery is used to flood into the overly discharged battery.
And then the charging procedure... runs thru the 2nd battery first...
then flooding into the overly discharged battery


sometimes it works... sometimes it don't

In your case... you probably got lucky.

either way... it's hard on the battery
well not the recovery in of itself...
But the discharge below the cut off voltage is ;-)

Maintaining LiPo's without pushing their limits...
ensures a longer consumable life (cycles).

Granted some folk aren't concerned
about a LiPo's safe use/consumable life (cycles)...
but they probably should be.

I've seen a few LiPo battery fires...
and it's something every user should wish to avoid ;-)

 

[JohnRobHolmes]

On higher amp draw vehicles I set the cutoff at 3 or 3.1v, since the pack voltage will dip under load and it must be allowed to compensate for heavy burst loads. On crawlers I set it at 3.4 or 3.5v, and typically charge to 4.18v. It nets about 80% of the total pack capacity, but extends service life about fourfold. Keeping a lipo from hitting the extremes of voltage range keeps them happy. Most of my crawler lipos last 5 years or longer, it is more common for a mistake to kill them than to wear them out.

The reason I use such a high cutoff voltage is because there isn't much energy left below 3.5v when discharge rate is low, and if the cells aren't closely matched then a straggler cell can get ruined very quickly. Look at the multi rate discharge graph, and see how steep the cells drop near 3.5v with the 1C and 10C rate. Since most crawlers fit this "low rate" use, it is good practice to adjust the LVC up if battery service life is a concern.


As the battery voltage goes up, it becomes riskier to use lower cutoff voltages. Runt cells can hide among the other ones when only looking at bulk voltage. Also attached is a 1c discharge graph for a 6 cell zippy pack, with bulk cutoff at 3.5v per cell. As you can see, at the end there is a big dip and the weak cell is running towards destruction. Even at 3.3V cutoff the runt would have been pulled low enough to lose capacity, and thus it would become a reoccurring event of a bit more damaged with every cycle.

 

[mikebecher]

Thank you John for the excellent, concise explanation backed with SCIENCE! It highlights the fact that your LVC also depends on your driving style and that this is not a one-size-fits-all situation. As with most aspects of the hobby, you can play it safe or push the envelope. You've provided the information that allows us to make that decision for ourselves and I, for one, appreciate that!

 

[FLOKI-81]

I have always used 3,25V as cutoff on my crawlers,, Holmes BR mini dual esc`s
on my 1/10 buggy I have a tekin rsx on auto lipo cutoff
and the same on 1/8 buggy/truggys...(auto lipo) also tekin RX8

 

[Digital]

edit, nevermind, Travis told me about the auto-lipo feature, just enabled that, thanks.