I need to know at what voltage my battery should be after a flight.

I have a 3000mah 25-50c 4s 14.8v battery

After a flight the over all voltage is 14.8 cell1 3.72, cell2 3.73, cell3 3.73, cell4 3.71

This is after a 5:30 flight.

Is this OK?

Whats the calculatoions on this?

Thanks

I need to know at what voltage my battery should be after a flight.

I have a 3000mah 25-50c 4s 14.8v battery

After a flight the over all voltage is 14.8 cell1 3.72, cell2 3.73, cell3 3.73, cell4 3.71

This is after a 5:30 flight.

Is this OK?

Whats the calculatoions on this?

Thanks

Paul,

After flight voltage is not really an issue as long as you have not gone below about 3.2 volts. Fully charged the voltage per (new) cell should be 4.2 volts. As the cell ages/ is used, that maximum voltage will drop a small amount. The maximum voltage is more of an indicator of battery health than after flight voltage.

 More important is the amount you withdrew from the battery. We want that to be not much more than 80% of the battery's capacity. So for your 3000 mAh example you should be drawing around 2400 mA's max for each flight. Drawing more is possible if you have deeper pockets.

You may however want to make it a practice to measure the voltage of any battery you have not just charged prior to installing in the model. Once you start the model your ARE going to go flying for several minutes. (yes I know, some people use the low voltage cut off but your model will always be worth more than your battery so you should not set a LVC.)

As far as checking the voltage a simple meter is all that is required.

http://www.hobbyking.com/hobbyking/store/__19945__H_King_Cellmeter_6_Lipo_Life_Li_ion_Cell_Checker_Alarm.html

Kim

I have set 3.2V cut off UNDER LOAD

Castle Phoenix Edge:
Considering the in-flight (under load) low voltage cutoff as an emergency measure keeping me from a battery catching fire in flight only, I do set the in flight low voltage cutoff at 3.0 V  or 15 V for 5S. Furthermore, I activate the Voltage Cutoff Type  "soft cutoff" to give me a chance to emergency land the airplane in case the system decides to shut-off (sowly, that is) So far, I've had this happen twice, once when trying to do a flight with a partially discharged battery and the other time when adding an inch to the prop diameter without adjusting RPM before take-off.  Both the batteries and the airplane survived.

As far as the separately programmable Current Cutoff is concerned, I use the "high sensitivity 75A" and "hard cutoff" settings, hoping this would work fast enough in case of a prop strike on take-off. A recent log did show cutoff within approx. 1 sec from the moment when the Amps went over 75.

Thank guys this is helpful.

The battery is at 4.2 per cell when fully charged at 16.7v.  So I just need to only use about 20% of the battery?

So not that I would but could take it down to 13.36v and be within a safe range? 3.34v per cell.

Just making sure I understand.

Thanks again guys for the feedback.  

Thanks John

These are 3000 mah batteries.

I guess the question is - after my flight they are down to ~3.72v per cell.  Is that too low that it could damage the battery?

It is about what my storage level is.

Still learning from you guys

Castle Phoenix Edge:
Considering the in-flight (under load) low voltage cutoff as an emergency measure keeping me from a battery catching fire in flight only, I do set the in flight low voltage cutoff at 3.0 V  or 15 V for 5S. Furthermore, I activate the Voltage Cutoff Type  "soft cutoff" to give me a chance to emergency land the airplane in case the system decides to shut-off (sowly, that is) So far, I've had this happen twice, once when trying to do a flight with a partially discharged battery and the other time when adding an inch to the prop diameter without adjusting RPM before take-off.  Both the batteries and the airplane survived.

As far as the separately programmable Current Cutoff is concerned, I use the "high sensitivity 75A" and "hard cutoff" settings, hoping this would work fast enough in case of a prop strike on take-off. A recent log did show cutoff within approx. 1 sec from the moment when the Amps went over 75.

It does not belong to this thread, but I will answer, may be it can be usefull ..

That low cutoff is not only emergency for me, it also warn when battery gets abused. 3.2V is highest possible on Jeti Spin, so I simply have it there. It is voltage which will cut off during last laps of pattern if battery does not have enough capacity anymore, but still enough in clower leaf so I simply use it at 3.2V. If it happens, I can still set it down to 3 or 2.9 and do few more flights on that battery, knowing that battery is already on way. However difference between 3.0 and 3.2 is very small and does not mean anything in case of flight with discharged battery, but I think it is still better to stop at 3.2 then 3.0, it will be more gentle to battery.

Regerdarding grass strike, we learned not to tighten nut so hard, and it is very good prevention in case of grass attack :-)) ... it works like a prop saver ... the last thing I want is to stop motor in contest just because it cut little grass :- ))) ... at least it was good practice on very bad surface in Hungary when I got grass to prop several times.

Thank guys this is helpful.

The battery is at 4.2 per cell when fully charged at 16.7v.  So I just need to only use about 20% of the battery?

So not that I would but could take it down to 13.36v and be within a safe range? 3.34v per cell.

Just making sure I understand.

Thanks again guys for the feedback.  

It was already written, but yes, 3.7V is good value for short time storage. That is exactly voltage I have after flight, and that is how I leave it till next flying. The problem could be if the voltage drops to or under 3.6V, it will need immediate recharge at least little bit.

3.7V means you DISCHARGED 80% of battery capacity ... not that paper capacity, but real capacity, battery loses capacity every flight and one day you must change it, so if you fly always the same flight, you will end up say at 3.7V when the battery is new, and later, when battery is abused, it will fall to 3.65, then 3.6 and that is close its end. Beacuse 3.6V means you discharged 100% its capacity.

Hi all,
And different brands of batteries do not yield identical voltages versus state of charge, and there is a change with temperature as well.
It's all small differences, but that's why you shouldn't trust a "fuel gauge" when you first put your battery on a charger that has this feature.

Regards,
  Dean

Paul, you probably can't tell much just by the voltage until the battery gets pretty low, as most any battery, when not under a load, will show most of its potential rating.

That's true of a lot of battery chemistries, but not LiPo.

Most batteries work by plating or dissolving metal from the electrodes, and the voltage of one cell is the difference in electrode potential between the materials used to make the two electrodes.  There's always some "virgin" material on each electrode, so if you give the battery time to rest, you always see that same electrode potential at zero current.

The reasons this type of battery (lead-acid, dry (Leclanche) cells, NiCd) show a voltage drop under load is because the electrolyte either gets less and less conductive, or because the 'used up' electrode material doesn't go into solution as the battery is discharged.  In either case, the electrical resistance of the battery goes up as the battery is discharged, but the open-circuit voltage (after the battery has had time to rest) stays pretty constant.

Lithium Ion batteries are just different.  I'm not even going to try to explain it, because I don't fully understand it myself.  But if you really want to know, look on the Battery University site or Wikipedia for a "Scientific American" level explanation.  The long and short of it is that Lithium Ion batteries don't work by plating and deplating the electrodes, so there never is any "virgin" electrode material maintain voltage stability, so the cell voltage isn't constant.

I thought the best judge of usage is what it takes to recharge the battery.  Am I wrong?

The problem is, that you do not know real capacity, so you do not know how much is in the battery after flight. The only way is to discharge the rest and see (and abuse the battery discharging to 0%) or believe that 3.7 means ~20% still in and 3.6 means empty at all.

3.2V is OK? I thought Paul wrote about UNLOADED voltage. If Lipo battery shows 3.2V unloaded it is way overdischarged.

3.8V means battery is somewhere at 50%,
3.7V means aproximately 20% what is very good stage after flight.
3.6V is somewhere at 0% and it will probably switch off on undervoltage during flight in near future (if it did not happen already) and it needs to be replaced

but 3.2 V is totally off, I have set 3.2V cut off UNDER LOAD

Hi Igor,

Call me "OLD" but I am using the information from the Astro 109 Charger:
(I have also found repeated references to these numbers on R/C Groups Batteries Forum). I agree that running a pack down to 3.2 volts is BAD but not fatal.

"If ANY cell in your pack is discharged below 2.5 volts,
permanent and irreversible chemical damage will slowly and completely
destroy the cell within 30 days. If a cell is exposed to this low state of
discharge overnight it can sometimes be saved by applying a slow
“trickle” charge until the cell voltage reaches 3.2 volts or more and
remains at this voltage after charging current is removed. By “trickle” we
mean a charge rate between 5% and 10% of cell rated mahr capacity.
For example on a 2000 mahr cells, “trickle” means 100 to 200 milliamps.
I have recovered cells as low as 1.4V by trickle charging for one to two
hours. It doesn’t always work, but I have recovered cells most of the
time. The longer the cell has been exposed to low voltage, the lower the
chances of recovery. After recovery I recommend fully charging the cell
to 4.2 volts, and then running a discharge test at a “1 Cell” rate to
measure its capacity. “1 C” means discharging a 2000 mahr cell at 2
amps. If the battery capacity has deteriorated to less then 75% of its
rating when new, it is time to discard that pack.

IF ANY CELL IS DISCHARGED TO BELOW 3.2 VOLTS BUT
ABOVE 2.5 VOLTS it is in a stable voltage region and may remain in
that condition for a long time without damage. But the internal
resistance of the cell may have become much higher than normal. If you
try to charge this cell at a normal “1 C” rate, its voltage may jump up by
as much as one volt or more. But if the charging current stopped, the
voltage will drop back the original value. This cell is not ACCEPTING
the charge. Stop at once. If you continue to charge at a “1 C” rate,
the cell will puff up and be ruined and may even start BURNING. Always
monitor the voltage behavior of any lithium battery pack for the first
minute to be certain that the charge is progressing normally. In multi cell
packs that have no taps this is about the only way of detecting a problem.
If your cell has a separate connector with battery taps, use a battery
balancer like our Astro Blinky #106. It will detect a low voltage cell even
if the total pack voltage looks OK. If you do not have a balancer or a
balance connector on your pack you can still detect the problem by
observing the abnormal voltage rise when attempting to charge at the “1
C” rate. Good condition packs will show a very small voltage rise of less
than 0.1 volts per cell. A three cell pack in good condition will only
show a 0.1 to 0.3 volts rise. If you observe a large jump in voltage, stop.
Something is wrong with your pack."


I have "brought back" several packs discharged to this voltage (and maybe a bit more....ooops!!!) using the 109 charger with no obvious degradation. My Thunder Power charger will not even attempt to charge a pack at this low voltage.

Kim.

Call me "OLD" but I am using the information from the Astro 109 Charger:
(I have also found repeated references to these numbers on R/C Groups Batteries Forum). I agree that running a pack down to 3.2 volts is BAD but not fatal.

I do not see any reason to call you anyhow, I was speaking about normally discharged battery, and as I read you also agree that 3,2V "is bad" ... I know it can be restored, I did not write that it is fatal state ... everything under 3.6V is already overdischarged and 3.2V is simply far beyond that limit and if it happen after normal flight, then it is reason to solve existing problem.