Batteries Lipo Battery Charge Level

[Derek]

If a 1 cell lipo has 3.7v, 2 cell lipo has 7.4v, 3 cell lipo has 11.1v, etc, etc

Several of my lipos show higher than the standard cell voltage. I'm told that is normal and is to be expected, for example my 3 cell lipos (11.1v) will show 12.2 and 12.3v...again, I'm told that's normal.

What is the lowest amount of voltage that I should run my lipo's down to without damaging them?

 

[coolgabsi]

The volatages that you listed 3.7... 7.4 .. 11.1 are all the base voltage levels.. At that level the battery has no power or punch..

For a lipo battery a fully charged voltage is 4.2V per cell..

So a lipo 1S : 4.2
2 Cell : 8.4
3cell: 12.6 so on and so forth

So lowest voltage.. Should never come below 3.7... to be safe be above that a bit. After any less than 3.7 .. your lipos IS DEAD and dangerous

 

[RandyDSok]

coolgabsi is actually a little wrong in what he posted...

First.... 3.7v per cell is called the nominal voltage level and as he stated, the fully charged amount is 4.1-4.2v ( depending on the cell chemistry... most used in the hobby are 4.2v ). This ( 3.7v ) is also the voltage suggested for storage when not using a lipo...

A lipo is considered at the bottom of it's voltage at 70-80% of the fullest voltage.... so between 3.0-3.3v is the lowest recommended voltage you should drain them too. Taking them further risks damaging the cell and limiting its expected lifetime. Just as draining a cell too far... overcharging one can also damage them... so they recommend to not charge more than 4.1-4.2v at the most in order to get the best life out of your lipo's.

 

[Lee]

In short, like your car oil tank
4.2V Full
3.7V Low
3.2V Empty
Less than 3V Dead
You can run it below 3.7V but you are at the level of damage.

 

[RandyDSok]

None of the expert websites for batteries I've read state that anything below 3.7v starts to damage the lipo.... They do differ slightly but usually they list 3.1-3.3v is where any damage may begin ( a couple mention 3.0 which is why I listed that above )....

Another direction to look at this in order to support what I'm saying... A lipo like used in our hobby will not retain power on the shelf for long... The recommended storage voltage is 3.7v. If damage were to happen after a lipo went below 3.7v then it would happen in short order after storing the battery for some time and they would recommend a higher storage voltage than 3.7v

The 3.7v mentioned is the recommended storage voltage... it isn't the point that damage starts to happen if you go below it... Dropping below the 70%-80% of the highest charge voltage for the cell is where the damage may occur. By damage, I mean that it will shorten the potential lifespan of the battery.

I typically will shoot for only taking a battery down to 3.4v-3.5v ... this gives me just a little overhead in case I need to go around for another landing etc.

 

[Derek]

Thanks for the clarification guys. I'm back to work tonight and tomorrow night but I'm sure I'll be back around to harass ya's some more this weekend, lol.

- - - Updated - - -

I've seen dozens of those Low Voltage Alarms out there on many websites. Do any of you have them on your planes or heli's? If so, which ones do you have? I'd be very curious to see what variety are used.

 

[breeze400]

I use them on my quad. Couldn't tell you witch one it is but, there all about the same. Got mine off e bay.

 

[Lee]

To clarify "Damage" doesn't mean you're going to see a drastic change quickly. It just means that the battery life is being reduce more rapidly, just as you car engine would be of you kept the oil level at a low level. Also its not only the voltage, its the Mahs too. A 2200mah bat should only have 80% of its capacity used, so 1760 mahs to keep in a healthy state. If you drop the voltage below 3.7V per cell, you will be using alot more than 80%
With all the batteries i have used, the only ones that have lost balance and overall power are the ones i let drop to 3.5V or less. The best ones i have used where my Zippy 2200mah 3S batteries i got with my first heli 3 years ago, that are still working today. They have always been kept above the 3.7V.
As far as i have seen on most websites and all the chargers i have used Storage charge is set at 3.85V, not 3.7V
But as Randy said there are thousands of people with different opinions on batteries and how to treat them.

 

[RandyDSok]

Ok... now I'm starting to see where the discrepancies are that we are discussing here... and I also see a discrepancy in what you wrote which I'm assuming is just a typo of sorts ATM...

The numbers I gave were the lowest voltage a battery should be taken to under load... depending on who you are listening to ... between 3.1-3.3v. Note that I said under load... at rest numbers are naturally going to be higher. These numbers represent the 70-80% of the voltage that the experts are talking about. I'd guess that the rebound voltage ( at rest instead of under load ) would be higher than the values I mentioned. The at rest voltage is likely to closer to what you were saying... than the under load values I mentioned.

The capacity left, if discharging 80% of it's capacity of a 2200mah battery, is 440mah... not 1760mah which is the amount discharged ( a 70% number is probably a bit safer, but that is besides the point at the moment I think )

 

[Lee]

Totally agree. 3.7V at rest. I think to the beginner, if not made very clear they would be running there batteries down to a 3.2V at rest level and damage there battery. I will make sure from now that I specify the difference between Under Load and Resting Voltage.
I did say capacity used was 1740, not what was left.

 

[Derek]

Excellent! I have a firm grasp of this now. Thanks everyone!

 

[callsign4223]

I'm curious about something. What's the point of storage charge on lipos? Why not just fully charge them and leave them that way until your next outing? Does it reduce their lifespan?

 

[breeze400]

That's what they say!

 

[Lee]

It will increase the Internal resistance over time, reducing the capacity and power. In the short term, they'll be fine, but if its going to be a couple of weeks or more, putting them at 3.85V storage and in a cool place, will keep them in better condition.

 

[xokia]

Generally when you are speaking of batteries the voltage is what matters not the capacity. So if your battery is 4.2 volts fully charged then 80% of that is 3.36volts.

Capacity will change over time so 80% of the capacity today wont be 80% of the capacity tomorrow. Volts stay the same. 80% of 4.2v today will be 80% of 4.2 volts tomorrow.

Volts is what your LVC is using it has no idea of capacity. That is why the common LVC cut off is 3.1, 3.2, 3.3,3.4 and 3.5 usually with a default of 3.3

 

[Westy]

if you are not sure on the times your batteries have..... do some flying for say 4 mins (fly like you normally do .... if that is like a crazy man ... then so be it!)

then let the battery rest for about 5 mins to normalise. then whack it on your charger and run it through a quick charge. once finished the reading on the right bottom of your charger (Usually) shows how many units were added to your battery.


So for example a 3000 MAH battery (Using the 80% rule) if you only replaced it with 2000 units. add another minute and see where it comes to. the limit on the 3000MAH is 2400. Once you get close to this (preferably a little under) you can write the time on the battery!

That is your fly time.... I do this .... look at my battery I am putting in and set my timer for that.

also I always put my batts on Parallel charge in either pairs or more.... this allows all the cells to drop down to an even level and gives a nice even charge.

Just my 10 cents worth

 

[xokia]

What I am saying is you are making things too complicated. If its what you like to do so be it. Your battery capacity will continue to change over time. So you will have to do what you're describing often. The 80% rule when it comes to batteries is speaking of battery voltage not capacity in mAh. If you run the battery below 80% of it's fully charged voltage you will damage the internal chemistry of the battery, this is what you are trying to avoid.

Now keeping the flight time recorded to enter your flight time in the timer is a probably a good idea. But you should run them to about 3.36 volts per cell then record the time. But IMO if I cant reach my standard flight time I'll probably toss the cell or run it to LVC anyway. At that point I wouldn't care about the battery anyway.

If you have some really expensive cells then I could see doing all you can to preserve there life. So far the biggest I have is a 5000mAh 3S battery and they are relatively cheap. On my HPI Savage I just set the LVC to 3.4V and not worry about it.

Would be nice if some of my helicopter ESCs had this feature.

 

[Westy]

sweet as. Each to their own.... at the end of the day, if you compare replacement time to engine maintenance. just thrash them and toss em when they will not charge up. I always feel the temp of the batt when pulling them off the heli.. if it is hot to touch .... = too long ... warm = Perfect! haha

 

[xokia]

I always feel the temp of the batt when pulling them off the heli.. if it is hot to touch .... = too long ... warm = Perfect! haha

I do the same but I also buy the highest current capacity batteries available for my particular application too. This ensures the ESR of the battery is the lowest possible so the battery always remains cool.

 

[Lee]

In every article i have read about batteries, I have never heard them describe the 80% rule in relation to Voltage. Its always been Mah.
This guy has a great blog on Everything battery related. Heres the page on the 80% rule.
80% Rule - TJinTech