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Lithium Polymer Etiquette: A Comprehensive Guide to Working with LiPo

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Picture of Lithium Polymer Etiquette: A Comprehensive Guide to Working with LiPo
In this Instructable I will be going over the basics of proper charging, discharging, handling, usage, storage, and care of lithium polymer batteries so you can use them safely and effectively in your future projects.  Now, this is by no means the be-all and end-all of information, and it's always important to consult the instructions for your specific equipment, but I think this Instructable will provide a good basis of knowledge on the subject of these awesome batteries.
 
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Step 1: Terminology

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If you're new to lithium polymer/LiPo/LiPoly batteries, there are a lot of terms you will need to know before we get started.  Everything may seem a bit daunting at first, but with some basic understanding, it's all pretty simple, so let's jump in.

When you look at a LiPo's data sheet or casing, you will notice it has a lot of specs.

Cell arrangement - Described using the format xSyP (where x and y are integers), this tells you how the cells in the battery are wired up.  Batteries are made up of cells, whose voltage is determined by cell chemistry and whose capacity is determined by energy density and physical size of the cell.  S stands for series and P stands for parallel.  As you may know, series adds the voltage of the cells and parallel adds the capacity of the cells, so a combination of cells in series and parallel results in a battery.  The battery shown in the second image reads that it has an arrangement of 3S1P, meaning it has 3 cells that are all in series with no parallel wiring.  This may seem confusing because it says "1P," but think of the arrangement as a grid.  By multiplying the 3 and the 1, you get the total number of cells in the battery, which in this case is 3.  If it were a 3S2P battery, there would be 2 sets of 3 series-wired cells in parallel, resulting in 6 cells total.  Often times the parallel arrangement is omitted when discussing batteries, because most packs are 1P (so instead of saying you're using a 3S1P pack, you may as well just say 3S).

Capacity - Usually measured in mAh (milliamp hours), this is determined by the cell arrangement (parallel) and tells you how long you can expect the battery to last on a charge (although it's not quite that simple).  2600mAh as shown on the battery in the picture is equal to 2.6Ah (amp hours), a format you may be more familiar with on larger batteries, like the SLA (sealed lead acid) one in your car, which is probably around 50Ah.  A capacity of 2600mAh means that the battery can discharge at 2.6 amps for one hour (hence "amp hours"), 1.3 amps for 2 hours, etc., before it runs out of "juice."  Because the battery shown has a 1P arrangement, each cell has a capacity of 2600mAh.

Voltage -The voltage of a battery is also determined by the cell arrangement (series), and there are a few common voltage measurements worth noting:
        Charged - the voltage of a fully-charged LiPo cell is 4.20V, and charging above this will damage the cell.
        Nominal - this can be considered a sort of "half-charged" voltage, as it is 3.70V, in between charged and discharged.  Nominal voltage is what manufacturers use when describing the voltage of their batteries.
        Discharged - the voltage of a discharged LiPo cell is 3.00V, and discharging below this will definitely damage the cell.
Because the battery shown has a 3S arrangement, it is marked with its nominal voltage of 11.1V (3.70V*3 cells).  A fully charged 3S pack is 12.60V and a fully discharged 3S pack is 9.00V.

Constant C Rating (Discharge) - The constant C rating (in relation to discharge) tells you how many amps can be safely drawn from the battery constantly.  The "C" in a rating of xC (where x is an integer) actually stands for the capacity of the battery in Ah.  By multiplying the C rating's coefficient by the capacity of the battery in Ah, you can determine the sort of amperage you can draw.  In the case of this battery, with a capacity of 2600mAh (2.6Ah) and a C rating of 55C (that's pretty high, FYI), I can multiply 55*2.6 and get the max constant output of my battery, which is 143A.

Burst C Rating (Discharge) - In addition to the constant C rating, there is also a burst C rating, which is higher.  Most of the time, the "burst" is rated for 10 seconds.  Although it is not marked on the battery itself in the picture, it says in the documentation that this battery's 10 second burst rating is 80C.  So, 80*2.6 is 208A burst. That's a lot!  It's worth noting that your LiPo won't last long when that many amps are being drawn from it.  At 208A, a 2600mAh LiPo will last approximately 45 seconds.

C Rating (Charge) - Determined in the same fashion as the C ratings for discharge, the C rating for charge tells you at what amperage you can safely charge your battery.  This information is generally listed on the back of the battery with all the safety information.  For the battery shown, it happens to be 5C, which means that it can be charged at 13A (2.6*5).  We'll be talking a lot more about charge rates later...
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BrentB131 minutes ago

Excellent write up - Thanks!

MatteoF128 days ago

It's a great guide, I suggest you may add:

- "reviving" undercharged LiPos (as this guy did:http://electricrcaircraftguy.blogspot.it/2014/10/r... ) It's a dangerous procedure but it works good!

- charging more than one LiPo at the time, for example 2 x 3S 4500mAh can be charged by putting them in SERIES (with an adaptor for the "main",red and black, and single cell cables) and setting the charger to 6S, with 1C (4.5A) charging current.

Cheers

VanceB11 month ago

I plan to use a lithium polymer battery to power an Arduino project, but to charge it from a solar cell. I will use a charger such as this one from DFRobot http://www.dfrobot.com/index.php?route=product/product&product_id=1139, but can you advise on whether it is OK to charge the battery on a much lower current than the rated values or will this reduce battery capacity?

It would be great if you could add a section on "conditioning" a new battery for best performance. I know that charging and discharging is how you do it, but not the specifics for best results.

DavidT102 months ago

Hi there!

Other than the obviously high cost, what do you think about using a small, say 3.7v/1200mah in a Solar/PV charged LED lamp as opposed to Nimh batteries?

Thanks,

Dave

Hi.

I have a 4S 8000mAh LiPo battery from Hobbyking and i'd like to
integrate it in a system where the battery would be powering a load (up
to 80A discharging, typical 40A) and i'd like to charge the 4S LiPo
battery while the system is working. Is it possible? I wanted to have
the charging board inside my system. I justed wanted a DC cable to plug
and charge the system (even when in use).



I found things like this: http://www.batterysupports.com/12v-1...tem-p-245.html



But i don't know if this is what i need for charging or if this is just a protection.

hi and thanks for the great instructable! I wanted to know if you could charge and discharge from a lipo battery at the same time? I have heard that it isn't recommended, but is it possible to do it taking necessary precautions?

And if it isn't, will this be possible with li ion batteries?

NRG4UandMe3 months ago

thanks for the nice explanation of tech terms on a lipo which I am still learning about !

MomenIbrahem8 months ago

I have had a problem with my LIPo battery it's working and its 3 pack voltage is 1.39 volts , btw it dropped suddenly from 9 volts to this voltage (2200 mA 3s1p )
my charger is not charging to when connecting the balanced charging pins too

Does this means that it has been damaged ?

Radioactive_Legos (author)  MomenIbrahem8 months ago

I would advise against trying to save that battery. It's worth checking the voltage of each cell by measuring from the common ground on the balance tap to each of the other wires. I'm curious as to whether or not all the cells drained evenly or if one or two are dead entirely. LiPos have a different discharge curve from most batteries because they drop some voltage at initial discharge, remain near their nominal voltage for most of their capacity, then drop off voltage very rapidly at the end of their discharge cycle. Check out this graph to see what I'm talking about.. As you can see, it's very easy to over-discharge a LiPo if you don't stop using it in a timely fashion.

Capture-2.PNG

It also appears (from your chart) that charging beyond 3.8V at room temperature (20C) is nearly useless because you gain less than 300mA from 3.6 to 3.8V.

I'm not convinced your chart is accurate though... it also indicates that the max. charge is 3.8V at room temp, yet I routinely charge lipos and standard lithium ion cells (same chemistry I believe) to 4.2V even at room temp, and both my Accucell and Nitecore chargers show that it puts a substantial charge on from 4.1 to 4.2V.

Radioactive_Legos (author)  JB163 months ago

I think you may be interpreting the graph incorrectly. It's a discharge graph and it says at the top that the battery was charged to 4.2V. I believe the reason the 25C discharge curve begins at 3.8V is simply due to the voltage drop from the large load (drawing 105A). You can see that when the load is small with a 1C draw from the battery (4.2A), the battery's voltage does not drop much, and is much closer to 4.2V.

HansBaumann7 months ago

Hello,

I am wondering if anyone can tell me if I am going in the right direction here:

Item:
lipo battery 551419 3.7v
75mah lithium li-polymer
battery for rc helicopter

We want to use this battery for a back up system as follows:
1. We have 24VDC that are usually running our device (a valve actuator)
2. When the power supply fails, we need about 20-22V @ 2A for 0.5 seconds and then @ 1A for about 5-10 seconds
3. The power supply will fail less than once every month
4. What is your recommendation to keep this battery pack connected to the charger (6 cells in series), so that it can perform this service the longest time possible?
5. The battery does not need to be good for longer than 10 minutes after power failure of the supply

My reading so far suggests that for the best batter life I would have to do the following:

Since LiPo battery life is counted in "cycles" and temperature, I think that charging when it goes to 3.6 and only up to 3.7V would be best.

I would like to know if anyone has experience with something like that and particularly, if its reasonable to believe that a battery pack built based on this outline wile have a good chance of surviving for 4-5 years.

JB16 HansBaumann3 months ago

It sounds like you could get by nicely with three 9-volt alkaline cells connected in series. These would be non-rechargeable, but it sounds like with your small monthly current draw they may last for the actual storage life of the batteries.

Certainly the heli battery (3.7V, .075AH) would also be sufficient (connecting 6 in series, or "6S"), but massive overkill. You need 1A for 10s, 2A for .5s:That's 11 Amp-seconds, or about (11/60) Amp-minutes, or .003 Amp-hours, or 3mA-Hrs, which would be enough for about 25 of these cycles. Depending on the self-discharge, you could safely charge it manually once a year! Since a typical 9V alkaline has over 500mAh of capacity, your 3S 9V battery pack would theoretically last 170 cycles. Assuming this to be a monthly occurrence that's over 12 years!

Great guide! Really helpful! Just a couple of questions though, will the charger automatically balance the cells, or would I have to set it up? Also, Alot of people say to discharge/charge my battery to a certain voltage when not in use. What would this voltage be? I have a 7.4V (3.7V per cell) 2s 5000mah LiPo. Thanks!

Thanks! The answers to your questions are actually in the Instructable, but I'll answer them separately here for clarity. If you have a balancing charger, it will automatically balance the cells if you charge the battery in balance mode with the balance tap connected. As for the voltage people are talking about, that's covered in Step 7: Storage. 3.85V per cell should do the trick. Hope this helps!

Thank you very much. But wait, what does 3.7 V per cell stand for on my battery? If it can go higher..

3.7V is the nominal voltage of the battery, you can think of it as an average voltage during discharge. For more info, check out Step 1: Terminology, under "Voltage"

Thank you so much, but I'm going to ask a couple more questions just to clarify. For my battery, to fully charge it, I have my charger set to 4.2V per cell, at 5 amps per cell, which'll charge in an hour. For storage, I charge each cell to 3.8V but at how many amps and for how long? Thank you very much, and merry Christmas!
Ooh, and what voltage should I set up my lipo cutoff on my esc? Thanks so much man, you're a life saver!

Excellent guide, well laid out with very good illustrations.

One request for the future.

What is the best way to prolong the life of lipo batteries in use ?

E.G. fully discharging to just above 3 volts and then charging - Or charging as soon as I have finished one flight in order to keep them fully (balanced and )charged?

calex44 months ago
chargers are sticked as 5v 500mah......then I have connected batteries in serial and parallel giving 8v and about 5000mah and used 7805 to get output of 5v..what is the output mah like as sticked in charger

I want to charge my 12V bike battery with my Turnigy lipo charger. Plz suggest which battery type i should select??

I want to charge my 12V bike battery with my Turnigy lipo charger. Plz suggest which battery type i should select??

I want to charge my 12V bike battery with my Turnigy lipo charger. Plz suggest which battery type i should select??

I want to charge my 12V bike battery with my Turnigy lipo charger. Plz suggest which battery type i should select??

I want to charge my 12V bike battery with my Turnigy lipo charger. Plz suggest which battery type i should select??

How many A can i charge it on if i have a 14,8V 4s 4500mAh 25c lipo

Using one of those balance charger (they do not usually charge at more that 1C for lipo), anything up to but NOT exceeding 4.5A. The lower you set the current (A), the longer it takes to fully charge. Check your user manual for information on the C rating for lipo batteries. Hope this helps.

thanks it was a lot of help

I'm a rookie , so please understand....I have a 11.1 5200 LiPo & was wondering if it is OK to charge after every flight , even if the battery isn't dead ? I have a Walkera quad copter. Thanx !!

Totally! It's perfectly fine to charge after every flight, no matter the current charge in the battery (whether you flew for just a bit or until you hit cutoff). That's what I do. You only need to "store" your LiPos (i.e. charge/discharge to 3.7V/cell) if you don't plan on using them for a while, on the order of weeks or months. Hope this helps!

Sorry, meant 3.85V/cell for storage.

Hm, I must've accidentally closed my browser window before I last post made it through. I'll try again.

Suppose you wanted to fly your helo 4-5 times a week, on one battery, and each time you fly you want to use as much of the battery as you can. From the sounds of it you shouldn't need to store every night at 'storage' charge (3.85v). Would you just charge batteries to 4.2v after every flight and leave it at that state for the 1-2 days until the next flight?

Thanks again advance.

Hey there! You have the right idea. If you're using your battery frequently, you shouldn't need to charge/discharge it to a "storage" state - charging it fully will do just fine.

I have one of these batteries: http://www.wheelspinmodels.co.uk/i/80486/. Its label has a "1.9Wh" printed on it. What does that mean please? Thanks in advance.

That's just another measure of the power it can deliver. P (watts) = I (amps) * E (voltage). So since it's a 3.7V nominal pack (single cell) with a 500mAh capacity, it's a 1.9Wh pack. So basically no new information, just another way to display what it already says.

That was fast, thanks!

sghosh216 months ago

"don't throw it on fire more fire will happen"...............lolzzzz

How to measure the voltage of each cells using multimeter??.........Nice guide by the way...

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