Instructables

Lithium Polymer Etiquette: A Comprehensive Guide to Working with LiPo

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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

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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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!

sghosh2124 days ago

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

HansBaumann1 month 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.

MomenIbrahem2 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)  MomenIbrahem2 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

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

You can measure each cell's voltage by connecting the multimeter to the contacts on the balancing tap. There's a common cathode (usually the black wire) and an anode for each cell.

trussell157 months ago

I have been researching all I can about Lipo batteries since I recently got into RC helicopters. I have to say, this is a VERY good guide as it pretty much covers everything you will need to know about these batteries (Charging/discharging/storing/balancing/safety)....everything! I especially like how you emphasized on safety. If this guide saves just one persons home from negligence, then it was well worth it. Thanks ;)

This should be read by all people who are going to use LiPos. I was just about to start working with LiPos and did not realise the dangers that can very easily happen. I am looking forward to your update. Thank you.
modulosa2 years ago
One-cell lipos don't have balance leads, and some smaller lipos have just single lead that works for balance and discharge (eflite 2s for the UMX AS3X models, for instance)

If you wanted to add any info based on those.
Tomdf2 years ago
Very nice!
Radioactive_Legos (author)  Tomdf2 years ago
Thanks!
bkallen52 years ago
Excellant Information & well presented! I'm a member of our local R/C Aero club & if you are going to fly electric then you are required to attend a short seminar on LiPo batteries & there care & feeding..
At our flying field we have a special place for LiPo charging, it has ceramic tiles on a wooden table (reasonably fireproof! You must use a the proper charger as you mentioned BUT it can only be connected to a 12V (DC) Battery for input power NOT via a 115V AC connection. This can be a Car battery NOT still in the car..

We recently had a demonstration of a LiPo battery fire in an safe open area by a proffessional fire fighter. Check this YouTube link for video:

http://youtu.be/8X-AJj1Znek

We now have several buckets of sand around our pits just in case...
Radioactive_Legos (author)  bkallen52 years ago
Thanks! Sounds like an excellent setup for charging, too! What's the reasoning for limiting chargers to batteries? I'd imagine it's to isolate the chargers from one another in the case of a charging mishap that could backfeed voltage to the input.. seems like a good idea
You hit the nail on the head! Bare in mind we also fly Glo-Plug & Gas 4 stroke engines which use obviously inflammable fuel so that is another consideration.

PS I am also a Judge for FIRST for the San Diego Regional both FTC & FRC, great fun...
Very informative. However, I have always wondered and never really been able to find out an answer to this question. How long can a lipo be left in a stored state? I enjoy using my rc car, but it is usually pretty long between uses. I learned a valuable $100 lesson a few years ago when I went to run my car, and the battery was completely dead and it just could not be charged. I was, and still am a very basic amateur, and I didn't read up and learn what I should have about lipo's, and didn't use the storage function on the charger. Can I leave it stored all fall and winter and spring and then use it again in the summer? That's usually the only time I get the urge to run it. Or do I need to try to charge and run it every few weeks or months? I enjoy the hobby, but can't afford to keep on buying expensive (to me) lipo's. Thanks!
Thanks! I hear all the time about people storing their LiPos through an entire season and sometimes longer. LiPos don't have memory like NiMh does, so it's not really necessary to cycle them in between uses. What I would do in your position is "store" the LiPo on the charger, then just check on it every month or so and store it again to 3.85V per cell to make sure it's doing okay. If you want, you could even cycle it at that same time. That is, discharge it fully on the charger, then charge it, then discharge it using the "storage" function back to proper storage voltage. It should be fine to stay in storage for multiple months at a time, but it's better to check on it and see it's fine than leave it alone and come back to it 9 months later to find it dead. Hope that helps!
dawp2 years ago
thanks for the information. I will look elsewhere for info on LiFePo batteries. I will check with Theprofessor W8ESE later. Thanks.
n-2-stuff2 years ago
Nice guide. You can use my video of what not to do to a lipo if you like.
http://www.youtube.com/watch?v=tatq8KcaGY0
Trike Lover2 years ago
Thanks for this very comprehensive guide. I'm looking at various rechargeable batteries to put inside and power two guitar practice amplifiers. The first is adding battery power to a 10 Watt (audio) amp in a 12" x 12" x 6" enclosure, and the 2nd a much smaller LM386-based headphone practice amp that fits in a cigarette-package-size enclosure. My original intent was to use a SLA battery for the 10 watt amp, as there's room in the cabinet, and to use 4 AA NiMH batteries in the headphone amp.
However, energy storage vs. weight considerations have me looking at other battery technologies. The SLA is fairly heavy for its low storage capacity; the four AA NiMH cells are adequate for power, but are heavier and bulkier than the rest of the amp put together. It would be nice to find something lighter and more compact. Power draw is not high in either instance, but being able to recharge easily is important. The larger amp runs on 115 VAC, but its internal power supply drops this to 12 VDC, so a 12 Volt battery will work nicely. The pocket amp will run on anything from 5 VDC to 9 VDC, and current draw is low - typically 60-100 mA.

I would also like to investigate Lithium-based batteries for a larger application - in this case an adult recumbent trike with electric assist. However, the $ needed makes this quite daunting, even though the weight saving would be tremendous.

I see that RC modellers seem to be the biggest users of the small-scale battery packs; I don't know what's available in larger voltage/current capacities. Off to the hobby shop, I guess! Thanks for a well laid out and informative presentation.
Radioactive_Legos (author)  Trike Lover2 years ago
Thank you for your comment! For the 10W guitar amp, I image it draws slightly more than 10W, say 15W just to be safe, to account for inefficiencies. If you want to be sure, you could hook it up to a Watts-Up or something similar to measure the actual wattage it draws under use. So 15W/12V=1.25A draw. So that means you need around 1.3Ah of battery capacity for every hour you want to be able to play (at full volume, mind you) on a charge, which seems very reasonable. You can easily find a good 1300mAh 3S LiPo battery for $10 or less, but I imagine you want to play for more than an hour! A 5500mAh 3S LiPo like this one http://www.hobbypartz.com/98p-25c-5500-3s1p.html is $40 and should be good for close to 4.5 hours of use at full volume. A 3S LiPo will be 12.6V fully charged, but at cutoff it will be 9V, so I'm not sure if that's an issue. It's worth noting, though, that LiPos hold voltage very well over their discharge, meaning that they drop voltage slightly at the beginning of discharge, but stay relatively stable as they discharge, dropping slowly, until they near the end of their capacity, at which point they drop off quickly. What this means for you is that a 3S pack in your 10W amp will probably stay between 11 and 12V for most of the time. Good luck, sounds like a great idea!
jollyboy12 years ago
Cool guide...im part of the aeromodelling club in college and ive shared this page with the group...hope u dont mind
Radioactive_Legos (author)  jollyboy12 years ago
I certainly don't, In fact I'm rather honored! Glad you liked it!
k.aderer2 years ago
Excellent info!
Radioactive_Legos (author)  k.aderer2 years ago
Thank you!
dawp2 years ago
Thanks for the info on LiFePo batteries. I am not a model enthusiast as most of the writers above appear to be. I'm a radio amateur and thought with their increased voltage they might be useful in mobile applications.

I am encountering them in solar-powered outdoor lights. I also bought some cells for experimentation, but so-far haven't done anything with them. I cannot find really coherent instructions on charging them or a purchasable recharger that is safe for them.

I went to a local store that specializes in batteries and he has encountered them. In answer to my charging question he could only point me to a manual for a recent LiIon charger which said. DO NOT ATTEMPT TO USE THIS CHARGER WITH LiFePo batteries. THEY WILL EXPLODE.

There are LiFePo batteries for motorcycles and automobiles now (12.6V and very expensive)  which i would expect to be rechargeable via the vehicles electrical system without alteration.

I suppose the quickest way to obtain a charger would be to blow $20.00 or so on a yard light and disassemble it for the charging circuit. I have also thought of putting a tiny bypass device between the battery negative terminal and external leads to which i could connect a multi-meter and determine the charge characteristics.

NOTE: The batteries I purchased at True Value hardware for $9.99 a pair are the same diameter but 1.5 cm shorter than a AA. They are labelled: Yards and Beyond; LiFePO4 14430 3.2V 400 mAh, made in China JIAWEI  Solar; WARNING Batteries must be recycled or disposed of properly. Do not short circuit or dispose of in Fire. Do not swallow. No instructions on charging.

There is another size 14450 that is larger in diameter but about same length as a AA. Slightly higher price. They are rated at 800mAh. I didn't buy any of them.

Any suggestions or further information?


Regards: David
Radioactive_Legos (author)  dawp2 years ago
Yes, please note that this Instructable is about Lithium Polymer batteries (LiPo), not Lithium Iron Phosphate (LiFePo). LiFePo batteries are significantly different, and although some of the information I have shared might carry over to LiFePo, I would NOT recommend using this as a guide. Good luck!
This is for LiPoly, Iron phosphate are a totally different technology. If you want more info about ironphosphate batteries for ham application please contact me, I would be happy to help.

-W8ESE
very nice guide keep up the good work
Thanks!
naeger2 years ago
Thanks for this great instructable!

When looking for lipo cells on ebay I came across single lipo cells "with protective circuit". Unfortunately, it didn't say what this protective circuit does. Can i use these cells like ordinary batteries and the circuit prevents drawing to much current or discharging the cell too much?

Furthermore, I am looking to include lipo cells into my little arduino robots. For ease of use reasons I would like to be able to charge those via USB (or some other standard power supply). Do you know some instruction on how to build a circuit (arduino-based?) to charge a lipo cell itsself without a charger? A kind of simple DIY-charger? I think the whole balancing thing would unnecessary if you use only one single cell (1s1p), wouldn't it? My little toy helicopter can also be charged via the battery powered remote control without some sophisticated charger. I am trying to build something similar. Any ideas where I can find more information? -- Thanks!
Protective circuit will likely be present on all lithium rechargeable packs you can buy whether it is mentioned or not. This is because all packs have to be tested to UN/DOT transportation standards for shipping. Batteries go thru a 50 cycle burn in then are subjected to
T1 – Altitude Simulation
T2 – Thermal Test
T3 – Vibration
T4 – Shock
T5 – External Short Circuit (
T6 – Impact
T7 – Overcharge
T8 – Forced Discharge

in addition to packs having to pass these tests, individual cells typically go thru all except T7 to be able to be shipped to battery assemblers.
Radioactive_Legos (author)  naeger2 years ago
I imagine the "protective circuit" prevents over discharge (ie below 3.0V or something similar). If you want to charge single-cell LiPos with USB, check out this PCB from SparkFun: https://www.sparkfun.com/products/10161?
As for balancing, you're right in that a single cell LiPo doesn't need balancing, as it is already balanced with itself, so to speak. The charger in your RC heli's remote actually does all the necessary things to keep the LiPo safe, but because the LiPo cell in your helicopter is small (a few hundred mAh, I would assume), it's an easier task to charge it properly. One thing to consider if you want to use LiPo with your Arduino is voltage requirements. If you have a 5V Arduino, you'll need at least a 2S LiPo to run its internal regulator. You'd only be able to power it with a 1S LiPo if it was a 3.3V Arduino. Hope this helps!
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