LiPo battery care and basic information

Batteries, Chargers, and Battery Management Systems.

LiPo battery care and basic information

Postby recumpence » Sun Mar 15, 2009 3:25 pm

I am starting this thread in response to many emails I have recieved, asking about LiPo batteries and their applicability to E-bike use.

To that end, I am starting this thread for information related to the use of LiPo (Lithium Polymer) battery packs, (not to be mistaken as LifePo4, Lithium Ion, and other Lithium based chemistries).

Now, let me begin by staying I am not an electronic engineer (or any sort of engineer, for that matter). However, I have been involved in RC for many years, both as a user and a manufacturer. As such, I have a large amount of accumulated knowledge and experience using LiPo packs in RC cars, helis, planes, motorcycles, etc, as well as E-bikes. So, I will share my experience here.

There are many pros and cons to each Lithium chemistry on the market. LiPo is no different in that respect.

I will start with the cons;

The primary [negative] issue with LiPo is safety. There are far more reported problems related to safety in the use of LiPo than any other chemistry (with the possible exception of very early Li-Ion cells). Their safety problems are mainly related to over charging and sometimes related to overdischarging. ----------- If LiPo cells are charged to more than their rated capacity (normally 4.2 volts or so), they can, and often do, explode in quite a spectacular fireball! Now, being that is such an extreme outcome of misuse, most people stay away from LiPo. I must say, I completely understand! I have had one small LiPo pack explode in my house. That happened when a low quality charger locked on the wrong cell count and overcharged the pack. They are dangerous! However, proper care is quite simple, and that proper care is all that is needed for a long, trouble free life of your LiPo pack (more on that later).

The other negative is related to the first and that is charging. For safety reasons, a very high quality charger is needed to properly charge a LiPo pack. This is frustrating because it adds cost to an already expensive chemistry. I will explain more on charging later.


The positives;

#1 Extremely high power density. I have one LiPo pack in my recumbent that is 48 volt, 10ah pack. That pack weighs in at 5 pounds with all wiring and connectors! That is crazy compact and light weight!

#2 Light weight and small size. That pack I just mentioned measures 7 inches long, 6 inches wide and 2 and 1/2 inches thick. With that tiny pack I can go 25 miles at 18 to 20mph or 12 miles at 40mph!

#3 Very high discharge rate. Even relatively basic LiPo cells can run 10C continuous. Most higher quality packs can sustain 25 to 30C. There even extremely high end packs that are 60C! These are true discharge capabilities, not overestimates. I have run packs at well over 50C before and, yes, they handle it!

#4 Price. Now, LiPo cells are not the cheapest cells, but, for the technology you get, they are quite resonably priced. I paid $435 for that 48 volt, 10ah pack (of course, I also need a $250 charger to charge that pack properly). So, price is also relative.

#5 Cell ballance. I have had hundreds of LiPo packs. I have abused them and treated them nicely. I have over charged them, over discharged them, and just plain worn out a few and I have never, EVER had one go out of ballance! I have a cell ballancer. But, every pack I have ever hooked it to, has always been ballanced within spec (I think 2%) of each other. So, active cell ballancing is completely uneccessary. It is best to just check them with a ballancer occasionally to assure proper ballance.



Now, considering the charging issue (overcharging resulting in possible catastrophic failure), I will walk you through specifics of cell care, both charging and discharging;

Discharging;

When running a LiPo pack, the first rule is NEVER discharge the pack beyond 80% of its capacity (20% remaining). So, on my 10ah pack, I always keep at least 2ah of power left in the pack. This is extremely important. If you do not keep at least 20% capacity in the pack, the cells will have a VERY short life!

Second, never pull more C out of the pack than it is rated for. If you have a 15C pack, do NOT exceed 15C! That rule, combined with the 20% rule stated above, are critical to a long life for your pack. Also, those rules are interrelated and relative. What I mean by that is, the less C you pull from the pack and the more capacity you leave in the pack before each recharge, the longer the pack will last. I have one pack in an RC transmiter that is always recharged with 40% of the capacity left and I never pull more than 1C out of that 10C pack. That particular pack is over 5 years old and runs like new! However, if I pull the rated C out of a pack and discharge it down to 20% capacity, it will need replacement in roughly 500 to 1000 recharge cycles depending on the pack and how careful I am with it.



Charging;

The primary concern with LiPo charging is to keep the voltage constant while varying the current. So, a "Constant voltage, current tapering" charger is required for safe recharging. I personally like Hyperion chargers. However, there are many good chargers out there. Again, as long as the pack is not over-volted, it will normally charge perfectly without any issues at all.




In closing, I want to stress, in general, unless you are already experienced with LiPo, I would say to run A123 cells instead. They are safer, still very powerful, and not so fussy.

That being said, for those looking for the lightest pack and are willing to pay for a good charger and learn what they need to learn for safety, LiPo is a good viable option.

Matt
Last edited by recumpence on Mon Mar 16, 2009 8:45 pm, edited 1 time in total.
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Re: LiPo battery care and basic information

Postby GGoodrum » Sun Mar 15, 2009 5:44 pm

Great thread, Matt. I've thought about doing the same thing, as I too get lots of PMs and emails about using RC LiPo packs in ebike applications. I think we need to get the powers that be here make this a "sticky". :)

I just posted this in another thread, but I think it is worth repeating here:

What concerns me the most with using RC LiPo packs in an ebike or other EV application, is not discharging, although I agree that it is quite possible to have cells go into thermal runaway, and not stop burning until there's nothing left that is even remotely flammable, but shortcuts made in charging. About 75% of the LiPo fires I'm aware of, including those of three friends of mine who had their garages burn down, were caused by malfunctioning chargers. Almost all of the newer LiPo/RC chargers in use today, however, have safety features that monitor each cell, during charging, to make sure not one goes over 4.25V, period. Above about 4.35V, or so, the fireworks begin. :shock: One issue with all these very safe RC chargers is they are designed to be used at the flying field and so they use 12VDC on the inputs. To use them at home means you need an "extra" AC/DC 12V supply. Most of these also are limited to 6, 10 or 12 cells, so if you have a larger pack configuration, it becomes complicated.

What some have done instead, which worries the heck out of me, is to simply use big bulk chargers, and charge the whole pack. This is absolutely a recipe for disaster, in my opinion, becuase there is not only no balancing going on, more importantly, there's no cell level monitoring that will absolutely shut off the charger if any one cell goes over 4.25V. Even using a modified version of our BMS board is not really the answer, because if the charger control section is not "throttling" properly, the shunt circuits can get swamped, and th voltage will rise. If people are going to heed Luke's advice, and decide to go down the path of using cheap LiPo packs, my hope is that they will also figure out a way to also use the dedicated LiPo chargers, with the built-in safety interlocks. These chargers are the reason why you don't hear much these days about LiPo fires. It has nothing to do with advances in the cells. They are as volitile now as they've ever been, maybe more so. It is the advancements in how they get charged that has caused the reduction in fires, etc.

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Re: LiPo battery care and basic information

Postby recumpence » Sun Mar 15, 2009 6:48 pm

I agree.

I have been puting off writing this thread because of possible battery battle arguements. Everyone has their preferred chemistry. But, I finally realized that LiPo is the most dangerous chemistry and is the one chemistry not really addressed here (in a dedicated thread, anyway).

I know there is much more that can be said about LiPo and I am sure we will add to this thread as time goes on. But, for now, this is a good start.

Anyway, I love my LiPos! But, I am an expert in their use (or at least extremely experienced). So, I am confortable with them. That being said, for those who want the ultimate, this is the way to go. Just, be warned, you need to become thoroughly familiar with LiPo before you get them and make sure you threat them REALLY nice! :mrgreen:

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Re: LiPo battery care and basic information

Postby liveforphysics » Tue Mar 17, 2009 3:09 pm

You don't need to treat them nice during discharge or charge, as long as you follow the golden rule. You can abuse them harder than anything else out there, short of perhaps A123s.

***Golden Rule of LiPo*** If you break this rule, you are pulling the pin on the grenade.

Absolutely NEVER Exceed 4.3v/cell, never Discharge below 2.7v/cell, never puncture the cells.

With other cells, they often give warnings similar to that, and you can break the rules as much as you want, and suffer nothing, or maybe a little drop in cell capacity. LiPo is NOT like other batteries in this regard, when you break the golden rule, often even just one time, you are effectively telling the battery to fail into a ball of fire.


If you wish to use LiPo, you MUST follow that rule. No exceptions here. No room for error. No Oops, my charger reset, no excuses.

The most simple way to follow that rule is to use the wide range of awesome microprocessor controlled chargers made for LiPo batteries. They will never let the first part of the rule be broken.

For the second part of the rule, you need to watch your pack voltage while riding, or setup a LVC if you are the forgetful type. If you do ever deep discharge a cell, you are in no immediate danger. As long as the cell doesn't reverse polarity it wont explode just from excessive discharge. However, when you go to re-charge that cell, this is when you will see the fireworks. If you want to attempt to re-charge a deep discharged cell, do it in an area that you wouldn't mind making a bonfire. Maybe invite buddies over to watch. You can always stab it to make it go off if it doesn't go by itself. A deep discharged cell should never be trusted again in a string with good cells.

The cells need to be mounted in a place where they won't be poked by anything. If they get stabbed, they often just burst into flames. If you don't protect them, you are risking a fireball when you wreck. Other unprotected batteries generally just get damaged by a wreck, LiPo may burn your bike to the ground in a wreck.





If you follow these rules, you will enjoy LiPo as the highest energy density and highest power density battery you can buy. It's also been having prices rapidly fall, and now you can find quality LiPo for around the$ 0.50-0.55/wh mark.

Electrically, these batteries are incredible and extremely robust. It's basically impossible to discharge the cells to hard, as long as they are quality cells with Ri <10mOhm. When the internal resistance is that low, the cells just can't seem to get any warmth in them even under extreme loading, like 50c+ for burst of acceleration. Cells with higher internal resistance need to have the C rating obeyed, as they do get warm, and the voltage drops on them under load as well.

They have a unique safety factor built into them. In properly designed packs, the cells are the failure points if the battery is shorted. I've done it by mistake a few times, even very serious shorting, like 8awg wire plopping onto another piece of 8awg wire. The cell tabs have always acted like a fuse and vaporized in an instant to protect, just like a fuse would. I've never had cell damaged from this, but it does require re-soldering the vaporized area of the tab, which requires special solder for aluminum.

For a high performance application, or for ultimate range, or for keeping a bike as light an stealth as possible, no other battery can compare with LiPo. However, if you aren't prepared or capable of following the golden rule of LiPo, you need to choose different battery chemistry.
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Re: LiPo battery care and basic information

Postby swbluto » Tue Mar 17, 2009 4:00 pm

I think Liveforphysics basically won this thread. He actually outlined definite operating parameters and tolerances, which is one of the key things to know about LiPo.
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Re: LiPo battery care and basic information

Postby recumpence » Tue Mar 17, 2009 4:17 pm

swbluto wrote:I think Liveforphysics basically won this thread. He actually outlined definite operating parameters and tolerances, which is one of the key things to know about LiPo.


Ahh, good point. My post had no definative information what-so-ever. :?

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Re: LiPo battery care and basic information

Postby swbluto » Tue Mar 17, 2009 4:32 pm

I apologize if I implied superiority and subsequent inferiority and in the process created animosity.

Your post is very informative and "lays out the land of LiPo" in showing its applications, potential and so on. I'm just the type that has absolutely no experience with LiPo and am very scared of accidentally burning down an apartment complex and/or blowing myself up and having well-defined operating limits kind of assured my fears(I also like numbers - I'm a pseudo math major). So, I had gained quite a bit from liveforphysic's post although I suspect I won't be jumping onto LiPo any time too soon given how strict the boundaries are as I know how easy it is to make a silly mistake.

Many people who have had little experience and great interest in high performance batteries would also gain quite a bit of your post, but my applications are more pedestrian compared to the drag racers among us.
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Re: LiPo battery care and basic information

Postby recumpence » Tue Mar 17, 2009 5:00 pm

I am kidding around. :wink:

As I mentioned, I am not an engineer. I was hoping others with more technical knowledge would jump in.

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Re: LiPo battery care and basic information

Postby steveo » Wed Mar 18, 2009 12:40 am

Hey everyone,

thanks for starting this tread with some valuable info on lipo batteries..

I'm presently doing battery testing on lipo's atm! these 4p packs consist of 4 individual cells rated at 2c & 2500mah with my guess.. I don't have absoulotly no battery specs on these... all i know is they came out of many china made bikes that were recall as per the bike frames where braking right where the lipo batteries where kept within the bike frame .. the cells are all new .. some sat with resonable voltages for over a year at 3.7v .. some lower around 3-2v

Image
Image

I just wanted to ask, I know it was metioned earlier .. but i've found that lipos that i got that were really low in voltage tend to have higer capasity then those that were stored at a higher charge, the mah readings and resistance readings i've had are perfectly sound. Do you still think the cells are bad to use?...

-steveo
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Re: LiPo battery care and basic information

Postby MitchJi » Wed Mar 18, 2009 2:19 am

Hi,

I think more information on the safety issues involved in building packs and safe enclosures (Lipo Sacks?) would be useful.
Best Wishes!

Mitch


The best quality batteries and lowest priced batteries for DIY EV's are tier 1 OEM Quality Cells from salvaged (wrecked) EV packs. Two examples are Chevy Volt and Nissan Leaf packs.

Nissan Leaf Module specs are here
Chevy Volt Pack Info - Salvage 16kwh Packs Under $2k here
The cells are rated conservatively by GM at 7.8C, Yabert's tests of Volt packs on the DiyEv car forum suggest a higher C rate, 15+ C!.

$1,400 plus $360 freight. Still over $1k less than new lead!
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Re: LiPo battery care and basic information

Postby liveforphysics » Thu Mar 19, 2009 3:21 am

The charger is such a crucial part of the saftey of using LiPo batteries. I made an elaborate post about charger options, and I'm going to include it in this thread.


I have 4 of these:

http://www.hobbycity.com/hobbycity/stor ... oduct=6609

I have a fluke 189 meter, and this charger drops them off at EXACTLY the voltage I set it to charge each cell. Works fantastic, never had a problem with any of them. You do need a 30amp supply for each charger to run it at full potential. If you don't have a 30amp supply, it runs fine off even a little 5amp supply, but you obviously have to lower the charging current settings. It does 1-10s cells, and as long as you run each one from it's own 12v source, you can easily run a pair of them for charging an 11-20s pack. They never get above luke warm during charging, and they are very quick, painless, user friendly, plug-it-in-and-walk-away. If they detect any errors or funny stuff, they will shut down the charging.

And one of these:

http://www.aero-nuts.com/product_info.p ... cts_id=570


This charger is elaborate in every way except the stupid little spining clicking wheel. You use that wheel for most everything, and it's tedious to setup things, but it does save 10 battery pre-sets, so you just select the one you want and plug in the battery once you have it all programmed. It will do fancy pants graphs of each indivdual cell voltage as it charges, much like a CBA, and it lets you discharge packs as well. If you have computer skills you can use it's data output port to connect it to a computer and make neat graphs of charging/discharging performance. It also has a temp sensor to shut down charging if a pack gets above the temp you set. It will do 12s cells, and if they detect anything funny during charging, they shut down the charging cycle. It has a disadvantage. It only balances at 80mA, so if you get a pack way out of balance, it may not be able to get things corrected in a timely mannor. However, the balancer does also have a mode to function as a standalone balancer, and it's very accurate, just slow for E-bike sized packs.

I also have one of these that I use for my very small helicopters.

http://www.hobbycity.com/hobbycity/stor ... /_Balancer

It charges only directly through the balance taps, and treats each cell like it's a seperate battery. Because of this, you can't get a pack out of balance enough to bother this thing. It takes anything you throw at it. You could build a pack with a 1ah cell and a 50ah cell and a few full cells and a few drained cells all tied in series together, and this charger will top them all off at 4.25v/cell no matter what. No settings, no fooling around, no possible way to make an error with anything, you just plug in the balance taps and hit the power switch and wait for the cell LEDs to all turn green. It's not fast, it only does 5 cells at a time, but it has it's place.


For running these chargers, you need a 12-16v supply.

For running just a single 250w charger:
http://cgi.ebay.com/250W-13-8V-18A-Swit ... m153.l1262

For running a single big charger:
http://cgi.ebay.com/350W-12V-29A-Switch ... m153.l1262

If you are looking to power 700w of chargers, this little pair would run in series to give you that:
http://cgi.ebay.com/2-Pcs-350W-7V-Switc ... m153.l1262

If you are looking for a monster 1000w 12v power supply, they are available here.
http://cgi.ebay.com/1000W-12V-83A-Switc ... m153.l1262
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Re: LiPo battery care and basic information

Postby liveforphysics » Thu Mar 19, 2009 3:28 am

As far as charging saftey goes, guys claim that you can set a big pack in a LiPo sack, set it on your carpet and over-volt the pack until it blows, and it just leaves a smoke stain on the carpet.

I personally have no experience with LiPo sacks other than holding them. They appear to be a layer of nomex with a layer of fiberglass, and another layer of nomex sewn together. It would be pretty easy to make your own custom enclousure for a pack.


I have this big stainless steel baking pan that I have sitting on a couple bricks. I have a sheet of 1/4" scrap steel that I set over the top of it with a 1/2-1" gap on the edge for the charger wires to poke through. It's never been needed, because I follow the golden rule of LiPo, but I'm pretty confident if a pack were to burst, it would not cause any damage outside of smoke stains.
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Re: LiPo battery care and basic information

Postby dogman dan » Thu Mar 19, 2009 6:08 am

Nice post guys, I knew lipo had issues with charging, and now I know why. I'd be pretty worried if I had lipoly charging in my house every night but there are places to do it safely. How about just tucking it into the oven, off of course, so if it pops, it's in a metal box with an exhaust hood over it?

With my long ride home every day, I have had thoughts about adding a small lipoly, emergency pack to my bike. Something about 3-4 pounds, and just enough capacity to limp home at 10 mph. But more likely is I'll just buy a 48v ping and then have a bigger capacity to begin with.
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Re: LiPo battery care and basic information

Postby liveforphysics » Thu Mar 19, 2009 7:19 am

If you put a LiPo pack in the oven and over-voltaged it to blow it up, it would be fine. Oven would be a great place to charge, good idea.

You mentioned a Ping pack. For energy storage, it's fine. About twice the weight and bulk of LiPo for the same energy storage, but still fine. Now, lets talk about POWER differences. This is what LiPo is all about.

Let's choose Ping's biggest battery, the 48v 20Ah. This is a 2c battery, which tells us that this pack can discharge at 40amps. This battery weighs 20lbs, and can discharge at 1920w.

How much weight in LiPo do you need to match that?
Not picking anything fancy, just economical 30c zippy LiPo packs from hobby city, we can work out what it takes to equal the power of the biggest Ping pack in LiPo. What does it take? It just takes a single tiny 4cell 5Ah zippy pack, and it can all ready sustain 2200w VS the Ping battery 1920w, but the big difference is weight. The LiPo battery is just 1.2lbs vs the 20lbs of Ping battery! Yup, that's about 17 times the power density. It's also about the size of a regular non-flip-type cell phone, VS the size of a couple stacked shoeboxes. If you are looking for energy storage, lead-acid, LiFePO4, NiMH all offer energy storage at low prices if you don't mind a lot of weight and bulk. However, if you are looking for performance and power with a reasonable cost, nothing matches LiPo.

Just incase anyone wanted more specs on the battery I choose to compare power to the biggest Ping pack, here is a link. It's not anything special, just the upper model of zippy LiPo.



http://www.hobbycity.com/hobbycity/stor ... _4S1P_30C_
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Giving my time to the electric revolution is done with pleasure. It is no longer fashionable to spit carcinogenic combustion by products in peoples faces as a part of sating daily transport.

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Re: LiPo battery care and basic information

Postby recumpence » Thu Mar 19, 2009 7:22 am

Very good stuff!

I could not agree more.

Lipo is fantastic, but you need to understand what you are doing before you go off and jump head-first into them.

Luke, thanks for the detailed info.

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Re: LiPo battery care and basic information

Postby Dave-s » Thu Mar 19, 2009 11:27 am

After seeing pictures of LiPo fires on the web, I intend on buying one of those sacks on Ebay for $12, and then sewing it to perfectly fit my pack.
But I read on the RC forums that the guys there either charge their packs in a clay pot, or in a metal ammunition box.
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Re: LiPo battery care and basic information

Postby stew007 » Sun Mar 22, 2009 5:20 am

I use lipos, but I have lot of experience with them, and I would say that if any of you do fancy trying them, always keep safety in mind. It really is best to charge them in a place where, in the unlikely event they do vent, it wont damage your property. I have an outdoor garden weatherproof charging station that I use, made from scrap aluminium sheets, so I have 100% peace of mind, it took me around an hour to build, it looks a bit like a bird box :D

You must use a safe charging method!! I cannot emphasize how important this is. The best way is to spend a bit on a good quality branded Lipo balance charger. Never use a charger that does not monitor each cell during the charging process, your batteries MUST have balancing taps fitted, the most popular type now is JST-XH type. Chargers are coming out now with dual outputs, Hyperion do the EOS 0610i DUO which can charge up to 12s (2 x 6s packs) at a time at 380 watts, Graupner also do a duo now that can do up to 14s. All these chargers run from 12-24v power sources, you can get high powered ones cheap now on ebay direct from Hongkong. Another bonus with lipos is that you can charge identical packs in parallel (so long as they are in a similar state of charge, and in a good state of balance) by the use of a parallel balance charging harness, so from a duo charger one can charge 2/4/6/8 packs at once if required.

I also think that for ebike use, each pack needs to be fused, my ebike uses up to around 35a at stall, so I have 30a 24v fuse on each 6s pack before the deans connector.

I would strongly advise to use a LVC, the best I have found for this purpose is the fully adjustable one built in to the cycle analyst which limits your ESC, I say set it to around 3.3v per cell, that gives plenty of margin, and keeps your packs from deteriorating, also you can monitor your packs voltage on the readout, and keep in mind your min total voltage just to keep on the safe side.

Also they must be mounted to they are protected from knocks/sharp edges, I have mine mounted in a felt lined ply box mounted inside my frame, so in the event of a crash they should be safe enough.

They have their place amongst us enthusiasts, esp if you want really light weight, stealthy, high power to weight bike, but they are not for everyone ;)
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Re: LiPo battery care and basic information

Postby kZs0lt » Thu Mar 26, 2009 11:46 am

It was mentioned earlier that discharging to only 80% of full capacity improves significantly cycle life.
I've read a while back that charging them to less than full voltage let's say 4.1v instead of 4.2v as usual for lipos does again improve dramatically cycle life. You get around 30% less capacity if I remember correct, but lot more cycles.
Does anyone know how much more cycles, does it worth getting higher Ah rated batts and charging them to only 4.1v?
However cycle life is not the best measure because if you get less Ah per cycle and more cycles, it's almost the same thing.
But an estimate on total Ah(Wh) charged into and discharged from a battery would be a better estimate on what a battery can serve for on the long run, given a specific care.

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Re: LiPo battery care and basic information

Postby drunkencat129 » Fri Mar 27, 2009 2:45 am

lol u guys wory to much just take a tub or minaral oil throw thoes bad boys in and call it a day me and steveo already tryed thiss it helps a lot we forces the cells to catch fire and thay just bubbled in the oil and made black oily crud lmao and nice under oil red glow lmao lol worked well we got vids here look lol same cells in the pic to http://www.youtube.com/watch?v=H-u4wl6yfno&feature=related
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Re: LiPo battery care and basic information

Postby liveforphysics » Fri Mar 27, 2009 7:29 am

kZsOlt- Discharging to 80% does help the packs a lot. I don't have any info for the percentage of cycle life it increases by, but it's signifigant. I saw some pretty amazing figures on the 4.1v vs 4.2v full charge effect on life cycle. Something like 10 times the number of cycles before the battery reaches 90% capacity. A very big increase in cell life. The test was done for the same chemistry, but in 18650 cells using liquid for electrolite rather than polymer. I do not know if it effects polymer batteries to the same extent. I think DoctorBass has the white paper with the testing that showed the 10x increase in lifespan from using a 4.1v cut-off. It has caused me to set my cut-off voltage to 4.1v rather than 4.2-4.25v.

Drunkencat129- I have $2,000 into my battery pack. The idea is to prevent un-needed damage to the cells, and to treat them in a way to avoid explosions. I also would not use my pack if it were covered in mineral oil. I tested Argon gas submersion for LiPo protection, and it also couldn't create any flame when I over-voltaged the cell to cause it to fail. No mess with Argon gas, and it's cheaper than mineral oil. But again, the idea is to charge in a safe place, but to put emphasis on correctly charging the pack so you don't cause a failure. Just about every LiPo problem in a modern pack is from improper chargeing. They used to fail from ESC's failing and shorting the packs, but with properly designed tabs on high C cells, this is no longer a problem, as the tab acts as a fuseable link in a short.


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Re: LiPo battery care and basic information

Postby ZapPat » Fri Mar 27, 2009 9:22 am

There's one issue that I have not seen mentioned yet in this thread: Lipo charging rates.

The zippy 15C packs I have here state using 1C max charging rate. I know they can take more than this, but wonder why they say only 1C? Liability issues maybe? If charging with a good CC/CV charger with cell level cutoff at 4.1/4.2V, is cell life much reduced by charging faster like at 4C rates or maybe a bit more in small bursts?

This is specially important since I'll be using regen with the Lipos eventually, and would like to know at what max regen current to set my controller at.
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Re: LiPo battery care and basic information

Postby recumpence » Fri Mar 27, 2009 10:14 am

Luke eluded to charging rates.

Basically, you need to make sure not to overvolt the cells. Some cells can take 4C charging, some caonnot. You just need to monitor the input voltage. Also, yes, high charging rates are hard on the cells. How hard, I don't know. One thing I always monitor also is cell temperature. If my cells are getting warm, I know to back off on charge/discharge rate.

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Re: LiPo battery care and basic information

Postby ZapPat » Fri Mar 27, 2009 11:27 am

recumpence wrote:Luke eluded to charging rates.

Basically, you need to make sure not to overvolt the cells. Some cells can take 4C charging, some caonnot. You just need to monitor the input voltage. Also, yes, high charging rates are hard on the cells. How hard, I don't know. One thing I always monitor also is cell temperature. If my cells are getting warm, I know to back off on charge/discharge rate.

Matt

Thanks Matt... I re-read Luke's charging posts and still did not notice where he talks specifically about charge rates and their effects on battery life, only charge voltages which I understand fully must be controlled at a cell level.

Why would Lipo's be more limited during charging when compared to other Lithiums? Most other lithiums can take maybe about half the charge rate compared to their discharge rate without problems (always checking for max cell volts of course). Of course if they are anywhere near full charge I would not even think of pumping the max charge current into them, but I'm talking more like a battery with 25-75% SOC, which should be able to goble it's full charge current without heating much.
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Re: LiPo battery care and basic information

Postby swbluto » Fri Mar 27, 2009 11:56 am

I thought when he said eluded, he meant that a higher charging current requires a higher voltage and this increases the risk of over-charging. It takes a little "jump" to see that link, I'll admit, and it's suspicious if Luke even intended that association.
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Re: LiPo battery care and basic information

Postby recumpence » Fri Mar 27, 2009 12:22 pm

From Luke's first post on page one of this thread;

liveforphysics wrote:
Absolutely NEVER Exceed 4.3v/cell...........



This is not only for absolute charge state, but input voltage into the cells during charging. Some cells can be pushed harder during charging, while others (if pushed) will allow the voltage to increase beyond that magic 4.3 volts per cell during the charge cycle causing catastrophic failure............

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