LiPo battery care and basic information

[liveforphysics]

Every LiPo battery I've ever seen has something on the back that says "never exceed 1c charge rate".

I've charged some small helicopter 2Ah 30C packs at 10Amps for lots and lots of cycles, and the batteries still perform fine. That's 5C charging, but again, this is a very low Ri cell, and the charger automatically reduces current if it see's any cell voltages climb about 4.2v. That's the crucial part, otherwise you end up with a LiPo fire.

Now, more importantly, I want to know what charger you have that can put out more than 2-3C on an E-bike sized pack. I have to run my chargers of 2 dedicated circuit breakers because they draw 2,500w. E-bike sized packs, getting the energy we need into our packs faster than about 20-30mins (AKA, 2-3C) is going to require 220v chargers on dedicated breakers to be practical.

 

[ZapPat]

Well that's what I wanted to know, cell Vmax is the limit then.

As for you wondering about why I wanted to know this, Luke, it's because I also read the "charge at 1C" label which sounded like BS, and so wondered what experienced Lipo people have charged their own cells at without problems. 5C charge with a 30C pack gives me an idea. I just didn't want to be doing heavy regen into such a nice battery if it would be destroying it. And don't worry I'll hook up the high voltage cutoff circuit of the BMS to the controller to protect against cell level overcharging past 4.2V if doing regen with Lipos!

 

[CGameProgrammer]

I know very little about electronics, but if I were using lithium-polymer, I would want a circuit applied to each bank of cells that cuts off power if they get too low or too high, designed in a way that more than one circuit could be applied for redundancy. Yeah this'd be a pain to do by hand, I'm sure, but I'd feel better about it than relying on a charger to not do something stupid.

Of course it doesn't address the issue of physical damage, which is highly unlikely in a car but can happen on a bike or motorcycle. But overcharging/discharging is more likely anyway.

 

[mingonn]

Hi guys,

I am running both my bikes on rc lipo packs but would really like an individual cell motiored LVC. I have been thinking about using rc lipo battery meters but they would have to be plugged in and un plugged after each ride if I am not mistaken.

Any one know of an off the shelf LVC with adjustable voltage?

Cheers
Derek

 

[GGoodrum]

Actually, I have two new LVC-only boards, one that is setup for 16 channels, and a second one that uses the same "tear-off" feature used on the full BMS board that allows it to be used with anywhere from 8 to 24 channels. Actually, multiple board sections can be tied together to support pretty much any number of cells/channels. Both boards have the option for on-board active cutoff, or can be used with most controller's brake input, which causes the controller to cut the throttle, whenever any one cell goes below the cutoff.

I did the 16-channel version, mainly to be mounted on the front of my 16s5p a123 packs:

There is a multipin AMP connector on the board that I use to plug in a matching plug connected to 16 3.7V/20A DC-DC convertors. Here's what the schematic looks like:

The 24 channel version is basically the same circuit:

I have the 16 channel version of the boards now, and the 24-channel boards will be here tomorrow. Initially, at least, I will do the same thing I do with the BMS boards, which is to offer the boards only, plus a BOM and a set of illustrated instructions. Eventually, I might offer complete kits, and/or assembled versions. These are much easier to assemble than the BMS, though, as there is basically just 3 parts per channel, plus a few for the active cutoff, if that feature is implemented.

Anyway, to use either of these with LiPo packs, all you need to do is use the 3.0V version of the TC54 chip.

-- Gary

 

[Drunkskunk]

Hi guys,

I am running both my bikes on rc lipo packs but would really like an individual cell motiored LVC. I have been thinking about using rc lipo battery meters but they would have to be plugged in and un plugged after each ride if I am not mistaken.

Any one know of an off the shelf LVC with adjustable voltage?

Cheers
Derek

I lost 2 expensive lipo pack due to the BMS/LVC units failing, each for a different reason. Now I don't run them.
What I have instead is a Cycle Analyst with a LVC setup, plus the voltage always displayed.

its my experiance that if, while riding, one cell goes low, there is nothing you can do about it. even if you catch it before that cell goes below 3.0v, its already dead, or it wouldn't go prematurly low during the ride. Screw it, let it die and keep riding. An LVC on each cell would make the bike inoperable to save a cell that is dead anyway. I prefer to ride home.
the trick to keep this safe is to use a balance charger, so you catch the bad cell when charging. I also use a CellDiagX6 on each pack after each ride, to check the voltage of each cell and note any drift in the balance.

 

[stew007]

I know very little about electronics, but if I were using lithium-polymer, I would want a circuit applied to each bank of cells that cuts off power if they get too low or too high, designed in a way that more than one circuit could be applied for redundancy. Yeah this'd be a pain to do by hand, I'm sure, but I'd feel better about it than relying on a charger to not do something stupid.

Of course it doesn't address the issue of physical damage, which is highly unlikely in a car but can happen on a bike or motorcycle. But overcharging/discharging is more likely anyway.

Use these, You cant really go wrong with them, it takes a few seconds to put them on your packs, I use them now together with the LVC on my cycle analyst, also, if you have the CA, set it to 3.3v per cell, that gives a good safety margin so the weakest cell should not over discharge, unless the said cell is knackered. You are best to charge with a proper balance charger, this keeps your packs accurately balanced after each charge

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWNX:IT&item=290303803710

 

[GCinDC]

Hey folks, Not sure if I should start a new thread, but thought this might be useful for others...

I'm about to start charging my LiPo with a standard SLA charger in my wooden garage... Just kidding! But seriously, I need HELP!

I recently had this 18.5V 10+Ah booster battery pack made for me:

It's 5 groups of 4 cells (each cell being 3.7V) wired in series (i think!).

All taped up, it's got a BMS on the charger port (deans connector), and also Red/Black leads. So, only 4 Wires....

It came with a cheap 21V 2A charger (w/ deans connector).

I was recommended to buy a better (4A) charger/balancer: a 21V power supply unit and this:
http://www.hobbycity.com/hobbycity/...ct_Name=MKS_3in1_Balance/Discharger_System_6S

I REALLY want to buy a charger/balancer ASAP and I can't figure out what's relevant from RC sites/products.

So, here are my questions!

BALANCER
__ In order to use a balancer, do i have to have a mulitpin connector???
__ If so, would i have to unwrap the pack and solder new wires off the tabs?
__ If so, what do I need, and how should I do it!?
__ Or, can the balancer just be connected to the pack's red/black deans connector?
__ I don't need to understand, but how can it possibly sense the V of individual cells...???
__ Does it just sit on red/black wires between PSU and battery charger port?

CHARGER
__ If the MKS 3in1 Balance/Discharger will work, can somebody link to a charger that will work?!
__ Or, what charger specs would work, ie: 21V 4A...? I can't find any such thing...
__ If the total pack is 18.5V, so how could a 12V psu be enough???

PM's welcome!

 

[ev.entually]

i shouldnt have read this thread! i really dont know enough on the subject, but i can do sums well enough to work out that lipo is absolutely the best bang for your buck (as long as the bang doesnt take the roof/walls of your house with it)

if anyone ever markets a ready to go idiot proof pack, count me in. surely with a professionally built charger, and a standalone cycle analyst set appropriately to prevent deep discharge........( i only go max 10 miles each way on my bike, maybe towing my kids in a trailer, and run a 48v 10ah lifepo4)

 

[GCinDC]

Answering my own questions here:

BALANCER
__ In order to use a balancer, do i have to have a mulitpin connector???

Appears so...

__ If so, would i have to unwrap the pack and solder new wires off the tabs?
__ If so, what do I need, and how should I do it!?

I found a nice "lipo pack and balance wiring demo" here: http://scriptasylum.com/rc_speed/_lipo.html


Based on the looks of this pic, I shouldn't need to solder the tabs... I should be able to clip wires, splice & solder in the multipin wire... Any comments??

Suggestions where to get a multipin connector?

 

[GCinDC]

Hmmm, but what about the BMS wiring there...?

 

[stew007]

Based on the looks of this pic, I shouldn't need to solder the tabs... I should be able to clip wires, splice & solder in the multipin wire... Any comments??

Suggestions where to get a multipin connector?

You can get them from the rc shops http://www.rcdude.com/servlet/the-Connectors-&-Cables/Categories

Personally, I use the JST-XH type, they are by far the most common now, and they fit most of the current lipo chargers.

I built my own lipo packs from individual cells, I got the jst xh connectors ready to solder on from ebay, my cells had copper tabs, so they were easy to solder, I think normal alloy tabs need special flux/solder for the job.

ps, Lots of ready wired deans parallel and series leads on that page, perfect for making up a harness for lipos, good for many combinations 8)

http://www.rcdude.com/servlet/the-Connectors-%26-Cables/searchpath/5591/start/61/total/207/Categories

 

[HTB_Terry]

Lithium polymer is safer than LiCo cylinder cells. LiFePO4 is all the rage now but Lipoly cells make really good packs. As mentioned, they are the lightest and highest power density. They are about half the size and weight of a LeFeO4 pack. The lifecycles is going to be less than the LiFePO4, that's the trade off. Most of the problems people have mentioned seem to be from kludging together smaller packs from the RC market. Some people didn't even use a BMS! This is really dumb, for any lithium battery. All lithium packs need a BMS that monitors for low voltage, current discharge, and has a balancing function. All modern ebike packs have this. LiPoly is used by many ebike manufacturers, especially small and light models. Development has continued and improvements have been made. With the proper charger, a professional pack will give reliable service. Don't be scared off by the horror stories. We offer a nice pack enclosed in a hard plastic box, 36V 10AH, 10AH cells. It's available now on our website www.hightekbikes.com/battery.html

 

[recumpence]

I agree, but disagree.

Here is what I mean;

In 5 years of running over 150 lithium polymer packs and many thousands of charges, I have never, EVER had one pack go out of ballance! Not even one! Lipo packs just tend to hold ballance. I also disagree that problems occur when smaller capacity RC packs are used. RC packs are typically the highest quality cells out there (nrmally by a very large margin).

Every single Lipo problem I have ever seen has been related to charging, not the type of cells used and/or ballancing or BMS.

I also disagree that the number of cycles is less than other cell types. For very long Lipo life, I recommend charging only to 98% capacity, keeping 40% capacity in the pack before recharge, keeping the cells over 3.3 volts under load, and keep them in a constant temperature (somewhere between 50 and 100 degrees. Very high and very low temp can shorten Lipo life as well). If they are run very hard repeatdly, yes their life will shorten. However, if you take care of them, you should see 1000 cycles or more out of your Lipo packs.


Matt

 

[HTB_Terry]

Matt, I agree with most of what you said. You have alot of valuable experience and made some good points, mainly that Lipoly makes a good pack. My comment about the RC packs related to the fact that some users do not use a BMS and drained the cells or otherwise operated them out of spec. Or used an improper charger that damaged the cells. The main point being a properly designed pack will not have those problems.

On the BMS, the absolute required part is the low voltage cutoff, and the output current limit with high voltage detection desirable. Detecting high voltage and over current from charging with a cutoff (or limiter) would be desirable. From your experience, this would be even more desirable with the Lipoly. I don't know if the Lipoly cells need balancing or not, but it's always good to have. They will probably need it as they get old.

The spec of 1000 cycles is correct for a well cared for pack, and it sill may retain 80% capacity. LiFePO4 will be at least 1500 cycles, so has a longer lifetime.

Due to it's low weight small size, the Lipoly packs are the best option for certain applications.

 

[recumpence]

I wanted to share a trick about Lipo (this works with other chemistries too).

If you have multiple cells or packs that you want to series together, it may seem proper to charge each cell or pack separately to the same state of charge, then series them. However, that is time consuming. You can simply parrallel them together for a day or so. They will all stabilize at the same charge level. Then the cells or packs can be separated and put in series.

That is far faster and more exact than merely charging each cell separately before completing the pack.

Matt

 

[MitchJi]

Hi,

I have the impression that quite a few people on ES are starting to use Lipo without being aware of the precautions listed in this thread. I think it might be a good idea to change the thread title from:

LiPo battery care and basic information

to something like the following to encourage all potential Lipo users to read the thread:

LIPO WARNING: Follow these four simple rules or Risk BOOM!

Also is cell level or parallel group level LVC important or necessary? If so I think that should be clearly stated and explained, hopefully in one of the first posts of the thread.

Thanks!

Mitch

 

[GGoodrum]

A few comments:

Almost all Lithium-based packs I've dealt with will have the cells stay pretty closely balanced, if the pack is not run down to LVC cutoff. This is why Doc never sees his giant konion packs get out-of-balance, nor Matt with his high C-rated RC packs.

At a minimum, a pack should have an individual cell LVC function, in order to keep the cells from killing themselves. This is especially true, I think, if you have a setup that uses multiple RC packs that are paralleled to get a higher capacity. All it takes is one busted lead off a Deans adapter plug and you could end up with a 5Ah pack when you think you have a 10Ah capacity. Chances are, because of the high C rating of the RC packs, you'd never know your capacity is half what you think it is. When I first started making a123 packs, my first ones were 16s1p "stick" packs that I paralleled together at the pack level in order to get enough capacity. I used a 5-plug Deans adapter "manifold" to parallel all five together:

One day I got distracted ond only ended up connecting two of the packs before taking off on a ride. Needless to say, I didn't get anywhere near as far as I usually did and ended up killing a bunch of cells. It was this experience that sent me on a quest to develop/use the simple, 3 part per channel LVC circuit Bob Mcree designed.


I do not think it is necessary to have over-current protection on a BMS for any pack that uses cells with double-digit C-ratings. The controller and/or a CA current limiter is all that is needed, as you will hit that before you'd reach the pack's "burst" current limit, for 99% of the ebike setups out there. If you have, for example, a 10 Ah pack made up of 10C-rated cells, that's 100A. Also, unlike voltage protection, the current going through a pack goes through all the cells. You can't have a case where each cell is providing a different amount of current, but you can have the case where different cells in series have different voltages. Anyway, that's why current limiting can be done at the pack level, but it only needs to be included in a BMS if cells used could be damaged by the load demanded by the controller. A 2C duct tape pack with a capacity of 20Ah means it shouldn't be loaded with more than 40A, which many ebike setups can do, hence the need for a BMS current limit.

The one area where extra precautions must be taken is with charging any Lithium-Cobalt - based packs/cells, including all the RC-type packs. These cells simply can't be allowed to have the voltage rise above 4.3V, period, or they will go into thermal runaway, resulting in an impressive fireball. The RC chargers solved this problem by integrating cell-level monitoring of voltage during the charge process, and will shut down the charger if it detects any cell going above 4.25V. These chargers also integrate a balancer function as well, but this is only because it is easy to do, once you are monitoring the voltage anyway. What makes me cringe, however, is when people try and charge RC LiPo-based setups with standard SLA CC/CV chargers, or with big DC current limited power supplies. You can do this with LiFePO4 cells/packs, and also with Lithium-Magenese - based cells, like the emolis and konions, because they won't go into thermal runaway and/or blow up if a cell is allowed to overcharge. LiCo-based LiPo packs need to be used with chargers designed to absolutely protect each cell from thermal runaway conditions.

-- Gary

 

[nitecheck]

Hi going to add my 2 cents here..

After unsuccessfully obtaining yet another Ping or other Chinese LIFEPO4 pack for nearly a year - (seems the prices are always on the rise, ppl are always willing to pay more & more (no prob. with that) - but half a K+ for a battery & still getting out bid - this is just ludicrous) I can buy a rebuilt car motor for a little more than these packs are selling for!. Where’s sense in that? Now with exchange rate as it is & with the country being in a recession for months - funny the Govt only acknowledged it today..

I’ve given up on getting LIFEPO4 until realistic prices, quality (higher C rating a become available)

For those who can afford the LIFEPo4's or are simply willing to pay the prices asked ...kudos2u.

So - with the above in mind - I have been testing a 16.8v 10AH booster pack…this pack performs much better than the main LiMn pack. I balance charge the 2xLipo packs with a quality LIPO charger, monitor max drain - never under 3v per cell & have found they run great & without problems.
After quite a bit of trialling, I have come to conclusion that despite all the hype in forums about lipos - if they are quality units to begin with & if charged/discharged within their specs - they are quite a suitable chemistry for a e-bike. IMHO. Yes.. charging is not Plug & Play...you can not have everything..on a budget..…please no flames...."pun intended"

I will be building a 48v 10AH in the near future as my prototype - correctly discharged/charged I do not have concern that pack will meet my needs - without playing the game of buying over priced a LIFEPo4's. Yes I considered the limitations of cycles etc - but at this time - the lipo seems to be a much better option than Lifepo4

Maybe that was 4 cent’s worth…

Feel free to disagree & add danger disclaimers etc...

 

[MitchJi]

Hi,

I think method's recommended solution for an LVC sounds good and I think his advice is worth heeding:

http://endless-sphere.com/forums/viewtopic.php?f=14&t=9229&p=142742#p142742

Best damn 6S lithium monitor on the planet for $15

Here they are:
http://cgi.ebay.com/Chargery-BM6-2S...5|66:2|65:12|39:1|240:1318|301:0|293:1|294:50

http://www.chargery.com/cellMonitor.asp

Works for both Lipo and Lifepo4
$15
Reads 6S lipo via 0.100 spacing (perfect for JST-XH balancer plugs)
5mV accuracy - most balancers quit at 20mV
Shows you 8 things in sequence:

Total Pack Voltage
Largest Imbalance
Cell voltages for 1 to 6 (or however many you hook up)

The monitor beeps if you go under 3.0V or over 4.22V
EDIT: I forgot, you can set the LVC to any desired voltage.

Absolutely dead on voltage.
AWESOME product. Works perfectly every time.
I have been running 4 of them for several months on my big Lipo packs and they have saved my ass!

Let me say this... Anyone who goes to "Full Pack LVC" on a lipo pack is retarded to some degree. . . If the total pack has reached LVC then it is absolutely certain that at least a few of the cells are way under 3.0V.

LVC must always be handled on a cell level basis like is done with the 24 channel BMS.

If you plug these into your lipo packs then you will hear a loud BEEP BEEP BEEP any time one of your cells drops below LVC. I think you will be surprised about what happens under load :wink:

Anyone who is a nOOb getting into Lipo MUST own one of these.

Will save your butt while charging, discharging, and comes in damn handy for checking out cells.

The beeper output can drive an optocoupler that can be used to TAP TAP TAP your ebrake when you hit LVC
Does not cut you off, just gives you a warning.

In closing, please do not waste your money on these "Hobby City Lipo Monitors" as many of them suck wind. Of the many I have tried out all of them were off by at least 50mV cell to cell. Many being off by as much as 200mV.

Look through the Chargery site. Everything that guy makes rocks.

P.S. Using two BM6's for a 12S pack works well. The only thing you lose is the ability to see the Max Delta. The alarm feature still works exactly the same.

 

[mud2005]

I’ve given up on getting LIFEPO4 until realistic prices, quality (higher C rating a become available)

For those who can afford the LIFEPo4's or are simply willing to pay the prices asked ...kudos2u.

I'm a bit confused by the mention of price as a deterrent for buying lifepo4 over lipoly :?

for my bike I can get a 24volt 20ah ping pack with bms and charger for $200

if i get some zippy lipos from hobby city a 22volt 20ah pack would be >$300 , no bms and $250 more for a good charger.

on top of that I can get over 1000 cycles from a ping compared to 200-500? (I'm guessing) for lipos?

so yeah your argument about cost is quite confusing. I own a ping and wish I could afford lipos.

 

[nitecheck]

so yeah your argument about cost is quite confusing. I own a ping and wish I could afford lipos.

Hi ya Mud.. exchange rate may be at play here....& don't think for a minute that I would not luv a P&P Ping...but alas $ per value - or bang for buck (it's just way to easy ...but go ahead if u wish... :wink: )

...lipos seem a better alternative for "me".
nb: they must be discharged/charged within spec....
Why? If a unit starts to go bad - I can simply discard it - add another & keep wheeling...no "duct tape surgery" involved..No sad story that XYZ BATTERY PACK or BMS IS KAPUT...etc

True - no BMS but since I will monitor the discharge of the batteries & charge each battery manually - should not be an issue - though don't get me wrong I would love Plug&Play charge option & not have to be so mindful of discharge rates...but helps that I have a few quality chargers already...but charging will be much longer than a P& P pack.

So as to costs .... Remember these little fellows $$$...It's not what u want that is important - but what u are willing to pay.

i.e.: a perception of value. Value is not just $ - but a measurement of other factors - such as lower costs up front, higher C, adaptability - versus - lower total recharges, no BMS, lower C, higher weight per w/h capacity etc - ....somewhere we settle on a compromise depending on our individual requirements.

I will need 6x 5AH 16.8 lipos @ $47.15 a piece = $283.00 AUD
I already have 2 batteries - so cost comes down to $189.00 AUD
I have plenty of spare connectors & wire - so no real cost to wire up.

Since the batteries are rated at 15c - which are probably 7-8c in the real world E-Bike terms - they will out perform a 2c - 3c variant.
As I plan to run parallel (2x5AH's) to make a unit - then 3 units in series - the current will be shared across 2 batteries - thus be much kinder to each battery than running 10AH is batteries in series & cheaper...down side - 3x10AH batteries would only need 3 chargers.

Pack spec should be: no BMS, fiddly to charge (longer charge times - due to fewer chargers than batteries) min 7C 10AH 50v 7c pack - weight 2.9kg
or 8 packs as above - 67v 10AH 7c pack - weight 3.9kg ($376.00 AUD - If needed 8 batteries) - $282 as I do not ...but I would guess 67v would be too much for my controller - so better off not being so ambitious - plus I do not really want a bike that can go faster at a "twist of the wrist" than I cycle on non-E-bike...after all - "to me" -the E= assistance. Not, no pedalling required. I already have a motorbike - so am not looking at making an “electric” scooter out of my bicycle.

 

[GGoodrum]

One slight mistake in your figuring, I think, is that LiPo cells may get charged to 4.2V per cell, but their nominal voltage is 3.7V, so a 4s pack will have a voltage of 14.8V, not 16.8V as you have indicated. Three of these packs in series will be 44.4V, and four in series will be 59.2V.

-- Gary

 

[nitecheck]

One slight mistake in your figuring, I think, is that LiPo cells may get charged to 4.2V per cell, but their nominal voltage is 3.7V, so a 4s pack will have a voltage of 14.8V, not 16.8V as you have indicated. Three of these packs in series will be 44.4V, and four in series will be 59.2V.

-- Gary

Hi Gary - very true. My goal is to make pack with higher volts, good C rating, light & small - 10AH. The nominal voltage of the lipos's I'm currently using is 14.8v & they charge to 16.8v - however after a 30km ride they consistently measure between 15.3v-15.5v. I have stressed tested the lipos to around 3.22v per cell & they perform well even when getting close to depletion. Since the volts are "really" there I used 16.8v as a base line for a safety margin on the controller :wink: My current controller is very happy with
56.8v (40v main pack & 16.8v booster - measured at max readings for both batteries as above).

Howeber If I could add another unit & get a "safe" "nominal" 59.2V that would be great - I can always swap out my current controller to my spare - that has the same Amp rating but is beefer - being able to handle more volts. Am I wrong in thinking that the controller "sees" & therefore must be able to handle the peak voltage of a battery rather than the nominal volts?
Tx

 

[GGoodrum]

A typical sensored ebike controller is typically rated using SLA nominal voltages (2.0V per SLA cell...), but needs to be able to handle the Pack voltage fresh off the charger (2.45V per cell...), so if you have a 36V controller, it will be able to handle a voltage of 18 x 2.45V, or 44.1V. Similarly, a controller rated for 48V will be good up to at least 58.8V (24 x 2.45V...). I think most controllers add a bit of margin to this, so a 36V controller can probably handle a max voltage around 50V, and for the 48V controller, maybe 60V. That os no gaurantee, howver. Anyway, all you need to do is make sure your off-the-charger LiPo pack voltage is at, or less than max SLA voltage, right off the charger, and you should be fine.

-- Gary