Battery F.A.Q - Compilation of good stuff !

[Ypedal]

Updated march 27, 2013

SAFETEY WARNINGS....

word of caution on batteries, ALL batteries.. treat them like gasoline or any volatile materials we encounter daily.

Some batteries are more dangerous than others, but all batteries have the potential to release their energy in an accident.. do your homework and take anything you read below or from the forum in general with a grain of salt, just because someone has their opinion does not mean they know what they are talking about.

It is YOUR responsibility to read, learn, and proceed in the safest way possible, when in doubt, stop, and ask questions until you firmly understand...


Building cylindrical battery pack for Dummy!
http://www.endless-sphere.com/forums/vi ... 12&start=0

Lipo noob thread links.
http://www.endless-sphere.com/forums/vi ... 14&t=19956

LiPo battery care and basic information
http://www.endless-sphere.com/forums/vi ... 70&start=0

The care and feeding of a123-based packs
http://www.endless-sphere.com/forums/vi ... 98&start=0

Lithium Battery Reports & Tests' 9/08
http://www.endless-sphere.com/forums/vi ... 86&start=0


Prius Batteries - How to make them work
http://www.endless-sphere.com/forums/vi ... 26&start=0

[Ypedal]

This guids is being written and saved as i go, so bear with me...
Batteries !!..

alkaline.JPG (34.07 KiB) Viewed 20378 times

We are all familiar with the old trusty Duracell and Energizer batteries, these are called " Primary Batteries " and are one time use.. however.. for ebikes we need re-chargable batteries ! obviously .. These are called Secondary batteries..

There are many options and when first starting out it can be quite daunting to learn all the required details... so i'll try to outline the basics here, this is not a complete guide to batteries but a simple starting point ..

Volts, Amps, Watts, AmpHours and more, are all terms you will need to eventually understand, but to make a long story short, the basics are as follows :

As far as ebikes are concerned

Volts = Speed, rpm, add more voltage to any given motor and it will spin faster, a 36v ebike will generally go 20mph ( 30 kph ) , if you plug 48v into the same bike it will go faster..

Amps = Torque, more amps will result in better acceleration ( more on this below , see : " Watts " )

Watts = Volts multiplied by Amps, ( V x A = W ) , this is a number given to express the power of the system. A 36v ebike with a controller rated at 20 amps will deliver ( 36v x 20amps = 720w ).. but at the same voltage with a larger controller rated at 40 amps this bike could deliver ( 36v x 40amps = 1440w ! ).. both would go the same speed on level ground ( because the voltage is the same) but the higher wattage ebike will climb a steeper hill..

Ah = Amp Hour, capacity, range, more Ah means longer run time

Wh = Volts x Ah= Watt Hour, another method to determine capacity or consumption( wh/km ).. Just like gasoline cars use mpg ( miles per gallon ) electric vehicles use watt hour per mile or wh per kilometer..

Nominal Voltage= The working voltage of the cell or pack, since a battery will have a higher voltage hot off the charger and a lower voltage when completely discharged the Nominal voltage is what you can expect during the majority of it's operation while under load.

C or C-Rate = The C rate of a battery determines how quickly it can be discharged and recharged, it is a specification directly related to the Internal Resistance of a cell.

Why is this important ?

1C = 1 hour
2C = 30 minutes
3C = 20 minutes
4C = 15 minutes
etc..

C/20 = 20 hours
C/10 = 10 hours
C/5 = 5 hours
etc

==========

Sealed Lead Acid batteries are rated C/20, so a 10ah lead acid battery will deliver 10 ah if it is drained over a period of 20 hours, the problem with this is that on an ebike we use energy at a much faster rate and if we were to drain this 10ah battery in one hour ( 1C ) it would only deliver 5ah of usable energy, Lead acid batteries canot delivery their entire capacity when drained quickly, this is refered to as the Peukert Effect.

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Cycle Life : All batteries eventually die, either from use, abuse, or from time, the number of cycles you get from a pack varies quite a bit. You will see claims of 100 to 5000 cycles on the internet, but this number is very subjective, depending on how deeply you discharge your pack, how well your charger recharges ( some chargers overcharge, while some do not, this is a big factor and is why you should get a quality charger !! ). more on this later...

Most SLA packs will last one season, sometimes 2 if treated nicely... nicad packs can go for 5 years or more .. while lithium packs should last at least 3 years but sometimes longer.. it all comes down to how hard you push them..

Battery packs can be destroyed in a matter of days if you abuse them or they can last many many years if you treat them well...

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" SLA " Sealed Lead Acid, is the most common, lowest cost, heaviest options available for an ebike.. Similar to what you have under the hood of your car but the acid is gelled to prevent leaks, they can be mounted in any direction and will not spill acid ( usually.. ) .. Most common are 12ah capacity ( 12 amp hour ), but when used on an ebike they can only deliver about half the rated capacity, so expect a usable 6ah from a 12ah battery.

You should always keep SLA battery packs charged, after every ride, as soon as you can, re-charge !! Leaving an SLA pack discharged and sitting for weeks will destroy it.. and it will no longer keep and deliver energy.. Even a 5 minute trip up the street, plug it in when you get back for the most life possible from your lead pack.


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Nicad and Nimh, these have been around for a long time, most commonly in cordless tools, but also available in larger cell format and can be used for ebikes if you need low to medium power. They are lighter than SLA, smaller in size, and provide their rated capacity when used within their limits.. Nicad is more abuse tolerant than nimh.

Nicad and Nimh cells will self-discharge when left sitting, they are best when used frequently and charged before you use them, unlike SLA there is no problem with leaving them sit in any state of charge, after a ride you can leave it drained and simply recharge it the night before your next ride..

Charging nickel cells requires a Nickel charger, never use any other charger with this chemistry. Better chargers will use voltage profile and a temperature sensor embedded inside the pack to detect when the pack is fully charged and then goes into trickle charge mode to ballance the cells.

Do not parallel Nickel cells while charging, Ni should always be charged in single series strings.. search the forum if you need more details on why..

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Lithium, the latest and greatest, alot to cover here, so pls take the time to read it over a few times if it's not clear at first.. You will find terms like " Lipo" and " Li-Ion " and " LiFePo4 " etc.. all lithium batteries are basically Lithium Ion.. but there are many different chemistries available.

example :

Lithium Manganese ( LiMn )
Lithium Cobalt ( LiCo )
Lithium Iron Phosphate ( LiFePo4 )
Lithium Titanate
And more mixes and blends etc.. the most common for ebikes right now are LiMn, LiCo and LiFePo4 so i'll concentrate on those.

LiMn and LiCo both have the same voltage profile, fully charged at 4.20v and fully discharged at 3.0v per cell

LiFePo4 is different, it is fully charged at 3.6v and fully discharged at 2.0v

In order to make a 36v pack from LiMn/LiCo you need 10 cells in series

In order to make a 36v pack from LiFePo4 you need 12 cells in series, because of the lower voltage per cell..

Lithium packs often use a BMS to prevent the user from damaging the cells, see info on BMS further down..

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Charging batteries, no matter what kind, should be done in a safe area and with supervision, regardless of how " safe " you may think batteries can be they are simply chemical vessels that hold electrical energy, if anythying goes wrong while charging, "things" can happen, with luck you will end up killing the pack without too much drama but any battery that gets overcharged has the potential to " vent " .. .. I include LiPo, Lifepo4, nicad and SLA in this statement... I personally never to go bed while my batteries are charging, some people do but i do not..

Thread by Dogman :
http://www.endless-sphere.com/forums/vi ... 14&t=26709

" LiPo " explained:

LiFePO4 and Lipo are both "lithium ion" Batteries - lithium ions are used as charge carriers within the batteries (Charge: from Cathode, through electrolyte, to Anode. Discharge: the reverse; anod -> electrolyte -> cathode).

generally a more or less liquid electrolyte is used (compare to the acid in an old fashion car starter battery) between a lithium-metal-cathode and a graphite anode.

charging is done by applying an electric potential over the battery causing the lithium-ions to flow over and place themselves between the 2-dimensional sheets in the graphite anode.

"Lipo-batteries" is short for "Lithium polymer batteries" due to the fact that they use POLYMERS as electrolytes.
hence:
A "lithium (Li) iron (Fe) phosphate (PO4)"-battery can therefore also be a "lipo" battery when a polymer electrolyte is used.

Depending on the metal added to the lithium in the cathode, different battery properties can be achieved - Iron and phosphate for example makes the battery much safer at the cost of weight and electric potential (lower cell voltage).
Different electrolytes also change the properties (eg. polymers allow for pouch cells and often better (power) performance).
lastly, also the anode can influence the performance; eg titanate is much more robust than graphite (carbon), but is also more expensive and heavy...

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Series and Parallel :

Series will increase voltage, by placing cells head to tail in a long string you can add as many cells as you need for what ever votlage you need.

s2.JPG (31.27 KiB) Viewed 20142 times

Parallel will increase capacity, by placing cells in parallel the voltage of the group stays the same but they all act like a larger cell.. longer run time

Parallel.JPG (31.58 KiB) Viewed 20142 times

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Lifepo4 vs the other lithiums.. :

LiFePo4 ( LFP for short ) having a voltage profile of 2.0v to 3.6v per cell makes them compatible with standard 12v devices, by using 4 cells in series :
4 x 3.6v = 14.4v

This does not work as well with Li-Cobalt or Manganese that range 3.0 to 4.2v per cell
3 x 4.2v = 12.6v ( slightly low and only when fully charged )
4 x 4.2v = 16.8v ( too high for 12v devices )

[Ypedal]

BMS and Chargers.

BMS : Battery Management System ( active ).. and in other cases... Battery Monitoring System ( passive )

Why do you need a BMS ?

I'm not going to go into too much detail but here are the things you need to know..

A battery pack is made from a group of cells, in a perfect world these cells would all charge and discharge equally, in harmony and the BMS would pretty much not be needed or just sit there and do nothing fancy....

Lithium batteries have a voltage range they must be kept within ( varies by chemistry ) , over-charge or over-discharge them and they die a quick death, to prevent you from doing that, the BMS will shut you down if you do something bad or if there is a problem with one or more cells in the pack alerting you to a problem before you do yet more damage.

Alot of people, myself included, use lithium packs without a BMS, and by never, i repeat.. ' NEVER ' draining the pack to full capacity and by charging below maximum high voltage this can work... but it's not for everyone..

Not only can a BMS actively cut off the power, it can also " Ballance " the cells while charging, this simply means making sure that no single cell ( or parallel group of cells ) is allowed to go over-voltage and will drain energy from the higher voltage cell(s) to allow the lower voltage cells to catch up.. This, in a way, insures maximum capacity from the pack and prevents cells from drifting apart over time and cycles..

Some BMS's only monitor pack voltages and report to a secondary system, some of them tie into the throttle wires or activate the controller's E-brake signal to prevent you from using any more energy keeping the empty cells safe..

And, sometimes a faulty BMS can itself cause a healthy pack to quit working and even kill cells .. so it's not a perfect world..

a BMS needs to be sized to the battery pack's limits, and to the system it will operate, some BMS's do " Over-Current Protection " acting like a breaker, they can be reset by disconecting the pack and reconnecting it while some others will auto-reset once the condition that caused them to " trip " is corrected....

Each battery type has specific charging needs, in general, you should not use a charger meant for one type for other chemistry types... there are exceptions but educate yourself before attempting such things..

SLA : A 12v lead acid battery is made up of 6 x 2v cells in series inside one block, it should be charged to 14.5v and then trickle charged to keep it into the 13.x volts..

Nicad/Nimh : each cell is 1.2v but when charging they can peak well into the 1.7v range and a good Nickel charger should have a temperature probe inside the pack to detect heat increase at the end of charge.. once full charge has been detected a nickel charger can ballance cells in series by trickle charging the pack at low rate for a period of time, Ni cells can tolerate low rate over-charging

Lithium : varies by chemistry but they all should have a CC~CV ( Constant Current, then Constant Voltage ) charge profile.

[Ypedal]

Ok, at the risk of repeating myself, here are things you should try to do in order to make your battery pack last as long as possible !

Get the right Size battery pack for your application !

What does this mean ?

Most of us on the ES forum use Lithium, individual cells have specifications supplied by the manufacturer, sometimes these are quite specific, and sometimes they are complete lies from resellers/vendors .. seriously...

So, consider what motor / controller / conditions you plan to run and size your battery pack accordingly..

For example:

If you build an average " 500w " ebike, running on 36v, you need a battery pack that can sustain 20 amps ( remember that Volts x Amps = Watts )

If you build a more powerfull system, with a larger motor and controller, you need a more capable battery ! There are 2 ways to accomplish this, either use a larger capacity battery, or a pack made from more powerfull cells ( see " C " rate above )

Most cheap lithium cells can deliver 1C, meaning that a 10ah pack can deliver 10 amps.

However, some expensive Lipo cells rated at 50C are capable of delivering their charge quickly and a similar 10ah pack made from 50C cells would be able to deliver 500 amps ! but only for a couple minutes.

[wesnewell]

How to wire a lipo pack.
viewtopic.php?f=14&t=39666

[TheBeastie]

I came across this, thought it could be really good to help understand battery chemistry electron attraction.
http://www.youtube.com/watch?v=_M9khs87 ... r_embedded

[spinningmagnets]

Since the first post had the biggest and best compilation of LiPo info links, I felt it was useful to add METHODS LiPo care kit link. I know its a "new items for sale" thread, but it includes the info from respected members on why the included parts should be a part of a LiPo users system.

"Complete Hobby King Lipo Protection Kit"
http://endless-sphere.com/forums/viewtopic.php?f=31&t=36414

[spinningmagnets]

icecube57 has become a respected supplier of custom battery charging/riding wire-harnesses, found here:
http://endless-sphere.com/forums/viewtopic.php?f=31&t=30367&start=405

EP-Buddy is also a frequently listed supplier of wiring harnesses and parts
http://epbuddy.com/index.php?main_page=index&cPath=26_14

From GCinDC, his method for wiring a LiPo pack for charging at 5S, but riding at 15S:
http://endless-sphere.com/forums/viewtopic.php?f=6&t=14842&p=226580&hilit=discharge#p226580


"Hyena's super isolated 6S high current balance chargers"
http://endless-sphere.com/forums/viewtopic.php?f=31&t=41107

[agniusm]

[Hillhater]

Some useful 18650 cell data..
http://lygte-info.dk/review/batteries20 ... %20UK.html
and also here
http://www.dampfakkus.de/liste_akkus.php

[dogman]

BATTERY INTERNAL RESITANCE TESTING

Good vid that shows how to do it. Even I found it easy to understand, so you know it's easy.

viewtopic.php?f=14&t=48739

[llile]

Here is a good question to get on this thread: What charging time can I expect wit LI-ION?

Check me out on this calc, since I haven't tested it out:

Lets say I have a honkin' 18S8P pack, arranged in three 8P groups of 6s 5000mAH 20C cells. This is 24 battery packs (8P times 3S) Per the helpful wiring diagram a couple of posts back, I could hook them all up to ahobbyking iCharger which would be charging them at some particular rate.

"C" is supposed to be the rate a battery can charge or discharge in an hour, but Li-Ion are odd ducks, and the one linked above can discharge at 20C or charge at 2C. So we could charge this battery at 2C in half an hour.

Now the cells could handle being charged at quite a lot of power: 5000mAH = 5A * 2C = 10 amps * 24 batterypacks = 240 amps. The iCharger won't deliver that much juice all at once. In fact it is likely limited by the power of the DC power supply behind it. Lets say we hook it up to a Turnigy 1200W 24VDC power which will deliver up to 50A at 24V. The iCharger claims it can handle only 1000W at 23V, so that's going to charge batteries at 1000/23 = 43 amps. 43 amps is 43/5 = 8.6 times the C charging rate.

But wait! We are putting a crapload of these batteries in parallel, so each battery is seeing 1/(24) of this current, or 1.8 A That means they would theoretically charge up in 5A / 1.8A = 2.76 hours

Yer certainly not going to charge this battery up over your lunch hour. Does this actually turn out to be a real world charge time?

[amberwolf]

Charge current drops as voltage rises, so no, it's not really going to charge that fast.

I suppose you could double whatever constant current charge time you come up with, and figure the charge would take less than that time, but how much is dependent on the charger and teh cell resistances.

[dogman]

This is where thinking in watthours can help make it easier to calculate.

Say your charger is putting out 1000w. You won't charge more than 1000wh in one hour. And it will slow at the very end.

Each of your packs is going to have approximately 125 wh of capacity. So 24 of them should have 3000wh. So three hours to completely charge from completely discharged. So that's a long lunch for sure.

Then if you are balancing 24 packs, that could double.

[ftanka0]

where can i find pictured details on building a lifepo4 battery pack?

[Hillhater]

BROKEN LINKS !
unfortunately most of the links to data and graphs in the older threads above are broken / corrupt.
I dont know if the Mods can do anything , but it must be very frustrating for anyone data mining on here now !