This guids is being written and saved as i go, so bear with me...
Batteries !!..
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
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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.. :lol: ) .. 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/viewtopic.php?f=14&t=26709
" LiPo " explained:
mattetjus said:
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.
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
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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 )
