21Ah DIY Lithium Ion Battery Pack 72V Electric Bicycle Battery used in Samsung 18650 Battery Pack

21Ah DIY Lithium Ion Battery Pack 72V Electric Bicycle Battery used in Samsung 18650 Battery Pack 

How to select the correct battery pakc (General Knowledge) ?

• First of all, you must get to know your device:
  • What is device's input voltage? ( V)
  • What is its power consumption ( Wattage ) ?
  • What is Maximum current drain ( A) ?
  • What is your expected running time by a battery pack ?
• Decide battery pack voltage you will choose
• Battery pack voltage must be equal or a little higher than your device’s need.
• If you need a exact voltage, which battery pack can not provide, you may consider to use a DC-DC regulator
• Decide Battery pack's Capacity  ( mAh or Ah)
• Battery capacity is depended on how long you need to run your device ( hours ), which can be calculated as the follow:
• ( Ah) = Device's Wattage (W) x Time to run ( Hours) / Battery Voltage (V)

For example, if using a 12V battery pack, and run 10W DC device for 10 hours, you need choose a battery pack with capacity > 8.3Ah, e.g (10x10)/12 = 8.3

• 1000 mAh = Ah,  higher mAh will provide longer running time.
• Decide Battery pack’s Max. discharging current
  • Before order battery pack, you must pay attention on battery pack’s Max. discharging rating on the specification or description. Please don’t think any battery can take any current drain.
  • You shall know your device’s max. discharging current. If you don’t know , you must measure it by a multi-meter.

The battery pack’s Max. discharging rate of the chosen Battery must be higher than that device requires

How to Maintain Lithium Battery

Lithium batteries are presently the most commonly used energy storage devices on electric bike, electric scooter, golf car, mobile phones, laptops, digital cameras and other electric devices. Learning how to maintain lithium batteries can not only prolong battery lifetime but also protect your device from potential damage.

1. Charge new batteries. It's not necessary to charge over 12 hours when first used. When a device powered by batteries is purchased, sellers will usually tell us the batteries must first be charged 12 hours before using. Actually, this is unnecessary. Unlike common Ni-CD or Ni-MH batteries, most lithium ion batteries are activated before leaving the factory. Due to their low self-discharge, it’s unnecessary to charge lithium ion batteries for such a long time when new. Lithium ion batteries are ready for use when the charger indicates so, and they will reach their best capacity after 3 or 5 cycles.

2. Use appropriate chargers. Many people take great care with their electronic gadgets, but often neglect the consequences of bad chargers on their lithium ion batteries. When choosing a charger, the original charger is the best choice. If that's unavailable, a high quality charger that has an overcharge protection function, or a brand name charger will do. A low quality battery charger can lead to shorter run times, premature battery failure, or even fire or explosion.

3. Avoid frequently over charging. Over charging with a low quality charger may let the battery's interior rise to a high temperature, which is bad for the lithium ion battery and charger. Thus, simply fully charging is good enough - overcharging will make your lithium battery into a little bomb if overcharge protection function is missing.

4. Avoid touching metal contacts. All batteries' contacts need to be kept clean for best performance. When carrying batteries around, do not let the contacts touch metal objects such as keys; this could cause a short circuit, damaging the battery or potentially resulting in a fire or an explosion.

5. Avoid using often in high or low temperature environments. Lithium ion batteries have optimal working and storage temperatures. If they're continually used in extreme temperature environments, this will negatively affect battery use time and useful cycles.

6. Avoid long periods without using or recharging. If batteries will be left unused for 3 months or more, partially recharge them (to around 30-70% of capacity, depending on planned storage time), then store the device to prevent battery damage. You may need to take the device out of storage and charge again after a few month

                                                                                                 Friendly Tips:
Material:
LiFePO4 (Lithium Phosphate ion), Li-CO2, Li-NiCoMn(ternary battery), Li-MnO2.
The price is from high to low. LiFePO4 cost is most expensive but the security and stability is also highest.
Li-CO2 cost is lower than LiFePO4 Higher than Ternary and Li-MnO2, the life is more than Ternary and Li-MnO2 100-200 times.
Li-NiCoMn(ternary battery), the cost-performance ration is high and the technology also is mature.
Li-MnO2 is cheapest but the life is short.
Nominal voltage:
LiFePO4 is 3.2-3.3V (the highest voltage is 3.75V), Li-NiCoMn is 3.6V, ternary and Li-MnO2 is 3.7V (highest voltage is 4.2V)
Battery combination:
series increases voltage, parallel increases capacity. For example 3.7V 2A battery 10 series 6 parallel, the voltage is 37V (10*3.7), capacity is 12Ah
What is BMS ?
A Battery Management System (BMS) is any electronic device that manages a rechargeable battery (cell or battery pack), such as by monitoring its state, calculating secondary data, reporting those data, protecting it, controlling its environment, and / or balancing it. A BMS may monitor the state of the battery as represented by various items, such as: * Voltage: total voltage, voltage of periodic taps, or voltages of individual cells Temperature: average temperature, air intake temperature, air output temperature, or temperatures of individual cells State Of Charge (SOC) or Depth Of Discharge (DOD): to indicate the charge level of the batteryState Of Health (SOH), a variously-defined measurement of the overall condition of the battery * Air flow: for air cooled batteries * Current: current in or out of the battery.