Spotlight on the Battery Pack That Powers Our Electric Skateboard Drive

17 January 2017
Lithium ion batteries have a higher energy density than dynamite.
mellow electric skateboard battery pack cells

Don't worry - it’s all safe and stable as long as the battery pack for our electric skateboard drivetrain is well monitored and managed. Badly designed skateboard battery cells or constant mistreatment lead to fire, flammable gases and even explosions.

'Thermal runaway' - aka 'venting with flame' - starts small and invisibly. Cheap or inadequate battery management causes damage to cells by letting them overheat, pulling too much current or forcing too much charge into them. This causes irreversible changes in chemistry or structure that leads to internal shorting. The battery's concentrated energy is turned inward in a chain reaction by rocketing temperatures that can spread to cells in close contact, like in cheap shrink-wrapped packs.
 
Not every battery failure makes the news – most just hit your wallet. Settling for bargain skateboard battery packs means that the originally rated 500 to 1,000 charge cycles will drop drastically, losing capacity and requiring a replacement much earlier.

How did Mellow design safety, performance and an electric skateboard battery life target of over 1000 discharge cycles?
Mellow electric skateboard truck with attached battery pack


Go with what you know

Mellow deliberately avoided superthin and immature battery formats, selecting the dependable 18650-sized cell as used by Tesla and other electric vehicles. The model Samsung INR18650-20R used in our packs has a rock-solid reputation since 2013 and is easily capable of delivering high constant current for awesome torque while keeping cool.
Mellowboards battery pack with individual cells visible 

The care and feeding of lithium ion electric skateboard batteries

A lithium ion battery should be handled almost like a infant: cosy (flame-retardant) bedding, constant monitoring and gentle feeding. These particular babies will spend their time hanging on the bottom of a skateboard, hurtling downhill at over 40 km/h, or being banged against sidewalks, rocks, mud, and snapper turtles, so Mellow (the manufacturer of a battery powered skateboard) doubled (and tripled) down on battery pack design.

Having external BMS and cell balancers is like hiring a babysitter from the shady pages of Craigslist. That’s why we’ve integrated such systems directly onboard in each Mellow battery pack. Moreover, our babysitter (uh…battery pack manufacturer) is experienced: 25 years in the business, supplier of Airbus and Siemens.
Mellowboards cell balancer component of battery powered skateboard kit


What you get with our electric skateboard battery pack


PERFORMANCE 
• Industry-grade dedicated onboard Battery Management System (BMS) microprocessor 
• Constant cycle life, state of health, voltage and temperature monitoring 
• Drive rideable without pack (1 kg reduction)
• Waterproof (IP65) USB and charge port plugs (double gasket and hook) 
• 3A integrated USB charging port 
• 99Wh capacity (9 full charges of iPhone 6) 
• up to 3 packs allowed in carry-on baggage when flying (up to 45 km range)

PHYSICAL PROTECTION
• Halogen-free LG brand injection plastic 
• Drop-proof, anti-rattling external TPE rubber layer 
• Dual inner anti-shock vibration-absorbing cell holders 
• Waterproof IP65/67 battery connector
• Waterproof IP65 battery pack 
• Integrated snap lock system with no mechanical parts that can fail 
• Integrated GoreTex waterproof membrane for pressure/venting control when flying 

PREVENTION AND SAFETY
• Max rated (UL-94 “5VA”) flame retardant inner cell holders and outer shell
• Cells air-gapped for higher heat dissipation 
• Onboard electrostatic discharge protection 
• Onboard cell balancing with 20 mV accuracy 
• Redundant onboard temperature sensors 
transparent battery pack of Mellows battery operated skateboad drivetrain


Battery Pack Juice delivery

Mellow has eliminated two critical performance issues in other motorized skateboards on the market today, including pricier models: 'voltage sag shutdown' (following hill climbing due to inaccurate reading of batteries are empty due to voltage fluctuations) and 'regenerative brake shutdown' (braking cuts off or doesn't work on downhills due to full battery.)

The BMS uses triple fuel gauge measurements (voltage, Coulomb counting, Impedance Track) to accurately read battery level and eliminate false alerts. Mellow’s dual brake makes it immune to the dark side of regen braking, which shuts down or even damages full batteries on e-skates not equipped with a backup brake system.

Together with Mellow's custom high efficiency motors, the motorized skateboard battery pack safely delivers the power needed for speeds up to 
40 km/h top speed, along with 20% hill climbing and 15 km range.


The transparent Battery Packs featured above are for demonstration purposes only. Production units are black with a TPE blue rubber layer.
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