Lithium batteries for skateboard

These batteries have a battery management board which cuts off the current if the discharge rate goes too high. I believe it's meant to protect the battery. For example the following specs are copied from pingbattery.com (36v15ah) and the important numbers to look at are "max continuous discharging amperage" and "discharging cut-off protection". These numbers will help you in comparing different batteries.

Specifications:
Suitable Wattage of Motor: up to 600 Watt, 450 Watt suggested
Voltage: 36 Volts
Capacity: 15 Amp Hours
Dimension: 225x105x150 mm / 8.9x4.1x5.9 inches
Weight: 5.6 kg / 12.3 lbs
Charging Voltage: 45-46 Volts
Charging Current: <5 Amps
Rated Discharging Amperage: 15 Amps
Max Continuous Discharging Amperage: 30 Amps
Maximum Discharging Current: 60 Amps
Discharging Cut-off Protection: 40 Amps
Lifecycle of the whole pack: >85% capacity after 1000 cycles. Lifecycle of single cell: >85% capacity after 1500 cycles, >70% capacity after 3000 cycles. (<1C discharge rate and <1C charge rate)

Yeah. A hint is 600 watts / 36 volts = ??? amps

Hm, I was trying to educate by leaving an exercise for the reader ;-) ..

What I meant is that "watts" is volts times amps. For example your typical incandescent lightbulb is 120 volts and 100 watts. That means the bulb takes 0.83333 amps because 120v * 0.83333 amps = 100 watts.

You know the controller you have is rated for 600 watts, and the system runs at 36 volts. Hence 600/36 = 16.6666 amps is the peak current the battery pack will be asked for. This is assuming the rated power is actually the peak power.

Hey Reikiman,

Sounds like you have a good electronics background, I have just enough to get myself in trouble. Maybe you can help me with with an issue. I just purchased an electric skateboard with 36 volt LiPo batteries. I was running it up a pretty steep hill and it started cutting out on me. I took it home and recharged it and when I went to turn the board on the next day, no power. I took the battery pack apart and I have a little over 40 volts at the battery pack and no voltage on the other side of the BMS. I can bypass the BMS with a jumper on the negative side with the charger hooked up and the batteries charge fine. When I reinstall the battery pack, install the charger and turn on the controller the board will run. When I remove the charger, the board dies. Is the BMS fried or is it locked up and can it be reset?

Thanks for any info you can provide me.

Hi,

The standard BMS's that come with some of the smaller skateboard LiFePO4 packs don't last to well due to the high current drain the skateboards have.

Example: I run 36V 20Ah LiFePO4 packs in my boards and the BMS's have to cope with 25-30Amps constant, and 50Amps peak (when you're climbing a hill). With some of the 10Ah packs, the standard BMS's have the constant set at 20Ah and the peak set not much higher at 35Amps (approx).....also, they have a low cell group voltage cutout (when one of the groups of cells ... most 36volt packs have 12 series) drop too low, which happens under high current drain .... a couple of good hill climbs and they cut out everytime (I know from experience). And once they start cutting out 9/10 of the cheaper BMS's don't recover, ie you end up bridging the BMS to get them to work again :(
I've used 10Ah, 12Ah, 15Ah and 20Ah packs in my 800watt boards ..... and the only ones which have delivered constant results have been 10Ah Headway cells, or at least 15Ah packs (if you are using 3Amp cells), but either way the BMS's have to be sized properly :)

Hope that helps

Cheers
Nigel
www.greenskate.co.nz