Electronic – How plausible is the claim about a 200 kW battery solution

lithium ion

Following this question posted on Aviation:SE:

which is related to a hovering board described on the vendor site:

enter image description here
(source)

I would like to assess the claim this device really exists. In particular I wonder if it is possible to use the batteries to deliver 200 kW as claimed. I'm not trying to evaluate the aerodynamic aspects.

I don't see what technology could be used other than Li-ion cells. Assuming this is true, would this solution be compatible with the claimed characteristics:

  • Power delivered: 200 kW,
  • Running time: 3 min for a 110 kg user, to 6 min for a 82 kg user,
  • Charging time: 6 hours, reduced to 35 min using a docking station.

Taking into consideration the Li-ion characteristics with the knowledge of an electrical engineer, is there any aspect that would prevent this solution to work, e.g:

  • Weight, volume of the batteries (the board measures 145×76×15 cm),
  • Wires size (there is little room available in the box),
  • Current for charging (is this feasible to charge in 35 min),
  • Discharge time (would cells allow to be discharged in 3 to 6 min),
  • Cost (replacement of batteries is offered at $6,840).

No speculation please, but known facts that would definitely contradict or support the possibility of the solution. For instance, I think these deductions are correct:

  • For a 3 min hovering, with 200 kW, about 10 kWh are used.
  • Due to specific energy and density for Li-ion, this means 40 kg and 14 dm3 for the batteries.
  • Price of the batteries: With an optimistic 0.40 $ / Wh, this would be $4,000.
  • Charging 10 kWh in half an hour requires a 20 kW charger.
  • Assuming cos φ = 1, this would mean 91 A for 220V (well past what is usually found at home), and 5,000 A for the Li-ion cell voltage (this would require large wires that are not visible in the picture).

Best Answer

203kW / 36 fans = 5.6kW per fan.

Working voltage of 38V implies 10S Lipo (3.8V per cell).

5.6kW / 38V = 150A. We want 3 minutes at full power. At half power it will draw 75A for 6 minutes (max duration). A battery capacity of greater than 150*(3/60) or 75*(6/60) = 7.5Ah per fan will be required.

Can it be done?

Looks like 120mm diameter fans will fit in the space provided. Here's a 120mm fan that weighs 1kg and produces 7.5kg thrust on 12S:-

120mm 11 Blade Alloy EDF 700kv - 7000watt

On 10S it would draw about 30% less power and produce about 15% less thrust, so let's say 5kW and 6.5kg (the fans they are using may have different motors, but we can expect similar performance at the same power level).

And here's a 10S 4Ah battery that weighs 905g:-

ZIPPY Compact 4000mAh 10S 25C Lipo Pack

The board appears to use a total of 72 batteries - two batteries per fan. 2 x 4Ah = 8Ah, close to our required capacity. Max discharge rate is 4 x 25C = 100A per battery or 200A per parallel pair (and we 'only' need 150A!). Max charge rate is 5C, well above the 2C rate required for a 35 minute charge. At $67 per pack the total battery cost is $4824.

Our 72 batteries weigh 905g x 72 = 65kg. The 36 fans weigh 36kg. Add another 10% for ESCs, wiring and support structure, and we get a total board weight of ~110kg. This board should generate 6.5kg x 36 = 234kg thrust in free air. At half power thrust would be reduced to about 75%, but could be boosted by ground effect - so perhaps 210kg of 'duration' hovering thrust. Take away the weight of the board and you have a payload capacity of 100kg.

Looks possible!

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