1000 HP dragbike with Ultracapacitors

15323 Views 35 Replies 8 Participants Last post by Karter2, Nov 8, 2016

kennybobby

Discussion Starter · Oct 18, 2016 (Edited)

i want to split out the discussion from the other thread to focus on the technical details of the fast-charge.org dragbike project.

Sifting thru their blog pages seems to be the only way to find little bits of info about the details.

Their goal is to do 1/4 mile in 6 seconds at 200 mph, and they call out 1000HP. The electric power supply will come from ultracapacitors, looks like the Ioxus Titan 60 x 108mm axial cells, 2.7/2.85V-2000F, weighing 390 gms each. The drawing indicates 3px210s, so it's ~600V pack (somebody double check my count on that). 630 cells x 390 gms = 540 lbs per dcb.

No word on the motor, but some about the gearbox:
a single speed reduction gearbox, using two sets of 31:59 gears to give an overall ratio of 3.81:1. This reduces the motor's peak speed from 22,000 rpm down to 5,750 rpm, after which a standard motorcycle chain/sprockets set gives us 2.5:1 reduction to the rear-wheel rpm of 2,300.

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kennybobby

Discussion Starter · #2 · Oct 18, 2016 (Edited)

Calculatus eliminatus:
[edited]
[The acceleration for a 6 second 1/4 mile is 73.33 ft/sec^2, or about 2.27 g., from x=.5A t^2]

Take [their advertised] 1000 Hp over 6 seconds to determine the energy (or work over 1/4 mile) to determine that the [force on the accelerated mass] is 2500 lbs.

[1000 hp x 550 x 6s = 3,300,000 lb-ft, or 1,243 Whr.]

[Divide the 2500 lb force by the acceleration to get the mass = 34.1 and the bike weight is ~1100 lbs.]

Equate the kinetic energy, [1243 Whr] to the capacitor energy, 1/2 CV^2, using 3p = 6000F and 6000/210s = 28.6 F for C, it looks like they are assuming a voltage drop of only 9.4 V in the pack during the 6 second burn.

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kennybobby

Discussion Starter · #4 · Oct 18, 2016 (Edited)

just trying to run back-of-the-envelope numbers to see where/if any assumptions run off the tracks...

so they need a motor that turns 22,000 RPM and makes 1000 HP, so 238 ft-lbs of torque at 22k using 1255 Amps from a 600V pack.

1255 Amps/3p is about 420 Amps per cell over 6 seconds is 2520 A-s or 2520 Coulombs. Each 2000F cell holds 5400 Coulombs at 2.7V, so theoretically there is enough charge. Another way to look is the entire pack, 28F x 600V, holds 17,160 Coul and a 6-second burn of 1255 Amps is about 7,600 Coul.

Now here is where the problem surfaces, when the cells give up their charge the voltage drops. From a best case 2.85V x 2100F = 5985 C full less the 2520C burn leaves 3465 C. Now what is the capacitance of the cells? If 2000F, then the voltage will be 1.73 per cell, or a sag/drop of 1.11 V per cell. Over 210 cells, the pack will sag 234 Volts, which is a big difference to the 9.4 V sag used above to determine the capacitance required for the pack. This is a big deal breaker, plus can an inverter be made to tolerate this much sag and still drive the motor with the required power to make the run?

i think this should be tested with just one cell to prove whether or not it sags under 420 Amps for 6 seconds (and how hot it gets).

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kennybobby

Discussion Starter · #11 · Oct 19, 2016 (Edited)

Karter2 said:
Just a couple of points..
Did they clearly statr the pack configuration of 3p, 210s ? Or is that a guess ?
On their facebook page they stated 640 caps in the pack ?..just a estimate ?
How sure are you they are not using the 3000F caps ?

Im not being critical here, just trying to understand why yesterday you were suggesting it would need 22,000 of the 3000F caps to do this, but now it looks like they are a lot closer with <1000 caps ??

# of cap cells was from reading the blogs, and then:
i just counted the 3p modules as shown in their diagram above, and
i counted the number of boxes in their mock-up picture, 8 top row, 16 middle and 18 bottom. Each box holds 15 cells. Both methods gave 630.

i didn't look at the facebook, so unaware of 640.

Cap size 2000 vs 3000:
This was determined both by weight and length.
A ruler was shown in the mockup photo on the boxes, ~3 boxes per 12" ruler, so about 4" length per cell (the 2000F cell is 108.1mm),
The caption under the shipping pallet indicated 250 kg, the 2000F cell weighs .39 kg, the 3000F cell weighs .51 kg. 640 cells x .39 = 249 kg. Maybe they got 10 extra to use for prototype and spares.

i think yesterday we were using standard EE math for series and parallel strings of capacitors to get to the 3600F, which was calculated by equating the kinetic energy of a 2500lb bike at 200 mph with the Capacitor energy with a 50V sag--this was before parsing thru all the blog pages trying to find tech details.

After finding the hive drawing and photo with the 3p connecting plates, etc. it was possible to determine the actual capacitance and voltage of a 3p210s pack made using the 2000F cells. This configuration yields a total capacitance of 28F at 600V, and could only work if the pack voltage only sagged ~9 Volts. Feel free to double check and challenge my numbers, i don't want to make a mistake in the basic data that affects the calculations and predictions.

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kennybobby

Discussion Starter · #13 · Oct 19, 2016

i'm puzzled by it also, hence the investigation--do they know something that we don't know?

It's almost as if they are using the caps as battery cells with no consideration for the reduction due to stacking in series...

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1000 HP dragbike with Ultracapacitors

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