Ultra capacitor?

I'm looking for a mathematician..

Hello..

This is about a theory:

I have 10 ultracaps of 2.7v and 3000f each.

I would like to build these 10 capacitors in series for a 24v system.

How long can I operate my 1000 watt water pump with the capacitors?

Thank you

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ddddddds
2 months ago

In order to calculate this, I assume that the 1000W applies at a voltage of 24V and the pump has a constant resistance.

How fast a capacitor is discharged depends on the time constant τ (Tau). Calculate by multiplying the capacitance C with the load resistor R.

1000W / 24V = 41,67A

24V / 41,7A = 0.576 Ohm

So your pump has about 0.58 ohm resistance.

The capacitance of capacitors (also Supercaps) is reduced in series connection:

3000F / 10 = 300F

Multiplies with the resistance of the pump:

τ = R * C = 0.576Ohm * 300F = 172,8s (This is not the final result, but only the time constant)

With the time constant, the voltage can then be calculated after a certain time. The pump will keep running slower and stop at some point. When that happens, you can only try. Depending on the model, this can be at 20V or even at 5V.

If I didn’t get involved, the formula is for the time after which the voltage has fallen to a certain value:

t = -ln(U/U0) *

“ln” is the natural logarithm, which can be expected by any reasonable calculator. U is the voltage to be reached. U0 is the voltage at the beginning, in your case 27V. τ is the time constant, in your case 172,8s.

For a voltage of 20V you get a time of 51.9 seconds. 10V are reached after 171.6s, and 5V after 291.4s.

ddddddds
2 months ago

No problem;)

During parallel switching, the capacitances are added. Then, as a new capacity, you have the double, so 2 * C from before. Thus, the double time constant and the voltage decreases half as fast. For example, 10V are not already reached after 171.6s but only 343.2s.

ddddddds
2 months ago

Thank you

Sometimes school and interest in something useful is really beneficial ^w^

Gnurfy
2 months ago

3000F correspond to 3000 coloumb or there to a storage quantity of 1A × 1V × 1s in this unit as 1C.

At 2,7V × 3000F, the electrical storage capacity per cap is m.W. 8100 Vas

Stacked to 27 volts on a 24V/1000 watt pump should therefore m.W. after approx. 8 seconds to be under load.

ddddddds
2 months ago
Reply to  Gnurfy

3000F correspond to 3000 Coloumb

Although capacity and charge are connected, it is not that way.

Q = C * U

The charge is the product of capacity and voltage. At 2,7V and 3000F, 8100C.

Coulomb is by the way synonymous with As (amperesis customers) and technically also VF (Voltfarad). You can’t mix it. VAs (Voltamperesiscus) would be equivalent to Ws (Wattsecus), i.e. already an energy unit, but the energy in a capacitor is calculated differently.

E = (C*U^2)/2

This results in 10935Ws per condenser, i.e. 109350Ws for all ten.

At 2,7V × 3000F, the electrical storage capacity per cap is m.W. 8100 Vas

You divide energy through power here to calculate the time. Would also work – if the performance would remain the same all the time. But the voltage of a capacitor decreases during deading, as a result the power becomes smaller and smaller over time. Apart from the questioner, there is a DC-DC converter that keeps the voltage constant, it could be expected. If this is the case, he would have to explain himself.