# Supercapacitor charge time at constant current

#### anishkgt

Joined Mar 21, 2017
549
Hey All,

I am trying to estimate the charge time required to charge a 3s2p bank of capacitors. Wish to know things here what is the total capacitance and how to determine the total time required to charge the capacitors to 81.at a constant current of 10A.

Search for the formula to determine the time V = IT/C So rearranging T = VC/I is that correct ?

#### Papabravo

Joined Feb 24, 2006
16,783
Hey All,

I am trying to estimate the charge time required to charge a 3s2p bank of capacitors. Wish to know things here what is the total capacitance and how to determine the total time required to charge the capacitors to 81.at a constant current of 10A.

Search for the formula to determine the time V = IT/C So rearranging T = VC/I is that correct ?
Yes the charging time at constant current is mostly linear until you get close to the open circuit voltage of the charging source and then it slows down a bit. The closer you get to the asymptotic voltage limit the more it slows down. In fact it takes infinite time to actually reach the limit. The actual formula is:

$V\;=\;\frac{1}{C}\int idt$

as long as i remains constant it comes out side the integral. At some point in the charging cycle it will flatten out to a very slow charging rate.

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#### sparky 1

Joined Nov 3, 2018
576
In this video you can count the seconds it takes to charge and see the ammeter drop.

The 500 Farad is charged at 2.7V using constant current set at 3 Amps
during the top off charge the current drops. Which leads to the question:
When is the best indicator on when to stop charging a super capacitor ?

Is it a good idea to charge beyond 2.7V ? The rate of charge from 0 to 2.695V 3 amps ?
When it gets puffy on the top the metal can get deformed the dielectric is compromised and leakage is higher,
who is the fastest, just toss it, it's blown out. Topping off, don't think it is good idea, I think best to start tapering off from 2.6V to 2.695

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#### anishkgt

Joined Mar 21, 2017
549
So what is the capacitance of a 3s2p configuration ? Digikey has a series and parallel capacitance calculator but not for a pack.

#### sparky 1

Joined Nov 3, 2018
576
When the charging circuit is complete there is another improvement that is interesting.
A boost converter that would modify the discharge curve. Because that curve can be remedied the faster charge time makes it rival standard rechargeable battery. The battery would last much longer, charge faster and have a much better discharge curve.