# switch capacitor and series battery equalization

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#### yassin.kraouch

till know i didn't find the answer to my question

---------- Post added at 12:16 ---------- Previous post was at 11:53 ----------

i know that TxI=CxV, but i am confused, the current that can a battery ( 3.3V, 10Ah) give can exceed 10 A if a capacitor is connected directly to the battery ? in order to reduce the time charging of the capacity ?

I answered that question in Post#2 for the previous thread. You have failed to give any additional information whatsoever about the battery, except that it is "lithium ion" and supposedly rated at 10AH (ampere-hour).

In all probability, the answer to your question, "Can the battery provide more than 10A current" is yes.

John

I answered that question in Post#2 for the previous thread. You have failed to give any additional information whatsoever about the battery, except that it is "lithium ion" and supposedly rated at 10AH (ampere-hour).

In all probability, the answer to your question, "Can the battery provide more than 10A current" is yes.

John

this is the battery **broken link removed**

i know that the battery can produce more than 10A, but if a capacitor is connected, does the capacity absorbe more the 10A in order to charge it ?

Here is automated calculator for charging capacitor

Charging a Capacitor

Try yourself..............

with R=0.1ohm _ C=470µF _ Ustart=3.3V
RCtime constant = 47µs

at time = 0 ................... Icharge = 33A
at time = 10µs .............. Icharge = 26.7A
at time = 50µs .............. Icharge = 11.4A
at time = 100µs ............. Icharge = 3.9A

I think starting current is smaller than this
( chemical reactions in battery has decelerative function )

Regards KAK

Here is automated calculator for charging capacitor

Charging a Capacitor

Try yourself..............

with R=0.1ohm _ C=470µF _ Ustart=3.3V
RCtime constant = 47µs

at time = 0 ................... Icharge = 33A
at time = 10µs .............. Icharge = 26.7A
at time = 50µs .............. Icharge = 11.4A
at time = 100µs ............. Icharge = 3.9A

I think starting current is smaller than this
( chemical reactions in battery has decelerative function )

Regards KAK
i understand this, but when i connect directly the capacitor to the battery, withour resistance, does the capacity obsorbe current more then 10A ( provided by the battery ?

The initial charge current is ruled by battery and capacitor series resistance and additional resististive and reactive circuit impedances. Assuming the battery and capacitor impedance can be described by a single series resistor (which isn't exactly true) and circuit inductances can be neglected (depends on the setup), the charge operation can be described by a simple exponential function. If the inductance matters, you get a second order differential equation with most likely oscillating solution.

So what do you need to know to answer the question exactly?
- the battery inner resistance. According to the datasheet, it will be lower than 22 mohm to allow at least the maximum specified discharge current of 150 A
- the switch and wiring resistance and inductance
- the capacitor series resistance (ESR) or more exactly, it's frequency dependent impedance and respective equivalent circuit

do you know the said parameters?

Besides calculating the expectable initial current and charge current waveform, it may be reasonable to check, if battery, capacitor or other parts of the circuit may be damaged by the charge current amount.

• yassin.kraouch

### yassin.kraouch

Points: 2
The initial charge current is ruled by battery and capacitor series resistance and additional resististive and reactive circuit impedances. Assuming the battery and capacitor impedance can be described by a single series resistor (which isn't exactly true) and circuit inductances can be neglected (depends on the setup), the charge operation can be described by a simple exponential function. If the inductance matters, you get a second order differential equation with most likely oscillating solution.

So what do you need to know to answer the question exactly?
- the battery inner resistance. According to the datasheet, it will be lower than 22 mohm to allow at least the maximum specified discharge current of 150 A
- the switch and wiring resistance and inductance
- the capacitor series resistance (ESR) or more exactly, it's frequency dependent impedance and respective equivalent circuit

do you know the said parameters?

Besides calculating the expectable initial current and charge current waveform, it may be reasonable to check, if battery, capacitor or other parts of the circuit may be damaged by the charge current amount.

it is one of the best answer that i found, but the battery inner resistance is ( if the battery is full charged 3.3/10 =0.33 ohm) not 22 mohm

but the battery inner resistance is ( if the battery is full charged 3.3/10 =0.33 ohm) not 22 mohm
Clearly a wrong assumption. What's the meaning of the 60A and 150A numbers in the datasheet in your opinion?

Typically, the inner resistance is even lower than 22 mohm, otherwise there won't be a danger of exceeding a maximum discharge current.

P.S.: I previously overlooked the specification of Ri < 6 mohm in the datasheet.

Clearly a wrong assumption. What's the meaning of the 60A and 150A numbers in the datasheet in your opinion?

Typically, the inner resistance is even lower than 22 mohm, otherwise there won't be a danger of exceeding a maximum discharge current.

P.S.: I previously overlooked the specification of Ri < 6 mohm in the datasheet.

ah so the inner resistance could be <6mohm ? and what about the value that i give ? 3.3/10 ?? in the datasheet of the capacitor i didn't find the inner resistance of the https://www.farnell.com/datasheets/438325.pdf

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