# Supercapacitor charging?

1. Mar 22, 2015

### cosmos1226

I have supercapcitor 2.7V, 350F. I want to charge it by 0.001mA 20V power source. Is it safe?
Thanks you!.

2. Mar 22, 2015

### davenn

hi
welcome to the forums

well its a 2.7V capacitor ... what do you think ?

Dave

3. Mar 23, 2015

### Staff: Mentor

What arrangement will you use to charge it? How do you know your power supply is limited to 0.001mA?

4. Mar 23, 2015

### willem2

A 350 F capacitor charged to 2.7 volt contains a charge of 2.7*350 = 945 Coulombs.
If the current is really limited to 0.001mA, it would take 945 / (10^-6) = 9.45 * 10^8 seconds = 29.9 years for it to charge to 2.7 volts, so you'd be ok for a long time.
In practice there will be a lot more leakage current than 0.001 mA and the capacitor would never charge to 2.7 volt.

5. Mar 23, 2015

### cosmos1226

I'm experimenting power supply 20V for charging 27V capacitor 350F. Supercapacitor is loaded, but does know it safe???

6. Mar 23, 2015

### Staff: Mentor

Is the capacitor rating 2.7V or 27V?

7. Mar 24, 2015

### cosmos1226

. maxwell supercapacitor 2.7V 350F. thánks you

8. Mar 24, 2015

### Staff: Mentor

You could connect a pair of resistors as a potential divider to reduce your 20V down to a safe level, say 2.2V. Then the supercapacitor could be safely left to charge unsupervised, and you'd know that in a few decades it should be almost fully charged to 2.2V

You haven't answered why you want to charge it at 0.001mA, and I presume that is not the figure you intend.

9. Mar 24, 2015

### cosmos1226

Although the voltage is 20V but only amperage 10mV (it as a leak). so, I do not want to pass any parts change any power consuming.

10. Mar 24, 2015

### Staff: Mentor

10mV is not a current

In theory, you could connect a parallel 2.2V zener diode to limit the capacitor's voltage at 2.2V, but a practical zener would have significant leakage current below a capacitor voltage of 2.2V.

11. Mar 24, 2015

### cosmos1226

I'm sorry, 10mA

12. Mar 24, 2015

### Staff: Mentor

So it's 10mA now!

Up until this, it has been one-thousandth of a milliamp (0.001mA).

Are you sure it's 10mA??