# Calculators

## Capacitor energy from capacitance and voltage online calculator & Python code

TechOverflow calculators:
You can enter values with SI suffixes like 12.2m (equivalent to 0.012) or 14k (14000) or 32u (0.000032).
The results are calculated while you type and shown directly below the calculator, so there is no need to press return or click on a Calculate button. Just make sure that all inputs are green by entering valid values.

C

V

#### Formula

$$E = \frac{1}{2}\cdot{}C\cdot{}U_p^2$$

#### Python code

You can use the UliEngineering library like this:

from UliEngineering.Electronics.Capacitors import capacitor_energy
from UliEngineering.EngineerIO import auto_format, auto_print

# These are equivalent:
energy = capacitor_energy("100 uF", "24 V") # energy = 0.0288 (J)
energy = capacitor_energy(100e-6, 24.0) # energy = 0.0288 (J)

# ... or get out a human-readable value:
energy_str = auto_format(capacitor_energy, "100 uF", "24 V") # "28.8 mJ"
# ... or print directly
auto_print(capacitor_energy, "100 uF", "24 V") # prints "28.8 mJ"


In case you can’t use UliEngineering, use this Python function:

def capacitor_energy(capacitance, voltage):
return 0.5*capacitance*voltage*voltage

# Usage example:
print(capacitor_energy(100e-6, 24.0)) # prints 0.0288 (J)

Posted by Uli Köhler in Calculators, Electronics

## X1/X2/Y1/Y2/Y4 impulse withstand rating voltage calculator (IEC 60384-14)

IEC 60384-14 specifies that X1/X2-rated capacitors shall be tested to withstand an impulse voltage of 4 kV (X1), 2.5 kV (X2, Y4), 8 kV (Y1) or 5 kV (Y2).

However these values only apply for a capacitance $\leq 1 μF$ (except for Y1/Y4 capacitors). Use this calculator for X1/X2/Y2 capacitances $> 1 μF$!

TechOverflow calculators:
You can enter values with SI suffixes like 12.2m (equivalent to 0.012) or 14k (14000) or 32u (0.000032).
The results are calculated while you type and shown directly below the calculator, so there is no need to press return or click on a Calculate button. Just make sure that all inputs are green by entering valid values.

F

#### Formula:

$$Up = \frac{Up_{\leq 1 μF}}{\Large\sqrt{\frac{C}{1\,000\,000\frac{μF}{F}}}}$$

where:

• $Up$ is the impulse withstand voltage rating
• $C$ is the capacitance in Farads
• $Up_{\leq 1 μF}$ is the voltage rating for that capacitor class with a capacitance of $\leq 1 μF$:
• For X1-class: 4 kV
• For X2-class: 2.5 kV
• Y1-class impulse withstand voltage is always 8 kV no matter what capacitance
• For Y2-class: 5 kV
• Y4-class impulse withstand voltage is always 2.5 kV no matter what capacitance

#### Why is the impulse withstand voltage lower for larger capacitors?

The rationale behind the derating of the impulse withstand voltage is that larger capacitances will have sufficient capacitance so that a given overvoltage doesn’t cause a large voltage spike in the capacitor.

The formula (see above) is chosen so that the energy in the capacitor:

$$E = \frac{1}{2}\cdot{}C\cdot{}U_p^2$$

is kept constant (i.e. at the same value as for a equivalent capacitor of 1 μF).

Posted by Uli Köhler in Calculators, Compliance, Electronics

## Inductive reactance online calculator & Python code

Use this online calculator to compute the reactance of an inductor in Ω at a specific frequency given its inductance.

TechOverflow calculators:
You can enter values with SI suffixes like 12.2m (equivalent to 0.012) or 14k (14000) or 32u (0.000032).
The results are calculated while you type and shown directly below the calculator, so there is no need to press return or click on a Calculate button. Just make sure that all inputs are green by entering valid values.

H

Hz

#### Formula:

$$X_L = 2\pi fL$$

#### Python code:

The preferred way is to use UliEngineering’s UliEngineering.Electronics.Reactance.inductive_reactance:

from UliEngineering.Electronics.Reactance import *
# You can either pass strings like "150 uH" or values like 150e-6

inductive_reactance("150 uH", "10 MHz") # returns 9424.77796076938

from UliEngineering.Electronics.Reactance import *
from UliEngineering.EngineerIO import *

# Compute value as a string
xc = auto_format(inductive_reactance, "150 uH", "10 MHz") # "9.42 kΩ"

# ... or print directly
auto_print(inductive_reactance, "150 uH", "10 MHz") # prints "9.42 kΩ"

In case you can’t use UliEngineering and you want to do it manually, here’s a minimal example:

import math
def inductive_reactance(f, l):
"""Compute the inductive reactance"""
return 2*math.pi*f*l
Posted by Uli Köhler in Calculators, Electronics, Python

## Capacitive reactance online calculator & Python code

Use this online calculator to compute the reactance of a capacitor in Ω at a specific frequency given its capacitance.

TechOverflow calculators:
You can enter values with SI suffixes like 12.2m (equivalent to 0.012) or 14k (14000) or 32u (0.000032).
The results are calculated while you type and shown directly below the calculator, so there is no need to press return or click on a Calculate button. Just make sure that all inputs are green by entering valid values.

F

Hz

#### Formula:

$$X_C = \frac{1}{2\pi fC}$$

#### Python code:

The preferred way is to use UliEngineering’s UliEngineering.Electronics.Reactance.capacitive_reactance:

from UliEngineering.Electronics.Reactance import *
# You can either pass strings like "150 pF" or values like 150e-12

capacitive_reactance("150 pF", "10 MHz") # returns 106.1032953945969

from UliEngineering.Electronics.Reactance import *
from UliEngineering.EngineerIO import *

# Compute value as a string
xc = auto_format(capacitive_reactance, "150 pF", "10 MHz") # "106 Ω"

# ... or print directly
auto_print(capacitive_reactance, "150 pF", "10 MHz") # prints "106 Ω"

In case you can’t use UliEngineering and you want to do it manually, here’s a minimal example:

import math
def capacitive_reactance(f, c):
"""Compute the capacitive reactance"""
return 1./(2*math.pi*f*c)
Posted by Uli Köhler in Calculators, Electronics, Python

## Volts to dBµV online calculator & Python code

Use this online calculator to convert a voltage in Volts to a voltage in dBµV.

TechOverflow calculators:
You can enter values with SI suffixes like 12.2m (equivalent to 0.012) or 14k (14000) or 32u (0.000032).
The results are calculated while you type and shown directly below the calculator, so there is no need to press return or click on a Calculate button. Just make sure that all inputs are green by entering valid values.

V

#### Formula:

$$U_{\text{dBµV}} = \frac{20\cdot\log(1\,000\,000 \cdot U_V)}{ \log(2) + \log(5)}$$

#### Python code:

import math
def volts_to_dbuv(v):
"""Convert a voltage in volts to a voltage in dBµV"""
return (20*math.log(1e6 * v))/(math.log(2) + math.log(5))

Posted by Uli Köhler in Calculators, Electronics

## Slope-intercept form from two points online calculator

TechOverflow calculators:
You can enter values with SI suffixes like 12.2m (equivalent to 0.012) or 14k (14000) or 32u (0.000032).
The results are calculated while you type and shown directly below the calculator, so there is no need to press return or click on a Calculate button. Just make sure that all inputs are green by entering valid values.

X

Y

X

Y

#### Formulae:

$$m = \frac{y_2 - y_1}{x_2 - x_1}$$ $$a = y_1 - m\cdot x_1$$ $$y = m\cdot x + a$$
Posted by Uli Köhler in Calculators, Mathematics

## dBµV to Volts online calculator & Python code

Use this online calculator to convert a voltage in dBµV to a voltage in Volts.

TechOverflow calculators:
You can enter values with SI suffixes like 12.2m (equivalent to 0.012) or 14k (14000) or 32u (0.000032).
The results are calculated while you type and shown directly below the calculator, so there is no need to press return or click on a Calculate button. Just make sure that all inputs are green by entering valid values.

dBµV

#### Formula:

$$U_{\text{Volts}} = \frac{10^{\frac{U_{dBµV}}{20}}}{1\,000\,000 \frac{V}{µV}}$$

#### Python code:

def dbuv_to_volts(dbuv):
"""Convert a voltage in dBµV to a voltage in volts"""
return (10**(dbuv/20.))/1e6

Posted by Uli Köhler in Calculators, Electronics

## Resistor power dissipation calculator

Use this online calculator to calculate the power dissipation in a purely resistive load. Continue reading →

Posted by Uli Köhler in Calculators, Electronics