Battery knowledge · Units and electrical basics
Capacitor
A component that stores energy as charge on two conducting plates separated by an insulator; its voltage rises in proportion to the charge, unlike a battery’s nearly flat curve. The large DC-link capacitors at an inverter’s input draw a huge inrush current when connected to a pack, which is why a pre-charge circuit fills them first.
- Unit
- F (farad)
- Relationship
- Q = C·V; E = ½·C·V²
Example
Explore the graph
Charge rises linearly with voltage; energy rises with voltage squared.
At 5 V: 25 C and 62.5 J.
Q = CV; E = ½CV²
Illustrative model. Ideal constant capacitance; leakage, series resistance and voltage rating excluded.
Use in Lemonergy
Lemonergy Studio blocks
Observe an RC time constant
An RC circuit uses source, resistor, capacitor and reference blocks.
Blocks to use
- Controlled voltage source
Applies voltage
Inputs & settings
- voltageV
- Resistor
Sets resistance
Inputs & settings
- resistanceOhm
- Capacitor
Stores charge
Inputs & settings
- capacitanceF
- initialVoltageV
- Electrical reference
Sets zero potential
Inputs & settings
- Connect p to reference net
This overview identifies the components to use. Follow the example in Lemonergy for their connections and settings.
- Keep R = 1 Ω and C = 1 F.
- Inspect capacitor voltage after one and two time constants.
Example. From zero initial voltage with a 1 V step, ideal capacitor voltage is about 0.632 V at 1 s and 0.865 V at 2 s.
Observe. Doubling resistance or capacitance doubles the time constant.
This generic circuit does not identify cell parameters from measurements.
Open the RC example →References & further reading
Further reading on this topic
These sources provide broader context; they are not presented as citations for every statement in this entry.
- The International System of Units (SI), 9th edition
Bureau International des Poids et Mesures · 2026
Topic background · Definitions of SI units and coherent derived units; 2026 revision.