23/02/2026
🔌 ESR — The Capacitor Flaw You Can't See
🤔 Spent hours on a fault... and the capacitor looked perfect?
Correct capacitance. No bulging. No burn smell.
Yet it was the problem all along.Here's why.
⚡ Every capacitor has a hidden internal resistance, that's the ESR.
⚠️ High ESR can stop a device from working or starting up, even when capacitance reads fine.
🔧 How to measure it?
You need a dedicated ESR meter (photos 02 & 03).
It applies a 250mV signal at 100Hz or 120Hz for large capacitors, 1kHz for small ones, and some meters go up to 100kHz, then calculates the resistance.
📊 What's an acceptable value?
It depends on capacitance and rated voltage, see photo 01.
For exact limits, use the datasheet formula:
ESR = tan δ / (2π × f × C)
📈 Why does ESR increase?
Old age. Excessive heat. Overvoltage.
🔥 The result?
— Extra heat inside the capacitor
— Power supply ripple disrupting digital circuits
— Device won't start
— Unstable output voltage under load
🛠️ Where I've seen it most:
📺 TVs : 160V supply rail
📡 Satellite receivers: 3.3V CPU line
💻 Motherboards: VRM circuit
🔋 Chargers: output stage
🍳 Induction cooktops: power stage
▶️ Almost every device: startup circuit
🌡️ Quick tip: Heating capacitors one by one to find the fault works sometimes, but an ESR meter is faster and more reliable.
✅ Bottom line:
Strange symptoms + capacitors look fine = measure the ESR first.
💬 Share your experience with capacitor faults, let's grow together in this field.
Yasir • Electronics & Embedded Systems
📅 Feb 23, 2026 | Gaziantep