686 capacitor value
68 µF
68,000,000 pF · 68000 nF · 68 µF
| Marked code | 686 |
| Picofarads | 68,000,000 pF |
| Nanofarads | 68000 nF |
| Microfarads | 68 µF |
| Farads | 6.80e-5 F |
Reading the code
The three digits are not a part number. The first two are the value in picofarads and the third says what to do with them:
68 × 106 = 68,000,000 pF
So 686 is 68 followed by 6 zeros: 68,000,000 pF. The code is always in picofarads even when the part is sold in microfarads, which is the whole difficulty with it — a capacitor marked 686 is stocked as 68 µF and the two numbers look nothing alike.
What 68 µF does at frequency
A capacitor's opposition to a signal is its reactance, 1 ÷ (2πfC), and it falls as the frequency rises. Over the range of frequencies a circuit can put across it, a 68 µF part covers several orders of magnitude:
| Frequency | Reactance |
|---|---|
| 50 Hz — mains | 46.81 Ω |
| 1 kHz — audio | 2.34 Ω |
| 100 kHz — switching | 23.4 mΩ |
| 10 MHz — RF | 0.2 mΩ |
Ten times the frequency is a tenth of the reactance, every time — which is why choosing a decoupling capacitor is really choosing the frequency band you want it to be low-impedance across, and why boards carry several sizes in parallel rather than one large one.
The letter after the number
A code like 686K carries a tolerance letter. It is not part of the value:
| Letter | Tolerance | 68 µF means |
|---|---|---|
686J | ±5% | 64.6 µF to 71.4 µF |
686K | ±10% | 61.2 µF to 74.8 µF |
686M | ±20% | 54.4 µF to 81.6 µF |
686Z | +80% / −20% | 54.4 µF to 122.4 µF |
A Z is worth knowing about. +80%/−20% is a real tolerance on cheap high-permittivity ceramics, and it means a part marked 686Z can legitimately be anything from 54.4 µF to 122.4 µF. Those go in decoupling positions where only the rough size matters, never in a timing or filter position.
Where 68 µF turns up
Microfarads and up is bulk energy storage: holding a rail up between switching cycles, smoothing a supply, or coupling a signal that goes down to a few hertz. Above about 10 µF ceramics give way to electrolytics and tantalums, which is why the code runs out here.
Frequently asked questions
What is the value of a 686 capacitor?
68 µF — 68,000,000 pF · 68000 nF · 68 µF. The first two digits are the value in picofarads and the third is how many zeros follow, so 686 is 68 followed by 6 zeros = 68,000,000 pF.
What is a 686 capacitor in µF?
68 µF. Going from picofarads to microfarads is six decimal places, which is where most of the confusion with these codes comes from — 68,000,000 pF, 68000 nF and 68 µF are the same capacitor written three ways.
What does the letter after 686 mean?
Tolerance. 686K is ±10%, 686J is ±5% and 686M is ±20% — so a 686K is anywhere from 61.2 µF to 74.8 µF and still in specification. A Z means +80%/−20%, which is not a mistake: some ceramic dielectrics really are that loose.
What is the impedance of a 686 capacitor at 1 kHz?
2.34 Ω. Reactance is 1 ÷ (2πfC), so it falls as the frequency rises: the same part is 23.4 mΩ at 100 kHz and 0.2 mΩ at 10 MHz.
Nearby codes
- 826 capacitor — 82 µF
- 108 capacitor — 0.1 pF
- 128 capacitor — 0.12 pF
- 158 capacitor — 0.15 pF
- 188 capacitor — 0.18 pF
- 228 capacitor — 0.22 pF
- 278 capacitor — 0.27 pF
- 338 capacitor — 0.33 pF
- 398 capacitor — 0.39 pF
- 478 capacitor — 0.47 pF