How to Discharge a Capacitor Safely — Step-by-Step Guide
To discharge a capacitor safely: unplug the equipment and wait, clip a properly sized power resistor across the terminals with insulated leads, hold it in place for about five time constants (5 × R × C), then verify the terminals read 0 V with a multimeter before touching anything. Never short a capacitor with a screwdriver, never trust a part you have not metered, and never assume the internal bleed resistor still works.
Every part on this bench can bite after power-offPhoto: UnsplashThis guide is general safety reference information, not a substitute for qualified electrical service. Capacitors in microwave ovens, HVAC equipment and power supplies store lethal energy and can recharge through connected circuitry. If you are not trained for this work, do not open mains-powered equipment — have a licensed technician do the discharge.
Check
Unplug, wait 30–60 s, confirm the plug reads 0 V and spot the terminals.
Choose R
Pick a pulse-rated resistor from the voltage × capacitance table below.
Discharge
Drain the part through insulated leads, holding for about 5 × R × C.
Verify
Meter the terminals: 0 V (±1 V of rebound) before anything is touched.
5RC
the full-discharge wait (5τ)
20 kΩ · 5 W
HVAC field-service standard
2 kΩ · 10 W
microwave HV practice
0 V
verified before touching
Why Capacitors Hold Their Charge After Power-Off
A capacitor is a charge bucket with no floor drain. While the equipment runs, the supply pushes charge onto the plates and pulls it off again faster than you can blink; the moment the power is cut, whatever charge remains simply sits there with nowhere to go. Nothing about unplugging empties the bucket. The only things that drain it are a deliberate resistive path (your discharge resistor), whatever bleed resistor the designer fitted — and bleed resistors fail open like any other component — and the slow internal leakage that takes minutes to hours, far too slow and far too unreliable to bet your hands on.
The charge you drained can come back
There is a second effect that surprises people who have done this before: dielectric absorption, sometimes called soakage. Part of the stored energy lives not on the plates but in the strained alignment of molecules inside the insulating dielectric. When you short the terminals, the plate charge vanishes instantly — but the dielectric relaxes back over the following seconds and minutes, re-depositing charge on the plates. An electrolytic you drained to 0 V can quietly rebound to a few volts; high-K ceramics rebound proportionally more. This is why every procedure below ends with verify, not drain: the reading that matters is the one on the meter after the rebound, not the one right after the resistor comes off.
Banks add a third trap. In a series string, the sections share the total voltage inversely to their capacitances and leakages. Drain the string’s terminals to zero and the sections can redistribute charge among themselves — one section climbing back to a hazardous voltage while the overall bank reads empty. That is why section 6 treats banks separately, and why the step list ends with leave a bleed resistor in place.
How much energy are we talking about?
The stored energy is E = ½CV² — half the capacitance times the square of the voltage. The square is what makes high-voltage parts dangerous out of proportion to their size. A typical HVAC run capacitor, 45 µF at 440 V, holds about 4.4 J. A camera-flash capacitor, roughly 150 µF charged to 330 V, stores about 8 J — the same energy that makes the flash tube fire, and enough to weld a screwdriver tip or throw your hand across the bench. A microwave oven’s high-voltage capacitor is small in capacitance, around 1 µF, but charged near 2 000 V it still stores about 2 J — modest as energy, lethal as voltage, because 2 000 V is more than enough to push dangerous current through the chest. Historically, television CRTs sat above 20 000 V and remain the classic cautionary tale.
Run the arithmetic on your own part with the capacitor energy calculator — enter any capacitance and voltage pair and it returns the joules, so the decision to treat a part as hazardous is a number, not a guess. As a calibration point: a 100 µF capacitor at 400 V stores 8 J (½ × 100 × 10⁻⁶ × 400²), which is the energy of a rifle primer going off — delivered into whatever the terminals touch.
Clip first, drain, then verify 0 VPhoto: UnsplashThe Discharge Resistor, Sized Properly
A resistor between the terminals is what makes discharge safe: it limits the current, spreads the energy out as gentle heat instead of a welding arc, and drains every section it is connected across. Sizing it takes two checks. The first is time: a capacitor drained through a resistor R decays exponentially, losing 63% of its voltage in one time constant τ = R × C, and reaching an effectively safe level after five time constants, 5τ = 5 × R × C. Pick an R that gives a 5τ wait you will actually honor — a few seconds for a service call, a minute or two is fine too, as long as you then wait that long. The second check is power: the resistor sees an initial power of P = V²/R, decaying to zero as the capacitor empties. Use a pulse-rated wirewound or power film resistor whose rating survives that initial spike; what actually heats the part is the total energy, and the joules stored in almost any single capacitor are modest — it is the concentrated burst, not the total heat, that kills an undersized resistor.
One worked example shows both checks at once. The HVAC standard is a 20 kΩ 5 W resistor. For a 47 µF part at 440 V: the wait is 5 × 20 000 × 47 × 10⁻⁶ ≈ 4.7 s (in practice technicians hold 15–30 s to beat absorption rebound), the initial power is 440² ÷ 20 000 ≈ 9.7 W for an instant, and the total energy is only ½ × 47 × 10⁻⁶ × 440² ≈ 4.5 J spread over several seconds — comfortably inside a 5 W pulse rating. That is why the same two numbers, 20 kΩ and 5 W, keep appearing in HVAC guidance.
Discharge resistor selection table
The table below states experience-based standard practice — resistor values widely used in trade and hobbyist procedure, not datasheet specifications. Every resulting time is derived from t = 5RC with the stated values, so you can recompute any cell for your own part.
| Capacitor voltage | 1 µF | 47 µF | 470 µF | >1000 µF |
|---|---|---|---|---|
| ≤50 V2.2 kΩ · 2 W resistor | ≈0.01 s | ≈0.5 s | ≈5 s | ≈11 s |
| 100–240 V10 kΩ · 5 W resistor | ≈0.05 s | ≈2.4 s | ≈24 s | ≈50 s |
| 400 V20 kΩ · 5 W resistor | ≈0.1 s | ≈4.7 s | ≈47 s | ≈100 s |
| >1 kV100 kΩ · 5 W pulse-rated | ≈0.5 s | ≈24 s | ≈4 min | ≈8 min |
Sanity checks you can reproduce: 10 kΩ against 470 µF gives 5 × 10 000 × 470 × 10⁻⁶ ≈ 23.5 s; 100 kΩ against 1 µF gives 0.5 s; and 20 kΩ against 1000 µF gives 100 s. Where a cell looks slow, that is the honest cost of keeping the resistor’s initial power — V²/R — inside its rating at that voltage; the >1 kV row assumes single capacitors in the ~1 µF range typical of microwave high-voltage circuits, and a 470 µF part at that voltage is genuinely specialist work best left to the equipment vendor’s service documentation.
Never short the terminals with a screwdriver, and never short a capacitor through your meter’s test leads. The screwdriver dumps the full energy through a pinhead contact: it can arc-weld to the terminal, splatter molten metal, weld switch and relay contacts shut, and crack the part it was supposed to make safe. A meter lead is no better — the meter’s internal fuse and wiring are not made to swallow a capacitor’s full discharge, and a lead that whips while vaporizing is its own hazard. The only correct short is through the resistor sized above.
Step-by-Step: Discharging Any Capacitor
These seven steps apply to any capacitor from a 47 µF electrolytic to an HVAC dual-run part — the scenarios after this section add only the specifics. The tools are a digital multimeter, the discharge resistor your voltage band calls for, and insulated leads or alligator clips.
- 1
Unplug the equipment and wait
Disconnect from the wall — or pull the HVAC disconnect and lock it out — then wait 30–60 seconds. If the designer fitted a bleed resistor and it still works, this alone removes most of the charge. Treat the wait as a bonus, not the procedure.
- 2
Verify the absence of voltage at the plug
Prove your meter first on a known-live outlet, then meter the disconnected plug and cord and confirm 0 V. This checks both halves of the trust chain at once: the meter can actually read, and the equipment is actually de-energized.
- 3
Identify the terminals
Find every terminal before anything touches anything: HERM, FAN and C on a dual-run HVAC capacitor; the sheathed blade quick-connects on a microwave high-voltage capacitor; marked + and − on polarized electrolytics. Map which terminals belong to which internal section, because you will discharge every pair, not just the convenient ones.
- 4
Connect the discharge resistor with insulated leads
Clip the resistor across the terminals with insulated leads or alligator clips — never bare hands holding probe tips on live metal. Work one-handed, the other hand out of the equipment and away from ground: the one-hand rule keeps a fault current from crossing your chest. Your body should never be in the discharge path.
- 5
Hold for about five time constants
State the time from your own numbers: 5 × R × C. The 20 kΩ HVAC standard against 47 µF is 5 × 20 000 × 47 × 10⁻⁶ ≈ 4.7 s; 10 kΩ against 470 µF is about 24 s. In practice hold the connection 15–30 seconds regardless — the extra seconds cost nothing and drain the charge that dielectric absorption returns after the fast first drain.
- 6
Verify 0 V with the meter before touching
Meter directly across the terminals. Accept about ±1 V — that much rebound from absorbed charge is normal and harmless. If the reading climbs back above a few volts, connect the resistor again, hold, and re-verify. The number that authorizes touching is the one on the meter, not the one in your head.
- 7
Banks: leave the bleed resistor in place
While you work on a multi-capacitor bank, leave the discharge resistor clipped across the terminals — or fit proper shorting leads with built-in resistors — so series sections cannot quietly recharge through charge redistribution while your attention is elsewhere.
A discharged capacitor is not a discharged capacitor for long. Dielectric absorption can rebound a drained part to several volts within minutes, and in series banks charge redistributes between sections after the terminals read zero. Meanwhile the internal bleeder resistor you were counting on may have failed open — the reason the part held charge in the first place. Re-verify with the meter immediately before every touch, not once at the start.
Scenario: Microwave Oven Capacitor
The microwave high-voltage capacitor earns its reputation. It works in a voltage-doubler circuit with the high-voltage (HV) diode and the magnetron, so it can sit near 2 000 V or more while the oven runs — and after the oven is unplugged it has two ways of staying dangerous. First, its internal bleed resistor may have failed open, which is exactly the failure mode that leaves a part fully charged on the shelf. Second, the HV diode that feeds it blocks current in one direction, so there is no reverse path through the circuit to drain it for you. The professional habit is to treat the capacitor as live at all times until your own meter says otherwise.
The method: with the oven unplugged and the cover removed, connect a 2 kΩ 10 W (or larger) power resistor across the capacitor terminals using insulated clips. The 5τ arithmetic says the drain is essentially instant — 5 × 2 000 × 1 × 10⁻⁶ = 0.01 s for a typical 1 µF part — but hold the connection for 10–30 seconds anyway, because absorbed charge rebounds and the meter reading after the rebound is the one that counts. Verify the terminals read under 5 V before touching anything. Physical layout matters here too: the terminals are quick-connect blades, often sheathed, precisely because nobody is expected to touch them bare-handed; connect the clip to the insulated lead body, not by feel inside the shroud.
Two don’ts specific to this part: never grab or steady the blade terminals with your fingers while working nearby, and never discharge a high-voltage capacitor through your multimeter’s test leads — the meter’s input circuitry cannot absorb the pulse, and the failure sends the full voltage looking for somewhere else to go, often through the person holding the leads.
If the oven’s problem is the capacitor itself, the same caution applies to replacement: match the capacitance and the AC voltage rating exactly, and treat the HV diode and the magnetron terminals with the same live-until-metered respect.
Scenario: AC / HVAC Run Capacitor
The dual-run capacitor in an air conditioner or heat pump is the most frequently replaced capacitor in the world, and it holds real danger: terminals can sit above 300 V while the unit runs, and the part keeps a chunk of that after shutdown. The field routine is fixed. Unplug the unit or pull the disconnect and lock it out. Remove the access panel and find the capacitor marked 35/5/440 or similar — HERM for the compressor section, FAN for the fan motor, C for the common terminal shared by both internal sections.
Discharge every pair through a 20 kΩ 5 W resistor on insulated leads: HERM to C, FAN to C, and also HERM to FAN — that last pair matters because the two sections meet at C, and a fault or an odd wiring arrangement can leave charge between them even when both sections read drained to common. Hold each pair for 15–30 seconds, then verify each pair reads under 5 V on the meter before your hands go in. The whole dance takes two minutes and it is the difference between a routine service call and an ambulance call.
This procedure is the same one documented on the capacitor under load calculator page, which carries the full field protocol — measuring the part while the system runs, grading the result against the ±5%/±10% health bands, and the substitution rules for the replacement. Discharge is the safety bookend of that workflow: the resistor before the measurement, the meter after.
Scenario: Capacitor Banks and Supercaps
Series banks recharge themselves after you drain them
In a series string the total voltage divides across the sections inversely to their capacitances — and to their leakages, which are never equal. Drain the bank’s terminals to 0 V and you have not necessarily drained each section: charge redistributes through the leakage paths until the sections find a new balance, and one section can climb back to a hazardous voltage while the string as a whole reads empty. The fix is a bleed resistor across every section, which is why commercial high-voltage banks ship with balancing resistors fitted. For your own work: drain the string, then meter each section individually, and leave per-section bleed resistors connected while you work — the leave-it-in-place habit from step 7 exists precisely for this.
Supercapacitors: low voltage, enormous energy
Supercapacitors invert the usual danger profile: a single 2.7 V cell cannot shock you, but the capacitance is enormous, and energy is what starts fires and melts tools. A 100 F cell charged to 2.5 V stores E = ½CV² = ½ × 100 × 2.5² ≈ 312 J — ten times the camera-flash figure, delivered at a voltage gentle enough to make people careless. Discharge a large supercap through only a few ohms with a matching power rating — a 2 Ω 5 W resistor draws an initial 1.25 A and dissipates about 3 W, safely inside rating — and respect the time: 5τ = 5 × 2 × 100 = 1 000 s, roughly 17 minutes, so a supercap drain genuinely takes minutes and there is no way around it without forcing current the resistor cannot take. On series stacks of supercap cells, one more rule matters: never let current run backward through a cell. Reverse polarity destroys supercap cells, and an unbalanced stack that gets shorted can drive the weakest cell negative — drain stacks section by section, same as any series bank.
Common Mistakes and How They Hurt
Almost every capacitor injury traces back to one of five habits. Each has a cheap fix, and every fix appears somewhere in the steps above.
Shorting with a screwdriver
The full stored energy goes through a pinhead contact: the tip welds to the terminal, molten metal splatters, and relay or switch contacts elsewhere in the circuit weld shut. It also hammers the capacitor itself with thermal shock. The 2-joule microwave cap and the 8-joule flash cap both do this convincingly. Fix: a resistor sized from the table — it costs less than the screwdriver.
Probing before discharging
Touching meter probes across a charged high-voltage capacitor puts your hand at the terminal, sends the full voltage into meter input circuitry never built for it, and risks a lead that whips when the input vaporizes. Discharge first, measure second — and for high-voltage parts, discharge through a resistor rather than the meter, always.
Draining once and trusting it
Dielectric absorption returns a few volts to a drained electrolytic, and series sections redistribute charge after the terminals read zero. The single drain proves only that the drain happened — not that the part is safe now. Fix: the verify step, immediately before touching, every time.
Discharge resistor power rating too low
A quarter-watt resistor asked to swallow V²/R = 8 W for its first instant can crack open or go resistive mid- drain — exactly when it is your only current path. The initial power P = V²/R check exists for this reason, and the table’s wattages (2 W, 5 W, 10 W) are the floor, not a suggestion. Pulse-rated wirewound parts exist because ordinary resistors are not.
Forgetting the series sections
Draining the pair you can reach leaves the section you forgot — the HERM-to-FAN pair on a dual-run part, the middle sections of a series string, the second capacitor behind the first. Fix: map the terminals at step 3 and discharge every pair, then meter every section before the hands go in.
Learning how to discharge a capacitor safely is the entry ticket to every other capacitor job — testing, replacement, bank building, repair. When you want the measurement side, the homepage calculator computes charge, energy and reactance for any part, and the guides hub collects the full library, from code reading to the under-load test that pairs with this page’s HVAC scenario.
Frequently Asked Questions
What resistor should I use to discharge a capacitor?▼
Size it with two checks. First, pick a resistance that gives a full-discharge wait you can accept: t = 5RC. Second, check the initial power P = V²/R and use a pulse-rated power resistor. Standard practice: 20 kΩ 5 W for 370–440 V HVAC run capacitors (5τ with a 47 µF part is 5 × 20 000 × 47 × 10⁻⁶ ≈ 4.7 s), 2 kΩ 10 W for microwave high-voltage capacitors (about 1 µF, so 5τ ≈ 0.01 s), 10 kΩ 5 W for 100–240 V supply electrolytics, and 2.2 kΩ 2 W for parts at 50 V or less. The selection table in this guide lists all four voltage bands by capacitance.
How long does a capacitor take to discharge?▼
A capacitor discharging through a resistor loses about 63% of its voltage in one time constant (τ = R × C) and is effectively empty after five time constants, 5τ = 5RC, when less than 0.7% of the voltage remains. Worked examples: a 47 µF HVAC capacitor through 20 kΩ takes 5 × 20 000 × 47 × 10⁻⁶ ≈ 4.7 s; a 470 µF supply capacitor through 10 kΩ takes 5 × 10 000 × 470 × 10⁻⁶ ≈ 23.5 s; a 1 µF microwave capacitor through 2 kΩ drains in about 10 ms. In practice hold the resistor on for 15–30 seconds, because charge absorbed in the dielectric creeps back after the fast drain.
Can I discharge a capacitor with a screwdriver?▼
No. Shorting a charged capacitor with a screwdriver dumps the full energy through a contact the size of a pinhead: the tip can arc-weld to the terminal, splatter molten metal, weld relay or switch contacts shut, and shock the part itself with thermal and mechanical stress that shortens its life or cracks it. It also proves nothing — a series-connected bank can hold dangerous charge on individual sections after the screwdriver drains the terminals. The only correct short is through a properly sized power resistor, verified afterwards with a meter.
How do I discharge an AC (HVAC) run capacitor?▼
Unplug the unit or pull and lock the disconnect, remove the access panel, and find the dual-run capacitor terminals labelled HERM, FAN and C. Discharge every pair — HERM to C, FAN to C, and HERM to FAN — through a 20 kΩ 5 W resistor on insulated leads, holding each pair for 15–30 seconds. Then verify each pair reads under 5 V on a multimeter before touching anything. The pairwise routine matters because a dual-run part is two capacitors sharing one common terminal; draining only one pair can leave the other section charged.
How do I discharge a microwave oven capacitor?▼
Treat the high-voltage capacitor as live even with the oven unplugged — its internal bleed resistor may have failed, and the high-voltage diode in the voltage-doubler circuit blocks any reverse path. Connect a 2 kΩ 10 W (or larger) resistor across the capacitor's terminals using insulated clips; the theoretical 5τ drain is about 10 ms for a typical 1 µF part, but hold the connection for 10–30 seconds so absorbed charge can rebound and drain. Verify the terminals read under 5 V with a meter before touching. Never grab the sheathed blade terminals with your fingers, and never discharge a high-voltage capacitor through your meter's test leads.
Do capacitors recharge themselves after being discharged?▼
Yes, two mechanisms cause it. Dielectric absorption (soakage) means some charge trapped in the insulating material reappears on the terminals minutes after a full drain — an electrolytic can rebound from 0 V to a few volts, and high-K ceramics rebound noticeably. In series capacitor banks, charge redistributes between sections through leakage paths after the bank's terminals read zero, so individual sections can sit at dangerous voltages again. The defence is procedural: after the resistor drain, re-verify with the meter immediately before touching, and leave a bleed resistor connected while you work.
What happens if you touch a charged capacitor?▼
It depends on the voltage and the stored energy. Above roughly 50 V, a charged capacitor can drive current through your body — tingling at low energy, a violent involuntary jerk at 8 J or so, which is what a 100 µF part at 400 V stores. At kilovolt levels the risk is no longer the jolt but electrocution: a microwave capacitor near 2 000 V can push lethal current through the chest, and historical TV CRTs held over 20 000 V. Because discharge is exponential, the first fraction of a second carries the full voltage. Even a part that reads low can rebound through dielectric absorption, which is why the rule is verify 0 V, then touch.
Sources & Notes
The 20 kΩ 5 W resistor standard for 370–440 V HVAC run capacitors is consistent with this site’s existing field-service guidance on the under-load page and reflects widely used trade practice among HVAC technicians. The microwave and other high-voltage scenarios are presented as general practice: specific equipment varies, and the capacitor value, voltage rating and any internal bleed resistor in your particular unit should be verified against the manufacturer’s datasheet or service documentation before work begins.
The discharge mathematics is classical circuit theory, not proprietary analysis: stored energy E = ½CV², the exponential discharge curve with full discharge at five time constants t = 5RC, and the resistor’s initial dissipation P = V²/R. The resistor selection table above is experience- based standard practice rather than a specification, and every time in it is reproducible from 5 × R × C with the stated values. This is an operational safety page — the math tools live elsewhere: the RC time constant calculator computes τ = RC for any pair, and the capacitor energy calculator returns the joules stored at any voltage.
The page exists because discharge is where capacitor work is actually won or lost: the physics takes one paragraph, the table takes one screen, and the rest is the discipline the steps enforce — check, choose, discharge, verify. A reader who leaves owning that loop is safer than one who memorized joule values, and every number used here can be re-derived with the linked calculators in under a minute.
Maintained by the CapacitorCalculator.com editorial team · Last updated: November 2, 2026
Related Guides & Calculators
Types of Capacitors — Ceramic, Electrolytic, Film, Tantalum & Supercap Guide
The capacitor families compared: ceramics, electrolytics, film, tantalum and supercaps — structure, parameter ranges, pros and cons, failure modes and a selection decision path.
How to Discharge a Capacitor Safely — Step-by-Step Guide
Safe capacitor discharge from checklist to verification: resistor sizing by stored energy, worked scenarios for microwave, HVAC and bank capacitors, and the common dangerous mistakes.
How to Test a Capacitor with a Multimeter
Multimeter capacitor testing from meter setup to verdict: the capacitance dial and its µF/mfd symbols, safe discharge, offline and in-circuit measurement, and pass/fail grading thresholds.
What Is Capacitance? Definition, Formula and Units
Capacitance explained from zero: the C = Q/V definition, the farad and its five units, the µF/nF/pF symbols, what a dielectric does and the capacitor families, each linked to the tool that computes it.
RLC Circuit
Solve series or parallel RLC circuits: impedance Z, resonant frequency f₀, Q factor, bandwidth and phase angle from R, L, C and f, with damping state.
Snubber & Bootstrap Cap
Size RC snubbers from parasitic inductance and switch current — C, R and resistor power — plus relay contact buffers, bootstrap capacitors and surge caps.
Cylindrical & Spherical
Calculate capacitance of coaxial cylindrical and concentric spherical structures from dimensions and dielectric constant, with air-filled, vacuum variable, butterfly and wound capacitor variants.
Speaker Crossover Cap
Compute series capacitor (tweeter high-pass) and parallel inductor (woofer low-pass) for 8Ω or 4Ω speakers at any frequency. Covers 1st-order 6dB and 2nd-order 12dB Butterworth crossovers.
DC Link Capacitor
Size DC bus capacitors for 3-phase inverters, VFDs and motor drives: input power, bus voltage, switching frequency and allowable ripple. Output minimum C, RMS ripple current and precharge resistor values.
Capacitor Lifetime
Estimate capacitor life from rated lifetime (e.g. 105°C/2000h), ambient temperature, ripple current derating and voltage stress. Applies the 2^(ΔT/10) rule and outputs both hours and years.
ESR & Ripple Current
Compute equivalent series resistance from tanδ/DF/Q, dissipation, ripple current limits, temperature rise ΔT, ESL-limited SRF & impedance curve trough for aluminum, ceramic and film parts.
PFC & Capacitor Bank
Size kvar compensation for industrial power factor correction: input kW/kVA, PF, target PF, voltage, phase & connection. Output kvar needed, µF per phase (Δ/Y), rated current & inrush estimate.
Cap Voltage Divider
Split voltage across 2–4 series capacitors instantly: Vn = Q/Cn with equal charge Q = Ceq·Vtotal, plus per-cap bars, charge and rating warnings.
Power Supply Cap
Size rectifier bulk, buck-converter output and hold-up capacitors: C = I/(f·ΔV) and C = 2Pt/(V₁²−V₂²), with a ripple and voltage-rating table.
LC Resonance
Get f₀ = 1/(2π√LC) for parallel or series LC tanks, plus Q factor, bandwidth and a capacitor self-resonance (SRF) warning, from any L and C.
RC Filter Cap
Solve C = 1/(2πfR) for low-pass, high-pass, band-pass and notch RC filters, with a live Bode plot, gain readout and an R×C pairs table.
Coupling & Bypass
Size AC coupling, input/output, emitter and cathode bypass capacitors from impedance and cutoff: C = 1/(2πfR), with an audio stage value table.
Crystal Load Cap
Calculate C1 and C2 for a crystal oscillator: C = 2CL − Cstray, with PCB stray cap, transistor input cap and an AT-cut package comparison table.
Motor Capacitor Sizing
Size start and run capacitors for split-phase, cap-start, cap-run and dual-value single-phase motors with HP/voltage inputs and standard ranges.
Capacitor Color Code
Decode 3-band, 4-band and 5-band capacitor color codes to pF/nF/µF with tolerance and voltage, plus a complete reference table.
Capacitive Reactance
Compute Xc in Ω/kΩ/MΩ from frequency and C, with parallel-R || C and series-R + C impedance, phase angle and admittance.
Capacitor Charge
Calculate stored charge Q = CV in C, mC, µC, nC, pC from capacitance and voltage, plus peak displacement current over any R.
RC Time Constant
Get τ in seconds, ms, µs, ns from any R and C pair, plus the 5τ fully-settled time, charge/discharge curve values and cutoff frequency.
Capacitor Energy
Compute energy stored in any capacitor from E = ½CV² with live J/mJ/µJ/nJ/Wh outputs, plus the Q²/(2C) and ½QV forms.
HVAC Capacitor Under Load
Test an HVAC run capacitor under load: enter amps, volts and 60/50 Hz to get µF = 2652 × A ÷ V, graded good/marginal/replace against the rated value.
Parallel Plate Capacitor
Compute capacitance from plate area, separation and dielectric: C = K·ε₀·A/d with 25 real materials, mm²/µm to sq in/mil inputs and fringing warnings.
Series & Parallel Capacitors
Combine up to 12 capacitors in series or parallel with per-cap unit selectors. Live total capacitance, the rule behind it and voltage-sharing notes.
Capacitance Converter
Convert capacitance between pF, nF, µF, mF and F live, and translate any value to its closest EIA 3-digit code with the tolerance range shown.
Discharged? Now Test It Properly
The next step after a safe discharge is knowing whether the part is worth replacing at all: measure it with a multimeter, grade the reading against the health thresholds, and only then order the replacement — free, no account, entirely in your browser.