ElectroHub

Component Substitute Checker

Every parameter follows a rule, and the rules point in different directions. Voltage ratings may go up. ESR and on-resistance must come down. A fuse rating must not move at all. Enter what the original is and what you have, and each parameter gets its own verdict.

Can I substitute this component?

Every parameter follows a rule, and the rules point in different directions. Some may go up, some must come down, one must match exactly. Enter what the original is and what you have, and each one gets its own verdict.

The value has to match; everything else is headroom. The one people get wrong is power — a resistor of the right value in the wrong wattage runs hot, drifts, and eventually opens.

ParameterRuleOriginalYours
Resistance(Ω)± 5 %
Power rating(W)≥ original
Voltage rating(V)≥ original
Tolerance(%)≤ original
Fill in both columns for at least one parameter to get a verdict.

What the numbers cannot tell you

  • Same package, or at least one that fits the footprint and clears its neighbours.
  • Temperature coefficient, if the circuit is a reference or a precision divider.
  • Wirewound resistors are inductive — do not put one where a current-sense or RF resistor was.
Common trap: Substituting a higher wattage is always safe electrically, but a 2 W resistor is physically much larger than a ¼ W one and may not fit, or may bridge to an adjacent track.

The formula

at-least: candidate ≥ original | at-most: candidate ≤ original | match: within ± tolerance | exact: must be equal

at-least
a rating with headroom — voltage, current, power, temperature
at-most
a defect rather than a rating — ESR, forward drop, on-resistance, recovery time
match
the value the circuit was designed around — resistance, capacitance, zener voltage
exact
must not move in either direction — a fuse current rating

Worked example

Replacing a 100 µF 25 V 105 °C electrolytic with a 100 µF 50 V 85 °C part.

  1. Capacitance 100 µF vs 100 µF — matches ✓
  2. Voltage 50 V vs 25 V — higher is safe ✓
  3. Temperature 85 °C vs 105 °C — LOWER, and this one is an at-least rule ✗

Not a safe substitute. The voltage headroom is fine, but an 85 °C part in a 105 °C position has a fraction of the service life near anything warm.

Where you'll use it

Repairs, and any time a part is out of stock. Nine component families are covered — resistor, capacitor, diode, zener, BJT, MOSFET, LED, fuse and linear regulator — each with the checks a number cannot make: pinout, polarity, package, dielectric class and fuse speed.

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