12 V / 24 V DC simulation

Automotive circuit simulator: see the current before you wire it

Draw a car circuit and run it. WireForge solves the whole circuit — every wire is a real resistance — and shows the voltage at each pin and the current in each wire. Fuses blow, overloaded wires burn through, a 12 V bulb on 24 V burns out, exactly when the physics says so.

Open the editor · ▶ Run the live demo

What the simulator calculates

Voltage, current and power on every wire and component — click any of them to read the values.
Voltage drop on long or thin wires from copper resistance, length and cross-section.
Relays pulling in at 60 % of coil voltage and dropping out below 25 %; switches and momentary buttons.
Fuses blowing on a blade-fuse time-current curve (ISO 8820-3): they hold at 110 %, take minutes at 135 %, about a second at 2× and blow instantly on a short.
Wires burning through when the current is far above what their cross-section carries and no fuse stops it.
Bulbs and other loads burning out on too much voltage — a 12 V lamp on 24 V goes at once.
A battery with internal resistance, an alternator that charges when the engine turns, a starter that draws about 100 A.
An ECU that reads sensors and fires injectors and coils once it sees the crankshaft signal.

Warnings in plain language

The simulator explains what is wrong instead of only drawing numbers: a short circuit with no fuse in the path, a fuse that will blow in about N seconds, a wire that is overloaded or burned, a load running on too little or too much voltage, a relay that chatters because it feeds its own coil, relay terminals 30 and 87 swapped, a relay coil that never gets enough voltage, a ground that is not connected to the battery. Click a warning to jump to the part.

What it does not model

It is a steady-state DC model. It does not simulate AC, waveforms or transients, CAN bus or diagnostic codes, transistors, diodes or PWM dimming, or mechanical parts. Knowing the limits is part of trusting the numbers.

Try it on a short circuit

Open the “Short circuit and a fuse” demo below.
Turn on the fog lamp switch — the lamp lights, the wire shows its current.
Hold “Chafed wire”: the wire touches the body and the current jumps.
The 10 A fuse blows before the wire overheats; “Replace blown” puts in a new one.
Now open the editor, remove the fuse and try again — the wire burns instead.

Questions

How accurate is the simulation?

For DC circuits it is exact: wires, contacts, fuses and loads are resistances and the circuit is solved as a whole. Fuse and wire behaviour follow published time-current curves and conservative harness ratings.

Can it simulate a short circuit?

Yes. Put a momentary button between a power wire and ground and hold it. With a correct fuse the fuse blows; without one the wire burns through and the simulator warns about the fire risk.

Does it work for 24 V vehicles?

Yes, every voltage from 6 to 48 V. Put a 12 V lamp on a 24 V system and it burns out, as it would on the truck.

Is the simulator free?

Yes, the simulator is part of the free plan, and the demos open without an account.

More guides

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