What the port can actually deliver
A legacy USB-A port runs at 5 V, and at the 1.5 A most chargers will supply that is about seven and a half watts. That is the whole budget, whatever the iron is capable of. It heats a fine tip quickly enough for a header pin or a thin wire, and it will stall the moment you touch a ground plane or a chunky connector shell.
USB-C Power Delivery changes the arithmetic completely, because it negotiates higher voltages. The same physical iron on a PD supply that can offer 20 V will draw far more, and the irons sold as sixty, seventy or one hundred watt units are quoting what they can take under PD, not what they will get from a phone charger. The supply is therefore part of the specification: a 100 W iron on a 5 V charger is an 8 W iron.
Battery irons face the same physics with a different limit. A small internal cell can deliver a useful burst but has a modest total energy budget, so runtime is measured in joints rather than hours. They suit field repairs and a few connections away from power, not an afternoon of assembly.
| Supply | Realistic power | Suits |
|---|---|---|
| USB-A at 5 V, 1 A | About 5 W | Fine wire, header pins, light rework |
| USB-A at 5 V, 1.5 A | About 7 to 8 W | Small joints, connectors on thin wire |
| USB-C PD, 20 V capable | Tens of watts, per the iron rating | General electronics, thicker wire |
| Internal battery | Short bursts, limited total energy | Field repairs, a handful of joints |
Why wattage alone does not predict performance
Soldering is a heat transfer problem, not a temperature problem. The tip has to put enough energy into the joint fast enough to melt the solder before the surrounding copper carries it away. A large ground plane, a battery tab or a brass connector is a heat sink, and it is the ability to keep supplying energy that decides whether the joint forms.
That is why a small iron sitting at 400 degrees can fail on a joint a bigger iron makes at 320. Turning the temperature up to compensate is the wrong lever: it damages boards, degrades flux before it can work, and shortens tip life, without solving the underlying shortage of power.
It is also why tip shape matters more than people expect. A fine conical tip has very little contact area, so it transfers heat slowly whatever the iron behind it. A chisel or bevel tip laid against the joint moves far more heat and is the right default for anything but the finest work.
Cartridge tips and why they heat so fast
The irons in this class that perform well almost all use a cartridge tip: the heating element and the temperature sensor are built into the tip itself rather than sitting in a separate barrel. The heat has almost no distance to travel and the sensor is measuring the working end rather than something further back, so the iron reaches temperature in seconds and recovers quickly when you load it.
The practical consequence is that the tip is a consumable that contains the expensive part. Tips are keyed to a family, and stocking a chisel and a fine tip for whichever family your iron uses is worth doing at the outset, because a worn tip presents as an iron that has lost power.
Look after them the same way as any tip. Keep them tinned, wipe on brass wool rather than dragging across a wet sponge, and never file or sand the plated working face, which removes the iron plating and lets the copper core dissolve into the solder.
Setting temperature and reading the display
Leaded solder melts around 183 degrees and is comfortably worked in the low three hundreds. Lead free alloys melt higher, commonly in the neighbourhood of 217 to 227 degrees depending on the alloy, and need a correspondingly higher tip setting. The listings in this range typically span roughly 180 to 450 degrees, which covers both.
Start at the lower end that works and go up only if joints are not forming. Excess heat lifts pads, cooks flux before it can clean the surfaces, and shortens tip life sharply. If a joint will not take at a sensible temperature the answer is usually more tip contact area, better flux, or more power, not more degrees.
Treat the displayed number as the controller setpoint rather than a measurement of the joint. Small irons vary in how closely the tip follows the display under load, and the useful check is how the solder behaves: it should flow and wet within a second or two of contact, not sit as a ball.
