Micro Changeover Relay — 12V 35A/20A 5-Pin Resistor Protected

Q: What does "changeover" mean on a relay?
A changeover relay has one common contact that moves between two outputs. In the resting state the common sits on the normally-closed pin, carrying 20 amps there. When the coil energises, the common swings to the normally-open pin and starts carrying up to 35 amps on that side. One relay switches two circuits in opposite phase, which saves pins and board space.

Q: What does the "280 Series" number refer to?
280 Series describes the pin and terminal pattern on the back of the relay: 2.8mm wide by 0.8mm thick blade pins at a standard spacing. Any socket or socket-base kit labelled 280 Series accepts this relay.

Q: What does "resistor protected" do in practice?
A resistor sits across the coil terminals inside the relay body. When the coil switches off, the collapsing magnetic field normally kicks a short high-voltage spike back down the trigger wire. The resistor burns that spike off as heat before it can reach the dash switch or the ECU driving the coil. Any 12V circuit with sensitive electronics upstream of the relay wants this.

Q: Why does the normally-open contact carry 35A but the normally-closed only 20A?
The internal contact geometry is biased toward the normally-open side, so it sinks heat more effectively when switching the heavier load. The normally-closed path makes a smaller contact patch, so it is derated. Pick the leg based on which load draws more. Mount the heavier load (fuel pump, cooling fan) on normally-open.

Q: Can I run a 24V system off this relay?
No. The coil is wound for 12V. Running a 24V trigger through it will burn the coil out inside minutes. For a 24V truck or heavy-equipment circuit, choose a 24V-coil equivalent (same 280 Series pattern, different coil winding).

Q: Which pins are coil pins versus switching pins?
Pin 85 is coil negative and Pin 86 is coil positive. Pin 30 is the common contact. Pin 87 is normally-open and Pin 87a is normally-closed. Pin 85 and Pin 86 are the only pair that carries coil current; the other three carry load current.

Q: Do I need a fuse on the load side?
Yes. The relay's 35A contact is the ceiling, not the fuse. Fit a fuse at the battery or power-distribution side rated below the ceiling; a 30A ATO blade fuse covers most mid-draw loads with headroom. The relay does not blow a fuse — it only carries current.

Q: How is this different from a mini (full-size) relay?
Same five-pin changeover function and same pin naming. The 280 Series micro pattern is roughly half the physical footprint of a mini and uses 2.8mm terminals instead of 6.3mm. Mini relays carry a bit more current (usually 30A or 40A) and dissipate heat better; micro saves loom-tuck space when 35A is enough. Pick micro if the gap is tight; pick mini if the load is near the ceiling.

Q: Can this handle inductive loads (motors, horns, small solenoids)?
Yes. The resistor across the coil protects the trigger side; the contacts handle inductive-load spikes without a snubber for most 12V automotive motors, fans and horns. For larger inductive loads (big compressors, large contactor coils) add a reverse-biased diode across the load coil to clamp its own spike.

Q: What is the expected cycle life?
Around 500,000 mechanical cycles at rated load, which is typical for a 280 Series automotive changeover relay. Switching below the rated load (say running a 15A circuit through a 35A contact) extends that; switching inductive loads at the ceiling shortens it. Normal fuel-pump duty gives years of service.

Q: Does it come with a socket or base?
No. The relay is sold on its own. Pair it with a 280 Series socket base (sold separately) for a plug-in install, or solder the blade pins directly into a loom.

Q: Is it weatherproof?
The body is dust-sealed but not fully waterproof. Mount it inside the cabin, under the dash or in a dry fuse box. Exposed engine-bay or external loom locations call for a sealed-pattern relay in a weatherproof holder.