N-Type Alternator Wiring¶

Power and field plug wired for an N-type alternator, terminals labelled Battery +, Ground and Field: the bridge spans terminals 2 and 4, and the field wire lands in terminal 3

Quick reference¶

Aspect	Specification
Wire	12 AWG tinned stranded on GND; 14 or 16 AWG acceptable on the other three
Regulator Ground Wire	Shortest run, on the battery post or the load side of the shunt
Wire termination	Bare stranded under screw, 5 mm strip maximum
Jumper	EBP 3-5 with middle blade removed
Screw torque	0.5 to 0.6 N·m
Field fuse	10 A
BAT+ fuse	10 A
Field supply fuse	10 A, only if the field is fed by an external wire
Cat6 tap fuses	1 A each, on the conductors that tap boat power
Fuse voltage rating	32 V DC on 12 and 24 V, 80 V DC on 36 and 48 V
Fuse holder	12 AWG: IHWOM12HD on 12/24 V, LPR-02B-12R on 36/48 V
Tap fuse holder	18 AWG: IHWO18 on 12/24 V, LPR-02B-18R on 36/48 V

Terminal assignments (left to right)¶

Terminal	Connects to
1, BAT+	Battery + (or, if using a Shunt on +, to the load side of the shunt) (thru a 10 amp fuse in either case)
2, GND	Battery negative post, or if using a shunt on -, to the load side of the shunt, and jumper
3, FIELD_FOR_N_TYPE	Regulator Field wire to the alternator, through the field fuse
4, FIELD_FOR_P_TYPE	Jumper blade only, bridged to terminal 2

Where to land the Power and Ground leads

Shunt on B+ example

Power (red): ① the battery positive post, or ② the load side of the shunt.

Ground (black): ① the battery negative post. This wire must be 12 gauge and as short as possible.

Leave software shunt compensation OFF.

Shunt on B− example

Power (red): ① the battery positive post.

Ground (black): ① the battery negative post, or ② the load side of the shunt. This wire must be 12 gauge and as short as possible.

Turn Shunt Resistance Compensation ON if you land the Regulator Ground Wire at ②, to avoid the error in the graph below.

Wire and Connectors¶

Wire. The GND terminal requires 12 AWG marine-grade stranded tinned copper, Type II or Type III stranding per ABYC E-11. The other three terminals take the same wire, and in a retrofit they also accept existing 14 or 16 AWG boat wiring. 12 AWG is a tight fit in the 5.08 mm plug, and it does go, including at the terminal that shares its hole with the jumper blade.

Wire termination. Plain stranded wire under the screw, no ferrule required. Strip back no more than 5 mm (0.2 in) from the insulation. See Short hazard below.

Jumper. The supplied Phoenix Contact EBP 3-5 (p/n 1733172) with the middle blade snapped out (already done by X Engineering) gives a 2-position bridge with 10.16 mm prong spacing, matching the regulator's terminal layout.

To install:

Insert the jumper blade flat into the wire entry hole, gray plastic angled down and away (towards the wall or bulkhead) to make the most space for wires.
Push the harness wire fully into the same hole, on top of the blade.
Torque the screw to 0.5 to 0.6 N·m.
Tug-test the wire firmly. If it pulls free, something is wrong, so re-seat and repeat.

Effect of Regulator Ground Wire gauge and length on Battery Voltage Measurement Accuracy¶

Regulator Ground Wire length is to be minimized! In XREG-010, the battery voltage sense chip shares a ground with the field itself, and wires that are excessively long or small gauge can lead to intolerable errors. In those cases, switch the voltage source to external, such as from NMEA 2000, including a BMS that publishes battery status, or Victron VE.Direct. These options will be offered during commissioning.

12 V system24 V system48 V systembench measured*

* battery voltages during test were typical nominal levels, i.e. 13.7 V for a 12 V system.

Short hazard at the bridged-over terminal¶

Uncontrolled full-field hazard — inspect carefully during installation

Bare copper of an excessively stripped wire can accidentally touch the jumper's broken-off middle blade stub. In both P-type and N-type configurations, this is the Regulator Field wire, and the bridge carries battery voltage or GND. Contact shorts the Regulator Field wire straight to the bridge, bypassing the regulator's field switch entirely. The field locks on at full drive, the regulator cannot shut it off, and the field fuse will not blow (full-field current is normal current). The alternator runs unregulated and drives the system into overvoltage. This is obviously extremely dangerous, and at that point only a BMS can save the battery and possibly the boat.

EBP 3-5 bridge with middle blade snapped out — bright conductive metal remains exposed at the break point in the center notch — The bridge after snapping out the middle blade. The bright metal in the center notch is the remnant of the blade — still live whenever the bridge is.

Bridge installed on the plug — the bridged-over wire entry hole is still empty, with the conductive stub directly under it — The bridge installed, no wire in the bridged-over hole yet. The stub lands directly under that hole (2nd from left).

Left hand black (and red!) wire in the bridged-over hole stripped too far — bare strands outside the housing, near the stub — The black wire (left) is stripped too far — exposed strands at risk of touching the stub. Fail.

Correct installation — the wire in the bridged-over hole is fully seated with no bare copper visible near the stub — A good installation: the black wire in the bridged-over hole fully seated, no copper showing at the stub. The red wire is still bad here, but the risk is lower since it's not near the stub.

Fusing¶

Regulator BAT+ wire, near the battery or + bus bar. 10 A.
Regulator Field wire, at the alternator end. 10 A. In N-type the field is fed from inside the alternator, so that end is the source and the fuse belongs there.
Field supply wire, if the alternator has one, at the end it taps. 10 A, the same part as the field fuse. Most N-type machines take the field's positive from an internal tap, so there is nothing to fuse. On the ones that bring it out to a terminal instead and feed it from B+ or the ignition circuit, that wire carries full field current and needs its own fuse, unless what feeds it is already fused. The excite or lamp terminal of a stock internally-regulated alternator is a different thing and carries well under an amp.
Every Cat6 conductor that taps a source of power outside the regulator, at the end it taps. 1 A each, the same fuse in every case: Cable 2 pin 11 (battery), Cable 1 pin 4 (stator), Cable 3 pin 6 (ignition), and Cable 2 pin 16 (BMS output) where one is fitted. Fuse, holder, and termination: Data Cables & Pinout. Nothing else on the four cables is fused: the rest are grounded, fed from the regulator's own current-limited rails, or land on a device output with no source behind them.

On N-type the BAT+ fuse is not a field kill switch

The field is fed from the alternator's own B+, so clearing the Regulator BAT+ fuse leaves it excited. With the battery leads reversed, the crowbar diode clears that fuse and the board goes dark, but the winding stays energized through the return diode for as long as the BAT+ terminal has a path to the battery. Do not run the engine until the wiring is corrected. A TVS that fails short above 71 V clears the same fuse with the same result. On a P-type installation the bridge feeds the field from downstream of that fuse, so blowing it removes field power. Where you have the choice, P-type is the safer configuration for that reason, and any alternator can be converted by rewiring the brushes.

Which fuse to buy, by system voltage¶

All three fuses are ATO blade fuses, and which one you buy depends on the system voltage. A standard automotive blade fuse is rated 32 V DC and the marine "high voltage" ones stop at 58 V; above its rating a fuse can hold an arc instead of clearing the fault, and a 48 V bank absorbs near 58 V. So 12 and 24 V systems take the 32 V part, and 36 and 48 V systems take an 80 V DC rated one.

The power and field fuses are 10 A, on 12 AWG holders:

System voltage	Fuse, 10 A	In-line holder, 12 AWG
12 V and 24 V	Sherco USATC10, 32 V DC	Sherco IHWOM12HD, waterproof
36 V and 48 V	OptiFuse ANR80-UL-10A, 80 V DC	OptiFuse LPR-02B-12R, 125 V DC, IP67

The Cat6 tap fuses are 1 A, on 18 AWG holders. NEC Table 725.144 rates a 24 AWG conductor in a single 4-pair data cable at 2.0 A, and less than that where cables share a bundle, so the fuse has to be small. These wires carry milliamps, which leaves the whole margin available to the conductor. 18 AWG is the finest lead these holders come on, and it splices to a 24 AWG Cat6 conductor in one step-down crimp:

System voltage	Fuse, 1 A	In-line holder, 18 AWG
12 V and 24 V	Sherco ATO1A, 32 V DC	Sherco IHWO18, waterproof
36 V and 48 V	OptiFuse ANR80-UL-1A, 80 V DC	OptiFuse LPR-02B-18R, 125 V DC and IP67 by its maker

Next step¶

Continue to Data Cables & Pinout for the four data-cable pinouts, then install the sensors: Current Sensor and Temperature Sensors.

Appendix: conduction paths

Output on. Battery positive → alternator B+ stud → internal tap → field winding → Regulator Field wire → FIELD_FOR_N_TYPE → Q3 → jumper → board ground → battery negative.

The full field current leaves the regulator through the Regulator Ground Wire every time the switch is on.

Output off. The field's freewheel current returns to the battery through the Regulator BAT+ wire, not through the Regulator Ground Wire.

Appendix: worst-case battery voltage error by Regulator Ground Wire length

Worst case across the full field current range, 12 AWG.

Ground wire	12 V	24 V	48 V
12 AWG, 2 ft	-0.040 V	-0.022 V	-0.011 V
12 AWG, 3 ft	-0.060 V	-0.033 V	-0.017 V
12 AWG, 6 ft	-0.120 V	-0.066 V	-0.033 V
12 AWG, 10 ft	-0.200 V	-0.110 V	-0.055 V

Appendix: fuse current rating and where to tap BAT+

The two numbers describe different things. The 10 A is the current that melts the element. The 1000 A is the largest current the fuse can actually cut off. A dead short does not draw 10 A, it draws whatever the bank can push, and a large bank can push thousands of amps. Past the fuse's limit the element vaporizes but an arc keeps burning across the gap, so the fuse goes on conducting instead of clearing the fault, and the body can rupture.

The wire covers most of this on its own. 12 AWG runs about 1.6 mΩ per foot, so a 6 ft run out and back is near 19 mΩ, which holds a dead short on a 12 V bank to roughly 700 A, and a longer run limits it further. What the wire does not cover is a short close to the fuse, because the fuse only has to break the current available at its own terminals, and that is set by the bank and the heavy cable feeding it rather than by the 12 AWG downstream.

Feeding the Regulator BAT+ wire from a distribution point downstream of the bank's main fuse rather than straight off the battery post keeps the worst case inside what the fuse is rated for.

Appendix: board input protection, what happens in each fault

The BAT+ input runs through an automotive protection controller (TPS48000-Q1) driving back-to-back MOSFETs, with a TVS diode and a crowbar diode across the input terminals. The field's return diode lands on the BAT+ input terminal, ahead of those MOSFETs, so the field always has a path back to the battery whether the protection stage is conducting or has tripped.

Battery leads reversed. The crowbar diode conducts and clears the BAT+ fuse. The board does not power up and is not damaged. Replace the fuse and correct the wiring before trying again — on an N-type installation the field is fed from the alternator, not from the fuse, so a blown fuse does not stop the field if the engine is run with the leads still reversed.

Bus overvoltage — a load dump, a BMS opening under charge, or a failed external charger. The controller trips somewhere between 60 V and 65 V and isolates the board in about 5 µs. The field's stored energy returns to the battery through the return diode rather than into the board, so the alternator de-excites while the board is dark. Power restores automatically once the bus falls back below about 58 V.

Short circuit on the Regulator BAT+ wire. The controller trips at about 15 A after a 14 ms delay and isolates the board, then retries about every 23 s. A short that is still there on retry leaves the board off. The threshold is a dead-short detector rather than a current limit: the board's own draw is a fraction of an amp, so anything between that and 15 A is the external fuse's job. The delay is deliberate, and covers ordinary load steps in the board's own supply such as the WiFi radio starting.

Battery voltage collapses. Below about 5 V at the input the controller shuts down and stays off until the bus recovers, so a flat or disconnected bank leaves the board off rather than browning out.

Regulator Field wire shorted to ground or to B+. The field switch sits outside the input protection stage entirely, so nothing in this stage sees that fault, and neither fuse does either: full-field current is normal current. This is the failure the short hazard section above is about: strip the wires short and inspect the bridged-over terminal.

Battery connection opened while the alternator is charging. Breaking the charging path under load is a load dump: the alternator's own output has nowhere to go, and the spike hits everything on the bus. The board's TVS clamps what reaches its input, but the alternator's rectifier is what usually pays for it. Shut down charging before opening a battery switch or a terminal.

Lightning nearby. Induced surges conducted along vessel wiring are clamped by the TVS and cut off by the overvoltage trip. A direct strike is beyond what any of this survives.

Field circuit

Field current does not pass through the input protection stage in either wiring type — see Fusing above. The field fuse is the protection for the field circuit.

For trip levels, timing, and the circuit itself see the Input Protection hardware doc.