P-Type Alternator Wiring¶
Quick reference¶
| Aspect | Specification |
|---|---|
| Wire | 12 AWG tinned stranded on GND; 14 or 16 AWG acceptable on BAT+ and field |
| Regulator Power Wire (BAT+) | A + bus bar or distribution point downstream of the bank's main fuse, not the battery post; on the shunt's load side when the shunt is in the positive lead |
| Regulator Ground Wire | Battery negative post or a bus bar at the same potential; on the shunt's load side when the shunt is in the negative lead; shortest run |
| 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 |
| 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+ | A + bus bar or distribution point downstream of the bank's main fuse (the shunt's load side when the shunt is in the positive lead), through a 10 A fuse, and jumper |
| 2, GND | The battery negative post or a bus bar at the same potential (the shunt's load side when the shunt is in the negative lead) |
| 3, FIELD_FOR_N_TYPE | Jumper blade only, bridged from terminal 1 |
| 4, FIELD_FOR_P_TYPE | Regulator Field wire to the alternator, through the field fuse |
Where to land the regulator's battery wires
Shunt in the positive lead
Power (red): the load side of the shunt, downstream of the bank’s main fuse.
Ground (black): the battery negative post, or a bus bar at the same potential. This wire must be 12 gauge and as short as possible.
Voltage sense, Cable 2 pin 11: the battery positive post, on the battery side of the shunt.
Shunt sense, Cable 2 pins 9 and 10: across the shunt.
Before wiring pins 9 and 10 to a shunt in this lead, read what it exposes them to, below.
No battery voltage correction is needed.
Shunt in the negative lead
Power (red): the + bus bar, or another distribution point downstream of the bank’s main fuse.
Ground (black): the load side of the shunt. This wire must be 12 gauge and as short as possible.
Voltage sense, Cable 2 pin 11: the battery positive post.
Shunt sense, Cable 2 pins 9 and 10: across the shunt. The battery voltage correction needs them.
The regulator corrects its battery voltage reading for the shunt’s drop by itself, once Shunt Location is set to Negative lead and Cable 2 pins 9 and 10 run to this shunt.
If your shunt is in the battery negative lead and its current reaches the regulator only over NMEA 2000 or VE.Direct, the regulator’s own battery voltage reading runs high while charging, by charging current × shunt resistance (10 mV per 100 A on a 500 A / 50 mV shunt). Wiring Cable 2 pins 9 and 10 to the shunt removes it.
With no shunt, the Regulator Power Wire lands on a + bus bar or distribution point downstream of the bank’s main fuse, the Regulator Ground Wire on the battery negative post or a bus bar at the same potential, the voltage sense wire on the battery positive post, and Cable 2 pins 9 and 10 are not used.
At the same potential. The Regulator Power Wire is not part of the battery voltage reading, so it does not need the post: it lands on a bus bar or distribution point downstream of the bank’s main fuse, on the correct side of the shunt (the fuse rating appendix below explains why). The Regulator Ground Wire and the voltage sense wire are the two ends of the battery voltage reading, so for them it means bolted to the post, or joined to it by a short heavy link with no fuse, switch, or shunt in it. Every milliohm between the post and the landing, times the battery current flowing through it, adds to the reading: 0.5 mΩ of switch, fuse, and cable is 50 mV at 100 A, five times the shunt’s own drop in the graph below.
The shunt inputs with a positive-lead shunt. A shunt in the positive lead puts the regulator’s two shunt inputs, Cable 2 pins 9 and 10, at battery voltage. They are rated to 85 V and have no surge clamp of their own, unlike the voltage sense input on pin 11. A voltage spike on the battery wiring, such as a BMS opening the battery while the alternator is charging, reaches them, and the chip they connect to is the one that measures the battery voltage the regulator charges to. On 12 and 24 V systems a spike that size is unlikely, and it would harm most of the other electronics on board too. On 36 and 48 V systems, 85 V is much closer to normal operating voltage: a 48 V bank absorbs near 58 V. Put the shunt in the negative lead on any system where you have the choice. On 36 and 48 V systems with the shunt in the positive lead, bring its current in over VE.Direct or NMEA 2000 instead of wiring pins 9 and 10 to it.
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 BAT+ and field 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 fits, 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, set Battery voltage for charge stage changes to an external reading: NMEA 2000, including a BMS that publishes battery status, or Victron VE.Direct. That moves the bulk, absorption, float, and rebulk decisions onto the external reading. The voltage control loop and the protections still use the onboard sensor, so the voltage the regulator holds keeps the error shown below. The choice is offered during commissioning.
* 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¶
Full-field and battery short hazards at the plug
In P-type wiring the bridge carries battery voltage, and two wires sit close enough to touch it.
Regulator Field wire, terminal 4. It sits beside the bridge's blade in terminal 3. Bare copper on an over-stripped field wire that touches the blade shorts the Regulator Field wire straight to battery positive, 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.
Regulator Ground Wire, terminal 2. The jumper's broken-off middle blade stub sits directly under it. Bare copper on an over-stripped ground wire can touch that stub, which shorts battery positive to ground at the plug and blows the BAT+ fuse.
Strip no more than 5 mm (0.2 in), push each wire fully into its hole, and inspect the plug to confirm no bare copper shows near the bridge or the stub.
Fusing¶
- Regulator BAT+ wire, at the end it taps: a + bus bar or distribution point downstream of the bank's main fuse rather than the battery post (the fuse rating appendix below explains why). 10 A.
- Regulator Field wire, near the regulator. 10 A.
- 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.
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 |
Field resistance¶
There is no meter step during wiring: the regulator measures the field resistance itself during setup, in the field resistance test right after the Prerequisites screen. On a 24 V and up boat with no battery shunt on Cable 2 pins 9 and 10, that test needs a DC clamp meter or a multimeter with a 10 A range. A 12 V boat with no shunt can skip it.
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 → board BAT+ input → jumper → Q3 → FIELD_FOR_P_TYPE → Regulator Field wire → field winding → alternator case → engine ground → battery negative.
Field current returns through the alternator case and the engine ground strap, so it never flows through the Regulator Ground Wire while the switch is on.
Output off. The field winding keeps its current flowing through the regulator's freewheel diode (D5) and back out to the field. That current is drawn from wherever the Regulator Ground Wire lands (the battery negative post, a bus bar at the same potential, or a negative-lead shunt's load side), up the Regulator Ground Wire, and into the regulator, so the freewheel path is what puts field current in the Regulator Ground Wire.
What the shunt measures. The battery supplies field current only during the on part of each switching cycle. During the off part the field winding keeps its own current circling through the alternator case, the engine ground, the Regulator Ground Wire, and the regulator, and the battery supplies none of it. Every other load on the boat lands on the shunt's load side. Whichever regulator wire shares the shunt's lead, power or ground, lands there too, as the drawings above show, and that keeps the loop out of the shunt. The shunt then reads exactly what the battery supplies: the field current while the switch is on, plus the board's own draw. Land the Regulator Ground Wire on the battery post with the shunt in the negative lead and the freewheel current crosses the shunt as well, and state of charge, tail current, and the battery-current limit would all count it as battery current.
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 | +0.036 V | +0.073 V | +0.114 V |
| 12 AWG, 3 ft | +0.041 V | +0.083 V | +0.130 V |
| 12 AWG, 6 ft | +0.056 V | +0.114 V | +0.177 V |
| 12 AWG, 10 ft | +0.075 V | +0.154 V | +0.240 V |
Appendix: fuse current rating and where to tap BAT+
A fuse carries two current ratings, and they describe different things. The 10 A is the current that melts the element. The interrupting rating is the largest current the fuse can cut off, and it is 1000 A for both 10 A fuses in the fuse table above. OptiFuse publishes 1000 A at 80 V DC for the ANR80. Sherco lists SAE compliance for the USATC10, and SAE blade fuses are rated 1000 A at 32 V DC. A dead short does not draw 10 A, it draws whatever the bank can deliver, and a large bank can deliver 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's own resistance limits most of this. 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 limit 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. On P-type wiring the field's off-time current runs through the freewheel diode (D5), which is connected between the GND and field terminals, and the loop closes through the Regulator Ground Wire, the engine ground, and the alternator case. That loop never passes through the protection stage, so it stays intact whether the 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 trips the controller somewhere between 60 V and 65 V, and it isolates the board in about 5 µs. The field's stored energy decays in the loop through D5 rather than into the board, so the alternator de-excites while the board is unpowered. Power restores automatically once the bus falls back below about 58 V.
Short circuit on the Regulator BAT+ wire. The external BAT+ fuse clears it. The controller trips on voltage, not on current, so the fuse is the only thing that ends a short on that wire. Fuse rating and holder are in the fusing section above, and the board's own draw is a fraction of an amp, so nothing the regulator does on its own comes near the fuse.
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 B+. The field switch is outside the input protection stage entirely, so nothing in this stage detects that fault, and neither fuse does either: full-field current is normal current. A short to B+ anywhere along the Regulator Field wire locks the field on at full drive, and the alternator runs unregulated into overvoltage. At the plug, that short is the field wire touching the bridge's blade in terminal 3. A Regulator Ground Wire touching the jumper stub is a separate fault that shorts battery positive to ground and blows the BAT+ fuse. The short hazard section above covers both.
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 reaches everything on the bus. The board's TVS clamps what reaches its input, but the alternator's rectifier is what is usually damaged. 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.