10.3 High-Output Heavy-Duty Alternators, Diode Rectification & Charging Regulation
Key Takeaways
- High-output commercial alternators (160A to 300A+ ratings) predominantly utilize brushless rotor technology, where a stationary field coil eliminates rotating slip rings, carbon brushes, and arcing wear, extending operational life beyond 500,000 to 1,000,000 fleet miles.
- Remote voltage sensing employs a dedicated fused wire connected directly to the chassis battery bank, enabling the solid-state regulator to detect and dynamically overcome charging cable voltage drops (0.5V to 0.8V) across long chassis runs.
- Commercial solid-state regulators provide negative temperature compensation (typically -3 to -5 mV/°C per cell), elevating charging voltage up to 14.8V–15.2V in sub-zero winter conditions and reducing it to 13.2V–13.8V in high summer ambient temperatures to prevent electrolyte boil-off.
- Comprehensive charging system evaluation requires testing full rated output under carbon pile load at high idle (delivering >=90% of nameplate rating) and measuring active circuit voltage drop (maximum 0.50V on positive, 0.50V on ground per TMC RP 129).
- A full-wave rectifier bridge of 6 or 12 silicon diodes converts three-phase AC into DC; an open diode reduces output current by 30% to 40%, whereas a shorted diode injects excessive AC ripple (>0.40V AC RMS) that corrupts SAE J1939 CAN bus data, sets false sensor DTCs, and creates severe key-off parasitic battery drain.
10.3 High-Output Heavy-Duty Alternators, Diode Rectification & Charging Regulation
Core Principle: Modern commercial diesel vehicles function as mobile electrical generation plants. Beyond powering engine electronics, electric cooling fans, transmission actuators, and exterior lighting, charging systems must support heavy sleeper cab "hotel loads," including multi-kilowatt DC-to-AC power inverters, electric HVAC systems, refrigerators, telematics, and trailer liftgates. Commercial alternators (rated from 160A to over 300A) must maintain stable voltage regulation across extreme temperature ranges without corrupting high-speed digital communications.
1. Commercial Brushless Alternator Architecture
Commercial line-haul tractors and severe-service vocational vehicles operate under harsh operating conditions: continuous high electrical loads, severe engine vibration, airborne silica, and corrosive road brine. Conventional automotive alternators use spring-loaded carbon brushes riding against spinning copper slip rings to deliver excitation current to the spinning rotor field coil. In commercial trucking, brush vibration, thermal arcing, and abrasive contamination wear brushes out rapidly, leading to alternator failure.
To achieve maintenance-free lifespans exceeding 500,000 to 1,000,000 miles, heavy-duty commercial fleets utilize brushless alternators (e.g., Delco Remy 24SI, 28SI, 36SI, 40SI; Leece-Neville / Prestolite IdlePro series).
+-----------------------------------------------------------------------------------------+
| BRUSHED VS. BRUSHLESS ALTERNATOR ARCHITECTURE |
| |
| CONVENTIONAL BRUSHED DESIGN (Automotive / Light Duty) |
| Spinning Rotor Field Coil <=== Carbon Brushes ride on spinning Copper Slip Rings |
| * Subject to brush bounce, mechanical wear, spring fatigue, dust arcing, & salt shorts|
| |
| HEAVY-DUTY BRUSHLESS DESIGN (Severe Commercial Service / Delco 36SI) |
| |
| +-------------------------------------------+ |
| | Stationary Field Coil (Fixed to Housing)| |
| +-------------------------------------------+ |
| | |
| +-------------------------------------------+ |
| | Spinning Iron Rotor Poles (No Windings) | <=== Drives magnetic flux |
| +-------------------------------------------+ across dual air gaps |
| | |
| +-------------------------------------------+ |
| | Three-Phase Stator Windings (Output) | |
| +-------------------------------------------+ |
| * ZERO moving electrical contacts. No brushes. No slip rings. 1,000,000 mile lifespan. |
+-----------------------------------------------------------------------------------------+
The Mechanics of Brushless Electromagnetic Induction
- Stationary Field Coil: The copper electromagnetic field winding is wound around a stationary iron spool that is firmly bolted directly to the alternator rear end-frame housing. It does not rotate, eliminating the need for slip rings, carbon brushes, and brush springs.
- Rotor Pole Geometry: The rotor assembly consists of a shaft supporting two precision-cast iron pole pieces featuring interleaved claw fingers. These iron pole pieces rotate around and through the stationary field coil across narrow, precision-machined air gaps.
- Flux Conduction: When the solid-state voltage regulator supplies direct current to the stationary field coil, an intense magnetic flux is created in the iron core. This flux jumps across the air gap into the spinning iron rotor poles, magnetizing one claw group as North poles and the interleaving claw group as South poles.
- Three-Phase Stator Induction: As the magnetized iron claw poles rotate past the stationary three-phase stator windings wound into the outer housing, alternating magnetic flux sweeps across the stator conductors. This induces three-phase alternating current (AC) purely through magnetic induction without any sliding electrical contacts.
2. Three-Phase Stator Windings & Full-Wave Rectifier Bridge
Commercial alternators generate three-phase alternating current across three distinct groups of copper phase windings spaced 120 electrical degrees apart around the internal circumference of the stator core.
+-----------------------------------------------------------------------------------------+
| THREE-PHASE FULL-WAVE BRIDGE RECTIFICATION |
| |
| Three-Phase Stator Windings Full-Wave Rectifier Diode Bridge |
| (AC Output) (Converts 3-Phase AC to DC) |
| |
| Phase A ---\ (+) Positive Diodes (3 or 6 Diodes) |
| +===> [ Rectifier Bridge ] =======================> Alternator B+ Stud|
| Phase B ---/ | (Filtered DC) |
| v |
| Phase C ---> (-) Negative Diodes (3 or 6 Diodes) |
| ==================================================> Alternator Ground |
| |
|-----------------------------------------------------------------------------------------|
| |
| OSCILLOSCOPE WAVEFORM SIGNATURES |
| |
| HEALTHY ALTERNATOR: Smooth, high-frequency continuous ripple (AC Ripple < 0.20V RMS) |
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| |
| OPEN RECTIFIER DIODE: Missing phase pulse creates rhythmic gap (Output drops 30-40%) |
| ^^^ ^^^ ^^^ ^^^ ^^^ ^^^ ^^^ ^^^ ^^^ ^^^ ^^^ ^^^ ^^^ ^^^ |
| |
| SHORTED RECTIFIER DIODE: Deep downward negative spikes; massive AC ripple (>0.50V RMS)|
| \ /\ /\ /\ /\ /\ /\ /\ /\ /\ /\ /\ /\ /\ /\ /\ /\ /\ /\ /\ /\ |
| \/ \/ \/ \/ \/ \/ \/ \/ \/ \/ \/ \/ \/ \/ \/ \/ \/ \/ \/ \/ |
+-----------------------------------------------------------------------------------------+
Stator Configurations: Delta vs. Wye (Star)
- Wye (Star) Configuration: One lead of each phase coil connects to a common neutral junction. Wye stators produce high output voltage at low engine RPM (idle), providing superior battery charging while idling in traffic.
- Delta Configuration: The three phase coils are connected in a continuous triangular loop. Delta stators allow current to flow through parallel paths, delivering higher total amperage output at highway operating speeds.
Full-Wave Diode Rectification
Because commercial vehicle electronics and storage batteries operate exclusively on direct current (DC), the three-phase AC generated in the stator must be rectified:
- Diode Bridge Construction: The rectifier bridge contains six heavy-duty press-fit silicon diodes (or twelve diodes configured in parallel pairs on high-output 200A+ to 300A+ models). Three positive diodes are pressed into an insulated aluminum heat sink connected directly to the Alternator B+ output stud. Three negative diodes are pressed into a heat sink grounded to the alternator rear end-housing.
- Full-Wave Rectification: Silicon P-N junction diodes act as one-way electrical check valves, conducting current with minimal forward resistance but blocking reverse current. As the three AC sine waves alternate polarity, the rectifier bridge routes both positive and negative half-cycles into a unidirectional direct current, generating a smooth, overlapping DC output with minimal residual ripple.
3. Remote Voltage Sensing (3-Wire Systems) & Cable Drop Compensation
In Class 8 commercial tractors, the battery box is mounted on the chassis frame rail behind the cab, positioned 10 to 15 feet (3 to 4.5 meters) away from the engine-mounted alternator. Under full electrical output (e.g., 200 amperes), natural electrical resistance in heavy 2/0 or 4/0 charging cables produces a significant voltage drop (0.50 to 0.80 volts).
+-----------------------------------------------------------------------------------------+
| REMOTE BATTERY SENSING CIRCUIT DYNAMICS |
| |
| LOCAL SENSING (Without Remote Sense Wire): |
| [ Alternator B+ Stud ] ------------ 12 ft Charging Cable (Drops 0.7V) -------> [ Battery ]|
| Regulator Senses 14.2V Battery Only Receives|
| Thinks Battery is Full 13.5V (CHRONIC SULPH)|
| |
| REMOTE SENSING (With Dedicated Battery Sense Wire): |
| [ Alternator B+ Stud ] ------------ 12 ft Charging Cable (Drops 0.7V) -------> [ Battery ]|
| Regulator Boosts to 14.9V Battery Receives True|
| ^ 14.2V (FULL CHARGE!) |
| | | |
| +====== Dedicated 16 AWG Fused Sense Wire Monitors Battery Post =======+ |
+-----------------------------------------------------------------------------------------+
The Mechanics of Remote Voltage Sensing
- The Failure of Local Sensing: In a conventional single-wire alternator, the internal solid-state voltage regulator samples voltage directly at the alternator B+ output terminal stud. If calibrated to 14.20 volts, it throttles rotor field excitation to hold 14.20V at the alternator. However, with a 0.70V drop across the long chassis cable, the battery bank terminals receive only 13.50 volts. Under this chronic under-voltage condition, the battery pack never reaches full saturation charge, leading to rapid lead sulfation crystallization, reduced CCA, and premature battery failure.
- The Remote Sense Architecture (3-Wire System):
- B+ Cable: Heavy 2/0 or 4/0 cable connecting alternator B+ to starter B+ or the battery bank.
- Ground Cable: Heavy ground cable connecting the alternator case to the engine block or chassis.
- Remote Sense Wire: A dedicated 16 or 18 AWG fused sensing conductor connected directly from the positive battery post in the frame battery box to the "S" (Sense) terminal on the alternator voltage regulator.
- Dynamic Voltage Compensation: The regulator monitors actual battery terminal voltage via the remote sense wire. When high accessory loads induce a 0.70V drop across the main charging cable, the regulator detects that battery voltage has dropped to 13.50V. It immediately elevates rotor field excitation, boosting alternator B+ output to 14.90 volts. Consequently, the battery terminals receive the exact calibrated 14.20 volts, guaranteeing a 100% state of charge regardless of electrical load or cable length.
- Sense Line Failure Modes: If the remote sense wire is severed, its terminal corrodes, or its inline 5A fuse blows, modern commercial regulators automatically detect the open sense circuit and revert to internal local sensing (regulating to ~14.0V at the alternator stud) or broadcast a diagnostic trouble code over the SAE J1939 network.
4. Solid-State Voltage Regulation & Negative Temperature Compensation
Lead-acid battery internal electrochemical resistance varies inversely with temperature: cold electrolyte slows chemical reaction kinetics, requiring higher charging voltage to drive current into the lead plates. Conversely, elevated summer operating temperatures accelerate chemical activity; charging at high voltages under hot conditions causes severe electrolyte electrolysis (water splitting into hydrogen and oxygen), rapid water boil-off, positive grid oxidation, and battery casing swelling.
+-----------------------------------------------------------------------------------------+
| TEMPERATURE-COMPENSATED CHARGING VOLTAGE CURVE |
| |
| Output Voltage (V) |
| ^ |
| 15.2V | * (-20°F / -29°C) WINTER: High voltage forces current into cold electrolyte |
| 14.8V | \ |
| 14.2V | ---* (70°F / 21°C) NOMINAL BENCHMARK SPECIFICATION (13.8V - 14.4V) |
| 13.6V | \ |
| 13.2V | ---* (130°F / 54°C) SUMMER: Low voltage prevents boiling electrolyte|
| +------------------------------------------------------------------> Temp |
+-----------------------------------------------------------------------------------------+
Negative Temperature Coefficient Specifications
Heavy-duty electronic voltage regulators incorporate thermistors that establish a negative temperature coefficient (typically -3 to -5 millivolts per °C per cell, or roughly -0.024 to -0.030 volts per °C for a 12V battery bank):
- Benchmark Operating Specification at 70°F (21°C): 13.8 to 14.4 volts DC.
- Sub-Zero Winter Operation (0°F to -20°F / -18°C to -29°C): The regulator elevates charging voltage up to 14.8 to 15.2 volts DC. This elevated potential forces charging current into cold, sluggish battery chemistry, preventing fleet batteries from operating chronically discharged in winter.
- Severe Underhood / Desert Operation (>120°F / >49°C): The regulator lowers charging voltage down to 13.2 to 13.8 volts DC, preventing thermal runaway and electrolyte boil-off.
5. Alternator Full-Load Rated Output & Voltage Drop Testing
An alternator cannot be accurately evaluated simply by checking battery voltage with an idling engine. An alternator with burned stator windings or failed diodes can still produce 14.0 volts with no active electrical loads. Technicians must test the alternator under full rated electrical output, followed by active circuit voltage drop testing per TMC RP 129.
+-----------------------------------------------------------------------------------------+
| ALTERNATOR FULL-LOAD RATED OUTPUT TEST |
| |
| [ Engine at High Idle: 1,200 to 1,500 RPM ] |
| [ Variable Carbon Pile Load Connected Across Battery Bank ] |
| [ Inductive DC Current Clamp on Alternator B+ Output Cable ] |
| | |
| v |
| [ Turn Carbon Pile Knob to Load System until Voltage Drops to 12.6V - 13.0V ] |
| | |
| v |
| [ Record Maximum Amperage on DC Amp Clamp ] |
| PASS THRESHOLD: Must deliver at least 90% of Rated Nameplate Amperage |
| (Example: 200A Rated Unit Must Deliver at Least 180 Amperes) |
+-----------------------------------------------------------------------------------------+
Step-by-Step Alternator Output Test Procedure
- Clamp an inductive DC current clamp around the alternator main B+ output cable.
- Connect a carbon pile load tester across the primary battery bank.
- Start the engine and elevate engine speed to high idle (1,200 to 1,500 RPM) to ensure the alternator rotor operates above its saturation speed.
- Switch on all vehicle electrical loads (high beams, HVAC blower on high, heated mirrors).
- Rotate the carbon pile load knob to apply an external electrical load until system voltage pulls down to 12.60 to 13.00 volts.
- Read the current clamp: the alternator must deliver at least 90% of its rated nameplate output (e.g., minimum 180A on a 200A unit; minimum 243A on a 270A unit). Output below 90% indicates an open stator winding, burned rectifier diode, or slipping drive belt.
Charging Circuit Voltage Drop Testing (TMC RP 129)
Voltage drop testing across the charging conductors must be performed while the alternator is delivering high current (loaded with accessories or a carbon pile):
- Insulated (Positive) Circuit Voltage Drop: Connect DMM Red (+) lead to the alternator B+ output stud; connect Black (-) lead to the battery bank positive post pad. With alternator delivering rated output, maximum allowable voltage drop is 0.50 volts DC.
- Ground (Negative) Circuit Voltage Drop: Connect DMM Red (+) lead to the bare metal casing of the alternator; connect Black (-) lead to the battery bank negative post pad. Under full output, maximum allowable voltage drop is 0.50 volts DC.
- Total Combined Drop: Must not exceed 1.00 volt DC combined. If voltage drop exceeds 0.50V on either side, clean oxidized ring terminals, inspect chassis ground studs, or replace undersized cables.
6. AC Ripple Voltage & Rectifier Diode Diagnostics
+-----------------------------------------------------------------------------------------+
| AC RIPPLE VOLTAGE DIAGNOSTIC BENCHMARKS |
| |
| 0.00V to 0.20V AC RMS (0 - 200 mV) ===> NORMAL: Full-Wave Rectification Functioning |
| 0.20V to 0.40V AC RMS (200 - 400 mV)===> ACCEPTABLE: Minor System Ripple |
| 0.40V to 0.50V AC RMS (400 - 500 mV)===> MARGINAL: Suspect Leaking / Degraded Diode |
| > 0.50V AC RMS (Over 500 mV) ===> SEVERE FAILURE: Shorted Rectifier Diode |
+-----------------------------------------------------------------------------------------+
Diode Failure Mechanisms: Open vs. Shorted Diodes
- Open Rectifier Diode:
- Failure Mode: The semiconductor wafer or internal bond wire burns open.
- Operational Effect: The alternator loses one-third of its rectification capacity. Maximum output current drops by 30% to 40% (e.g., a 200A unit cannot produce more than ~130A). The alternator whines under load.
- Waveform: An oscilloscope displays a missing hump or gap every sixth pulse in the DC ripple pattern.
- Shorted Rectifier Diode:
- Failure Mode: The silicon diode wafer melts, conducting current in both forward and reverse directions.
- Operational Effect: Raw, unfiltered alternating current is injected directly into the vehicle DC bus. Additionally, when the engine is turned off, the shorted diode provides a continuous reverse conductive path from the battery bank through the low-resistance stator coils to ground, producing a massive 2 to 10 ampere key-off parasitic drain that flattens the battery bank overnight. In operation, the alternator runs scorching hot and whines loudly.
- Waveform: An oscilloscope displays prominent recurring downward negative voltage spikes crossing the baseline.
Testing for AC Ripple with a Digital Multimeter
Technicians can verify rectifier diode health using a digital multimeter:
- Set the DMM to the AC Volts (V AC) or AC Millivolts (mV AC) scale.
- Connect the meter test leads across the battery bank terminals with the engine operating at 1,200 to 1,500 RPM under a moderate load (headlights on).
- Specification: Normal AC ripple is below 0.20 volts AC RMS (200 mV). The maximum allowable industry limit per TMC standards is 0.40 volts AC RMS (400 mV).
- Failure Threshold: Any reading exceeding 0.40 to 0.50 volts AC RMS confirms a failed rectifier diode. The alternator must be overhauled or replaced.
System Consequences of Excessive AC Ripple
- SAE J1939 CAN Bus Corruption: Heavy-duty microprocessors communicate across Controller Area Networks using differential voltage signals (CAN_H and CAN_L switching between 1.5V and 3.5V). Severe AC ripple voltage superimposes high-frequency electrical noise over the CAN data lines, corrupting message frame checksums and causing intermittent communication timeouts, erratic gauge sweeps, and transmission shift faults.
- Phantom Sensor Diagnostic Fault Codes: High AC ripple distorts analog 5-volt sensor reference circuits and pulse-width modulated speed sensor signals (crankshaft position, camshaft position, wheel speed sensors), logging false correlation DTCs.
- Accelerated Battery Destruction: High AC ripple subjects battery plates to rapid micro-cycling, causing electrolyte overheating, active lead paste shedding, and premature battery failure.
7. Diagnostic Decision Tree: Commercial Charging System & Diode Isolation
===================================================================================================
DIAGNOSTIC DECISION TREE: COMMERCIAL CHARGING SYSTEM ISOLATION
===================================================================================================
[ Complaint: Undercharging, Overcharging, or J1939 Noise ]
|
v
Inspect Drive Belt Condition, Tension & Alignment
|
v
Measure Alternator Output Voltage at 1,500 RPM
|
+------------------------------------+------------------------------------+
| | |
v v v
[ Voltage < 13.5V ] [ Voltage > 15.2V ] [ Voltage 13.8V - 14.4V ]
Undercharging Condition Overcharging Condition Normal Voltage Window
| | |
v v v
Check Remote Sense Wire Regulator Defective or Measure AC Ripple Voltage
Terminal & Inline Fuse. Internal Short. Replace with DMM on AC Volts Scale.
If Remote Sense Open, Voltage Regulator / |
Regulator Senses Locally. Alternator Assembly. +--------+--------+
| | |
v v v
Check Charging Cable Voltage Drop [ <= 0.40V AC ] [ > 0.40V AC ]
(TMC RP 129: Max 0.50V Pos, Normal Ripple. Severe Diode
Max 0.50V Gnd under Full Load). Charging System Failure!
| Healthy. Shorted Diode
+------+------+ Injecting AC Noise
| | & Causing Overnight
v v Drain. Replace
[ > 0.50V ] [ <= 0.50V ] Alternator.
High Cable Perform Full-Load Rated Output Test
Resistance: with Carbon Pile & Amp Clamp (High Idle).
Clean Lugs/ Must achieve >= 90% Nameplate Rating.
Replace Wire. If Output Low, Stator Open or Belt Slipping.
===================================================================================================
8. Clinical Diagnostic Case Studies
Case Study 1: Corroded Remote Battery Sense Fuse Causing Chronic Battery Sulfation
A regional delivery fleet equipped with Class 8 tractors experienced premature battery failure across multiple vehicles within 12 months of service. Batteries were chronically discharged (resting OCV around 12.20V), resulting in sluggish cranking on cold mornings. In-chassis inspection with the engine idling showed that the 200-amp alternator maintained 14.20 volts at its B+ terminal.
- A technician connected a digital multimeter between the alternator B+ stud and the battery bank positive post on the chassis frame rail.
- Under an active 100-amp accessory load, voltage at the battery bank measured only 13.45 volts, representing a 0.75V drop across the 14-foot charging cable.
- On a vehicle equipped with remote battery sensing, the voltage regulator should have detected the 13.45V reading at the batteries and boosted alternator output to 14.95V to compensate.
- The technician inspected the 16 AWG remote sense wire connected to the battery positive post and discovered that the 5-amp inline sealed fuse holder had suffered water intrusion, causing the fuse blades to corrode open.
- With the sense circuit open, the smart regulator had defaulted to internal local sensing, governing voltage exclusively at the alternator B+ stud and leaving the battery pack starved of charging potential.
- Installing a new weather-pack fuse holder and 5-amp fuse restored remote sense feedback. The regulator immediately elevated alternator output to 14.95V, delivering a full 14.20V to the battery bank and eliminating fleet battery sulfation.
Case Study 2: Shorted Rectifier Diode Causing Phantom J1939 CAN Bus Faults & Overnight Drain
A line-haul tractor arrived at the fleet maintenance terminal with two seemingly unrelated complaints: every morning following a 10-hour rest break, the batteries were completely discharged, requiring a jump-start; additionally, while operating under heavy highway pull, the instrument cluster needles intermittently swept to zero, and the Transmission TCM logged active SAE J1939 CAN bus data corruption fault codes.
- The fleet technician first investigated the overnight battery discharge. After waiting 45 minutes for all vehicle modules to enter sleep mode, an in-series ammeter revealed a massive parasitic drain of 4.2 amperes.
- While monitoring the parasitic drain, the technician disconnected the alternator main B+ output cable. The parasitic drain instantly dropped from 4.2 amperes to 45 milliamperes (normal sleep draw), isolating the current drain to the alternator.
- The technician reconnected the alternator cable, started the engine, set high idle to 1,300 RPM, and measured AC ripple across the battery terminals with a DMM set to AC Volts. The meter registered 0.92 volts AC RMS, dramatically exceeding the 0.40V maximum limit.
- Diagnosis: A positive silicon rectifier diode inside the full-wave bridge had shorted internally. When running, the shorted diode allowed raw three-phase alternating current into the vehicle DC network, inducing high-frequency AC ripple that corrupted high-speed CAN bus data packets. When the engine was shut down, battery current flowed in reverse through the shorted diode and stator windings to ground, drawing 4.2 amperes continuously.
- Installing a remanufactured 240-amp brushless alternator eliminated the 4.2A parasitic drain, reduced AC ripple to 0.08V AC RMS, and completely resolved all CAN bus transmission communication faults.
A commercial truck technician is troubleshooting a charging system on a Class 8 highway tractor equipped with a 240-amp brushless alternator and an external battery sense line. With the engine running at 1,500 RPM under heavy electrical load, the alternator B+ terminal voltage measures 14.20 volts, but the voltage measured directly across the battery bank terminals 14 feet away on the frame rail is only 13.40 volts. The battery bank remains chronically undercharged. What is the root cause of this condition?
An over-the-road tractor experiences intermittent SAE J1939 CAN bus communication dropouts, erratic instrument cluster needle sweeps, and a dead battery pack after sitting parked overnight. With the engine operating at 1,300 RPM, the technician measures 13.8 volts DC and 0.88 volts AC RMS across the battery terminals using a digital multimeter. What component failure explains both the dynamic electrical symptoms and the key-off battery discharge?
What is the primary design characteristic of a commercial heavy-duty brushless alternator that provides superior durability compared to conventional brushed automotive-style alternators?