Arco
ARCO Alternator - 12V 275A DF315 - Dual Foot 3.15" - Side Battery Post - Externally Regulated - Isolated Ground - 49mm K6 Pulley - 4021
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4021
The ARCO Zeus A275L is a large-frame 12V high-output alternator that delivers up to 311 amps cold and a sustained 227 amps while cruising, rapidly charging large battery banks in place of a generator. This version uses a 3.15 inch dual-foot common-rail mount with an isolated ground, fitting post-2013 Yanmar common-rail engines such as the 4JH range. As an externally regulated unit it pairs with the ARCO Zeus Bluetooth regulator for full control over lead-acid and lithium banks.
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Available for collection or delivery in ~2 days
Pickup available at Mercury Yacht Harbour
Usually ready in 2-4 days
Description
The Zeus A275L brings large-frame charging to 12V systems, letting one engine-driven alternator take over work that would otherwise need a noisy auxiliary generator. It suits demanding marine, RV and commercial use where big lithium or lead-acid banks must be replenished quickly and often.
ARCO builds the A275L to run cool under sustained load. Heat-shedding Cerakote and E-coat finishes, an externally mounted rectifier and twin internal fans hold temperatures down so it keeps producing rather than derating. Its hot ratings are measured conservatively, after a full hour at 3,000 RPM beneath a plexiglass heat shield rather than in cool ambient air, so they reflect real engine-bay conditions.
As an externally regulated alternator it needs a dedicated controller such as the ARCO Zeus Bluetooth regulator, which is essential for safe lithium charging. This version uses a 3.15 inch dual-foot common-rail mount with an isolated ground and again fits post-2013 Yanmar common-rail engines such as the 4JH series. It is SAE J1171 certified and proudly made in the USA.
PRODUCT DETAILS
- Up to 311 A cold output and 227 A sustained while cruising
- Native 12V large-frame design for rapid bank charging
- Externally regulated (EX); pair with ARCO Zeus Bluetooth regulator
- Runs cool via Cerakote and E-coat finishes, external rectifier and dual fans
- Conservative hot ratings tested at 3,000 RPM under a heat shield
- Charges lithium (LiFePO4) and lead-acid banks with the right regulator
- Dual-foot 3.15 inch mount, isolated ground, for Yanmar common rail
- 50 A avalanche diodes and 110C max continuous operating temperature
- SAE J1171 certified and made in the USA
- ARCO Zeus A275L 12V alternator
- External-regulation terminal block
- P-Type field harness
- Fitted 49K6 pulley (6-groove, 49mm)
- M17 x 1.5 x 24mm pulley nut
- 18mm ID x 29mm OD washer
No exploded diagram available for this product.
No compatible transducers listed for this product.
No spares or accessories listed for this product.
Key specifications
| Voltage | 12V |
| Max Output (Cold, 9,000 RPM) | 311 A |
| Sustained Cruising Output (Hot, 6,000 RPM) | 227 A |
| Sustained Idle Output (Hot, 3,000 RPM) | 198 A |
| Regulation | External Only (EX) |
| Standard Pulley | 49K6 (6-groove, 49mm) |
Electrical
| Field Type | P |
| Rotor Poles | 16 |
| Stator Size | 138mm |
| Diodes | 6 positive, 6 negative, 50A rated, avalanche |
| Output Voltage | 14.1V (default) |
| Cut-In RPM | 1,061 alternator RPM |
| Maximum Alternator RPM | 19,000 |
| Max Continuous Operating Temperature | 110C (230F) |
Mechanical
| Frame Size | Large |
| Weight | 6.7 kg (14.9 lb) |
| Finish | Black Cerakote or E-coating |
| Battery Post | M8 thread post, side mount |
| Pulley Mount | 17mm dia shaft, 25mm long, threaded M17 x 1.5 |
| Pulley Hardware | M17 x 1.5 x 24mm nut with 18mm ID x 29mm OD washer (included) |
Fitment
| Housing/Mount | 3.15 inch dual-foot common-rail mount |
| Ground Type | Isolated ground |
| Application | Yanmar common rail, post-2013 (JH-CR, 3JH40, 4JH45, 4JH57, 4JH80, 4JH110) |
Compliance
| Certification | SAE J1171 certified |
| Country of Origin | USA |
No videos available for this product.
Does this alternator include a regulator?
No. Every ARCO Zeus alternator is externally regulated (EX), so it has no built-in regulator and will not charge on its own. It needs a dedicated external regulator, and ARCO recommends the Zeus Bluetooth Alternator Regulator, which is designed to get the most from the alternator across 12V to 48V systems and is essential for safe lithium charging.
What do the hot output figures mean?
ARCO publishes deliberately conservative hot ratings. Instead of testing in cool ambient air, it runs the alternator for a full hour at 3,000 RPM under a plexiglass heat shield, with the stator reaching around 305F, far harsher than the industry-standard 140F ambient test. The hot cruising and idle figures therefore reflect what you can expect in a hot engine bay rather than an optimistic bench number.
Can it charge a lithium (LiFePO4) battery bank?
Yes. With a suitable external regulator it charges both lithium (LiFePO4) and lead-acid deep-cycle banks. Lithium in particular relies on the external regulator to control the charge profile safely, which is why ARCO recommends pairing it with the Zeus Bluetooth Alternator Regulator.
Which engines does this version fit?
This version uses a 3.15 inch dual-foot common-rail mount with an isolated ground and fits post-2013 Yanmar common-rail engines including the JH-CR, 3JH40, 4JH45, 4JH57, 4JH80 and 4JH110.
