Marine Alternator 12V 70A – Self-Exciting, Ignition Protected | SKU 57-20102
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You have 30 days to request a return. All sale items are final sale.
A 12-volt, 70-amp self-exciting marine alternator built for gasoline inboard engines where ignition protection is required. This unit features ignition protection screens that prevent internal sparks from igniting fuel vapours — a critical safety requirement for closed engine compartment installations on gasoline-powered vessels. The self-exciting design eliminates the need for an ignition exciter wire to initiate charging, simplifying the installation and removing a common fault point on older engine wiring. An internal voltage regulator, single groove V-belt pulley, and negative ground configuration complete the direct-fit specification.
This is a separate part number from the 57-20104 unit in the same self-exciting series — both share identical specifications but are matched to different engine mounting configurations and OEM applications. Confirm your existing part number or engine application before selecting between them.
Compatible Applications
- Gasoline inboard marine engines requiring a 12V ignition-protected alternator
- PCM (Pleasurecraft Marine) inboard engines with single groove V-belt drive
- Crusader Marine inboard engines with single groove V-belt drive
- Indmar Marine inboard engines with single groove V-belt configuration
- Other OEM gasoline inboard applications specifying a 70A ignition-protected, self-exciting alternator
- Verify fitment against your engine serial number and existing part number — mounting foot dimensions, pulley groove count, and wiring connector must match before ordering
Product Details
- SKU: 57-20102
- Voltage: 12V
- Output: 70 Amps
- Starting: Self-exciting (no exciter wire required)
- Safety: Ignition-protected — screens prevent internal sparks from igniting fuel vapours
- Regulator: Internal voltage regulator
- Ground: Negative ground
- Pulley: Single groove V-belt pulley
- Type: Aftermarket direct replacement
- Condition: New
Related Products
- Marine Alternator 12V 70A Self-Exciting Ignition Protected – SKU 57-20104 — same specs, different OEM application
- Marine Alternator 12V 55A – Replaces MerCruiser 817119A1 (57-60050)
- Marine Alternator 12V 65A – Replaces MerCruiser 805447T (57-60065)
- Marine Alternator 12V 75A – Replaces Volvo Penta 3862665 / 3884950 (57-60073)
Parts Desk Insights
This unit and the 57-20104 are the most common source of confusion in our alternator catalog — they share the same voltage, output, and feature set, but are matched to different engine OEM applications and may differ in mounting foot geometry or connector type. If you are replacing an existing alternator, the safest approach is to match the part number stamped on the original unit rather than relying solely on specs. If the original part number is missing or illegible, match the mounting foot dimension and pulley groove count physically before ordering. The ignition protection screens and self-exciting design make both units the correct choice for any gasoline inboard application — these are not optional features on an enclosed-compartment gasoline engine. At 70 amps, output capacity is sufficient for a full electronics suite on a mid-size inboard cruiser. Replace the V-belt at the same time as the alternator whenever possible — belt wear accelerates bearing wear on a new unit and is a frequent cause of early failure and undercharging complaints.
Shipping information
In-stock and OEM parts: ship same or next business day.
Locally warehoused items: ship within 1-3 business days.
Special-order items: timeline confirmed after order.
Returns & warranty
Returns & Satisfaction Guarantee
We stand firmly behind the quality of every product we sell. Your confidence matters to us — and we back it with a straightforward 30-Day Satisfaction Guarantee.
If you are not fully satisfied, you may request a return within 30 days of delivery. All returns must receive pre-approval prior to being sent back. Unauthorized returns will not be accepted.
To qualify for a return:
Item must be in new, unused condition
Product must be in its original packaging
All parts, components, hardware, manuals, and accessories must be included
Packaging must be undamaged and suitable for resale
Important:
Electronics are strictly inspected. No returns on open-box electronics. Exceptions may apply only with prior written approval. Any electronic unit that has been installed, powered, activated, or altered may not be eligible for return.
We are serious about product integrity — and equally serious about taking care of our customers. If there is ever a product issue, contact us immediately so we can make it right.
For return authorization, please contact our support team before shipping anything back.