Marine Alternator 12V 70A – Self-Exciting, Ignition Protected | SKU 57-20104
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A 12-volt, 70-amp self-exciting marine alternator built for gasoline inboard engines where ignition protection is a safety requirement. Unlike standard automotive alternators, this unit features ignition protection screens that prevent internal sparks from igniting fuel vapours — a critical safety specification for closed-engine-compartment installations on gasoline-powered vessels. The self-exciting design means it does not require an ignition exciter wire to begin charging, simplifying installation and eliminating a common fault point on older wiring. An internal voltage regulator, single groove V-belt pulley, and negative ground configuration round out the direct-fit specification.
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 — pulley groove count, mounting dimensions, and wiring connector must match before ordering
Product Details
- SKU: 57-20104
- 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
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Parts Desk Insights
The self-exciting feature is the key differentiator on this unit and the main reason customers select it over a standard replacement. On older inboard installations where the exciter wire circuit has failed, corroded, or was never wired correctly, a self-exciting alternator eliminates the fault entirely — it begins charging as soon as the engine RPM rises, with no dependency on the ignition circuit. This makes it a reliable upgrade as well as a direct replacement. The ignition-protection screens are not optional on gasoline inboard engines — they are required to meet ABYC E-11 and UL 1428 safety standards for enclosed engine compartments. If you are replacing an alternator on a gasoline inboard and the replacement unit is not ignition-protected, it should not be fitted. At 70 amps, this unit comfortably handles a full complement of navigation electronics, bilge pumps, and lighting on a mid-size inboard vessel. When replacing, inspect the V-belt and tensioner at the same time — a stretched or cracked belt under a new alternator is a common cause of undercharging and noise at idle.
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.