Mercury 90 EFI...No alternator

[tiki]

Just got a 2005 Mercury EFI 90hp and it doesn't have an alternator. It will not run when battery power is removed so it appears to not have a stator or magneto either. All my previous outboards have run without battery power so this caught me offguard. I am wondering if there is a way to add an alternator or at least a solution to keep the motor running without batteries.

 

[CharlieB]

Re: Mercury 90 EFI...No alternator

The charging system is stator driven AC Generator run thru a rectifier to convert to DC. Most EFI computers do not like the saw-tooth DC waveform as the voltage fluctuates too much, they much prefer a stable battery voltage as the battery 'cushions' that waveform to a smooth line.

You should double check to ensure the stator and rectifier are working correctly to charge the battery.

Use a volt meter and see what the battery voltage is with the engine OFF, then check again while running at 2500 RPM. You should see a rise in battery voltage at RPM.

I 'may' be possible to build a battery eliminator using a capacitor, or two, but I personally would not want to risk higher voltage damage to the ECU as the battery itself serves as a huge voltage 'cushion'. Excessive voltage will kill electronics.

 

[tiki]

Re: Mercury 90 EFI...No alternator

Thanks Charlie...looks to be a bad stator. The voltage is steady running or not.

 

[GA_Boater]

Re: Mercury 90 EFI...No alternator

Before assuming the stator is bad, test it using the CDI T-shooting guide. Might save you some $$$.

Technical Support | CDI Electronics

 

[Timestep]

Re: Mercury 90 EFI...No alternator

If it's like the 60efi of the same year the voltage regulator will have gone out to lunch. Mercury do a slightly discounted upgrade, ask them ?

 

[tiki]

Re: Mercury 90 EFI...No alternator

Turns out it's a pretty well known problem. Merc updated their $140 pos regulator with one that costs almost $500. You can, if fact get one of the Yamaha regulator/rectifiers for less than half of that and it will work just fine. The part number for it is:
67F-81960-12-00

 

[CharlieB]

Re: Mercury 90 EFI...No alternator

So you Ohm tested the rectifier and PROVED it bad?

Have you checked the CDI replacement?

 

[Timestep]

Re: Mercury 90 EFI...No alternator

So did you ask Mercury ?

 

[tiki]

Re: Mercury 90 EFI...No alternator

Yes...I metered and checked with the local Mercury dealer. Mercury never did admit a problem publicly but started offering only the updated regulator at $467. As many of you know this is a Yamaha powerhead and that regulator is $195. The only thing it is slightly larger than the Merc part but it fits fine.

 

[tiki]

Re: Mercury 90 EFI...No alternator

I also checked CDI but they did not list one for my particular motor.
Also found a great video on how to replace the VR with a $4 bridge. (Don't suggest it, but this would work)