Good morning guys,

Question I want to upgrade the factory alternator on my 2000 Mercruiser 502 Mag MPI. The current one is a Part Number #805844P which is a 65Amp output unit and I want o increase output. What have you guys used with good luck?

Go talk to your local starter/alternator rebuild shop. Most of them can be tweaked to put out over 100A.

I’m not seeing that as a part #. See here:
https://www.mercruiserparts.com/bam/.../31912/4854/10

Mechman marine alternators. 170 amps

https://www.mechman.com/alternators/...-applications/

Cool, thanks.

Any specs on what power they put out at rpm? Seems that most alternators don't reach rated output until close to 3,000 rpm...

Ran into this a few times years back. People i know in person asking me to put in bigger amp alternator’s. Did math on typical battery level after day at sand bar or etc, size of battery, trip home time - our lake isn’t huge do most trips home are 1/2hr -45 minutes at say 40-45mph , etc, etc and both times they would need to hook up battery charger to charge batteries to 100% anyways, so for them, why bother with $$$ for upgraded alternators. We Lol’d.

Btw: if you are upgrading your alt make sure you increase charging sire size also.

I just have a stock merc on mine but found this and it less than a mercruiser

https://www.cpperformance.com/p-1040...c-862031t.aspx

I think the majority is at idle, and the rest comes in around 1500 RPM? (trying to go by memory)

My card said I had like 110 amps at like 800 RPM and full 180 amps (more than advertised) at maybe 1700 RPM. They do not need to spool up like the smaller bodied alts.

And you can have them painted to match too.

Found this:

https://ceautoelectricsupply.com/pro...e%20V%20pulley

Thanks for the update I have a Mechman in my 2003 Mustang Cobra and it works awesome. I will look into one for the boat as well, I am on a VERY small lake do drive time is minimal, maybe 5min to cruise to the anchor spot and then 10 min to lap the entire lake LOL. Its about 7 miles to drive around it with a car but I just wanted an alt to withstand amps and lights when running plus top off the batts from engine off stereo time.

It’s not going to top off your batteries in such a short drive time. None will.