Mercruiser 5.7 Alternator issue

rockeater

Cadet
Joined
Feb 4, 2013
Messages
12
Hello everyone,
I purchased a Michigan Motorz 5.7 liter engine about 6 months ago. (long project). Problem now is that I want to purchase the correct alternator for the boat, but there are no engine tags to match parts to. So my question is, which alternator should I buy? Second, I have read all the posts about connections, (including yours Bond-O) and most say there is no purple wire, but on the alternators online, there is. Schematics have not been very helpful for me. I need caveman style explanations. Very confused at this point.

PS: My condolences to the Don S family, he was a awesome moderator and helped me greatly. He will be missed.

Rockeater
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
70,468
Re: Mercruiser 5.7 Alternator issue

Hello everyone,
I purchased a Michigan Motorz 5.7 liter engine about 6 months ago. (long project). Problem now is that I want to purchase the correct alternator for the boat, but there are no engine tags to match parts to. So my question is, which alternator should I buy? Second, I have read all the posts about connections, (including yours Bond-O) and most say there is no purple wire, but on the alternators online, there is. Schematics have not been very helpful for me. I need caveman style explanations. Very confused at this point.

PS: My condolences to the Don S family, he was a awesome moderator and helped me greatly. He will be missed.

Rockeater

Ayuh,.... Welcome Aboard,.. What motor was in the hull originally,..??

What happened to the old motor, 'n it's Parts,..??

Got the serial numbers of the transom or drive, just to get a handle on the Vintage,..??

A delco 1 wire can be Made to fit,... It probably had a Mando, but donno,...

'n regardless what the alternators on-line say,... What wires are available in the motor's harness for the alternator,..??
 

rockeater

Cadet
Joined
Feb 4, 2013
Messages
12
Re: Mercruiser 5.7 Alternator issue

Bond-O,
As always you are "johnny on the spot".

88 Glastron 195 runabout
Engine OB914637 5.0L LX 4 Bbl Carb 230 Horse 8cyl
Transom Assembly OB867745
Drive Unit OB978388

The old motor is stripped and sitting on an engine stand. The previous owner decided it was a good idea to substitute car parts for marine, so I have purchased all new marine parts.

Rock
 

rockeater

Cadet
Joined
Feb 4, 2013
Messages
12
Re: Mercruiser 5.7 Alternator issue

Additional question....Do I need a higher output alternator to drive a 750 watt amp? I installed a pretty serious stereo system.

Rock
 
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achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Re: Mercruiser 5.7 Alternator issue

Here's the beauty of having the engine serial number and the Mercury dealer parts program....

I plug your number in and I get all the details for YOUR engine... :)

That engine was available with 4 different alternators; 2 Mandos, a Prestolite and a Motorola. All were 55Amp.

Mando#AR-150
Mando#AC-155603
Prestolite#8EM2003KM
Motorola#8MR2039K

The Mando AC-155603 was supplied under (Mercury) part number -817119A4. The other 3 were under part number -92497A3 (which supersede to the other number).

750W is around 60 amps!!! If you'd like to run an engine at the same time, yeah, ya gunna need a bigger alternator! And if you turn that thing up while the engine's not running, yeah gunna want a second (and maybe third) battery, or you're not going to start the engine afterwards (and I'll hear it from my place :facepalm: :D) ;)....

Here's the link to the original on the iBoats site. In the text it refers to a 105A alternator. I suggest you chase that up with an email to the product support staff here....
Mercury Marine, Marine Power, Mercruiser Inboard Replacement Inboard Alternator 60050 - Arco - iboats

Just realise, that sort of power consumption will flatten out (to the point of not being able to start an engine) a standard battery in around an hour....

Chris.......
 
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Scott Danforth

Grumpy Vintage Moderator still playing with boats
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Jul 23, 2011
Messages
47,307
Re: Mercruiser 5.7 Alternator issue

Another thing. the original cables to and from the alternator were originally sized for the 55 Amp alternator. when jumping to the 105 amp, make sure you upgrade the cables too.
 

Walt T

Lieutenant
Joined
Mar 16, 2002
Messages
1,369
Re: Mercruiser 5.7 Alternator issue

You can send the original alternator to a rebuilder and they'll fix it up for ya. They'll know it is a marine unit. 750 watts, 12 volts = 62.5 amps. You need a minimum 100 amp alternator. Tell that to the rebuilder. They can make yours a 100. I suggest installing a second battery, perhaps a deep cycle to help run that amp to protect the rest of the electrical system. I'd put an isolator on it so you can Thump thumpa thump until it goes dead and still start your boat with the other one. I have two 450W amps in the trunk of my son's Lincoln which I'm pretty sure is my Lincoln but I'm not sure anymore, and I installed a battery in the trunk with them and a fan to cool them. Alternator is a 135 custom built by A1 auto electric. Cost me 175.00 and it bolts right in. I always know where he is, I just put my ear to the ground and listen for that ground shaking bass.
 

bruceb58

Supreme Mariner
Joined
Mar 5, 2006
Messages
30,454
Re: Mercruiser 5.7 Alternator issue

The average draw of a 750W stereo amplifier will be a LOT less than 60A. The type of music you will be playing and how loud you play it will determine the current draw. My bet it will be less than 30A.
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Re: Mercruiser 5.7 Alternator issue

The average draw of a 750W stereo amplifier will be a LOT less than 60A. The type of music you will be playing and how loud you play it will determine the current draw. My bet it will be less than 30A.

That may well be the case, but when setting up gear like this you must consider max consumption, not 'average'. You should always specify for worst case.... Then add a little for 'headroom'. Usually between 10 and 20%....

Chris....
 
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bruceb58

Supreme Mariner
Joined
Mar 5, 2006
Messages
30,454
Re: Mercruiser 5.7 Alternator issue

I don't agree but since the OP needs to get a new alternator anyway he could get the higher current model.

In some cases, you actually don't want a higher current alternator. Some batteries do not like to see such a huge current charge.
 
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