alternator size?

[Captcheetah]

Does anyone know the charging amps of a '88 Mercruiser 5.7 alternator?<br /><br />I was told 85 amps and am trying to verify.

 

[achris]

Re: alternator size?

Four different alternators used on these engine. 2 different Mandos, a Motorola and a Prestolite, all putting out 55 amps.

 

[Captcheetah]

Re: alternator size?

Thanks, that sounds more reasonable to me.<br /><br />Since you sound like a guy in the know, electrically. How much amp draw would require an alternator upgrade?<br /><br />I am putting in a small stereo system, if I add up all the fuses on the equipment, I get 65 amps. The system itself is producing less than 300 watts (rms) and by some calculations it comes out to less than 30 amps. Just not sure if I need to upgrade my alternator and I don't want to find out the hard way.

 

[Captcheetah]

Re: alternator size?

Thanks, that sounds more reasonable to me.<br /><br />Since you sound like a guy in the know, electrically. How much amp draw would require an alternator upgrade?<br /><br />I am putting in a small stereo system, if I add up all the fuses on the equipment, I get 65 amps. The system itself is producing less than 300 watts (rms) and by some calculations it comes out to less than 30 amps. Just not sure if I need to upgrade my alternator and I don't want to find out the hard way.

 

[achris]

Re: alternator size?

What other electrical equipment are you running? Even though your stereo is capable of outputting 300W, unless it is horribly inefficient (or you're stone deaf ) you would probably have it running at much less. I have a friend with a 1000W system in his boat (also running a 55amp alt) and he doesn't seem to have any problems. Easiest way to check is to monitor the 'battery' meter. It should sit on about 14volt (after the battery has recharged from the start). If it starts to drop then turn the stereo down.

 

[Captcheetah]

Re: alternator size?

What did you say? 8^)<br /><br />Actually nothing, I am going to add a 12v lighter plug in for the cell phones to charge on the boat, but other than the stereo and two amps, that would be about it.<br /><br />I am going to install a switch on the remote turn-on so that I can turn the equipment off if I want to sit for a while and not worry about draining the battery.<br /><br />Thanks again.

 

[salty87]

Re: alternator size?

your stock alternator can handle that load. now, if you want to hang out with the stereo playing and the engine not running, you might want to consider upgrading. that depends on how long you sit.<br /><br />you could also consider a separate battery for the stereo/amp but that raises new questions.

 

[Captcheetah]

Re: alternator size?

The sitting is more a battery issue than alternator, right?<br /><br />I am considering adding a second battery, just for backup. I have a Perko switch now, but it is just the on/off, not set up for a second battery. I thought if nothing else I can charge it put in the boat and just jump from it if I had too. I have also thought about getting a device that will monitor the voltage (battery tender), that will shut stuff off when the battery gets low.

 

[salty87]

Re: alternator size?

yep, the sitting is more of a battery issue but it adds to the charging issue. even if you add batteries so you can sit, you need to be able to charge them back up...unless you want to charge them on the trailer. lots of people do that with a second battery.<br /><br />that 55 amp alternator will do fine with your stereo until your charging needs increase. i'd consider the second battery before upgrading the alt.