Alternator Questions

[Mahoney]

1978 GM 350V8 225hp OMC<br /><br />I think my alternator is shot, I get a constant slow discharge reading on the ammeter and the current battery charge level is always a bit lower than it was after starting and running.<br /><br />Engine runs fine(no problem with ignition it seems)<br /><br />Questions:<br /><br />1)Can I assume the external regulator is fine since the engine seems to be running well?<br /><br />2)Is there a site somewhere that would list alternator part numbers for this application? I can't seem to find a site anywhere that I can be confident I am ordering the correct alternator.<br /><br />3)I have heard good things about the single wire alternators, however I was wondering if I went from my current 3 wire, how would this be able to connect to the ammeter, tach etc?<br /><br />4)When I do replace with a functional alternator can I expect to see a smoother idle than even to what I currently have?<br /><br />Thanks

 

[olbuddyjack]

Re: Alternator Questions

Easy check. Start the motor, put a volt meter on the battery and see if it reads more than 13 volts. Go from there.

 

[Mahoney]

Re: Alternator Questions

I currently don't have a voltmeter or ammeter to run the checks that are stated in the manual after checking the connections over(I will be getting those). But to the other question. When/if I do need an alternator, where can I find the correct part? I know there are $15 aftermarket marine conversion kits for alternators, and I would assume finding an alternator for a 350 shouldn't be that tough or expensive, but I don't want to make a mistake and endanger myself or others on the water.

 

[Chris1956]

Re: Alternator Questions

Mahoney, It is likely that one of the diodes in the "diode bridge" in the alternator failed. This can allow current to "leak" to ground. Sometimes these are available as a replacement for small money. It also may come as part of a replacement regulator kit. I do not know if these need to certified as "Marine". If you remove the regulator/diode bridge from your alternator, you may be able to match it up. Alternatively, I usually buy a rebuilt marine alternator from my my local Auto parts store. I would expect it to be in the $100-$150 price range.

 

[Mahoney]

Re: Alternator Questions

thanks, I am going to run some voltage checks on it today hopefully.

 

[Mahoney]

Re: Alternator Questions

Well I got as far as testing the voltage regulator, battery read 12.3 volts at idle. Voltage on lead coming out of regulator to the alternator read 11V. Says to replace the regulator if reading is below 13-14V. I guess I am in search of a regulator?

 

[Boatist]

Re: Alternator Questions

If you have 11 volts from the regulator going to the field winding on the alternator then the regulator is not the problem.<br /><br />Do you have a battery switch? Did you ever turn the switch with the motor running? I belive the number one killer of alternators is battery switches. The normal problem is all the diodes on the diode block are blown from turning the switch.<br /><br />You can replace the regulator or the alternator but if you have a service manual and a volt meter you can find the bad componet.<br /><br />Brushes are under $5, diode blocks about $20, diode triode under $5. It can be repaired for very little money.

 

[Mahoney]

Re: Alternator Questions

I don't have any battery switch that I know of, there is a switch on th dash marked assesory, but thats not what you are talking about.<br /><br />I have the manual and it has fairly extensive testing proceedures using both a voltmeter and an ammeter connected at the same time. <br /><br />I have a multitester that does both, so I guess I just need to spend some time and do some studying to <br />get it right. <br /><br />The volt meter on the dash measuring the state of charge of the battery is cooresponding to what I am seeing from the regulator to the field winding. But never goes into the 13-14v charging range.