trying to help a frend altenator

[bolo789]

hello everyone my friend merc 350 when at idle it charge 13 volt when you rev the engine the charging drop to 12 volt or less i clean all the terminals but the same thing happen. i think he might have switch the battery swith off while engine was running also can you switch from bat 1 to bat 2 while engine running without damage the alt <br /><br /><br />thanks for any input on this

 

[Reel Poor]

Re: trying to help a frend altenator

What is the battery voltage with;<br />1..key off...should have 12.5-13.0 volts<br />2..key on engine and accessories off...12.0-13.0 volts <br />3..engine running at idle...13.5-14.5 volts<br />4..engine running @ 1500rpm 13.5-14.5 volts<br /><br />From what you posted it could be as simple as a loose belt.

 

[Dunaruna]

Re: trying to help a frend altenator

Older type battery switches don't allow for curcuit completion which results in blown alternators.<br /><br />Newer types have 'make before break' and 'alternator field disconnect' so as to avoid this very problem.<br /><br />You need to test and probably replace the alt and then fit a newer style battery 3way switch.<br /><br />Aldo

 

[waterone1@aol.com]

Re: trying to help a frend altenator

Before you replace anything, test the voltage at the battery with a DVM (Digital Volt Meter). Do not trust what the dash mounted boat gauge indicates.

 

[bolo789]

Re: trying to help a frend altenator

thanks guy, well he took the altenator to a shop and the test state no good now he has two burnt alt both is not charging they are both arco alt can the part be order or how can they rebuild seems as if this alt guy dont want to mes with marine alt thanks again.

 

[Boatist]

Re: trying to help a frend altenator

I think poor quality battery switches and operators turning switch with motor running kill more alternators than any thing else. If you are not running a battery isolator then a loose battery cable can do the same thing. Battery isolator will save alternator from loose battery cable and from turning the battery switch even thru off. Switches with a alterntor field disconnect circuit will save alternators also if your have an external regulator.<br /><br />Internal Alternator parts the same as auto parts. There are different size and amp rateing. The common parts that go bad are the output diode block, voltage regulator and the diode triode. Slip ring brushes also. All these parts can be checked with a good ohm meter. The diode block can be $20 bucks on high output alternators. The other parts are cheap. Any good alternator shop can usually get the parts or have them in stock. While your inside check the bearing also and grease or replace.<br /><br />The alternator case is marine only and has special screens to prevent the sparks from getting out.

 

[bolo789]

Re: trying to help a frend altenator

update ok we, install a new alt now it is charging at 4.5 volt at the alt and the battery but the dash guage drop to about 11 volt when i rev the engine, does that means the guage is no good?? when rev the alt output read the same 4.5 no drop in volt. so what you guys think bad guage bad wires??<br /><br /><br />thanks for any info also thanks everyone for there input on this one my friend told me he even disconnect the battery while the engine was running to check it just like a car , i told him it is not a car,