Orange wire on alternator reads 14 then goes down to 12 volts

[brm0525]

Mercruiser 4.3

orange wire on alternator on start up goes to 14. +or- volts.

After a min or 2 as engine temp inreases (which don't know if it has anything to do with anything) the voltage drops down to 12 volts and stays there. This is being determined by volt meter.

I found a previous thread on how to test all wiring and components that don s. Had posted. I checked everything and it was fine.

Assuming it's the alternator but i had it bench tested at marine supply store and was charging 14.8 volts.

 

[alldodge]

Re: Orange wire on alternator reads 14 then goes down to 12 volts

Sounds like your either a real heavy load is coming and going which is not very likely, or maybe the field circuit is being disconneted somehow. Need to fin out if your loosing your 12V on the purple wire going to the Field winding on the ALT.

 

[brm0525]

Re: Orange wire on alternator reads 14 then goes down to 12 volts

Sounds like your either a real heavy load is coming and going which is not very likely, or maybe the field circuit is being disconneted somehow. Need to fin out if your loosing your 12V on the purple wire going to the Field winding on the ALT.

I put a test light on the purple wire at the ignition and had power. then took a jumper wire to the purple wire on the alternator while running and had power to the purple wire even when orange wire went to 12 volts. I never lost power to the purple wire.

Could alternator have something internally wrong and the alternator still show 14.+or- volts on the bench?

 

[sptjet90Reflexx]

Re: Orange wire on alternator reads 14 then goes down to 12 volts

your alternator wont charge well at idle most dont. Kick it up to 1200rpm and then check I bet its holding easy at 14volts.

 

[gm280]

Re: Orange wire on alternator reads 14 then goes down to 12 volts

Sounds like it is doing a perfect job without any issues to me... The reason it goes to 14 volts initially is because you used some current to start the engine. Then it settles down after replenishing the battery some...

 

[alldodge]

Re: Orange wire on alternator reads 14 then goes down to 12 volts

I put a test light on the purple wire at the ignition and had power. then took a jumper wire to the purple wire on the alternator while running and had power to the purple wire even when orange wire went to 12 volts. I never lost power to the purple wire.

Could alternator have something internally wrong and the alternator still show 14.+or- volts on the bench?

It is possiable but odds are not very likely. Should have mentioned when discussing the purple but you could also be loosing the ground on the black wire.

your alternator wont charge well at idle most dont. Kick it up to 1200rpm and then check I bet its holding easy at 14volts.

Agree

 

[brm0525]

Re: Orange wire on alternator reads 14 then goes down to 12 volts

your alternator wont charge well at idle most dont. Kick it up to 1200rpm and then check I bet its holding easy at 14volts.

This test is not at idle. 1800 RPM.

 

[alldodge]

Re: Orange wire on alternator reads 14 then goes down to 12 volts

With the engine off disconnect both black and purple wires. Run a jumper from battery ground to the black wire . Connect another to the purple wire. Connect your meter to the orange wire. Start the engine and then connect the jumped purple wire to the battery (+). The ALT should start charging if it doesn't its the ALT if it does you have a bad connection. If it stays at 12V and appears to be the ALT feel the orange wire and see its getting warm. If it is getting warm the ALT is fine but there is a heavy draw somewhere.

 

[Volphin]

Re: Orange wire on alternator reads 14 then goes down to 12 volts

I agree with gm280. Starters draw some serious amperage. The alt is simply doing it's job.

 

[achris]

Re: Orange wire on alternator reads 14 then goes down to 12 volts

Sounds like it is doing a perfect job without any issues to me... The reason it goes to 14 volts initially is because you used some current to start the engine. Then it settles down after replenishing the battery some...

Nope... The specification on these alternators is an output of 13.9 to 14.7 volts. Generally in automotive I've seen tighter specs, 14.2 to 14.5 volts.

If the starter had sucked a huge amount of power, then the battery voltage would be lower, rising up and then stabilizing at 14 volts, not the other way around... (Remember that putting a meter on the output terminal of the alternator is exactly the same as putting the lead on the positive post on the battery. The voltage reading at both point will always be the same, unless the wire's been cut.)

I would suggest you have a faulty regulator, bad diode, bad solder joint on the stator or rotor windings, failing as it warms up... Or a bad rotor brush (not uncommon)...

Chris.........

 

[Rd05lly]

Re: Orange wire on alternator reads 14 then goes down to 12 volts

Are the batteries being drained and not starting.

I chased a similar problem in a truck one time 05 Chevy with 4.3. Come to find out the alternator would shut off if there was no load on batteries to save fuel mileage. Just something to look in to I beat my head against that truck awhile.

 

[achris]

Re: Orange wire on alternator reads 14 then goes down to 12 volts

Are the batteries being drained and not starting.

I chased a similar problem in a truck one time 05 Chevy with 4.3. Come to find out the alternator would shut off if there was no load on batteries to save fuel mileage. Just something to look in to I beat my head against that truck awhile.

It's an inherent design of alternators that they will only output what's demanded... No load, very little output. I say very little because the ignition system and instruments still draw power... But regardless of demand, the output should remain at 13.9 to 14.7 volts....

Chris.......

 

[Rd05lly]

Re: Orange wire on alternator reads 14 then goes down to 12 volts

It's an inherent design of alternators that they will only output what's demanded... No load, very little output. I say very little because the ignition system and instruments still draw power... But regardless of demand, the output should remain at 13.9 to 14.7 volts....

Chris.......

I know 05 and newer GMs shut down the alternator. For a 1% fuel gain you can't make that up. Would they try using it on a boat who knows. But something to think about. Don't know what year OP is working with here either. Maybe mute point

 

[brm0525]

Re: Orange wire on alternator reads 14 then goes down to 12 volts

Nope... The specification on these alternators is an output of 13.9 to 14.7 volts. Generally in automotive I've seen tighter specs, 14.2 to 14.5 volts.

If the starter had sucked a huge amount of power, then the battery voltage would be lower, rising up and then stabilizing at 14 volts, not the other way around... (Remember that putting a meter on the output terminal of the alternator is exactly the same as putting the lead on the positive post on the battery. The voltage reading at both point will always be the same, unless the wire's been cut.)

I would suggest you have a faulty regulator, bad diode, bad solder joint on the stator or rotor windings, failing as it warms up... Or a bad rotor brush (not uncommon)...

Chris.........

Thanks, Chris. That has been my thought the whole time I was waiting to see if someone else had came to that conclusion.