high alternator output

[airshot]

I have a 1983 3.0 140 hp with delco-Remey alternator. The engine has been upgraded some time back with electronic ignition. At the end of last season my alternator showed a low charge rate so I bought a new one and installed it, everything was fine for two weeks. Then the new alt showed a reduced chg, but it was end of season so I put the boat to bed for the winter. Over the winterI was checking the wiring because the battery switch was not switching between the two batteries. Found the switch was not wired correctly along with a few other things so wiring was corrected per the mercruiser manual. Boat runs fine and battery switch functions correctly but now the alternator shows a 15.3 volt output all the time. Took the old alternator to our local guru who rebuilds these for the past 30 yrs and he completely disassembled the alternator and checked out each part, cleaned everything, replaced all the nuts and screws with new ones, cleaned all contact points and checked it thoroughly on his machine. Alternator is performing perfect. Put the just checked Delco unit on and still showing 15.3 volts output. Battery has a 13.04 charge and second battery shows a 13.3 charge at rest. Batterys are in great condition, voltage regulator was checked carefully as i had explained the problem to the repair person. Have checked and cleaned all conections, alternator shows 15.2/15.3 right at the post on the back of the alternator when running. What now? As always many thanks in advance for the excellent suggestions I get from this forum.

Airshot

 

[Don S]

Re: high alternator output

Hook up your DVM directly to the battery terminals and run the engine. Does your DVM show the same voltage as your helm gauge?

 

[airshot]

Re: high alternator output

Yes Don, all readings were taken with a digital volt meter both at the alternator as well as at the battery terminals.
Airshot

 

[Don S]

Re: high alternator output

How do you have the wiring hooked up at the alternator. The Delco is not the OEM alternator, and the wiring harness is not setup for a Delco

 

[wellcraft-classic210]

Re: high alternator output

Are you sure the dvm is accurate - Both readings about 1.3 volts higher than expected. If you verify / trust the readings then you most likely have a bad voltage regulator. Many are built into the alternators--- Not sure if yours is.

 

[airshot]

Re: high alternator output

How do you have the wiring hooked up at the alternator. The Delco is not the OEM alternator, and the wiring harness is not setup for a Delco

Using the markings on the alternator and the pictures in the mercruiser manual led me to this conclusion. Their is a small rubber plug near the top back side that has two wires, these plug into a red and a faded purple wire. Then there is the ground wire, and the large lug with an orange wire that goes to the fuse on the starter solinoid. Now that you mention this, is it possible to get the two wires from the black rubber plug crossed. I had reconnected them as they were originally connected, however as the boat was bought used they may have been wrong before. My wires seem to match the codes in the manual however there is a lot of color fading due to age. Thanks again for your input.

Airshot

 

[airshot]

Re: high alternator output

Are you sure the dvm is accurate - Both readings about 1.3 volts higher than expected. If you verify / trust the readings then you most likely have a bad voltage regulator. Many are built into the alternators--- Not sure if yours is.

Thanks for your reply, yes it is built in, the repair tech took the alternator apart and checked the regulator by itself and again after
reassembly. His machine showed a 14.8 max voltage output at 60 amps. This is why I am wondering how you get 15.3 vdc out of a 14.8 alternator? I have tried two alternators and get the same thing so what am I missing in the wiring?

Airshot

 

[Don S]

Re: high alternator output

Here is a picture from Arco of the alternator.



You should have a purple wire from your engine on the left, a red/purple wire on the right.

The purple wire is from your ignition switch. Just make sure it comes BEFORE the resistor wire. If it is wires to the coil, it will be showing the coil low voltage due to the resistor wire.

 

[airshot]

Re: high alternator output

What do you mean by " comes before the resistor wire" ? I am a tool maker not an electrician, wwhile I have no problem figuring things out sometimes I need very 'simple" language to understand things not in my field. When I check my coil (engine running) I have 15.3 at the battery and 11.6 at the coil. Could very well be the original resistor wire is still in the harness. Is there a simple way to bypass this, and would this be causing my over charge condition? Again thanks for your patience and help in sorting this out.
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[achris]

Re: high alternator output

The ignition coil runs at 7 volts. To achieve this a resistance wire is put in place of a 'normal' wire. If you hook the alternator sense wire to the end of the resistance wire it will think the voltage is low and produce more current than the batteries really need, elevating the voltage... Ensure that the feeds to the alternator are at full battery voltage, not the coil voltage...

Chris...

 

[airshot]

Re: high alternator output

Thanks for the explanation, if i understand the wiring correctly, the red wire senses battery voltage and going thru the harness there is probably a resistor wire causing the voltage to appear lower than it really is. Can this be bypassed by running a wire from the red sensor wire directly to the battery so as to eliminate the wiring harness for that lead? The sensor wire has a plug to plug into the harness, I would disconnect that and run a wire directly to the battery+ to eliminate the harness, does that sound feaseable?
Thanks again to all ..........
Airshot

 

[achris]

Re: high alternator output

Thanks for the explanation, if i understand the wiring correctly, the red wire senses battery voltage and going thru the harness there is probably a resistor wire causing the voltage to appear lower than it really is. Can this be bypassed by running a wire from the red sensor wire directly to the battery so as to eliminate the wiring harness for that lead? The sensor wire has a plug to plug into the harness, I would disconnect that and run a wire directly to the battery+ to eliminate the harness, does that sound feaseable?
Thanks again to all ..........
Airshot

Yes