3.0L Voltage drop - Alternator?

[Mark RSA2AU]

Hi Guys

I have a '99 180 with a 3L 4 cyl. This weekend I noticed a voltage drop from 13.5v to 12.1v when running at revs. When motor is off and ignition is on the voltage is 12.4. I have a nifty aftermarket electronic guage that measures a number of things including the battery voltage. Ideal for when we are relaxing with music on, it will beep when voltage drops to 11.9 so we dont drain the battery.

This weekend on our local lake the boat felt very slugish, way more then usual, then I noticed the voltage. 2 questions:
1. We ran for most of the afternoon with the voltage arround 12.1v. The battery is 3 yrs old and holding charge well. It has a green colour on the indicator, which is suppost to go black / dark when something is below par. I am sure if the alternator had failed the batttery would now be flat but even after about 3 hours of skiing at this voltage it still held 12.4V whith the ignition off.
Do you think the alternator needs repair / replacement. Can they be repaired? Even if it can be repaired is it better to just put a new one in?
2. Would this cause a loss of power at full throttle, I am a big guy and I need every horse available to pull me out, so I notice when it is down on power.

thanks in advance for your help.

Cheers
Mark

 

[cmount1]

Take the battery out and have it load tested at your local repair shop to ensure you have a good battery. If done properly it should be fully charged, if it will hold one. Normal procedure is to load the battery to half of its CCA for 15 seconds and monitor the voltage; it shouldn't drop below 9.5v, if so it's time to replace it. Two key points is the battery needs to be fully charged and loaded to half of the CCA.

Concerning the charging system, with the engine running at 2000 rpm the charging voltage at the battery should be ~14 - 15 volts depending on the accessory loads. If it’s less than that, say 12.5v verify the charging voltage at the alternator. Using a volt meter place the positive lead from your meter on the battery output terminal of the alternator and the negative lead on the battery ground, if your lead can't reach use a known good ground. If the voltage at this point is still 12.5 the alternator needs to be tested further to determine if the regulator is faulted or it’s the alternator itself. It’s best to remove it and have it bench tested or just replace it. If the voltage is at the 14 – 15v range and the battery is only receiving say 12.5 then there’s a voltage drop in the system. There shouldn’t be more than a .5 of a volt between the alternator and the battery. This can be tested by placing the negative lead from the volt meter on the positive side of the battery and the positive lead on the alternator output terminal, this will so how much of a drop is in the system. This is where it gets harder to diagnose, you will have to work backwards from the battery to the alternator to find the drop in the system. You need to find any connection points in that circuit and place the negative lead from the meter at each of those points while keeping the other lead on the alternator terminal, once the voltage drop goes away you found the issue. There will be a corrosion problem with the terminal or in the cable between that point and the alternator. Note there is a good possibility there are no extra connections between the alternator and the battery but, it still holds true that it’s a corrosion issue.
I hope I describe that comprehensible, I haven’t finished my morning coffee yet.

Carl

 

[Mark RSA2AU]

Thanks Carl

Battery load tested, still good. voltage drop between the battery and the alternator seems to be zero v. I have removed the alternator and will be taking it in to be bench tested and hopfully repaired at a reasonable price. There is no corrosion on any of the terminals but I have wire brushed them anyway just to be sure.


thanks agian, I will let you know what happens..

Cheers

Mark

 

[cmount1]

No problem and good luck.

Regards,

Carl

 

[Mark RSA2AU]

Hi Guys

It was the Alternator. The auto electrician showed me where all the wires had burned out, bugger! Replaced it and tested last week end - steady at 13.5V with all electrics running, and 13.9 with all off. Nice!

Cost it's weight in gold down here (Melbourne Australia), but as least we are back on the water.

 

[cmount1]

Glad your problem is solved.

Now you can go make some WAKE.