Bad Alternator?

[TeamPCBeach]

We have been out just a couple of times so far in our 1999 300SE. Running both refrigerators and an AM/FM radio we only get a couple of hours before we get a low battery warning and have to fire up the generator.

I have noticed since we go the boat that the STBD voltage is lower than PORT when running. Today I checked at the dock. At 1800RPM STBD engine is providing 13.5 volts, PORT engine is providing 14.5 volts.

Should I replace the STBD alternator or be looking for something else?

Engines are 5.7L Mercs if it matters.

Thanks.

 

[wifisher]

Re: Bad Alternator?

Check all of your cables for corrosion. You could be getting a voltage drop at one of the connections.

 

[kenmyfam]

Re: Bad Alternator?

We have been out just a couple of times so far in our 1999 300SE. Running both refrigerators and an AM/FM radio we only get a couple of hours before we get a low battery warning and have to fire up the generator.

I have noticed since we go the boat that the STBD voltage is lower than PORT when running. Today I checked at the dock. At 1800RPM STBD engine is providing 13.5 volts, PORT engine is providing 14.5 volts.

Should I replace the STBD alternator or be looking for something else?

Engines are 5.7L Mercs if it matters.

Thanks.

Couple of things. Do you get the low battery warning while you are under way for a couple of hours or anchored or drifting for a couple of hours with the motors shut down ??
Are you going with your readings from the boats gauges or your own independant gauge ??
Have you checked the battery condition ?? your charging system may well be fine but your battery can not hold the charge. You can get the batteries load tested for free at most places.
The difference of 1 volt is not at this time a reason for alarm, especially if you are not comparing the readings from the same gauge.
Check the free things first before throwing money at it.
Post back your results.
Good Luck.

 

[BSAFlash]

Re: Bad Alternator?

As Kenmyfam says, check the least expensive items first.

Are you taking the charge figures from the gauges or from a multimeter?
The gauges show the condition of the engine batteries not house batteries. Does your vessel have a house battery readout on the main circuit panel? (my port gauge has been showing 12.5v as against starboard at 14.5v for the last 13mths)
Possible issues before you get to alternators.
The condition of the house battery (is it holding a charge?)
The condition of the cables
Condition of seals on fridges (are the fridges or fridge running constantly?)
The main 240v (110V?) battery charger (is it charging correctly).

I get around 3 hours on a new house battery running 2 fridges, stereo, pressure pump, vacum pump for toilet, a couple of lights and the depth sounder (to warn me of tide change when in very close and drinking cordial) before things like DVD players refuse to operate properly. You need to run the generator for a long time to re-charge after a days use like that, hence my looking at a second house. battery

 

[TeamPCBeach]

Re: Bad Alternator?

The measurements are taken with a multimeter. All three batteries are AGMs that are less than 2 months old. No visible corrosion on cables or connectors. Battery charger is brand new. This is only an issue when we are on the hook. No problems while underway. Since we are getting about the same amount of time as BSA I am thinking the alternator is probably OK.

As I am thinking about it, the 1 volt difference might be due to the battery isolator. If I remember correctly there are only 3 wires going to the isolator. So my guess is the STBD alternator goes to the isolator and that charges both the house and STBD battery. Don't know why both engines are not tied to the isolator. Need to investigate this some........

 

[TeamPCBeach]

Re: Bad Alternator?

So went over to the boat at lunch since this is bugging me. Below is a photo of the isolator. No branding on it, but it looks like it is designed for 2 alternators w/regulator feedback and three batteries. This matches what is in my DORAL manual. The strange part is as you can see only a single alternator is hooked up driving two batteries with no regulator feedback. So as best I can tell the boat is wired currently so the STBD engine charges STBD and house battery via the isolator and the PORT engine charges the PORT battery directly. Don't know why it would be hooked up this way unless the isloator went bad at some time. Looks like I am going to have to spend a couple hours in the engine compartment tracing things out.