Alternator trouble shooting

[JAcob Nagle]

Im having charging issue with my alternator. Its the api 55amp/14.5v sold on this site. I don,t understand why I cant have it output 14.5v when running the engine in neutral at anchor. How much rpm should it be going for me to reach the ideal charging ouptut. If it runs in neutral at 1800 rpm it goes to maybe 13.8. Is it possible to reach 14 v at close to iddle speed or do I have rev the engine that high while i charge my battery.

Comming down the icw i never had the probleme because we where motoring a lot. Now we are anchor in the exumas struggeling to keep the battery up. Its a small bank of 2 west marine agm groupe 27 92ah bought a month ago.

What am i missing.?

[hanleyclifford]

Since you are at anchor it is not likely there is any shop assistance nearby where you could get an output test on the alternator. I suggest checking all your connections especially the negative path from the alternator case to the battery bank. IIRC that alternator has only one wire, the big one. Where do you have it connected? Also, where are you reading voltage?

[JAcob Nagle]

I had it test on a bench in a garage in nassau. It tested perfectly , went up to 14.2 and stayed there.

Output cable goes to starter soleinoid, excitation to coil. I added a strapped from cassing of alternator to main ground, recheck all connection.

One local mecanician came check to check out the system and when he was checking things over he was reading 14.5v on his voltmeter even at iddle. I thought everything was fine then Next day i monitor it and get only 13.2 at iddle and up to 13.8 if i rev up the engine at half throttle. I tripple check with 3 different voltmeter and get same reading.

Reading output at alternator directly

[hanleyclifford]

When you say "main ground" does that mean the engine block? What sort of cable do you have from the engine block to the battery itself? Can you remember where the mechanic who read 14.5 v had his negative probe or clip? Was he grounding his meter in the same place as you grounded your meter?

[Boat]

try running the output directly to the house bank pos. i have the same alternator and thats wheremine is.

[hanleyclifford]

try running the output directly to the house bank pos. i have the same alternator and thats wheremine is.

Interesting thought. The solenoid terminal is the other end of the main positive feed so you must be suggesting there is resistance between solenoid + and batt +?

[JAcob Nagle]

When i say main ground i mean boat ground that connects to engine block.

When he was testing it i vaguely remembers, maybe he was probing the ground directly to the battery and the + to the output, i will re check tommorow. If you put outpu directly to battery do you have to fuse it?

[JAcob Nagle]

So just to answer original question, alternator should output 14.5 at close to iddle speed? Correct?

[hanleyclifford]

I had it test on a bench in a garage in nassau. It tested perfectly , went up to 14.2 and stayed there.

Output cable goes to starter soleinoid, excitation to coil. I added a strapped from cassing of alternator to main ground, recheck all connection.

One local mecanician came check to check out the system and when he was checking things over he was reading 14.5v on his voltmeter even at iddle. I thought everything was fine then Next day i monitor it and get only 13.2 at iddle and up to 13.8 if i rev up the engine at half throttle. I tripple check with 3 different voltmeter and get same reading.

Reading output at alternator directly

If your output goes to the solenoid battery terminal and it is also sensing, and meanwhile your excitation wire goes to coil + and you have a resistor in front of coil + I can see a potential problem - not enough "excitation" to satisfy the field requirements. Make sure the excitation wire does not have resistance in front of it.

[hanleyclifford]

So just to answer original question, alternator should output 14.5 at close to iddle speed? Correct?

Yes, at least just above idle unless some big loads are in use.

[hanleyclifford]

We could use some input from Neil on this one.

[joe_db]

That depends.
14.5 volts would destroy my batteries, so no way would I set my regulator that high.
The other issue is the A4 is a poor engine to charge batteries with. The alternator pully is pretty small, so the alternator RPMs are lower than most other engines. You have little power available at idle, so unless the batteries are topped off and there are no loads turned on, you are very unlikely to hit your voltage target at idle.
Make SURE you have a good ground connection. I have a seperate 4 gauge ground wire going from my alternator to the main ground bus. I use 4 gauge and 2 gauge wire from the alternator to the battery as well.
Can you post any photos and diagrams of how you are set up?
Here is what I have:

So just to answer original question, alternator should output 14.5 at close to iddle speed? Correct?

[ndutton]

The first question I have is why are you reading voltages different than the mechanic even with multiple testers? I suspect poor tester probe technique. Wherever you place your test probes they should be "drilled in" to minimize or eliminate paint/rust/oxidation/corrosion resistance on the metal surface. Push in the point of the probe with gusto while twisting it. This is especially important on a boat.

Secondly, I'd advise against charging at idle even if the alternator is producing at such a low RPM. Charging at idle doesn't provide much air flow from the cooling fan and if your batteries are discharged deeply (sounds like they are) your alternator will be working pretty hard with very little cooling. According to Dan Pires of Lewco Electric in Newport Beach, internal alternator temps of around 200°F begin to damage the insulation on internal windings and the death spiral ensues.

Finally, AGM's do not fare well with fixed point charging. Here is an excerpt from a bulletin by Cadex Electronics http://batteryuniversity.com/learn/a..._glass_mat_agm

As with all gelled and sealed units, AGM batteries are sensitive to overcharging. A charge to 2.40V/cell (14.4V) and higher is fine; however, the float charge should be reduced to between 2.25 and 2.30V/cell (13.5 ~ 13.8V), summer temperatures may require lower voltages. Automotive charging systems for flooded lead acid often have a fixed float voltage setting of 14.40V (2.40V/cell); a direct replacement with a sealed unit could overcharge the battery on a long drive.

[JOHN COOKSON]

One local mecanician came check to check out the system and when he was checking things over he was reading 14.5v on his voltmeter even at iddle. I thought everything was fine then Next day i monitor it and get only 13.2 at iddle and up to 13.8 if i rev up the engine at half throttle. I tripple check with 3 different voltmeter and get same reading.

Fresh new batteries in each of the volt meters I presume?

TRUE GRIT

[JAcob Nagle]

Ok will trouble shoot a lot today.

But to answer some of the question, batterry are discharged a lot this morning, 12.02 V.

I had replace battery in the voltmeter and I am scratching the paint of the alternator when probing ground.

Some question that i will try to answer while trouble shooting today.

Is there resistance at the excitation wire. What is the best way to test that?
There is a ballast resistor connected between the + side of the coil and my fresh water cooling pump. Can it be the cause?

I will try to bring the battery to a full charge see if after that the target voltage is easier to acheive. When mecano came to the boat , battery where near full charge after being plug to shore overnight.

I will also try to connect output directly to battery terminal.