Alternator trouble shooting

[ndutton]

While you're troubleshooting the immediate problem you may want to consider the bigger picture regarding AGM's. It takes more than simply replacing the batteries, a complete new charging system is required too. Here is a little more reference material on the subject:

http://www.knowyourparts.com/three-misconceptions-agm-batteries/

I tried AGM's a while back, did not make any charging system changes from my original flooded cell system (fixed voltage @ 14.0V). My experience was poor at best. After researching things a little more I decided the benefit of AGM's was not worth the trouble and expense of changing the entire charging system to first regain the performance of the original flooded batteries before realizing the further benefits claimed in the advertising copy. For me and my boat usage it just wasn't worth it. It took only one Catalina weekend on AGM's to reach the decision. It was an expensive lesson.

FYI, that single Catalina weekend's experience was eerily similar (dare I say exactly?) to what you reported in your opening post.

[hanleyclifford]

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.

I do not like the idea of the excitation wire sharing the circuit with the ignition, let alone with the fresh water pump in the mix. Try putting that pump on a different source where it does not influence the ignition. Resistors change voltage and pumps with motors also draw down the voltage locally. Edit: Before changing anything, test your voltage at the excitation wire, hot and running thru the rpms.

[joe_db]

I used gels for years, went AGM, hated them, and went back.
One issue with AGMs on an A4 powered boat is they take a LOT of charge when low. The small alternator at low RPMs on an A4 is looking at what is close to a dead short and can't get the voltage up to the setpoint for hours when charging a big bank. BTDT
BTW - GET SOLAR!
I spend a week or two at anchor for sailing class every year and a solar panel cut my engine run times by about 2/3s

While you're troubleshooting the immediate problem you may want to consider the bigger picture regarding AGM's. It takes more than simply replacing the batteries, a complete new charging system is required too. Here is a little more reference material on the subject:

http://www.knowyourparts.com/three-misconceptions-agm-batteries/

I tried AGM's a while back, did not make any charging system changes from my original flooded cell system (fixed voltage @ 14.0V). My experience was poor at best. After researching things a little more I decided the benefit of AGM's was not worth the trouble and expense of changing the entire charging system to first regain the performance of the original flooded batteries before realizing the further benefits claimed in the advertising copy. For me and my boat usage it just wasn't worth it. It took only one Catalina weekend on AGM's to reach the decision. It was an expensive lesson.

FYI, that single Catalina weekend's experience was eerily similar (dare I say exactly?) to what you reported in your opening post.

[JAcob Nagle]

Ok after some testing this morning, it turns out the alternator output goes up as the battery is charging, i was on the impression that it needed to go to 14V right away. So after 2 hours of charging at close to iddle speed voltage slowly rises until it stopped at 14.2v.

I checked voltage at coil and it went up along with the alternator.

So in retrospect when mecano came to my boat since battery where close to 100% the output went straight to 14.5. Dont know if it's standard? I find voltage drop between output and battery. 0.11 v. Is it normal.

Thanks for your help, battery are getting charge it just takes longer. Will wait until we are in dominicaine republic before doing any major change.

Im learning boat system as i go , unfortunatley i bought these 2 agm cause i uad a good deal. Maybe later down the road i will look at other kinds.

I also have a 130w solar next on my trouble shooting list.

[hanleyclifford]

A voltage differential of 1 volt between alt+ and batt+ is quite normal and acceptable, and the difference will vary a lot depending on state of charge and loads in use. BTW, as the battery charges the voltages will rise but the output (amperage) should decline. For a cruiser like you it is valuable to have both voltmeter and ammeter on line.

[ndutton]

Jacob,

I suspect you are actually reading battery voltage rather than alternator output. Unless you have a three stage regulator, the alternator output voltage strives to remain constant. As Joe explained, the discharged battery bank is likely drawing down the system voltage even during charging due to the low internal resistance and therefore high amperage demand of the AGM's coupled with reduced alternator output (in amps) due to low RPM.

Several years ago during a regulator-ectomy and replacement by a pro shop I had them test my alternator on a dynamometer. At an arbitrary 2000 RPM my 100 amp alternator produced around 60 amps. This is an example of the reduced performance due to low RPM Joe was talking about.

Your 0.11V drop between alternator and battery is excellent. It calculates to roughly 7/10ths of 1%. Nowhere in your engine electrical system should you have greater than a 3% drop so in this portion of the circuitry you're good.

A voltage differential of 1 volt between alt+ and batt+ is quite normal and acceptable

Uhh, no it's not. That is a 7% voltage drop, over twice the allowable 3% standard specified by the ABYC. The corrective action is a shorter wire run, larger wire gauge or both.

[smosher]

There's a sensor input for the voltage. I connect this to my common on the AB Switch. For my installation this means the common will be at 14.2 and the
excitation, connected to the coil+ is 14.5

The Alt will monitor the sensor wire, if its left floating I believe
it would monitor the excitation wire. Which probably reduces the vdc at the battery depending on the loss in the path.

The best thing I did was to install a 20 watt solar panel, Battery is always charged.

Steve

[hanleyclifford]

There's a sensor input for the voltage. I connect this to my common on the AB Switch. For my installation this means the common will be at 14.2 and the
excitation, connected to the coil+ is 14.5

The Alt will monitor the sensor wire, if its left floating I believe
it would monitor the excitation wire. Which probably reduces the vdc at the battery depending on the loss in the path.

The best thing I did was to install a 20 watt solar panel, Battery is always charged.

Steve

Steve - Is your alternator internally regulated? Does your alternator have 3 wires - output, excitation and sense?

[smosher]

Hi Hanley, Yes Internally regulated with the sensor and output

Just the stock api 55 amp alternator.

I found this thread on wiring the alternator.

http://www.moyermarine.com/forums/archive/index.php/t-4065.html