Alternator Output/Testing Question

[c130king]

All,

You have been most helpful in answering my questions. I have some more but to simplify I will post each question seperately to make it easier to keep on track.

For you electrically smart guys. I am having some doubts about my alternator. How do you test the output of your alternator?

With motor running at 2200 RPM I used multi-meter to check voltage at battery terminals and got a reading of around 13 volts. Gauge on instrument panel says 14 (but it says 14 when the motor is off if the key is left on...which doesn't seem right). Volt meter on my electrical panel show slightly less than 13 with motor running.

Voltage when motor is off is around 12.4 ish.

With battery charger running on shore power I get a reading on the volt meter on electrical panel of 13.5 volts.

A couple of days ago I had a morning and an evening sail and I didn't hook up shore power in between. Frig was running some...but not all the time. And following the evening sail I had no juice in the selected battery to start the motor. Switched to the other battery and it started just fine. I guess I drained that one battery with all the use that one long day...but I did run the motor 3 times for a total of probably one hour.

What could I do to verify that my alternator is working properly?

Thanks,
Jim

 

[Stu Jackson]

Jim, you might want to read the earlier 310 discussions about how electrical systems should work. Like the last two or so.

You're correct in measuring voltage. A battery monitor would eb a great help in dealing with current.

What makes you think your alternator is not working?

Try these, too:

Basic Battery Wiring Diagrams This is a very good basic primer for boat system wiring: http://c34.org/bbs/index.php/topic,6604.0.html

This is another very good basic primer for boat system wiring: The 1-2-B Switch by Maine Sail (brings together a lot of what this subject is all about)
http://forums.catalina.sailboatowners.com/showthread.php?t=137615

 

[rpwillia]

Let's keep this simple

If your battery reads 12.4 volts and when you are running your engine and you have 13+ volts something changed, like your alternator is working and putting out a higher voltage than your battery. The voltmeter on the panel on my boat is about 1.5 volts high, but there seems to be no way to adjust it so I compensate for it in my head.

A better way to know what is going on is to read your battery voltage, start you engine and read the voltage on the leads on the alternator and then compare it to what is on your engine monitor to get the difference.

You should see your alternator put out different voltages at different rpms, perhaps not a lot but some. If your voltage is the same all the time, engine running or not, then you probably have an alternator problem.

I suspect you should probably not run your refrigerator for more than a day or two on just one battery. You could see what capacity your batteries have, what the refrigerator should draw per day and do the calculation, but then we would not be keeping this simple. OTOH, if you post the details in Ask All Sailors someone will calculate it for you. :wow: It's just what they do.

 

[c130king]

Thanks guys. I do have a basic understanding of how the electrical system works. I was just concerned that my alternator was not working correctly for a few reasons:

1. When I turn the key on the engine instruments at the pedastal come on and the voltage goes to 14 volts...even when the engine is not running. That doesn't seem right. And the voltage at that gauge never changes at different RPMs.

2. The voltmeter on my electrical panel shows less than 13 volts when the motor is running. Seems low.

3. I used my multi-meter on the battery terminals when motor was running and I think it was 13 volts.

4. Looked at the leads on my alternator but wasn't sure which was positive and which was negative...and the boat was moving and belt was spinning so I decided not to try to check alternator leads directly at that time. But I will check it today.

So even if my alternator is working I think I may have an issue with the voltage/alternator gauge on my instrument panel.

And for what it is worth I can't get my engine temp gauge to work either. Still trouble shooting that as well.

Got another couple of boater friends coming over today and we are doing lots of work...including my first ever trip up the mast to replace the steaming light bulb. But we will be looking over these motor/alternator/instrument issues as well.

And yes, the frig will definitely drain the batteries. When I first got the boat several months ago I left the frig on and the battery switch on...on purpose...but forgot to turn on the battery charger on the AC panel. Something came up and I didn't get back to the boat for 3 days and the batteries were dead. They did recharge and seem to work fine but I am sure they are not as "good" as they were prior to that.

Thanks,
Jim

 

[JK_Boston_Catalina310]

Thanks guys. I do have a basic understanding of how the electrical system works. I was just concerned that my alternator was not working correctly for a few reasons:

1. When I turn the key on the engine instruments at the pedastal come on and the voltage goes to 14 volts...even when the engine is not running. That doesn't seem right. And the voltage at that gauge never changes at different RPMs.

The voltmeter at the pedestal should read between 12-13 volts initially. When you engage the preheat/starter, it will briefly drop. After the engine has started it should read between 13-14 volts.

2. The voltmeter on my electrical panel shows less than 13 volts when the motor is running. Seems low.

That is a cheap voltmeter that can't be adjusted, IIRC. I wouldn't put to much into the exact reading on that voltmeter. I would trust my multimeter more.

3. I used my multi-meter on the battery terminals when motor was running and I think it was 13 volts.

See the attached page from the Universal Diesel Operation Manual. It should be 13.5 to 14.5 volts.

4. Looked at the leads on my alternator but wasn't sure which was positive and which was negative...and the boat was moving and belt was spinning so I decided not to try to check alternator leads directly at that time. But I will check it today.

Be careful! The positive is shown on that same page from the manual, if you still have the Mando alternator. For the negative, you can just use the engine.

So even if my alternator is working I think I may have an issue with the voltage/alternator gauge on my instrument panel.

See above, this is also why many of us install battery monitors. (http://www.pbase.com/mainecruising/battery_monitor) Just did mine this year. (http://svsmitty.wordpress.com/2013/03/04/electrical-charging-system-upgrade-mostly-complete/)

And for what it is worth I can't get my engine temp gauge to work either. Still trouble shooting that as well.

There are other ways to check for proper operating temp. (http://www.pbase.com/mainecruising/engine_temp)

Also, in a previous post you said that the batteries were reading 12.4 volts. Was that fully charged? They should be reading 12.7 volts. When was the last time you did a full charge? An equalization charge? Checked the water level?

Good luck and fair winds,

Jesse

 

[c130king]

All,

Turns out the problem was that the power cable on the back of the alternator was disconnected. the wire broke off from the ring terminal...inside the plastic/rubber boot that was covering it.

So no power coming out of the alternator to the batteries.

Fixed all of that today and now the alternator seems to work well. Used a better multi-meter and batteries were 12.7 with everything off. And 13.96 with alternator running.

I have been this way since I have owned the boat. But I was always back on shore power with battery charger every night so never became a big issue.

My batteries are okay I think. I check the fluid levels and the hydrometer check on the 1st of every month.

Also installed a new engine temp gauge today. Think it was working but I didn't run the motor for very long so I will keep my eye on it for a few weeks and see what it says.

And I got up the mast for the first time ever. Steaming and Deck light working great.

All in all...a very good day working on the boat.

Cheers,
Jim

 

[Stu Jackson]

I had similar experiences with the factory installed terminals from the harness on my Balmar MC-612 - all of them failed at one time or another.

The real test of your system will this: when your batteries are NOT completely full from a shorepower charge - like being on anchor for a night with the fridge running.

If the AO (alternator output) is disconnected when charging, sometimes it fries diodes. When the banks are full, many times they don't fry.

So, if it was my boat, I'd run at night without being connected to shorepower and then run the boat, both at the dock and then at engine cruising speed (your choice in the slip or not) and carefully check everything.

So far, what you've reported looks good.

Good luck.

 

[alexco38]

Modern alternator output 14.4 volts. Older one output 13.9. You can change the regulator to output 14.4v from the same alternator.

If you have internal regulator, auto electric guys can change it for you. About $50 in parts.

 

[c130king]

I had similar experiences with the factory installed terminals from the harness on my Balmar MC-612 - all of them failed at one time or another.

The real test of your system will this: when your batteries are NOT completely full from a shorepower charge - like being on anchor for a night with the fridge running.

If the AO (alternator output) is disconnected when charging, sometimes it fries diodes. When the banks are full, many times they don't fry.

So, if it was my boat, I'd run at night without being connected to shorepower and then run the boat, both at the dock and then at engine cruising speed (your choice in the slip or not) and carefully check everything.

So far, what you've reported looks good.

Good luck.

Stu,

Thanks for the advice. I will give that a try tonight.

Cheers,
Jim

 

[JK_Boston_Catalina310]

Another thing to consider is the wire carrying the current from the alternator to the bank.

Under the factory setup, there is a 12 gauge wire going from the alternator to the starter and then 1/0 gauge from the starter to the 1/2/both/off switch at the panel and then 1/0 gauge going back out to the selected battery. That 12 gauge wire from the alternator to the starter is undersized.

The quick fix would be to run a larger gauge wire, like 4 gauge for the factory alternator, from the positive of the alternator to the starter. Here is a sizing chart that is decent: http://bestboatwire.com/catalog/includes/languages/english/wire_gauge_chart.html. I'm sure MaineSail has a better one. Just remember when you size wire it's based on round trip, meaning that you count the number of feet for the positive and typically double it to account for the negative. MaineSail has a how to on this: http://www.pbase.com/mainecruising/catalina_36_alternator

The other fix would be to run the alternator output directly to the batteries. This might need to include the addition of a ACR. I just finished this project: http://svsmitty.wordpress.com/2013/03/04/electrical-charging-system-upgrade-mostly-complete/

There is a lot of information on both options here if you do some searching.

Fair winds,

Jesse