Time For an Alternator Rebuild?

[Chotu]

Getting 0V between the large lugs here where the battery cables are attached to the alternator when the engine is running. I also made sure the belts were nice and tight and not slipping.

This is a recent development. It used to charge the batteries just fine.

Now I’m not getting charging current when the engine is on.

Any other tests or thoughts other than remove and bring to a shop for a rebuild?

Diodes? Not too familiar with that part.

[a64pilot]

If it’s internally regulated, I’d take it to a shop, and if I paid for them to take it apart, I’d want new bearings and brushes In it, even if they aren’t worn out.

On edit you may want to ensure it’s getting power to the regulator, easy to do.

[Chotu]

Thanks. I think it’s internally regulated.

Checking the diodes is putting an ohmmeter between the positive terminal and the alternator case and checking to see if the resistance is less than 550 ohms?


What are the smaller red and blue wires coming out? There is a sort of connector and box between them. It’s visible in the pic.

Not too familiar with any of this. Alternator have always just worked for me.

[GordMay]

Alternator Testing ➥ https://dam-assets.fluke.com/s3fs-pu...00_ENG_A_W.PDF

“Beat the Book" - Testing Electrical Systems with a Digital Multimeter: ➥ http://support.fluke.com/find-sales/...547394_j_w.pdf

[Chotu]

Originally Posted by GordMay

Alternator Testing ➥ https://dam-assets.fluke.com/s3fs-pu...00_ENG_A_W.PDF

“Beat the Book" - Testing Electrical Systems with a Digital Multimeter: ➥ http://support.fluke.com/find-sales/...547394_j_w.pdf

Wow, Gord. What a find. Thank you!

[GordMay]

Originally Posted by Chotu

Wow, Gord. What a find. Thank you!

More at ➥ https://www.cruisersforum.com/forums...ml#post3129370

[Scubaseas]

Getting 0V between the large lugs here where the battery cables are attached to the alternator when the engine is running. I also made sure the belts were nice and tight and not slipping.

Should be battery voltage here regardless of running or not.

[rslifkin]

Just for fun, with the engine running, hit the alternator firmly with something and see if it temporarily outputs power. If it does, the brushes are worn and losing contact.

[Windcall]

Heading South last year I noticed, the positive lug on the 100 amp Balmar akt was loose during a belt change. Our Grand Niece was on board, when motoring the engine RPM s would drop, She was using the microwave, didn't tell me. Decided to take it to Vero Beach Battery. The stator, abd rectifer, were going bad, they rebuilt it.
Now when the microwave runs no noticable change in RPM. Swear the engine sounds better too. Just putting it out there, not as bad idea to check yours if it's old Cheers

[bradfordharley]

Originally Posted by Scubaseas

Should be battery voltage here regardless of running or not.

As said above, if your alternator is actually connected to your battery, you will have voltage regardless of alternator functionality. Also check voltage between positive lug and alternator case....
is your alternator on a breaker? If it blew, and you ran it, you would blow your internal regulator. It would explain no voltage. Breaker blown disconnecting from battery and nothing being output.

[Scubaseas]

What are the smaller red and blue wires coming out?

Blue is probably field the wire or DF


Small gauge red with fuse is likely D+ or exciter diode circuit which should be hot with ignition or circuit 15.

[cottonsail]

Originally Posted by GordMay

Alternator Testing ➥ https://dam-assets.fluke.com/s3fs-pu...00_ENG_A_W.PDF

“Beat the Book" - Testing Electrical Systems with a Digital Multimeter: ➥ http://support.fluke.com/find-sales/...547394_j_w.pdf

Fluke makes fine instruments. A digital volt meter can NOT properly test an alternator. Only a lab scope can. You have to look at alternator "ripple" on a lab scope. That is the only sure test.

[GordMay]

I agree that the described test proceedures are not scientific lab' quality, but they are mostly suitable for the typical amateur DIYer.
From “Beat the Book”:
Figure 4. Checking Ripple Voltage*
Ripple voltage or (ac voltage) can be measured by switching your DMM to ac and connecting the black lead to a good ground and the red lead to the “BAT” terminal on the back of the alternator, (not at the battery).A good alternator should measure less than .5 V ac with the engine running. A higher reading indicates damaged alternator diodes
See page 5 ➥ http://support.fluke.com/find-sales/...547394_j_w.pdf
* A ripple voltage is a small, regular variation, in a direct current voltage that remains after rectification and filtering, of an alternating current voltage.

[smac999]

if you alternator is not going through a battery isolator. then you should have battery voltage at the alt. even with the engine off. 12.8v or whatever.

if the cable to the battery has come off. and you have 0v. it likely won't self ignite.

if you have a battery isolator, then the 0v is normal.


the red wire with fuse looks like an external regulator power wire, and blue is standard color for field, and it looks like the both go into that black loom. which is standard for ext regs.... if too. and there is no power at the pos post. then the ext reg is also not going to get power, and the start the alt

[Chotu]

So my alternator is going through a Heart Link battery charger in which every other charging and inverter function is working.

So, I think I need to start there with settings and double checking what I’m getting. It controls the alternator charging the House bank and allows a nice, proper 3 step charging off the alternator.