Alternator questions

[Islander53]

I have recently taken my prestolite 100 amp 12v externally regulated alternator to a repair shop to be rebuilt in Mexico.

I received the alternator back, and now it only puts out about 40 amps max, what did they replace to reduce the output? I would like to inform myself A little bit and go back to the shop, one problem is my Spanish is not so good yet. But I'm looking for specific terminology of parts replaced that would result in reduced amperage.

Another question... Are there any consequences for having an alternator hooked up to the engine and spinning for long periods of time but not being excited?

[Wotname]

Originally Posted by Islander53

I have recently taken my prestolite 100 amp 12v externally regulated alternator to a repair shop to be rebuilt in Mexico.

I received the alternator back, and now it only puts out about 40 amps max, what did they replace to reduce the output? I would like to inform myself A little bit and go back to the shop, one problem is my Spanish is not so good yet. But I'm looking for specific terminology of parts replaced that would result in reduced amperage.

Another question... Are there any consequences for having an alternator hooked up to the engine and spinning for long periods of time but not being excited?

Last question - no, apart from the obvious - very minor wear of the bearings.

First question - maybe they fitted an internal regulator if it had one in the past? I would first ask them what they did to repair it.

What was wrong with it for you to take it to them? The answer may help us to work out what they did to repair it.

The only thing I can think of for the reduced output is if they have left some of the stator coils disconnected or fitted a faulty diode pack or somehow increased the rotor resistance.

[Wotname]

Did they give you a parts breakdown on the invoice?

[Dsanduril]

Automotive/boat alternators are generally three-phase devices. They have three sets of windings in the stator and three pairs of diodes to rectify the AC power and convert it to DC. You can think of it as 3 devices, each providing one-third of the output. 40A is a bit more than one-third, but is an option for a set of bad winding connections or bad diodes. You could ask them to confirm all of the windings are properly connected and also that all the diodes (rectifier) are good.

Did the shop “rewind” the alternator? If so, if they did not rewind to the original specs (wire size and number or turns) then the output (and RPM curve) will change. The wire count in the windings determines the strength of the magnetic field and thus the output.

Running it without field current (excitation) is no problem.

[EDIT] Wottie types faster than me

[MORE EDIT] If they didn’t recognize it as a 100A alternator there’s a chance they put in diodes that are too small and some of them blew as soon as you started it up and it put out, for a short time, more current than they could handle.

[CharlieJ]

@Islander 53: The advice above is good. I have a solution for your other problem...weak Spanish language skills in a Spanish speaking country.

A former cruiser wrote "Spanish for Cruisers" and used illustrations of items found aboard and an extensive index to help somebody like you work their way through repairs and services when cruising. The first edition had an exploded view of an alternator and all of its parts identified in English and Spanish. I have not seen the second edition but I know the author and she is very thorough. Here is a link to the book on Amazon: https://tinyurl.com/ucf5tns

Good luck.

[Islander53]

The big issue is the language barrier... They only speak Spanish and I am only learning Spanish and trying to translate.. This wasn't the most professional looking shop, and no receipt or invoice. I dropped off the dead alternator which would not produce any power but bearings seemed fine and paid them 1600 peso , after the originally said it would be 1200 peso

I had the alternator hooked up to a balmar external regulator. When I noticed the reduced out put I bypassed the regulator and just supplied 12 volts to excite the alternator to measure the output. . I have done this in the past before the rebuild and measured the alternators output at full capacity and it would put out almost 50 amp close to idle and close to 100 amps at higher rpms ...
I'm almost 100 percent they did not fit an internal regulator. . After bypassing the balmar regulator I was able to get my batteries up to 15 volts for a minute , most internal regulators wouldn't go that high right? I also tried to explain to them it was externally regulated.

It just went to test the alternator again, I saw a few brief readings with clamp meter of 60 amps but it dropped off after a few seconds.... Then because it was dark I noticed a bunch of sparking coming from inside the alternator!!

[Islander53]

Originally Posted by CharlieJ

@Islander 53: The advice above is good. I have a solution for your other problem...weak Spanish language skills in a Spanish speaking country.

A former cruiser wrote "Spanish for Cruisers" and used illustrations of items found aboard and an extensive index to help somebody like you work their way through repairs and services when cruising. The first edition had an exploded view of an alternator and all of its parts identified in English and Spanish. I have not seen the second edition but I know the author and she is very thorough. Here is a link to the book on Amazon: https://tinyurl.com/ucf5tns

Good luck.

I have that book and carry it everywhere I go..

[Dsanduril]

I’m guessing you’ll have a hard time finding the phrase “the alternator is sparking inside” in the book

That argues either a bad/loose connection on a winding or bad/broken insulation in the winding.

[NYSail]

I would try to find a translator and bring it back.... obviously with sparks there is a significant issue. Or better yet, find a better shop where you can communicate and they give you an invoice and write off the $80 usd you paid to have your broken alt not fixed. Sometimes best not to keep going back and cut your losses.

Good luck

[mickt243]

It’s possible that the carbon brushes are worn beyond their limit, but still partially contacting the slip rings..... this could explain the low output and internal sparking.

The other obvious explanation would be a shorted winding or (as per someone else’s suggestions, blown diodes)

If a winding is shorted, it’s probably cheaper to buy a new alt.... if it’s brushes, less than $10 in parts...