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High Output Alternator Repair

footrope

Contributing Partner
Blogs Author
Some background. My boat came to me with a dual alternator charging system, installed by the previous owner. It has the regular 50-amp alternator in the usual top left position but it charges only the gel-cell start battery. The second alternator charges the house batteries and has its own regulator that is switched on with two switches. One breaker on the DC panel puts 12V power to the regulator and there is a switch on a separate panel in the nav station that connects the field wire between the alternator and the regulator. The engine sill on the left was carved out to accommodate the second alternator. The PO expanded the house batteries to four 105-AH AGM batteries in two banks. AGM batteries can take a large charge current when they are discharged to 50%. I see 60-70 amps initial charge going into each bank, using the nice battery monitor he also installed. So, this 190-amp rated alternator earns its keep despite the loss of horsepower while underway. All the electronic nav gear is hooked to the house system and I can keep the house batteries at full charge until we anchor, thus giving us the maximum life when not on shore power charging.

The house alternator was removed when I began the engine work (Oil in Coolant thread). I connected the house alternator up a few days ago, but with reverse polarity. When I turned on the house battery switch there was smoke and crackling noises. The smoke and noise came from a small component that is connected across the alternator terminals. Turns out that is a Motorola MR2535L transient voltage suppressor. So, off to the local alternator rebuilder for repair. It had been rebuilt 12 years ago, with a new rotor, bearings and brushes, for about $250 by the same outfit.

Before taking it in I cracked it open just to see how complicated it was and found it quite easy to work on. The brushes still had a lot of life in them and the bearings were nice and tight. But, with the burned up device (unknown device at that time) and the probability of some rectifier damage, I took it to the repair shop. The damage was two blown rectifiers and they offered to replace them, clean it up, new brushes and bearings, and test it for $460. I expected some inflation :0, but that was too much so I declined the extra work and they replaced the bad rectifiers and re-assembled and tested it for $120. They had no idea what the burned up device was and just gave it back to me.

I cut the shrink tubing off of the device, fearing it would break into a million pieces, but it didn't. There is a crack in the case, but the component number is quite readable. The MR2535L is obsolete, but I have the spec sheet and will be able to find a suitable replacement. Why is it there in the first place? I think that the high output alternator could throw a big DC voltage spike when it's switched into the system with partially depleted batteries. That's an educated guess, now that I know what the device actually is. It burned up with the reverse polarity because it can only withstand micro-amps of forward current flow. It may have protected the rectifiers from more damage by sacrificing itself.

I will be making some new markings on the alternator terminals to ensure this does not happen again.

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bgary

Advanced Beginner
Blogs Author
I will be making some new markings on the alternator terminals to ensure this does not happen again.

And photos. Lots of photos.

At Christian's suggestion, I've gotten in the habit of taking photos of everything I work on. "before" pictures so I know how it goes back together, and "after" photos, if I've made any changes, so I have a record of the current configuration.

I keep them on a "cloud" drive so they are accessible anywhere, including on my phone at the boat.

Digital storage is cheap. Time isn't.

$.02

folders.JPG
 
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footrope

Contributing Partner
Blogs Author
Definitely photos

Agree on the photos. I think what crossed me up was that the positive and negative wires (0 gauge) naturally hang towards the wrong terminal. Even though I noted this, I promptly forgot it while searching for a wrench. Then I didn't double check before turning the battery switch. There are only three wires since the tach isn't connected to it.
 

footrope

Contributing Partner
Blogs Author
Gone too far?

It's a rainy day, so I opened up the re-assembled alternator to look for a squeak that I could hear when I rotated it. I was concerned that my cost consciousness caused me to reject needed maintenance, too. When I split the case I noted that there were apparently three rectifiers that were replaced. There are three shiny ones in the first picture. One next to the "X" at the top and two directly below. Not really a problem if that is what it took to repair it.

I couldn't resist disassembling the front half when I found play in the front bearing that felt excessive. You can't feel it when the alternator is all together and the rotor is secure at the back end in the roller bearing. So I knocked out the rotor from the front bearing and then pounded out the bearing from the housing. In my spares kit, during an inventory check this past week, I re-discovered two sets of spare brushes, a new front bearing and a new roller bearing. Nice. I also found out how to retract the brushes while putting the case halves back together. A little trick I didn't know about that uses a piece of piano wire thru the brush holder that sticks out the back of the case. Note in the close-up of the brushes that the 12-year-old brush isn't really any shorter than the new one.

The front of the rotor shaft that fits into the bearing has a little rust that I will carefully address with emery paper. It doesn't really hurt anything. It is forced into the center of the bearing. I think before I re-assemble it I'll buy a plastic hammer and a tool that might be better than a large c-clamp to press in the front bearing.

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Martin King

Sustaining Member
Blogs Author
Craig you want to press the bearing on carefully. Horror freight has cheap arbor presses if you don't already have one. Do not reach for a hammer!

Martin
 

footrope

Contributing Partner
Blogs Author
Craig you want to press the bearing on carefully. Horror freight has cheap arbor presses if you don't already have one. Do not reach for a hammer!

Martin

Thanks Martin. I didn't seek any advice prior to disassembling the alternator. I wish I had, but it looks like I lucked out. The front bearing removal by hammer blows can cave in or crack the front housing if the bearing boss is not supported from below. A press would have been better all the way around. Fortunately this bearing wasn't glued in with Loc-Tite or anything. I checked over the housing and the boss is still square with the rest of the housing. I will either find a press or use a threaded rod with appropriate size washers to squeeze the new bearing into place.

I did visit HF but didn't see any arbor presses on the shelf. Maybe I'll check another one. I don't think the arbor presses are large enough for the diameter of the housing.
 

Martin King

Sustaining Member
Blogs Author
Thanks Martin. I didn't seek any advice prior to disassembling the alternator. I wish I had, but it looks like I lucked out. The front bearing removal by hammer blows can cave in or crack the front housing if the bearing boss is not supported from below. A press would have been better all the way around. Fortunately this bearing wasn't glued in with Loc-Tite or anything. I checked over the housing and the boss is still square with the rest of the housing. I will either find a press or use a threaded rod with appropriate size washers to squeeze the new bearing into place.

I did visit HF but didn't see any arbor presses on the shelf. Maybe I'll check another one. I don't think the arbor presses are large enough for the diameter of the housing.

If this is a one time thing, take it to a shop that deals with electric motors or a machine shop that can press it on for you.
 

Emerald

Moderator
and thinking of pressing bearings, don't forget that careful application of heat with a torch often will give you that few thousands expansion that makes it all go easy. Just make sure you don't destroy something it's attached to when it all gets hot....

:egrin:
 

footrope

Contributing Partner
Blogs Author
It's done!

Thanks for the suggestions. As it turns out, the bearing could be pressed in with a large c-clamp and a thin coating of silicone grease. I just placed the front case on the table face down and put an old aluminum sheave wheel on top that was a larger diameter than the bearing. It was easy to center the clamp and it slid in with light resistance. No problems. I cleaned up the rust on surface of the rotor with 600 grit sandpaper and then with a little grease it slid into the center of the new bearing without any persuasion. So it is back together.

I think the squeak was a brush that didn't slide out properly when the shop put it back together. Based on the rub marks on the slip rings it was making contact on its long side rather than the end. It may have tested ok under light load anyway. Not sure what would have happened with wear and time or high current. So, it's quiet and smooth now.

I didn't replace the rear needle bearing this time. Based on the wiggle in the new front bearing, I could have put that job off also.

I have a 50-amp Motorola to tackle next. It was on the boat when we got it and it cost more at shop labor rates to refurbish than a new one. I preserved the wiring diagram so I can re-use it. And it's a beautiful copper color!
 
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footrope

Contributing Partner
Blogs Author
Transient Voltage Suppressor

This is kind of a footnote to the alternator repair. I found an exact replacement for the obsolete MR2535L suppressor diode on eBay and bought two of them. I didn't find any others with similar specs on the electronics sites I usually hang around on. They arrived today and I'll give them the ohmmeter test tomorrow before adding the rings and wires that will make them fit on the alternator. I'll make them both up and keep one on the boat for a spare. I just gotta get the polarity right and mark them.

I also have a plan to paint polarity markings on the alternator so I don't repeat this episode. :dunce:
 

footrope

Contributing Partner
Blogs Author

I went to Mouser and looked at quite a few of those. Knowing just enough about electricity to avoid getting toasted, but not enough about whether a 200V would be adequate (against the 600V rating of the actual MR2535L) on this application, I spent a few bucks more. The new diodes are exactly like the old one and pass the ohmmeter test. And the shipping was free!

Thanks for the link though.
 
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footrope

Contributing Partner
Blogs Author
When all you have is black paint

The TVS diodes passed the ohmmeter test. There's one all crimped in and ready to go. The blown one's polarity wasn't marked on the outside of the shrink tubing so I looked up TVS circuits to make sure I get it right. Then I used the black-red convention on the pigtails.

Not too many places around here carry 5/16" diameter ring terminals for 14-16 gauge wire. I found some at Ace Hardware.

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footrope

Contributing Partner
Blogs Author
The 190-amp alternator is installed and works well. I did have to split the case open after the first installation attempt and rotate the rear housing, with the terminals, 90 degrees to the left. The terminals were hitting the cooling fitting just above and to the right. I now have a mark on the two halves of the case for the next time it has to come apart.

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Loren Beach

O34 - Portland, OR
Senior Moderator
Blogs Author
Lots of Amps

I have not heard of a 190 amp alternator before.
Lordy.... the wiring must be Huge.
:0
 

footrope

Contributing Partner
Blogs Author
I have not heard of a 190 amp alternator before.
Lordy.... the wiring must be Huge.
:0

Yes, the wiring is 0 (zero) or perhaps 0-0 if there is such a gauge. I could try to read the stamp on the insulation to confirm. Their stiffness must have required an epic contest of wills to stuff it in around the battery switch and route it between there and the two battery banks. The ends that attach to the alternator have some excess but they also have to move backwards to get the alternator into the brackets. The installation and removal of the 190-amp is something I had to learn. It requires the regular alternator to be loosened first, because the bracketry is all connected.
 

jim mccarthy

New Member
that looks like a half inch v belt to high output 190 amp alternator. would it not require a minimum of double v belt to drive that powerful an alternator?
 

tenders

Innocent Bystander
A second or very large belt would not be necessary if the alternator isn't being driven near its capacity. My guess is that's what's happening here - the engine probably never runs fast enough for the alternator to produce even half of its 190A capacity.

West suggests no more than 110A from a 1/2" belt, 80A from a 3/8" belt, so it's probably fine.

http://www.westmarine.com/WestAdvisor/Selecting-an-Alternator
 

footrope

Contributing Partner
Blogs Author
Au contraire mon ami

A second or very large belt would not be necessary if the alternator isn't being driven near its capacity. My guess is that's what's happening here - the engine probably never runs fast enough for the alternator to produce even half of its 190A capacity.

West suggests no more than 110A from a 1/2" belt, 80A from a 3/8" belt, so it's probably fine.

http://www.westmarine.com/WestAdvisor/Selecting-an-Alternator

This alternator does see as much as 150 amps when I'm charging depleted batteries. When we're on the hook or at a dock with no power, and the voltage of the two banks (four 105 ah AGMs) drops to about 12.0, I run the engine for 2 to 2-1/2 hours to charge them. I have the charging profile (output amps vs. time) on a scrap of paper somewhere. That is the heaviest duty that the alternator endures. The amperage output drops below 100 pretty fast, probably within 15-20 minutes. During the charging time I run the engine at 1500-1600 rpm. The engine speed drops 75-100 rpm initially, in this scenario.

The other scenario for this alternator is a very easy duty cycle. When we're heading out on an overnight, particularly if we know we're going to be without shore power, we'll start the alternator after about 30 minutes and run it until we shut off the engine on arrival. If we sail, we usually shutdown the engine and take what we get on arrival. Our motoring power setting is about 2000 rpm.

I am aware of the recommendations regarding belts for large alternators. Since I inherited this configuration and it works very well in these two scenarios, I've left it as I received it. If this alternator was running for long periods at 100+ amps, I'd probably be going through belts fairly quickly and would have to make some changes. I take the precaution of warming the engine (and thus the belt) for about 10 minutes before engaging the alternator. The installation requires a short belt, a Gates 9290, and the bracketry is quite sturdy. The pulleys are aligned well. I'm sure that helps avoid belt issues like overheating or glazing. I've never had belt problems but just the same I do change the belt every couple years at most. I usually keep the old belt while the new belt breaks in.

So, you're mostly correct. The alternator and belt lead a pretty easy life. The cutoff voltage for our diesel heater is 12.1 volts. So that's really the lowest voltage we like to see.
 

Christian Williams

E381 - Los Angeles
Senior Moderator
Blogs Author
Amazing. 150 amps is a real whammo without slippage.

I recharge daily, myself, which shortens the time and reduces the output. Max I ever saw was 80 amps fora few minutes with a 100-amp Balmar.
 
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