I think I toasted my alternator - now what?

[Rusty123]

I'm rewiring much of my boat, including the batteries and charging system. I accidentally reversed the leads on the alternator, and when I connected the battery, there was an arc, and I blew the main fuse.

Now, there is zero ohms between the "B" and "E" terminals on the alternator. I've not measured this before, but I'm thinking this is abnormal, and indicates damage of some sort.

Engine is a 1980-ish Yanmar 2QM15, and alternator is a stock 55 amp Hitachi.

Manual talks about testing diodes, is this worth my time, or should I just take it to a repair shop, perhaps for a full rebuild?

I'd planned on converting to an externally regulated setup at some point -- if I invest in a rebuild, would now be the time to do so?

Other suggestions?

[belizesailor]

Probably just cooked some diodes. Not a big repair. Find a good local alternator shop. Their rates are usually very reasonable, and they can fully test to comfirm if it needs anything else.

They could also mod it for external regulation, but typically alternators are set up for one or the other (int or ext reg)...so probably best to wait till you have your ext regulator for that mod (also easy).

You might also pick up a spare bridge rectifier while you are at it...just in case you blow diodes in the boonies one day.

[Celestialsailor]

What belizesailor said...
If it's old,,,doesn't hut to replace the bearings.

[Rusty123]

Manual says the regulated voltage is 14.3 volts. Any reason to ask shop to modify this? Any other upgrades to consider? (like bearings - thanks).

[forsailbyowner]

Alternators are an easy rebuild. I took mine in the first couple of times and had it repaired, which was all of putting in a new diode trio. Get two alternator kits and do it yourself, its not a big deal. The guy tridiode on ebay has had every starter and alternator part ive needed to date at good prices. Kits include bearings and all necessary parts for a refresh. Now I keep a spare kit and can fix it underway if necessary. The kit for my alternator runs around $15.

[bobconnie]

Ive been useing GM 100 amp truck alternators. Ya can buy em a dime a dozen at junk yards! Same cost to rebild as any other alt out there! works as well as the Big Boys sold for ten times the price! Ya may need to work out the mounting, but Ive put them on a bunch of different diesel boats over the years useing stuff from other cars and trucks! makes it nice when your way off some place to get parts or your alt fixed localy!! just a thought

[Rusty123]

As I continue researching, I'm learning that a major drawback of the Hitachi units is temperature compensation, which significantly drives down output. For that reason, I'm considering installing a new unit (though not the high dollar Balmar/external regulator type).

Any suggestions regarding a similar capacity, same frame, internally compensated, non-thermally regulated replacement?

[bill good]

Don't replace it with a bigger capacity alternator, you might find the engine wont like the extra load on starting. I fell for that trick.

regards Bill

[smaarch]

Originally Posted by Rusty123

Manual says the regulated voltage is 14.3 volts. Any reason to ask shop to modify this? Any other upgrades to consider? (like bearings - thanks).

it's an alternator and you cooked it
most sailors i now have done the same (including me)
just get it rebuilt at a local shop.
this isn't rocket science

[belizesailor]

Originally Posted by Rusty123

Manual says the regulated voltage is 14.3 volts. Any reason to ask shop to modify this? Any other upgrades to consider? (like bearings - thanks).

No, thats a safe max charge voltage for most applications. If you install a smart, temp compensating, external regulator it may drive the voltage higher, but it knows what its doing. A dumb internal regulator does not, and could cook batteries if you crank up the volts.

Re other mods, I think it would be handy to have an alternator which could be set for internal or external regulation by a switch or how its connected. Would be very useful as a backup when external regulator fails...and of course they do.

[belizesailor]

Originally Posted by Rusty123

As I continue researching, I'm learning that a major drawback of the Hitachi units is temperature compensation, which significantly drives down output. For that reason, I'm considering installing a new unit (though not the high dollar Balmar/external regulator type).

Any suggestions regarding a similar capacity, same frame, internally compensated, non-thermally regulated replacement?

Thermal protection is not a bad thing, sure beats a cooked alternator. If you install an external regulator, it will drive the alternator much harder, internal thermal protection and/or a hot rated alternator is more important with external regulation.

[forsailbyowner]

Originally Posted by bobconnie

Ive been useing GM 100 amp truck alternators. Ya can buy em a dime a dozen at junk yards! Same cost to rebild as any other alt out there! works as well as the Big Boys sold for ten times the price! Ya may need to work out the mounting, but Ive put them on a bunch of different diesel boats over the years useing stuff from other cars and trucks! makes it nice when your way off some place to get parts or your alt fixed localy!! just a thought

I will second this, I have 100 amp one wire Delco 10si alternator on my diesel and a modified one in my homemade wind generator. Its like the chevy 350 of alternators. Parts are cheapest because they made so many of them. They are available new for less than $70 delivered on ebay. Bolted in with no mods to my perkins 4.108. Puts out 20-25 amps, never seen anything close to the 100 that its rated at.

[colemj]

Originally Posted by belizesailor

Re other mods, I think it would be handy to have an alternator which could be set for internal or external regulation by a switch or how its connected. Would be very useful as a backup when external regulator fails...and of course they do.

The Sterling external regulators do this automatically. You solder a wire to the brush and lead it outside the case, leaving the internal regulator connected in place. If the external regulator fails (or you just want to turn it off for some reason), the internal regulator takes over immediately.

Alternately, Balmar 6-series have and internal regulator where they bring the regulator leads outside the case. If you want internal regulation, you connect the leads. If you want external regulation, you connect the field lead to the external regulator and it disconnects the internal regulator. If the external fails, you simply reconnect the internal - although this is not automatic like the Sterling.

We have both and they both work well. I like having the internal regulators in place as backup.

Mark

[JazzyO]

Amazing coincidence. I actually alternated my toaster.


Onno

[Roy M]

This is great. Last weekend I went out sailing on someone's boat. He asked, "What's the green light on panel mean?". I said, "Increase the RPMs and we'll see if it goes out". No dice. I asked him, "How do you turn off the engine?". He answered, "Well, first I turn off the ignition switch, then I turn off the battery switch, then I pull the kill cable." I laughed and shook my head. He was still producing 14.3 volts and couldn't understand why he had to take the alternator in for new diodes. I wasn't successful at explaining it to him, but at least he understands, now, the correct sequence to stop the engine in the future. Thank goodness for the green light.......