Will any alternator do?

hertfordnc · #1 (**permalink**) 10-30-2007

I just blew the alternator on my Yanmar 2QM20. Given that I am going to rework the electrical system how much difference does it make to have that specific alternator? I'm fairly new to this. The mount itself is adjustable and all the marine alts I've seen seem to have the same general mount.

Am i missing anything?

cardiacpaul · #2 (**permalink**) 10-30-2007

what... did you blow? diode plate, rectifiers, regulator, and how do you know its blown? was it a victim of "smoke technology?" (works till the smoke comes out)

Bermuda · #3 (**permalink**) 10-30-2007

You do not need to go with original equipment. The key is the yoke size and pulley alignment. That particular alternator is probably a Hitachi with a built in regulator. Built in or not is another important question. If you want better battery charging management you might consider an alternator sans the regulator and install a smart regulator. Another thing you want to consider is the alternator output, you do not want a 100 amp alternator for an engine of that size for everytime it kicks in you would lose 15 to 25 percent of your engine horses.

There are many aftermarket 'marine' alternators, Balmar and Ample Power to name two. I know of a company down in the Marathon region of the keys who supposedly builds very inexpensive replacements, I dont have any information handy but would be happy to get his number if you ask.

Lastly, if the boat is up for the season you might cosider having yours rebuilt, always a cheaper alternative to new if done by a reputable shop.

Good luck in any case.
Captain Bruce

kenstuber · #4 (**permalink**) 10-30-2007

If it would help with your problem, I have a used but good Yanmar 35-amp alternator that came off my 2QM20 available.

Regards, Ken

hertfordnc · #5 (**permalink**) 10-30-2007

More than likely it was a direct short.

The boat is new to me. I had one battery. I added a second battery. Some time after that I discovered the alternator was not charging. SOmetime after that I was finding my way in the dark to an anchorage. THe next day I got to looking over everything and found a black battery wire that really should have been a red wire.

There was no voltage at the alternator. I suspect i fried the VR. I can probably get it rebuilt. That's why I want to slap some cheap marine alt in ther and rebuild the first one and have a spare or maybe even mount both of them.

cardiacpaul · #6 (**permalink**) 10-30-2007

welcome to the joys of boat ownership!
take your alternator to a repair shop, have them suggest a replacement, and have them rebuild yours.

HoffaLives · #7 (**permalink**) 10-30-2007

A couple of things to know about factory alternators:
1) they are designed to only charge light-duty starting batteries, no more. If you have a deep-cycle house battery, it will sulfate it and reduce the charge capacity fairly quickly.
2) the amperage of the alternator should be approximately 1/3 the amp-hr rating of your battery system in order to keep everything fully charged. For example if you have or one day want 200 amp-hrs of house capacity, you should install an 80 amp alternator.

If you are using the alternator to charge a house deep cycle, to get the most life and capacity out of it you should get a regulator-free alternator and install a three stage smart regulator. A built-in simple regulator will not properly charge a deep cycle battery leading to the sulfation mentioned above.

You can replace the marine alternator with an automotive one at a fraction of the cost. You can also keep a spare diode pack and brushes aboard very cheaply.

It's important to NOT run the alternator output through the power/bank switch (the usual configuration). These switches are unreliable and if and when they go they will fry your alternator diodes. Also if anyone switches it when the engine is running the same can occur. It is much better to use a dual diode isolator to connect the alternator output directly to the batteries and just switch the battery output.

Rewire your system so that there is a direct cable ground from the alternator to the batteries and B+ output to diodes and batteries. Bad connections are the source of most alternator failures and it is not uncommon to have twenty or more connections between B+ output and the ground return through the engine block. You can reduce this to 6.

hertfordnc · #8 (**permalink**) 10-30-2007

naahhh,

I can probalby rebuild it myself once I get it back in my hands but I left it on the boat 200 miles away. There are no such repair shops anywhere near me and I am a marginally competent aircraft electrician. I can probably figure this out with a little guidance from all you experienced boat folks.

hertfordnc · #9 (**permalink**) 10-30-2007

Hoffa,

THat's exactly the sort of theretical info I was looking for. My replay above was to cardiacpaul. I didn't realize this thread was going to be so hot.

Don't you people have jobs? oh yeah, i'm at my job. I should do some work.

thanks

kenstuber · #10 (**permalink**) 10-30-2007

Regarding my used but good Yanmar alternator. Sailnet won't allow me to post my email address or reply to a PM, because they say I don't have enough posts. Oh well. Frustrating.

Ken