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Old 26-09-2008, 02:10   #1
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Yanmar 2qm15 alternator upgrade

My motor has the stock 35amp alternator right now. In addition to some other charging system additions I think I would like to buy a higher output alternator (this would also let me use my current as a spare).

I've read some talk about alternators that are too big putting sidestrain on other pulleys- and robbing the motor of horsepower. Given that- what is the largest "still totally safe" alternator I should go with?

I've been looking on go2marine.com... Is there a better source?
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Old 27-09-2008, 07:01   #2
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Yanmar offers an optional 55 amp alternator for this engine. As far as I know this is the largest they recommend.
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Old 28-09-2008, 14:44   #3
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i just replaced mine with a 55 amp unit and it works fine.... and i have a 1 gm. it works just fine, the alt i have is made by arco and it cost me 145 locally with no core charge as its a new not rebuilt unit
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Old 28-09-2008, 22:56   #4
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Our 10 hp Volvo is driving a 60A A13234.

55 should be no problem.
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Old 29-09-2008, 00:27   #5
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Some of the smart regulators have a ramp up facility that will reduce the alternator output until the engine has warmed up. With one of these I would think the engine could manage close to 100a which is about the maximum for a single belt.
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Old 29-09-2008, 09:04   #6
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Scotty - Do you know the model # of your new alt? I have a 2gm, with teh stock 35A, and would like to get a new larger one (keep the old for spare, as well).
I looked on Arco's webpage, but didn't know what model I needed!
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Old 29-09-2008, 14:49   #7
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no i dont they just looked at the old one and went and grabbed the one i bought. it looks just like a hitachi from the auto parts store, i looked there first. does yours have the 3 inch spacing between the mountings or the larger spacing, the place i went had both. if i can find the receipt i will look but iirc it just said marine alt.
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Old 29-09-2008, 17:27   #8
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I will have to look at mine closer, and get some measurements. My manual is on the boat as well. The boat is being hauled for the winter, in about 3 -4 weeks, so I will be ordering over the winter months, on-line likely - as there is no reasonably priced walk in store near me.
I assume that mine is the original, stock alt that came with my 1982 2GM.
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Old 29-09-2008, 21:14   #9
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okay if you have the small spacing now you can change that with a spacer and a longer bolt, so feel free to order the larger one. the orignal is a 135-105, the 55 amp is a 155 something. but that is hitachi's numbers so it does not mean much so buy the hitachi 55 amp replacement with the larger spacing. the easiest way is to look at the back mounting arm if it is straight off the back with out a bend its the larger one, the smaller one has an offset to the pulley end. now for the loop hole somewhere around 81 or 82 hitachi changes if it is internal or external reg but yanmar may have changed that too, so you do need to look for that
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Old 30-09-2008, 05:48   #10
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Didn't mean to steal the thread, but others may benefit as well.

Scotty - I assume my old alt is internally regulated, as I have never seen an external one. Is your new one set up for an external regulator?

I will likely go with an external reg, as everything I have read says they are more efficient and better for the batteries.
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Old 30-09-2008, 06:23   #11
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Yanmar has a 60amp alternator. Hotwire Enterprise has a 100 amp I do believe. I took my old alternator down to a rebuild shop, and had them bump it up in Oakland to 80 amps.
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Old 30-09-2008, 10:36   #12
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Quote:
Originally Posted by Northeaster View Post
Didn't mean to steal the thread, but others may benefit as well.

Scotty - I assume my old alt is internally regulated, as I have never seen an external one. Is your new one set up for an external regulator?

I will likely go with an external reg, as everything I have read says they are more efficient and better for the batteries.
no the internal vrs external is a hitachi thing, around 1980 hitachi moved over to internal mostly , but they still made some external. so if you want to go external that should be easy. a datsan ( nissan ) truck from 79 and 80 uses an external regulated hitachi alt ( 35 amp and it costs 60 bucks and bolts right in), just beware that the plug looks the same but the pins are different. i am sure if you wanted you could find a 55 amp hitachi at you local car parts place ( or have them order it ) and it should cost around 60 to 70 bucks that uses an external reg. you might have to replace it every 5 years due to corrosion but at 60 bucks or so....

disclaimer putting a car alt on a boat that is not spark protected might be a problem but on a diesel it should be okay. also all info i have is from internet and auto parts store research, honestly about 3 hours in auto stores.

note the reason for the 3 hours is i am cheap and when i heard 60 bucks vrs 150 i had to explore the options
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Old 02-10-2008, 07:14   #13
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I believe my alternator is internally regulated but don't know for sure. The various electric books went on hold in favor of the diesel book and I need to make some decisions partially blind...

How can I be sure?

Second, I hear about people using car batteries and nobody freaking out... Is that a sign that this is one of those jihad topics that quickly turn into flame wars and everyone is behaving? Or is this a practice that is on the okay-to-do list?
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Old 02-10-2008, 07:25   #14
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I have two 2GMs on my boat, one has the factory 55amp and the other has a 80amp. The 80 amp has been there for a long time with no evidence of side loading when specs were checked on rebuild. My Yanmar guys don't recommend anything higher than a 100 if I remember correctly. But a 80amp from a 35amp is a nice improvement.
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Old 02-10-2008, 12:22   #15
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jack for a starting battery a auto battery is just fine, for a house battery you will kill it quickly with deep discharges.

it find out if it is internal there is 2 ways, one is to trace the wires from the alt if any go thru a box its probably external. or put a volt meter on all the wires coming off the if any read higher than about 13.7 its external. basicly the best way is to trace the wires out, less chance of something getting chewed by running belts, or the alt going bad and not putting out the right voltage making you think its internal till its too late
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