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My 28amp Bosch alternator just packed up. A new one is $300.

 

Anyone know a good source of second hand or reconditioned alternators that might be cheaper?

 

Even better does someone have one sitting around at home!

Its off a Yanmar 2GM20.

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This wont be much help, but you can typically get most alternators rewound by an automotive electrician.

 

If you do go new can you put a larger one on? Always nice to get the batteries charged quickly for cold beers. My Volvo D1-13hp has a 115amp alternator. Betteries normally charged in 20 mins motoring!

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So is there really no difference between a marine one and a car one? (other than the price)

I though that as im running a slow reeving engine it needs to be slightly different than a car one as they rev much higher. Is this true?

Also if I upgrade from 28amps to 40 or 80 (or bigger) will I need to replace wires and regulators or is it OK. I know that I have a voltage sensitive relay but dont know about the regulator other than whats on the back of the alternator.

Dont want to fry batterys or cables.

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Pop your pulley onto the 'new' one if it's not the same size but I think you'll find it is.

The regulator in the alternator will handle the output ok and will only push as much as the battery can take.

Good point about the load though, you may want to check that your wiring to the battery from the alternator can handle the extra amps.

Good upgrade and worth it though.

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A Marine Alt is different. It will or should have an Isolated Neg output. Or in other words, the metal frame of the Alternator is isolated from Negative. Both the Negative and Positive terminals should have a wire each.

Secondly, a Diesel Alt is different to a Petrol. They will have different "cut in" rev points.

Firstly, check the drive belt is not slipping.

Secondly, check the wiring is all good and connected.

If the Alt is Faulty, The most likely fault would be worn Brushes.

Second possible is the regulator pack.

It's very unusual for the windings to fail, although not impossible.

28A is small. A 45 to 50A should fit in nicely. Anything bigger and you will find frame sizes quite different. From 80A up, you need twin belts.

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I just got a call from auto electrical spares in henderson who I dropped the broken alternator to earlier.

My one has an unusual mounting system, pretty old school i think so its harder to find a replacement.

Im getting my current one fully restored for $168. If i had more time I would look into other alternatives but I need to be back out on the water friday

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A Marine Alt is different. It will or should have an Isolated Neg output. Or in other words, the metal frame of the Alternator is isolated from Negative. Both the Negative and Positive terminals should have a wire each.

Secondly, a Diesel Alt is different to a Petrol. They will have different "cut in" rev points.

Firstly, check the drive belt is not slipping.

Secondly, check the wiring is all good and connected.

If the Alt is Faulty, The most likely fault would be worn Brushes.

Second possible is the regulator pack.

It's very unusual for the windings to fail, although not impossible.

28A is small. A 45 to 50A should fit in nicely. Anything bigger and you will find frame sizes quite different. From 80A up, you need twin belts.

 

Thanks Wheels.

They said it was the regulator pack that was buggered.

I would like a bigger alternator one day but its not on my priority list right now. 40A would do me just fine. Its only when i rank up the big sounds that I need the extra juice but I have 2 x 130AH house batterys + the starter so got enough power for a good party!

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Also- I checked the power off the terminals at the back with a multimeter and there was nothing, it was reading 12.8v (battery voltage) when the key was off but as soon as the ignition was on the voltage dropped to 11.2v.

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We put Bosch tractor altenators on the 3JH2E Yanmar, 120 amp output.

Much the same size frame as the 60 amp standard unit.

We did have an excellent marine sparky in Nelson set it up but they (it was a cat so twin engine) worked fine.

Burnt out about one every 18 months live-aboard but way cheaper than Balmar or other "marine" high output altenators.

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The big problem with a non marine Alt and especially a high output unit, is that they will be generating a lot of stray voltage via the Engine block. The frame must be isolated, (which is part of the Alt design and can not be changed) so that you have a negative terminal. The cable connected to that must run to the Starter Motor bolt on the engine, or darn close to it, then the negative to the Start bank (or all the battery banks) are also connected at that point. The engine block is a poor conductor of such currents and the stray currents generated by both Starter and Alternator can cause many problems.

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Bosch make a dedicated above earth marine alternator, bosch no.BX929M, 0 986 ANO 541, K1-> 14V 10/90A Marine Universal, they make a larger and smaller amperage models as well. It has a built in regulator but It can be modified to a remote one if you so wish.

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I think marine alternators also need to be "hot rated" as there is no cooling air passing through the engine bay unlike in an automotive application. So if your marine one can be rejuvinated then well & good. :thumbup:

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Good point AA. You are correct. In fact many of them have very different bodies on them. Mostly all enclosed alloy bodies to protect from water spray and dissipate heat. Usually smaller vents front and rear and that's about all.

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This thread got me thinking about alternators. I'm not an expert, but I have some experience. Here is some basic info;

 

Most small marine diesels, (and some larger ones) come with basic non marine alternators that are not isolated neg. Most are 55 or 60amp, and designed only to replace the current used by the starter motor, and to supply lighting current for a vehicle.

 

The weak points are primarily the brushes, and 2ndly the reg packs. The regs are designed for automotive use, and are very inefficent at charging larger battery banks, regardless of alt max output. Brushes are cheap, and easy to replace yourself. You can by a packet of 10 of them (uses 2 at a time) for common alternators from supercheap or repco for under $20. Reg pack you should carry a spare.

 

However, the single best thing you can do to these alternators is to remove them, take them to an auto sparky, have him remove the internal reg and adapt it for external regulation. Then fit a real marine reg with temp sensing, and 3 level charging (Bulk, Absorbtion and Float). If you do this, you will get a better performance improvement than simply replacing the alternator with a larger one.

 

The primary diff between an automotive and a marine alternator, other than the insulated NEG that Wheels mentioned, is that the automotive ones are not normally hot rated. A hot rated alternator can run near it's max rated output continusly. If it is not hot rated and you do this to it it will die! However, on a small boat with only a few hundred AMP/Hrs of batt bank, the basic one (60 amp) that came with the motor, will be OK for a few years usually.

 

Also as Wheels said, a 75-80 amp hot rated Alt is the MAX for a single belt drive.

There are some modern alts that don't use brushes - known as self exciting - sounds dodgy! It is a great idea though, as the brushes do get mechanically worn down. Bearings also fail as do the windings, but that is much less common than the brushes and regs.

 

Happy to be corrected by anyone who knows more than me!! :D

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Our 120amp Bosch tractor lighting alternators, worked fine, on a marine diesel, with stuff all ventilation, mostly in the tropics, every day for five years on a single belt drive.

Yes we had smart regulators.

Just saying.

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