Alternator Side Loading Problem
I am in the process of repowering my sailboat and I have estimated the power requirements using Nigel Calder's Boatowner's Mechanical and Electrical Manual. Unfortunately the side load on the engine's cranksaft pulley from the alternator for the house bank will be too great and would cause engine damage.
Nigel Calder, in his book, recommends eliminating side loading by "adding a stub shaft to the crankshaft, and adding a separate pillow block bearing to the stub shaft to absorb the side load of the alternator." I have my boat at Delta Marine in Seattle, however they have no idea how to go about doing this.
Does anyone have experience with this or with eliminating the side load from a large big block alternator?
Are there any plans or diagrams explaining this process?
Is there a kit out there that could help with this project?
Engine: Yanmar 3JH4E
Alternator: Ample Power 4300 Large Case P-Type KKK rated (example)
Thanks in advance for your help.
You'll probably need to go to a shop that specializes in engine work to get this done. I don't believe any stock marine service yard will have the skill or technical chops to do this sort of work.
The stub shaft, essentially extends the crank shaft past the interior of the engine block, IIRC, and then it goes into the pillow block bearing, and adds a lot of lateral support , allowing the crankshaft to handle the side load of the alternator.
In layman's terms, the way the crankshaft is right now, it is supported only on one side, and the load from the alternator is heavy enough to torque it out of alignment slightly, causing serious engine problems. The stub shaft allows the load from the alternator to be supported on both ends... preventing the torque from causing serious engine problems.
I've taken a look at the parts catalog for the yanmar here...
and it says there are 4 main bearings in a set... you've got to have one set at the front and the rear of the engine, thats 2, then, maybe one set each between cyls 1 and 2, then another between 2, and 3? if thats the case, your crank should be able to handle the load.
It looks as though you have a non-dedicated belt running the alternator from this picture....
If thats the case, I'm not sure a really hi-output alternator is the way to go on a single belt. The crank pulley looks to be about 180 deg. contact area, spreading the load out, but the contact area on the alt. pulley is pretty small.
heres the tech drawings
the optional 80 amp alt. mounts on the opposite side of the motor, that may help a bit, or, another solution may be to add a pulley to your crank, and use that alternative site to add a second alternator, If you've got the space.
The Balmar site has some thoughts on pulleys, belts and alt. sizes here...
Another question to ask about this stub/pillow block installation. If your motor will be installed with isolation mounts, I would think that the normal vibration of the motor would cause wear and stress coming from the hard mounting of a remote pillow block as well, unless you iso mount that too. In addition, unless the stubshaft and mounting are in perfect rotational balance, thats going to add vibration as well.
Please keep in mind, I might be suffering from a cranial-rectal inversion.
The remote pillow block should be mounted to the engine block, at least in ideal cases, that way, any vibration or movement of the engine doesn't affect the alignment of the two with respect to each other.
Mithril, as sailingdog says, a stub shaft is really an extension of the main camshaft. It will NOT be cheap to have a machine shop fabricate that. As an alternative, you might (if space allows) remove the flywheel and have a machine shop fabricate a new flywheel with the stub shaft attached to that...still ain't gonna be cheap.
But I think Paul is more on the mark with his comments that adding a larger alternator on a single v-belt is just the wrong way to go. Once you hit 80-100 watts, an alternator v-belt slips so much that it is counterproductive. And using two belts (the old way to beat this) was an exercise in futility because unless you kept them matched, one always stretched more than the other, the load became uneven, and you're replacing belts again.
The new and more reliable way is to run the ribbed (serpentine style) belts for higher loads but that still doesn't help you with the shaft side load.
For that, the simplest solution is to use two smaller alternators, installed so they oppose each other and cancel out the side loads from each other. You may still need a custom double-pulley to make them fit, or some other machine work. Pulleys and shaft loads are all basic work for a machine shop, if you can take some pictures of the business end of your engine and stop by a machine shop in your area when things aren't frantic (not 8AM, not 4PM <G>) they'll often be able to give you some ideas. They may be able to install an idler pulley on the opposite side from the (one) alternator, to take up some of the side load.
But if the machine work gets too expensive...sometimes a genset makes a more effective solution. Or a wind generator, or solar.
The idea of using two alternators is a pretty good one. It has several major benefits, provided you have the space to do it properly.
First, it provides an easy way to get the power without the cost of the custom machine work.
Second, it provides some redundancy—if one goes, the second will probably still work, albeit, providing a lower amount of charging.
I personally prefer solar, as there are no fuel costs associated with it.
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