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Old 25-05-2016, 09:36   #1
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Large frame alternator under engine?

In my effort to add a big alternator to our engine, it occurs to me that I could possibly mount it below the engine. I have plenty of room there as and it would be an ideal spot to mount it. I'd need to have brackets make to attach it to the engine. I think I could mount it to the same bolts as what holds the engine mount brackets to the engine. Would be very sturdy. It would put its side load on the engine to the bottom, partly offsetting the normal side load from above from the water pump / stock alternator. The air below the engine would likely be cooler, so the alt would likely run cooler. I'd use a separate pulley and ribbed belt for the big alt. My concerns are: Access to the bottom mounted alt would be difficult if I needed to work on it for some reason. I could alleviate some of this with external diodes. Also, any water/coolant/oil/fuel spilled on or leaking from the engine could easily find its way into the bottom alternator. This could be a fire / safety hazard, but I'm not sure of the likelyhood. Any thoughts or has anyone else done this or seen it done. I've seen engine mounted refrigeration pumps mounted below the engine, but never an alternator. I don't really have room to mount a large frame alternator anywhere else, so this is my only option (for a large frame alt.) My other option is an Balmar AT-200 in the normal location, but it seems to me a large frame alt would be more robust. Some specifics: Boat is a Cabo Rico 38, engine is a Westerbeke W-46, Batteries are 2 x 8D Lifelines (510 AH) and so can take some significant bulk current.
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Old 26-05-2016, 07:32   #2
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Re: Mount large school bus alternator beneath engine?

Bump.
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Old 26-05-2016, 07:35   #3
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Re: Mount large school bus alternator beneath engine?

Automotive grade and Marine grade are different and it's not just the price tag. Marine grade is corrosion resistant and ignition proof. That cannot always be said of their automotive counterparts.
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Old 26-05-2016, 07:40   #4
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Re: Mount large school bus alternator beneath engine?

You might run the numbers, and you might not care, but that sounds rather heavy. I have seen purpose-built high-output alternators made for marine that I'd bet weight less than what you propose

bumped into this little primer
Selecting an Alternator | West Marine
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Old 26-05-2016, 08:13   #5
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Re: Mount large school bus alternator beneath engine?

This is exactly like ours is mounted. Welded a base mounting plate for the alternator to the plate for the engine mount. Then through bolted bracket for the alternator to this base plate. Originally was some misalignment with the main pulley and had to correct this last summer as it was eating belts and making a mess of the engine compartment. All good now though.

The big issue is to make sure that you are going to get the right rpm on the alternator with the pulley configuration so that you get adequate output from the alt. I will be in the bilge tomorrow and could likely get a picture of how it is done.
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Old 26-05-2016, 08:14   #6
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Re: Mount large school bus alternator beneath engine?

I'm proposing something like what this article describes , except that I'd mount the alternator below the engines oil pan, and not facing the engine but directly under it. There are lots of choices for large frame alternators. Balmar sell some that are allegedly marinized. Which alternator is not really the point. There are plenty to choose from. I'd like an alternator that can supply up to 200 Amps all day long without burning itself to a molten puddle. The experts all agree that small frame alts won't do this. Plenty of boats have large frame alts installed, I just dont have the room in the "normal" location to put them. My question is about whether putting it *below* the engine is a good or bad idea. Someone mentioned weight. I think that mounting a big alt below the engine would actually be better here as it would put the weight closer to the engine mounts and centered between them.
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Old 26-05-2016, 08:20   #7
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Re: Mount large school bus alternator beneath engine?

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Originally Posted by undercutter View Post
This is exactly like ours is mounted. Welded a base mounting plate for the alternator to the plate for the engine mount. Then through bolted bracket for the alternator to this base plate. Originally was some misalignment with the main pulley and had to correct this last summer as it was eating belts and making a mess of the engine compartment. All good now though.

The big issue is to make sure that you are going to get the right rpm on the alternator with the pulley configuration so that you get adequate output from the alt. I will be in the bilge tomorrow and could likely get a picture of how it is done.
Thanks! How large of an alternator did you mount?
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Old 26-05-2016, 08:24   #8
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Re: Mount large school bus alternator beneath engine?

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Thanks! How large of an alternator did you mount?
It is a 12v 200 amp Balmar.
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Old 26-05-2016, 10:02   #9
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Re: Mount large school bus alternator beneath engine?

What happens when you develop and oil leak? but I do like the idea of it being below the engine, it opposes the forces pulling up on the crank bearings!
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Old 26-05-2016, 10:08   #10
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Re: Mount large school bus alternator beneath engine?

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What happens when you develop and oil leak? but I do like the idea of it being below the engine, it opposes the forces pulling up on the crank bearings!
Yep, an oil leak (or fuel or coolant) is definitely one of my concerns. Maybe as part of the mount, there can be a sheet metal shroud, or roof if you will. Anything dripping down will then roll off the shroud and not get into the alternator. I'm looking for general opinions on the concept. I would guess that this is something that either has been deemed impractical or has been worked out with all the bases covered.
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Old 26-05-2016, 10:29   #11
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Re: Mount large school bus alternator beneath engine?

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Originally Posted by Saltyhog View Post
Yep, an oil leak (or fuel or coolant) is definitely one of my concerns. Maybe as part of the mount, there can be a sheet metal shroud, or roof if you will. Anything dripping down will then roll off the shroud and not get into the alternator. I'm looking for general opinions on the concept. I would guess that this is something that either has been deemed impractical or has been worked out with all the bases covered.

Just a couple of points from someone who's been using such alternators for a number of years --

Make sure it is located where it can get plenty of cool air

and

Make sure you can get to it easily to check and tighten and replace the belts -- the belts on these things need careful attention -- think about the horsepower being transmitted. In fact, if you can use a serpentine or toothed belt instead of dual v-belts, this might really be worthwhile.

and

Keep plenty of spares of whatever belt you use, on board, as these alternators will eat the belts in a heartbeat, if you don't have them perfectly tensioned.

And!

You're going to be really happy you're doing this. A heavy duty alternator is the cheapest piece of equipment you can put on a cruising boat, which will actually change your life on board.
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Old 26-05-2016, 10:47   #12
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Re: Mount large school bus alternator beneath engine?

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J

Make sure you can get to it easily to check and tighten and replace the belts -- the belts on these things need careful attention -- think about the horsepower being transmitted. In fact, if you can use a serpentine or toothed belt instead of dual v-belts, this might really be worthwhile.
and

Make darn sure you can get to the electrical connections on the back. They have been known to wobble loose.
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Old 26-05-2016, 11:04   #13
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Re: Mount large school bus alternator beneath engine?

Quote:
Originally Posted by Saltyhog View Post
I'm proposing something like what this article describes , except that I'd mount the alternator below the engines oil pan, and not facing the engine but directly under it. There are lots of choices for large frame alternators. Balmar sell some that are allegedly marinized. Which alternator is not really the point. There are plenty to choose from. I'd like an alternator that can supply up to 200 Amps all day long without burning itself to a molten puddle. The experts all agree that small frame alts won't do this. Plenty of boats have large frame alts installed, I just dont have the room in the "normal" location to put them. My question is about whether putting it *below* the engine is a good or bad idea. Someone mentioned weight. I think that mounting a big alt below the engine would actually be better here as it would put the weight closer to the engine mounts and centered between them.
Where are you going to send all that 200A??

For round numbers 200A is approx .4C in charge current, of a 510Ah bank. At .4C a Lifeline bank, when starting from 50% SOC, will hit absorption voltage at approx 19-20 minutes where the alt can no longer produce full output. In other words at .4C you need an alt that can handle .4C for about 20 minutes and just about any higher performance small case alt can do this. If you were charging 510Ah of LiFePO4 that is a completely differnt different story but with 510Ah of Lifeline AGM's at .4C, your bulk time will be in the 20 minute range and then the alt current will be continually cut back from there to 100% SOC....
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Old 26-05-2016, 11:18   #14
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Re: Mount large school bus alternator beneath engine?

Saltyhog,

I think this is a great idea. I have the same engine and a big empty sump below it. Alternators are not particularly sensitive to small amounts of water or coolant so I don't think drips would be a concern. Normal maintenance checks will prevent catastrophic dumps of water or coolant so the risk is acceptable.
I've been looking at the serpentine conversion and 160 amp small frame but your idea is probably a better solution at a better price.
Have you ball-parked the bracket price and design?
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Old 26-05-2016, 11:33   #15
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Re: Mount large school bus alternator beneath engine?

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Where are you going to send all that 200A??

.

If I could get that kind of amperage,
I could run things like my house AC off of my inverter IF I could get all 200 amps, but 200 amps at 14.3 VDC is only 23 amps at 120 VAC, so I could use it, and more if I had it.
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