Mount large school bus alternator beneath engine?

[Saltyhog]

Originally Posted by Maine Sail

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....

Excellent question. A little background: My plan is ultimately for LiFePO4. But I got an extremely good deal on a pair of virtually new Lifeline 8D's. So I figure I'll use them for a couple of years and in the mean time, LiFePO4 will likely come down a bit in price. I'm an EE by day, so managing a LiFePO4 bank is within my abilities. Thanks to you btw for a lot of the what works / what doesn't with LiFePO4. In addition to looking to the future for batteries which can take really large charge currents, I'd also like to be able to run the A/C on the boat for short-ish periods to cool but mostly to dry the boat. We have a long haired Golden Retriever who loves to swim. So lots of fresh water will be in the cards. I figure that every couple-few days I can run the engine to do a bulk charge to the batteries, and when the acceptance current drops enough, I can then run a largish (30 GPH) water maker (120 VAC via an inverter). If we need to dry the boat out occasionally, or if we just want to cool the boat down a bit in the evening before bed, we can run the A/C via the inverter. The plan is to only run the high current A/C loads when the engine is running. No plans to run A/C at anchor for long periods. There is no room for a genset, so I think this is my best second option. There will also be about 300 watts of solar and a wind-gen to hopefully top off the batteries after engine run. The real goal is to load the propulsion engine as much as possible for as short as possible making the most use of the run time for battery charging and making water.

[Saltyhog]

Originally Posted by bcboomer

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?

No, haven't priced anything yet. It's going to be a custom job, but will be made of steel, so any fab / welding shop could fabricate it. I'm still in the planning stage at this point, and am looking for input on things to watch out for and thought about why it might be a bad idea. But so far, I still think it's a good idea.

[Saltyhog]

Originally Posted by Dockhead

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
It'll be essentially in the bilge, probably the coolest part of the boat at any given time. I can duct and blow some fresh air down there if needed.
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.
The plan is for a serpentine belt. I'm not aware of a toothed belt setup that would work here, but I'm open to suggestions. A toothed belt would obviously require less tension and thus less side load on the main bearing.
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.

Thanks! I think you're right of course, else I wouldn't be going to so much trouble. I had been thinking of something like the MEPS SeaPower System. But with a large alternator and a largish inverter, I get the same utility for A/C loads, with the bonus of very large DC battery charging capability. With the MEPS system, I'd have to charge batteries with an AC powered charger, which tend to be smaller. The real bonus will be when I convert to LiFePO4 in a couple of years. Run the engine for an hour and put 200 AH back in!!!

[Saltyhog]

Originally Posted by Stu Jackson

and

Make darn sure you can get to the electrical connections on the back. They have been known to wobble loose.

You're right of course. That will be one of the challenges. There is not a lot of room there as the bottom of the engine is in the keel (full keel boat). I think there will be just enough room to be able to adjust and tighten things when the engine is cool.

[roland stockham]

My opinion for what it is worth is that this approach is completely wrong.
Standard alternators are fine for battery charging and any output above about 100a is a wast of money! There is a rational. Yes you can charge lead acid batteries fast if you give them enough voltage but the higher the charge the faster you reach a saturation point where the battery cannot take any more. This is due to charge build up on the plate surface. Effectively what you are doing is recharging the outer half of each plate but not the center. In order to finish the charge you then have to feed current at a much slower rate to get round that surface charge. the result is that you can charge to about 65-70% much faster but then loose all the gains finishing the charge or the center of the plates remains uncharged and sulfates. This can radically shorten the life of the batteries. All this applies even more to any sealed cell (but not non-lead based chemistry)
So fit a standard alternator rated at about C4 or 5 and it will charge you bateries in about 3hr from 50% with a final charge level at about 90%. Whenever you get the opportunity turn off everything and let the solar system or shore power take the batteries up to 100%.
This is well established proven technology and works fine but has limitations. If you daily power requirement is in the 150-200ah + region you are reaching the limit for an alternator based system. Fitting bigger batteries and alternators is then not he most efficient solution because of excessive loads on the engine, particularly side thrusts and alternator efficiency. At these outputs it is time to look at a dedicated generator. Either a large solar array (good solution for cats) or a small diesel genset with a proper generator running off the shaft at the rear. If it is producing lots of AC power (washing machine, stove, air con etc) a 110v set makes sense. If not look at a DC generator, in the 2-5kw range they are about twice as efficient as an alternator and can run is a super silenced housing plus will fit in a locker out of the way.
If your boat is two small to fit a genset take a serious look at energy efficiency, what is gobbling all that power and would it be cheaper for example to update the refrigeration system rather than the power system?

[Midnight Son]

Greetings my first post:
One thing no one has brought up, is that the engine mounts allow flex. The supposedly large alternator will be ridged mount. Whole lot of misalignment, small amount, but continuous, and resulting belt dust in the bilge below in just a few hours of running time.

[jason902]

Depends on which side of the flex mounts the alternator is mounted to. As long as he attaches the alternator to the engine side of the flex mount there should be no issues.....

Sent from my SM-G900V using Cruisers Sailing Forum mobile app

[Midnight Son]

Going to be a very interesting design for the mount, cantilevered out there.

[undercutter]

Sorry the pictures are not so clear as I did not get around to it until after dark. Had to replace a whale bilge switch in the sump box.

Hope you can see the base plate is welded to the engine mounting bracket with the alternator bracket through bolted to allow adjustment. The alternator can also swivel on the 3/4" bolt through the bracket to allow final tensioning. This whole assembly moves with the engine so there is no concern with pulley alignment here.

I do agree with others who have stated that DC alternators or even DC Generators are not the best option for driving your larger AC loads or even charging at a fast rate. 1 watt is 0.00134102209 hp so even 2000 watts only requires 2.7hp. This is virtually nothing and running the main engine at high enough rpm to attain the required output on the alt/genset can result in significant glazing of the cylinder walls. When we recently lost our diesel genset for a week waiting on parts, I discussed this with the mechanic who suggested engaging the transmission in reverse and pulling against the anchor to achieve some load on the engine. His other suggestion was to stay plugged in at the marina until the genset was repaired due to the possibility of damaging the main engine.

This setup works great when motoring at 1600 rpm as that big alternator can run most of the systems and still put a good charge on the house batteries without overworking the smaller alternator that was designed to just charge the start batteries.

If you are still interested I plan on cleaning the strainers over the next few days before we depart for Canada next week I usually pull the alternator so that it doesn't get soaked with saltwater while I am at it. this would probably allow you to see the setup a little better especially if I can take the pictures in the daylight.

[Dockhead]

Originally Posted by Saltyhog

Thanks! I think you're right of course, else I wouldn't be going to so much trouble. I had been thinking of something like the MEPS SeaPower System. But with a large alternator and a largish inverter, I get the same utility for A/C loads, with the bonus of very large DC battery charging capability. With the MEPS system, I'd have to charge batteries with an AC powered charger, which tend to be smaller. The real bonus will be when I convert to LiFePO4 in a couple of years. Run the engine for an hour and put 200 AH back in!!!

Great plan!

I would stick, personally, to fairly standard high output school bus alternators. One enormous advantage of these is that they are cheap, and can be repaired by any third-world auto electric shop without special tools or parts. There is nothing in the world which will give you so much bang for the buck, for your electrical system. Cheap, simple, reliable, field-repairable and very effective -- what's not to like about school bus alternators? I wish more things on board were like this.


One thing to be careful about for LiFePo batts, however, is not to overload and melt down the alternator, since LiFePo batts will absorb full output at all times. I think this is a matter of regulation -- Maine Sail I'm sure knows how to deal with that. I would want to derate the alternator somewhat, I think, if I were planning sustained full output use, especially at low RPMs where cooling is not as good.

I put a core temperature sensor on my Leece Neville and have been observing how it behaves in different situations. I have 420 amp/hours of lead acid (@ 24v) for a 110 amp alternator, and when the batteries are down, the alternator puts out 100 amps even from low RPM, and gets hot -- 120 degrees C in the core, even though the case stays relatively cool (less than 60).

I'm gaining experiencing and trying to learn how to manage the alternator better.

[Saltyhog]

Originally Posted by Midnight Son

Greetings my first post:
One thing no one has brought up, is that the engine mounts allow flex. The supposedly large alternator will be ridged mount. Whole lot of misalignment, small amount, but continuous, and resulting belt dust in the bilge below in just a few hours of running time.

The plan is that the alternator is mounted to the engine, not the boat. The bracket for the alt is is bolted to the engine mount brackets on the engine, not on the boat side of the vibration isolating engine mounts. Here is a simple drawing. The part in brown is the bracket. Red is the existing pulleys/belt for the original alt and water pump. Blue is the pulleys/belt for the large frame alt. These are in front of the existing (red) on the engine.

[Saltyhog]

Originally Posted by undercutter

Sorry the pictures are not so clear as I did not get around to it until after dark. Had to replace a whale bilge switch in the sump box.

Hope you can see the base plate is welded to the engine mounting bracket with the alternator bracket through bolted to allow adjustment. The alternator can also swivel on the 3/4" bolt through the bracket to allow final tensioning. This whole assembly moves with the engine so there is no concern with pulley alignment here.

I do agree with others who have stated that DC alternators or even DC Generators are not the best option for driving your larger AC loads or even charging at a fast rate. 1 watt is 0.00134102209 hp so even 2000 watts only requires 2.7hp. This is virtually nothing and running the main engine at high enough rpm to attain the required output on the alt/genset can result in significant glazing of the cylinder walls. When we recently lost our diesel genset for a week waiting on parts, I discussed this with the mechanic who suggested engaging the transmission in reverse and pulling against the anchor to achieve some load on the engine. His other suggestion was to stay plugged in at the marina until the genset was repaired due to the possibility of damaging the main engine.

This setup works great when motoring at 1600 rpm as that big alternator can run most of the systems and still put a good charge on the house batteries without overworking the smaller alternator that was designed to just charge the start batteries.

If you are still interested I plan on cleaning the strainers over the next few days before we depart for Canada next week I usually pull the alternator so that it doesn't get soaked with saltwater while I am at it. this would probably allow you to see the setup a little better especially if I can take the pictures in the daylight.

Thanks for the pics. I think I get the idea. It looks like your install has the alt low, but off to the side of the engine. That would not work in my engine space. It would need to be below the engine. See my (crude) drawing above. My drawing has the alt bracket as a single piece. I think I'd need to have it designed with some adjustability however so I can precisely align the belt. Plan is for a 8-rib belt.

[Saltyhog]

Originally Posted by Dockhead

Great plan!

I put a core temperature sensor on my Leece Neville and have been observing how it behaves in different situations. I have 420 amp/hours of lead acid (@ 24v) for a 110 amp alternator, and when the batteries are down, the alternator puts out 100 amps even from low RPM, and gets hot -- 120 degrees C in the core, even though the case stays relatively cool (less than 60).

I'm gaining experiencing and trying to learn how to manage the alternator better.

That's pretty hot for the core. Maybe moving the diodes out of the alt case would help. Not sure how much however. I know that Mainesail was going to try that with his small case alt. I'm not sure how much success he's had though. I think you're right that managing the alternator via the regulator is the thing to do. My plan is that if I'm going to use the alt to run a largish AC load (via the inverter), I'll dial down the regulator to force a float voltage. This should minimize current to the batteries thus reducing the load on the alt to the batteries. I'll need a different approach when I switch to LiFePO4.

I have to laugh when I see posts saying that I shouldn't use an alternator to supply large loads, and that rather I should just get a DC Genset. I wonder what they think a DC genset is composed of?

[a64pilot]

When you get your mount built, consider powder coat. It seems to hold up better than rattle can paint and is pretty inexpensive to have done.

[Saltyhog]

Originally Posted by a64pilot

When you get your mount built, consider powder coat. It seems to hold up better than rattle can paint and is pretty inexpensive to have done.

Good idea. Another thought is POR-15. That stuff is hard as rocks and really resistant to rusting. Any metal in the engine room is a candidate for POR-15. No UV resistance though, so only for below deck. My hot-rod buddies use it a lot on old rusty frames.