Battery Charging at Idle

[Oswego John]

Hi Dan,

I want to tell you that I thought your post on battery charging was great. It should enlighten many readers.

There are one or two things that I would like you to go farther with. I bet that I'm overlooking or forgetting about something. That's what happens when your hair gets grey.

Quote "I won't take anything on say-so, I have to understand it."

Right on. That's how I feel about many things. Always have. It doesn't make me a bad guy though, does it?

Quote " the alternator produces current at a rate designed to provide the the electrical components with the juice needed to perform at optimum levels. The ignition system uses the most," Please explain.

I notice that you sail a CD 25. I guess that you probably have a single digit HP outboard for power, with/without an alternator on it. These outboards, except for the starting motor, have self contained ignitions.

The larger CDs mostly have one or two lung Diesel engines. These Diesels don't rely on electrical ignition. Other than starting power, w/wo glow plugs, and some might possibly have electric fuel pumps, are you referring to gas driven engines on CD power boats for high ignition demand?

Again, thanks for a well written article.

Best regards,
O J






Dan[/quote]

[Dan & Pat]

O J

Yup, we do have a CD 25 with a 9.9 outboard, but its still a yard ornament, not a boat yet... although another few weeks and she should have a wet bottom

What I was referring to with regards to the electrical demands of today's modern automotive/marine propulsion is that just about every component that used to be mechanical is now either electrical, or electro-mechanical which creates stresses on the electrical systems. Take the timing for instance. Used to be you could loosen a bolt, hook up a timing light, and adjust the power curve of your motor by changing the timing. Not any more. Going back to the early 1990's, most electronic ignition systems handle the timing all by themselves. Also, think about the fuel mixture. Was a time when you could adjust your carb with a mixture screw to lean it out or rich it up to change the performance.. Again, now this is all handled by EFI Electronics. All these little things take juice. But, the ignition system takes the most, (on a gas motor anyways) requiring a hefty spark to light the fuel.

Hope that clears some more stuff up.

Dan

[Troy Scott]

Rich,

Thanks! I was beginning to think I wasn't clear. Your's was the first response that indicated an understanding of what I was suggesting. I'll continue to think about this. Surely gearing up the alternator when the engine is at idle would provide adequate load. Thoughts? Another possibility is to leave the gearing alone and build an alternator with additional windings that kick in at lower speeds. Could this work?

[Dan & Pat]

Actually Troy, that could work. The electical current is produced by windings passing a field.

As I see it though, there would be several issues to address. First would entail the logistics of fitting those windings inside an alternator housing. Second, coming up with a bracket or mounting assembly to accommodate the new device in a limited motor compartment. From an engineering standpoint though, I think the easiest solution would be to increase the rpm's of the alternator by installing either a smaller pulley on the alternator, or else running it from a bigger 'drive' pully.

Some years ago, I helped a young man in his late teens at my old marina to design and build a wind powered battery charger from scrap parts. It looked like something out of Battlestar Galactica. He used a belt driven radiator fan from an old truck motor that was still attached to a water pump. He bolted that to a long 2 X 4, hooked up a belt to an alternator, then was able to connect it to jumper cables. He experimented with several different alternators, because some simply required too much energy to spin up. I think he ended up with one out of a Toyota. He also tried different pulley sizes before coming up with the optimum, which would put out power in winds as light as 8 mph. He pop-riveted aluminum sheet stock to the blades as well to add surface area, but damned if it didn't work. The marina management made him take it down during the day, claiming that it interfered with radio reception . I think they were afraid it was sending out a beacon to the home world.

[Oswego John]

Rich,

Another possibility is to leave the gearing alone and build an alternator with additional windings that kick in at lower speeds. Could this work?

Troy,

Anything is possible (almost).

Many people don't realize that the vast majority of motors in everyday use, especially those that are subjected to starting under load, have multiwindings.

Many motors have a *Starting Winding* that gives the motor a boost to overcome inertia. As the motor approaches full RPM, a centrifugal switch opens and disconnects the starting winding, allowing the motor to run solely on it's running winding.

There could be many variations on this theme. A specially designed housing would probably have to be designed for an alternate purpose such as variable speed charging.

If you want to have a little fun with your experiments, try going back to basics, where it all started. Research generators, cutout relays, variable brush riggings, external tunable regulators, etc. etc. And the beat goes on.

Anything is possible (almost)

Three cheers for my patron saint, Rube Goldberg.

O J

[Maine Sail]

I read this post before I went sailing this weekend and actually took some photos of my alternator in action to help clear the air. At idle, with my Universal M-25 running 900 rpm's. I can get an 11.3 amp charge with an 89.9% charge meaning my batteries are 10.1% discharged or almost full. At this rate of discharge my 90 amp alternator puts out a very respectable 11.3 amps and 13.35 volts. At this almost full rate, which is when the batteries are rejecting full alternator current anyway, I'm still putting plenty of juice to them. I ran the throttle up to cruise speed and I was still putting out only 11.3 to 12.5 amps depending on current draw. While taking these photos I was running 12V refrigeration, GPS plotter, stereo, VHF and auto pilot and motor sailing in 2-3 knots of wind.

So to make a long story short yes alternators will charge effectively at idle but it depends on your set up. My house bank consists of two 4D batteries with 360 total amp hours. On a smaller bank I would guess my alternator would put out less because the batteries could only accept less. For those in doubt see the photos of my Xantrex XBM displaying amp output, percent of charge & voltage output. When batteries are almost full it does not matter wether you run at idle or cruise RPM the batteries decide how much they'll take.... Hope this is helpful! By the way the Xantrex XBM is some of the best money I ever spent and I purchased it from Jack Rabbit Marine!

[img]http://www.pbase.com/mainecruising/imag ... medium.jpg[/img]

[img]http://www.pbase.com/mainecruising/imag ... medium.jpg[/img]

[img]http://www.pbase.com/mainecruising/imag ... medium.jpg[/img]

[Troy Scott]

Hi Acoustic,

I'll be running a Balmar 85 amp alternator with a three stage controller and a Zantrex ProSine 2000 charger/inverter. I hope to have about 500 ampere hours storage capacity when I finally figure out exactly what I'll be doing for batteries. I'm guessing my performance numbers will be similar to yours.

Do you have any idea what your alternator RPM is compared to engine RPM? I know many pulley combinations are available, and that there is an optimum. Since you're charging well at idle, I suspect your alternator may be running a little faster that some relative to the engine. That's OK, especially if you never really rev up the engine. Thoughts?

[Maine Sail]

Do you have any idea what your alternator RPM is compared to engine RPM? I know many pulley combinations are available, and that there is an optimum. Since you're charging well at idle, I suspect your alternator may be running a little faster that some relative to the engine. That's OK, especially if you never really rev up the engine. Thoughts?

Troy,

I don't know what speed it turns but I do own a photo electric tachometer. If I get a chance later this week I'll scope the alternator pulley to find out what speed it's turning. My alternator pulley is a fairly standard size if not a tad smaller than the pulley that came with the original 51 amp alternator. I have seen my alternator put out as much as 21 amps at idle before depending on the batteries state of charge. I don't know what is going on with the guy who can't even get a positive charge at idle? Perhaps he needs his 12V sense wire to come directly from his battery terminal rather than running through the battery cable, switch etc. etc.. I have about a .01 loss through my battery wiring so I'm not running a dedicated sense wire. Maybe his regulator settings are incorrect??

You can charge at idle and you will have a decent load on the engine provided your alternator is working correctly. One trick I always do is to occasionally run the engine at full load wide open for about 1 minute. My diesel mechanic told me this is a good idea to keep the combustiuon chambers clean so I do it about once every 10 hours of run time..

[Matt Cawthorne]

Troy,
Sounds like you want a much bigger alternator. With 500 AH of battery capacity you should think about something more like a 150 amp alternator. The most you should try dumping into a lead acid battery (flooded) is 40% of its capacity per hour. I have been told AGMs take more. You will need to invest in new pulleys since the normal belt on a 4.108 will not be able to handle the load of a higher amperage alternator. 150 amps at 13 volts and a 60% charging efficiency turns out to be about 4 hp. Check your engine power curves to see what RPM you need to be running to get 4 hp. Now if you want to drive the boat sometimes at that RPM you would need to be running at the RPM that can drive the boat (with a barnacled prop) and run the alternator. You could size the pulley accordingly. Be careful not to run too large of a gear ratio or you will trash the alternator when running at full throttle.
The folks that make air conditioner compressors have electrical clutches that activate a the push of a button. You could hook one of these clutches to the alternator and have a special setup that you could run at idle without overspeeding the alternator at high speed.
I have built an alternator mount for a prop shaft driven alternator that I can use while sailing, but have not installed it yet. Perhaps in the next month or two. The Hurth transmission that I use can be freewheeled.

Dan,
Everyone with a mid sized boat uses alternators to charge their batteries and many with larger boats while at sea. Alternators are properly sized for the applications and special voltage regulators are designed for optimizing the charge schedule. I run a 100 amp alternator on my 4.108 and at a slow idle get only a few amps out. At 1500 RPM I can get 70 amps if the batteries are discharged. I have a 3 stage regulator that pushes maximum amps out during the bulk charging (below 14.3 volts), absorbs at 14.3 volts and then drops down as needed to float at 13.5.

Matt

[bottomscraper]

I have built an alternator mount for a prop shaft driven alternator that I can use while sailing, but have not installed it yet. Perhaps in the next month or two. The Hurth transmission that I use can be freewheeled.

When you get this done I would love to see pictures!

[Troy Scott]

Matt Cawthorne wrote:

I have built an alternator mount for a prop shaft driven alternator that I can use while sailing, but have not installed it yet. Perhaps in the next month or two. The Hurth transmission that I use can be freewheeled.


Matt, You're beginning to get into the realm of hybrid technology here. I've been reading about electric auxiliary sailboats that recharge while under sail.... That would probably be great for most casual sailors, but I doubt it would work for the ICW.

[Matt Cawthorne]

Troy,
My goal for this one is to not have to have the engine running when offshore unless it is to drive the boat. I do have refrigeration and between that and keeping the lights on one ends up running the engine every day at least for 45 minutes even when the sails are full and the boat is moving. If this goes well enough I'll be able to get a small but steady current to keep the batteries topped off. I have one major problem to overcome. I got a very small alternator from a yugo or a hundai or some small vehicle and it has it's own internal regulator. If it tries to generate too many amps it will break the round cross section, urethane belt that I am using. At that point I will be forced to make my own regulator to drop the torque or have a toothed belt pulley made. We'll have to see.

Matt

[Troy Scott]

Matt,

Your project sounds like one I'd like to follow! Keep me (us) posted!

[Matt Cawthorne]

Troy,
You can accomplish a higher charging rate, with off the shelf stuff, without introducing mechanical complexity. I don't remember what alternator you have now, but say that it is 70 amps. If you buy a 200 amp alternator and associated belts and get a smart regulator you would be charging at 3 times the rate that you currently are. Now, 3 times the rate could cook your batteries when you are running the engine fast, but Balmar has a feature in their regulators that allows you to limit the peak current. If you had 200 AH worth of batteries, you could limit the alternator to a max output of 80 amps yet still get more current output at lower RPMs. You still would not get much out at idle, but if you push the engine up to 7 or 8 hundred RPM you might be able to get 70 amps. You might need to run a 70 amp alternator at 12 hundred RPM or more to get that kind of output.
Now with that said, it would be dangerous to run the alternator at 200 amps (with 200 AH worth of batteries) if the programming got messed up in the regulator. To cover that you would want to build a 90 amp fuse between the batteries and the alternator.
I feel a winter project coming on.....another one that is.

Matt

[Troy Scott]

Matt,

I have an 85 amp Balmar and I plan on having 500 ampere hours of storage capacity. I think the 200 amp alternator for charging at 70 amps at idle is an excellent idea. With the regulator and a fuse it seems pretty foolproof. But I understand that nothing is really foolproof for a sufficiently talented fool. I might find a way to really screw up! I wonder what's the largest Balmar that will fit on my Perkins 4-108.....