Alternator?

[tdonoughue]

It is known that our boats have magnetos that provide electricity to run the engines and also recharge the batteries. It is also known that the amount of electricity that they provide is low, and generally will not be sufficient to fully recharge double batteries, particularly deeply discharged ones (like from a couple of hours of floating with music).

Question: Has anyone found anyway to hook an alternator or two to the engines to provide a better charging scenario?

 

[Scottintexas]

somebody back at YJB hooked up a car alternator and it worked great, I'll try to find the link,

 

[Scottintexas]

you can start here, https://jetboaters.net/threads/intermediate-bearings.2122/page-2#post-33986
@cybuch is your alternator post listed on this board ? I couldn't find it, if not would you mind posting it here for us that can't go back,

 

[David Analog]

If possible that would make for a great upgrade. A small case alternator could better handle higher rpms while a larger case might not. What is the top end rpms?
Any alternator that delivers more current would proportionally offer more resistance. That could be one reason why they limit the charging system on small displacement motors. So would you have to do the mod to both engines? Do you have the excess horsepower?

 

[Scottintexas]

here is the YJB link,

http://yamahajetboaters.com/forum/viewtopic.php?f=1&start=15&t=23672

 

[CrankyGypsy]

where is the "original thread" with pics he mentions?

 

[Julian]

Hopefully @cybuch can utilize our simple drag and drop image upload to share the pics....and describe the install process.

 

[Bruce]

Hopefully, i am wrong but I have a memory of some sort of mechanical issue occurring with that installation.

Personally I have an onboard charger and two group 31 AGMs. That is sufficient to run the stereo, refrigerator, VHF, underwater lights, etc.

 

[txav8r]

I don't think he contributes it to the alternator install, but @cybuch had an engine failure on the engine he mounted the alternator. IMO, it is a big load for our smaller engines to run. Secondly, this will not achieve what your after. Alternators are not used to "recharge" batteries. They are used to support electrical loads on the electrical system and keep the battery at a sufficient level. There is a balance, and if you do a bunch of water sports or cruise a great deal, you will keep them pretty topped off with a good alternator vs our stator/magneto system...however, if you anchor and enjoy a moderately amplified stereo system for a number of hours, say 3 hours or more, your depletion will require HOURS of engines running to recharge even a single battery fully. Again, the idea is good based on a supplement to your electrical system, just not a "charging" system...shore power is still needed to maintain the batteries correctly.

 

[tdonoughue]

Thanks, guys!

Sorry for the delayed reply. Been traveling over spring break. I was able to get to the pics on the 'other' site. Took a little digging, but I was able to get to it (though I don't get the 10 points from being banned yet, I suppose). Very neat. The key, of course, would be getting the right size pulley to get on the shaft... I am surprised that he had to lift the engine! Thanks everyone for pointing me to that!

@txav8r , you are right it would be a big load on our small engines, but I assumed that could be managed via a smaller alternator. But I am more interested in your comments with regard to it not achieving goals. I had assumed (incorrectly?) that the alternator would generate more amps than the magnito system does. In truth, I do not have a mega amp'd system and have never really run out of battery (and have two of them, etc.). We generally do not spend even all day out--only a few hours or half a day. So "need" is probably too strong a word. I was just looking for something that might top up the batteries better while we were running.

In further truth, what I really need to do is to figure out the amp output of the magnitos and the amp draw of what I have on the boat to see how far 'behind' I might be.

 

[David Analog]

Larger alternators are used to match up with larger loads. Big stereos are larger loads and depleted batteries are certainly larger loads. So a larger alternator can fit the application. While regulated, more so than a stator, an alternator is still a dumb and blunt device as compared to a smart charger. You generally cannot depend on an alternator to finish the job after an extended duration at rest with a big stereo because you rarely burn enough gas at the end of the day. The ones that typically invest in an alternator upgrade are those that routinely take long holiday weekends or vacation weeks at destinations where no AC power is available in combination with Mega-Watt stereos (mega may be a bit of an embellishment). Unless your usage is unusual and the size of your stereo system is extreme, you can easily get by and do very well with adequate battery capacity and adequate shore charging. For the 95% a few voltage measurements at key times will give you all the clues you need to construct the right battery reserves and recharging system to fit your unique usage.

 

[christopherglenn]

You *can* charge the batteries off the alternator, with a few rules. Generally alternators aren't designed to run hours on end maxed out, and fail. Batteries only accept large amounts of amperage when they are pretty far discharged. In the RV world, we try to keep the batteries above 50% state of charge, and only attempt to charge them to 90% with generators. A 50-90% on most any battery is possible in 3-4 hours without damaging the batteries. What you will run into is that last 10% of the charge the battery is only taking 10% or less of the amps as when it was closer to 50% charged. Dry camping at the lake 2-3 days, an extra battery and alternator would work well. A single day on the lake and towed home an extra battery or two and a good onboard charger would work far better. In either case you will have to top up the battery off shore power with a charger of some kind.

 

[txav8r]

The reality is that lead acid batteries can only absorb about 10 amps per hour, no matter how many Amps you put into them. An AGM can handle a tad more...so recharging becomes an event steeped in time, not amps. Handling the load is an alternators benefit.

 

[txav8r]

Also, there is a very big difference in 6v golf cart batteries and a 12v deep cycle, but even the 6v won't absorb much more than 15-20amps per hour.

 

[cybuch]

Wow! It's been a while since I have been on. So here is a little more information:

Yes, I had an engine fail and yes it happened to be the one that has the alternator. The reason for the failure was a bad ECU that was sticking one of the injectors open. Filled the engine oil with fuel. They also think my head was warped. (That's the short version)

I am not seeing much of a load from the alternator on the motor. When I have the stereo cranked with the engine running, I don't see any change in RPM, from being loaded down. I am guessing at full load I am only using 3 or 4 HP of the 160 I have available. Even at 5HP that's only 3% load. (All speculation of course).

As for the new motor, we have been running the new engine for quite a while with the alternator and that same motor is the one we use for flyboarding. It has been running great and because we are using the motor with the alternator for flyboarding, when we do have music on, we are not sucking power from the batteries. We also keep them topped off with an onboard charger.

I'm not saying anyone should run out and put an alternator in, but in our case it has worked out very well.

I would be more than happy to share the pix and write up the process.

 

[tdonoughue]

Thanks, @cybuch ! I did actually go look up your write up on the other site. I really don't think I need one yet, particularly with all you went through to get it in! That looks like it was quite a job. Very impressive.

I think I need to get another couple of amps and speakers. Then...