Automotive Alternators vs. Deep Cycle Banks

[Maine Sail]

This question came up again the other day and rather than answer it repeatedly over and over I devoted some time to an article on the subject so that in the future I can share a link.

Hope this helps..

Automotive Alternators vs. Deep Cycle Battery banks

 

[Gunni]

MS, I am constantly impressed by your ability to drill down on boat electric systems and resolve practical solutions!

An upgrade to a higher-output alternator is at the top of my list for my 4JH3E with the OEM Hitachi. With a 500 Ah AGM battery bank I could definitely use the high amp output, and voltage selection capability. And although we rarely motor sail, it would be great to get more amps and more fully load the Yanmar when running. At anchor I have a 100A Mastervolt that powers off my 5.5KW NextGen - I would rather rack the hours on that engine. And at the dock I have shore power. But then there are the long ocean legs where we stay moving for 4-5 days, and sometimes motor sail for hours to stay on track . Would be great to top the batteries. So I am looking for the middle road, a modest output alternator (~100 A) with sophisticated external regulation, and not have to endure an engine compartment dusted with belt particles. Want a systems approach so I am looking for experiences with the various manufacturers, Balmar, Electromaxx, and now I need to consider the CMI. I'm definitely over thinking this...but I don't want to make the wrong pick, or close off upgrade options

 

[Stu Jackson]

Maine Sail also wrote this one:

Hitachi Alternators 101 http://forums.catalina.sailboatowners.com/showthread.php?t=166123 This comes up so often on other boating forums...

The CONCEPT that Maine Sail has been trying to impress upon us for the past 20 years is that a boat electrical system is just that: a SYSTEM.

He has written eloquently and at length about the advantages and disadvantages of AGMs, and my conclusion is that most folks who install them have no clue about what they are getting into.

You can read his material on his website, on his Musings with Maine Sail right here (I surely wish he'd use more stickies though) or you can go here where I've tried to capture many of his highlights.

Electrical Systems 101 http://c34.org/bbs/index.php/topic,5977.0.html

 

[wufibugs]

Before I knew even the very little I now know about batteries and charging systems, I ended up with 3 group 31 AGMs just because I happened on them and they were cheaper than a decent flooded cell marine battery. I changed my Hitachi 35 to an 85 amp alternator, but it is still internally regulated, and I assume, temperature controlled. This probably works as long as I sail weekends and recharge during the week, but for longer outings away from the ac plug, I am chronically undercharging the batts. So the key here is find a wiring diagram that will allow me to convert internal regulation to external with temperature protection [almost always absent in automotive external regulators].

 

[Gunni]

Another problem is the verified output of some of these alternators. When a manufacturer wants to sell me a 140 Amp alternator that puts out 100 Amps at 3,000 RPM, I wonder why they call it a 140 Amp alternator? Dark arts.

 

[JohnShannon]

dog amps

 

[weinie]

Thank you for a very informative article!

 

[Maine Sail]

Before I knew even the very little I now know about batteries and charging systems, I ended up with 3 group 31 AGMs just because I happened on them and they were cheaper than a decent flooded cell marine battery. I changed my Hitachi 35 to an 85 amp alternator, but it is still internally regulated, and I assume, temperature controlled. This probably works as long as I sail weekends and recharge during the week, but for longer outings away from the ac plug, I am chronically undercharging the batts. So the key here is find a wiring diagram that will allow me to convert internal regulation to external with temperature protection [almost always absent in automotive external regulators].

On some alternators this is much easier said than done. It all depends upon the alternator and internal wiring. On the Hitachi it's a real PITA on the Motorola/Leece-Neville quite easy. One of the biggest problems, when away from the dock, is your usable capacity shrinks pretty fast because you can't put in the Ah's you often assume you can..

 

[Maine Sail]

Another problem is the verified output of some of these alternators. When a manufacturer wants to sell me a 140 Amp alternator that puts out 100 Amps at 3,000 RPM, I wonder why they call it a 140 Amp alternator? Dark arts.

Like anything alternators are rated by a standard rating and that is usually a cold rating.. Your car has a rated HP but how long can you run it at max before causing damage? What is your rated HP when you get to the top of Donner Pass? What is your HP in Denver vs. Boston? When I visit my friends in Steamboat/Hahn's Peak, and we ride snow machines in the mountains, that here in Maine would easily do 140+ MPH and at Hahn's Peak will only do about 70 MPH what is the HP rating?? Even an inverter/charger won't put out full current for long duration's and it too derates with temp as it heats up. Solar panels are the same too. A 140W solar panel is only 100W at 77F and at just 113F is only about 100W but everyone still assumes they have a 140W panel. Sadly a solar panel remaining at 77F is a fantasy just as an alternator remaining at 77F is.....

This is why I always council folks to up-size the alternator well beyond the current you actually desire out of it. Most alternators will put out more than the rating when cold and less than the rating when hot. If you want a 100A alternator, for more than a few minutes, you don't buy a 100A alternator. If you want a 140W solar panel, at typical temps, you don't buy a 140W solar panel...

 

[Gunni]

So I am confused, in your video you show an ElectroMaxx 140A alternator making a solid 140 A at 3,000RPM, and a respectable 100A at fast idle. Yet, when I check the ElectroMaxx 140A alternator output curve they spec. 100A @ 75deg, and 94A @ 150deg. Are they managing my expectations?

 

[wufibugs]

Since the 85 amp alt accepted the same wiring as the old 35 amp Hitachi, it is probably safe to believe it is wired similarly. This would put it in the PITA class you refer to. And you are, of course, completely correct that I no longer have any illusions that the amount of motoring I do with a heat regulated alternator is sufficient to do much for my Lifelines. That being said, I'm not yet prepared to give up the idea of adding external smart regulation with temp control. Because I love my AGMs and will never again have another trio of them for all the reasons you have educated me to, I'd like to have the best chance of keeping them alive for as long as possible. I think we all acknowledge this is a really important issue, Main, so if you or anyone else can recommend a source that explains how that rewiring might be accomplished, I'd like to see if it is feasible.

 

[Bill Roosa]

The wiring of a internally regulated alternator to external regulation is pretty simple as there is only one wire. The one that goes to the brush that is not grounded is the wire that goes to the regulator "output" wire. All you are doing is controlling the amount of current that is going to the rotor (rotating part in the alternator hense the name). This will require taking the alternator apart and nutering the internal regulation by cutting the same wire that feeds the rotor current. follow the external regulator manual for the rest of the wiring. email me if you have other questions.
Good luck

 

[Maine Sail]

So I am confused, in your video you show an ElectroMaxx 140A alternator making a solid 140 A at 3,000RPM, and a respectable 100A at fast idle. Yet, when I check the ElectroMaxx 140A alternator output curve they spec. 100A @ 75deg, and 94A @ 150deg. Are they managing my expectations?

Keep in mind that engine, at 3000 RPM, is spinning the alt at about 5400 RPM which gets it to its maximum output. That engine room was also open and at ambient air temp so the alt was performing about was well as it ever could. Once you close up the engine bay the performance will drop off due to heat. The E-Maax is rated at 190F but it is not uncommon for these alternators to be pushing 220F - 230F in an enclosed engine space, at which point the external regulator will reduce the field voltage and the alts current output will be cut back to protect the alternator.

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