I've just upgraded the batteries on my Hunter 335 to a pair of group 31 deep cycle 105 amp hour lead acid batteries. I'm now concerned about alternator output. The alternator on the Yanmar 3gm30F is rated at 55 amps which should be about right. However I understand alternator output varies significantly with engine rpms. Does anyone have a convenient source for determining alternator output at specifics rpms? Also has anyone tryied boosting alternator rpms by using a smaller pulley wheel to drive the alternator? This obviously raises the isssue of max alternator speed. Any help will be appreciated. Gary Wyngarden S/V Shibumi H335
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TONY B.
ALTERNATOR ANSWER
GARY; YOU CAN GO AHEAD AND PUT A SMALLER PULLEY ON YOUR ALTERNATOR. ON AVERAGE R.P.M. SPECS ON MOST MODERN ALTERNATORS ALLOW ALTERNATOR SHAFT R.P.M.,S AS HIGH AS 8 OR 9 THOUSAND. THEY GENERALLY BEGIN A DECENT RATE OF CHARGE AT ABOUT 1700 -2000 ALTERNATOR SHAFT R.P.M. IN GENERAL,ALTERNATOR BEARINGS SUFFER MORE FROM BELT OVERTIGHTENING,OR LONG PERIODS OF NON-USE THAN FROM HIGH REVS. YOUR ALTERNATOR IS A PRETTY TOUGH PIECE OF GEAR. YOU WONT HURT IT. SPIN THAT BABY! TONY B. "S/V SUMMER WINDS" MILFORD,CONN.
GARY; YOU CAN GO AHEAD AND PUT A SMALLER PULLEY ON YOUR ALTERNATOR. ON AVERAGE R.P.M. SPECS ON MOST MODERN ALTERNATORS ALLOW ALTERNATOR SHAFT R.P.M.,S AS HIGH AS 8 OR 9 THOUSAND. THEY GENERALLY BEGIN A DECENT RATE OF CHARGE AT ABOUT 1700 -2000 ALTERNATOR SHAFT R.P.M. IN GENERAL,ALTERNATOR BEARINGS SUFFER MORE FROM BELT OVERTIGHTENING,OR LONG PERIODS OF NON-USE THAN FROM HIGH REVS. YOUR ALTERNATOR IS A PRETTY TOUGH PIECE OF GEAR. YOU WONT HURT IT. SPIN THAT BABY! TONY B. "S/V SUMMER WINDS" MILFORD,CONN.
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Ed Schenck
Yanmar manual shows it.
For each model of Yanmar there is an amp curve illustrated. Shows the output for the range of RPMs. If you do not have the manual then maybe a call to Torreson or another Yanmar dealer. I can't help since mine is an old 35 amp Hitachi.
For each model of Yanmar there is an amp curve illustrated. Shows the output for the range of RPMs. If you do not have the manual then maybe a call to Torreson or another Yanmar dealer. I can't help since mine is an old 35 amp Hitachi.
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Mike D
No Expert
Gary, I am certainly no expert on charging. In speaking with the experts at the boatshows, they seem to concur that the slower you charge your batteries the more battery life you can anticipate. I think the key may be in how much running time do you expect to charge your batteries back to full level. I think some simple math can give you a pretty good idea of the overall picture. A bigger alternator will charge faster, creating more heat. Also, the smart chargers today back off when the batteries start to reach near full. I did read where it is best for battery life in gel deep cycle batteries to bring them down to half charge maximum drain. I realize that you used lead acid batteries but 50% of (2)105 amp hours equals 105 amp hours divided by a 55 amp output alternator nets out about 2 hours at full output. That sounds pretty reasonable. If your travelling, 2 hours of engine time is not too bad. If you run at less rpm's, you can probably get a feel for your alternator output with a temporary gauge setup. good luck and I would be interested in knowing how you make out, Mike D s/v Serenity H376 Tolchester Beach, Md
Gary, I am certainly no expert on charging. In speaking with the experts at the boatshows, they seem to concur that the slower you charge your batteries the more battery life you can anticipate. I think the key may be in how much running time do you expect to charge your batteries back to full level. I think some simple math can give you a pretty good idea of the overall picture. A bigger alternator will charge faster, creating more heat. Also, the smart chargers today back off when the batteries start to reach near full. I did read where it is best for battery life in gel deep cycle batteries to bring them down to half charge maximum drain. I realize that you used lead acid batteries but 50% of (2)105 amp hours equals 105 amp hours divided by a 55 amp output alternator nets out about 2 hours at full output. That sounds pretty reasonable. If your travelling, 2 hours of engine time is not too bad. If you run at less rpm's, you can probably get a feel for your alternator output with a temporary gauge setup. good luck and I would be interested in knowing how you make out, Mike D s/v Serenity H376 Tolchester Beach, Md
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Larry Watkins
Mike D. is right, he's no expert. In general, without a smart regulator, alternators only put out about half their rated output, and not for very long, at that. Gary, your best bet is to buy Nigel Calder's book, "The Boat Owners Maitenance Manual." It has an excellent section on alternators. Larry
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Mike D
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Paul Akers
Try this site for info...
Try poking around this site. I think you'll find engine specs somewhere. Good Luck! http://www.marinedieseldirect.com/yanmar/
Try poking around this site. I think you'll find engine specs somewhere. Good Luck! http://www.marinedieseldirect.com/yanmar/
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Don
I doubt that a smaller pulley will do anything.
The voltage regulator controls the output of the generator. On most systems, output is designed to be lower at engine idle. If it didn't, it would choke the engine down. Mid RPM and up, there will be no change in output. The most important question is what do you plan on doing. If you have refrigeration, big inverter, or radar you will probably need a bigger alternator and a "smart" regulator or plan on running the engine about 3-4 hours per day to replace the power used.
The voltage regulator controls the output of the generator. On most systems, output is designed to be lower at engine idle. If it didn't, it would choke the engine down. Mid RPM and up, there will be no change in output. The most important question is what do you plan on doing. If you have refrigeration, big inverter, or radar you will probably need a bigger alternator and a "smart" regulator or plan on running the engine about 3-4 hours per day to replace the power used.
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Tim Schaaf
Hitachi 55
My Yanmar manual shows the Hitachi 55 amp alternator (I presume you have a Hitachi) to put out its 55 amps at about 4,000 RPM. Since it has about a two to one pulley ratio, that means that the engine has to put out 2,000 PRM. The Hitachi gets up to about 50 amps at about 1,800 engine RPM. These figures are for a "hot"alternator. It will do better when cold. Many alternators cannot be run at max output for long....according to Ample Power (and my own personal experience), the Hitachi is one of the ones that can. Try it with a "smart" regulator. You will smell it if it can't run hot, but I would be very surprised to hear that was the case. The correct size of alternator is one that can put out about 25-35% of the capacity of your battery bank. If you want to use a bigger alternator, you will need bigger batteries to realize an advantage. Check on the maximum "power take-off" for your engine. The really big alternators can overload our small diesels. Yanmars that share a belt with the alternator and the water pump often experience problems with the bearings in the water pump, since they, too, are subject to the loading and tension of the belt. By the way, my recollection is that the Hitachi can go up to 9000 RPM, so you could use a smaller pulley....but, are you really going to run your engine that slowly? My guess is that you have the right alternator for your batteries. Add a smart regulator. By the way, the one made by Heart (used to be Cruising Design),available at West, requires you to provide some of the "smarts", but is very nicely adjustable to your requirements. Oh, and DO read Nigel Calder!!!
My Yanmar manual shows the Hitachi 55 amp alternator (I presume you have a Hitachi) to put out its 55 amps at about 4,000 RPM. Since it has about a two to one pulley ratio, that means that the engine has to put out 2,000 PRM. The Hitachi gets up to about 50 amps at about 1,800 engine RPM. These figures are for a "hot"alternator. It will do better when cold. Many alternators cannot be run at max output for long....according to Ample Power (and my own personal experience), the Hitachi is one of the ones that can. Try it with a "smart" regulator. You will smell it if it can't run hot, but I would be very surprised to hear that was the case. The correct size of alternator is one that can put out about 25-35% of the capacity of your battery bank. If you want to use a bigger alternator, you will need bigger batteries to realize an advantage. Check on the maximum "power take-off" for your engine. The really big alternators can overload our small diesels. Yanmars that share a belt with the alternator and the water pump often experience problems with the bearings in the water pump, since they, too, are subject to the loading and tension of the belt. By the way, my recollection is that the Hitachi can go up to 9000 RPM, so you could use a smaller pulley....but, are you really going to run your engine that slowly? My guess is that you have the right alternator for your batteries. Add a smart regulator. By the way, the one made by Heart (used to be Cruising Design),available at West, requires you to provide some of the "smarts", but is very nicely adjustable to your requirements. Oh, and DO read Nigel Calder!!!
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Thomas Ehmke
Gary! Let me add to the confusion!!
Gary, I'm going to get in a plug for the USPS Marine Electronics Course first of all. I took it last Fall. It helps to read something and discuss it with others who are trying to learn the same thing. I checked the manual and its recommendations are pretty much in line with Tim's. The guidelines in the manual are a charge rate of 20% of the rated amp-hour capacity of the battery, 40% if it is a deep cycle battery. Using your numbers for a 105 amp-hour deep cycle battery, that would yield a charge rate of 42 amps (105x40%). Now, when you get into single or dual output alternators, internal or external regulators, combiners or isolators, all those enrich the mix. Your existing alternator may do nicely if it is internally regulated and you have a combiner or isolator on board to control the battery bank being charged. As others have pointed out, making the alternator spin faster won't help if the alternator is internally regulated. 55 amps is 55 amps period. On the other hand, if you are considering replacing the alternator, a dual-output alternator may do the job without the combiner or isolator. External regulators "fine tune" the charging process, but are an additional cost. Bottom line here is that you can only cram so much juice into a battery without overheating it or blowing it to smithereens, and as far as I know with one alternator, you can only charge one battery at a time. Tom
Gary, I'm going to get in a plug for the USPS Marine Electronics Course first of all. I took it last Fall. It helps to read something and discuss it with others who are trying to learn the same thing. I checked the manual and its recommendations are pretty much in line with Tim's. The guidelines in the manual are a charge rate of 20% of the rated amp-hour capacity of the battery, 40% if it is a deep cycle battery. Using your numbers for a 105 amp-hour deep cycle battery, that would yield a charge rate of 42 amps (105x40%). Now, when you get into single or dual output alternators, internal or external regulators, combiners or isolators, all those enrich the mix. Your existing alternator may do nicely if it is internally regulated and you have a combiner or isolator on board to control the battery bank being charged. As others have pointed out, making the alternator spin faster won't help if the alternator is internally regulated. 55 amps is 55 amps period. On the other hand, if you are considering replacing the alternator, a dual-output alternator may do the job without the combiner or isolator. External regulators "fine tune" the charging process, but are an additional cost. Bottom line here is that you can only cram so much juice into a battery without overheating it or blowing it to smithereens, and as far as I know with one alternator, you can only charge one battery at a time. Tom
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