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Old 21-03-2007, 17:57   #1
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marine alternator

I am putting together a 6.5 hp Honda motor aux. which will be driving a 150-180 amp hour alternator to charge (with smart charger) a 800 amp hour agm battery bank.
I am finding that Auto type alternators of 180 amp are available for less that $100.00 and yet a Balmar or other marine type at 180 amp sell for close to $1000.00 or more.
Why? are the marine type really that much better or should I just have a spare and change it out every couple of years.
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Old 22-03-2007, 02:30   #2
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Marine Alternators

A good marine alternator will feature an external regulator, “hot” rating*, heavy-duty bearings brushes and slip rings, extra large diodes, voltage transient suppresser (Zap-Stop diode), an isolated (insulated) ground (2-wire vs 1-wire), silicon bronze output terminals, and ignition protection or spark arrester (for gas engines).

* Most automotive alternators are cold-rated, whereas a quality marine alternator is hot rated. When the alternator is cold, the winding resistance will be low, and the alternator will deliver a high current. The temperature of the windings quickly rises, increasing the internal resistance, and reducing the output. The difference between the two ratings can easily be as high as 25-30%, this means that a 140A marine alternator may actually provide more energy to the battery than a 180A automotive type alternator.

I don't believe these advantages justify a price premium of 10 times.
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Old 22-03-2007, 12:10   #3
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beau, If your automobile alternator is manufactured and sold in country as opposed to a Balmar which is imported and subject to duty, shipping, etc the cost difference can be significant.
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Old 22-03-2007, 12:27   #4
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To add to Gords Heat rating, Car alternators are designed to have air through them. That's why they are mounted at the front of the engine in full flow of air coming through the grill. Boat gens have to be a little more rugged to cope with the heat they generate and be able to disapate that heat.
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Old 22-03-2007, 15:11   #5
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I have found it difficult to buy anything over 90-100 amp alternators in Australia. However it appears that 150-200 amp alternators are available in the USA at a reasonable price. I think I will buy two from the USA and keep one as a spare. The alternator will be well ventilated.

The other problem we have in Australia particularly with electronics, is that we tend to get older stock here that has already been superceded in the USA
Thank you for your comments.
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Old 22-03-2007, 16:16   #6
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Adding to Wheels comments, just make sure that you get alternators that are externally regulated called, "P" type. That means that the field is internally grounded with one lead and the external regulator provides a connection to the "P"ositive battery voltge to make the alternator generate current. The other types are naturally called "N" types (usually internally regulated only). "N" types can be converted to "P" types but why bother if you can get the correct one first?

NEXT: I doubt that you can drive an alternator to get much above 140 Amps at 14.0 Volts with only 6.5 hp unless you use a current limited regulator. The problem with most current limited regulators is that the alternator current is limited over the whole rpm range which is only O.K. if you drive the alternator at a fixed speed. For sure, if you load up to about 170A using a good large frame alternator you will actually stall that Honda. With a small frame alternator it will stall at even lower currents due to their poor efficiencies in comparison.

Do not use a Balmar alternator because they powder coat them to make them look pretty and decrease their air-cooling capability compared to a rough-cast aluminum body like a motorcycle engine (can you imagine what would happen if you powder-coated an air-cooled motorcycle engine?).
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Old 22-03-2007, 16:39   #7
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Thank you again rick, you are right.

There is a company in Australia that sells a 120 amp 12 dc system with a honda 5.5 hp. but it is close coupled.
I want to run a CAT pump for desalination (with electromagnetic coupling) also with that same Honda motor when it is not being used for the alternator.
I could purchase a larger Honda such as a 8hp or 10hp.
There is available on ebay a Chonda (chinese Honda) which is 13 hp electic start for only $350.00 compared to the Honda at over $1,000 for 6.5 hp.
With the 13 hp what size alternator would you recommend. I obviously want to pump up the 800-1000 amp hour AGM batteries (at least to 80% capacity ) as soon as is practical.
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Old 22-03-2007, 17:01   #8
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Beware of the Chonda! I had a genset based on a small, air cooled Chanmar diesel engine. I think I got approx 100 hours out of it before it threw a rod and was useless, due to lack of parts for the unknown engine type. It was $1000 for 100 hours with the Chanmar. Not a good deal.

I have no idea what metals they use, but there are serious voids and it is very brittle.

The Italian made genuine Yanmar genset I replaced it with cost 3 times more, but the price difference was well worth it to know I'll get 10x the life from the unit.

You'll need to carry a few backup engines with you if you go the Chonda route.

Quote:
Originally Posted by beau
Thank you again rick, you are right.

There is a company in Australia that sells a 120 amp 12 dc system with a honda 5.5 hp. but it is close coupled.
I want to run a CAT pump for desalination (with electromagnetic coupling) also with that same Honda motor when it is not being used for the alternator.
I could purchase a larger Honda such as a 8hp or 10hp.
There is available on ebay a Chonda (chinese Honda) which is 13 hp electic start for only $350.00 compared to the Honda at over $1,000 for 6.5 hp.
With the 13 hp what size alternator would you recommend. I obviously want to pump up the 800-1000 amp hour AGM batteries (at least to 80% capacity ) as soon as is practical.
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Old 22-03-2007, 17:13   #9
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ssullivan,
I accept you point of view on your experience with Chinese motors.
I actually import products from China and the problem is China produces all sorts of different standards. Some are first class and some are rubbish.
The problem is finding out which is which.
The motors sold here in Australia are "supposed" to be made in the same factory that makes the Hondas. They look identical, but I do agree that it is a bit of a risk particually when your out at sea.

Are there any other experiences with these look a like motors.
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Old 22-03-2007, 18:43   #10
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Beau

It takes an honest 7.5 hp at the alternator shaft to get 165A @ 14.0 V with a "large frame" hot rated alternator. Don't wast your time and money on a small frame alternator.

You should be able to pump your AGM batteries to 90% state of charge before you are down to 80 A alternator output with an 800 A-hr bank. Keep going even then because the engine will still be decently loaded.
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Old 22-03-2007, 19:27   #11
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Rick,
What is a small frame/large frame alternator, are you talking about an small frame being an automobile alternator? or light duty versus Heavy duty.
I do understand "hot rated"
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Old 22-03-2007, 19:46   #12
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Small frame alternators are the normal automotive size like GM,FORD, Christler, Nissan have. Large frame alternators are about 9 inches in diameter (not much deeper) with much larger bearings and need to be driven either by double V belts or a serpentine belt unless using a special 3/8 " gates "green-stripe" 12 hp rated single V belt (not available in a wide variety of lengths). The front-end bearings are huge by comparison and the alternator runs cooler for the same abount of output current as a small frame.

Emergency vehicles often have large frame alternators to keep up with the load demands that small frame alternators will not reliably do. Maximum spindle speed ratings of large frame alternators are not as high as those of small frame units.
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Old 22-03-2007, 20:55   #13
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When you put a big side load on a small engine...you need to be sure the engine bearings can handle it. 150 amps is the equivilent of a 6HP pulling force.
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Old 22-03-2007, 22:24   #14
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Quote:
Are there any other experiences with these look a like motors
I have two of the 175cc petrol 4 stroke Chonda's. They run so sweetly and have clocked up some hard hrs on them. No problems at all. They start so easily and tick away very quitely. I am very impressed.
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Old 27-03-2007, 18:21   #15
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Quote:
Originally Posted by Alan Wheeler
I have two of the 175cc petrol 4 stroke Chonda's. They run so sweetly and have clocked up some hard hrs on them. No problems at all. They start so easily and tick away very quitely. I am very impressed.

Incredible...

Our different experiences with Chinese products is just amazing.

I suspect it's the profit hungry American importers buying up the bottom of the barrel from China that deliver these inferior goods to us. The wife and I were talking about this today. We were wondering if some good products were made in China, but we never see them due to the people importing them here.
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