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Old 05-10-2009, 08:17   #16
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Quote:
Originally Posted by Mule View Post
Am I hearing you guys right, that there is no reason not to use an alternator with internal regulator? I have stumbled on to a Bosh 150amp alternator that needs a rebuild for free. Came out of a Sprinter Van. The old noodle went click and ah sez to myself, "Self this might work"
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- - Only if your pulley arrangement can spin the unit at its designed working rpm's. That is the crux of our discussion getting sufficient rpm's to get an acceptable output from the alternator. At the above supposed 500 rpm's you would need a 28" diameter pulley on the prop shaft, which seems to me to be a might large.
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Old 05-10-2009, 09:17   #17
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If you use the windgen units, take two and make a bracket that positions them at both sides of the shaft so that the sideways loading of each cancels out and no extra shaft support is needed. This should be easy but you need a double pulley on the shaft.

A rectifier is far from inventing stuff. First, you could use what you find inside the windgen. If that's not available, it depends on what type of AC is generated: single-phase or 3-phase. It's easy to rectify either. An alternator shop should be able to sell you an external rectifier because big alternators have their diodes externally for better cooling; it will be overkill but it might be cheaper than other solutions. For single phase AC you can buy 1-component bridge rectifiers at Radio Shack or build them using 4 diodes. The diagrams are all over the net. You will need to mount them on a heatsink.

cheers,
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Old 05-10-2009, 13:24   #18
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My new system, as yet to be mounted and tested, is based on the prmise that a car lternator will work if it has a special winding to reduce the speed reqired to get the alternator to produce. With my previous attempt, my Bosh alternator would "put out" the charging light at 4 knots but only put out 6-8 amps over 6 knots. With the new winding I am hoping to get 15 to 25 amp max cruising speed about 7.5 kts, 8-15 normal sailing between 4 and 5.5 knots, about what I got on the original system. So I am using a 35 amp alternator to meet what think is needed as a power input to support the 15 amp average power used used while on passage (freezer, autopilot and computer) But remember, it needs the special winding to function at low RPM so just any car alternator will not work That was the problem with my last setup.

If I get this new attempt installed before I leave for Venezuala, I will have a good chance to test it on that sail and will post on result.

My non technical reaction to the 150 amp alternator is that that it will take too much umph to get it to turn initially and to get up to operating speeds where you will get 13+ volts , compounding the problem that already exists with typical car alternators. This is one of the reasons I decided on the 35 amp alternator.

Tom
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Old 05-10-2009, 14:00   #19
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Thanks for the replies but I am still a bit muddled

This is the direct link to the various power graphs for these PMA type used on Wind Gens They say it is suitable for a hydo application which I supose a freewheeling shaft generator is


Permanent Magnet Alternators PMA pmg Permanent wind grid turbine mill Magnet Alternator Permanent Magnet generator wind power PMG wind turbine wind turbines

My DC system is 24V and I draw about 32amps sailing underway with all fridges/ nav lights and autopilot working.

You say these power graphs badly show AC readings. How do I convert that to a DC reading so as to identify RPM needed from a particular model to achieve my 24V/32amp goal. (Say using the SC24 model)

I understand that a diverter is needed for this power source, since it cannot be shut off. I would probably divert to hot water element
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Old 05-10-2009, 14:41   #20
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Here is another site with PM alternators and parts.
WindBlue Power - The best wind generator parts and PMA Permanent Magnet Alternators on the web

Paul L
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Old 05-10-2009, 14:49   #21
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As far as I can see, those super core generators produce DC??? It indicates that the rectifiers are inside the units.

That SC24 looks okay. You're gonna need an indication of how fast your shaft is turning so you can select pulleys. You're gonna need a minimum os 1400 rpm on the alternator for charging a 24V system. The question is how many hp you generate. Every hp equals 745W. So, if you make 1400 rpm on the SC24, it will supply 50A at say 28V which equals 1400W so it'll need 2 hp power from the prop+shaft. If your prop+shaft can't supply 2 hp, the SC24 will spin slower or not at all.

Now let's say you go faster (or use different pulleys) and you spin the sc24 at 3000 rpm. Now you get 112A at 28V = 3136W equals 4.2 hp.

Don't forget you need a fan to cool the SC24. The rpm's you make have a linear relationship with how many cubic feet per minute the fan displaces. If the SC24 runs too hot, you are going to need more rpm's or a different design fan-blade.

All in all a nice experiment if you have your prop spinning when under sail. I would get a whole bunch of pulleys and a couple of fan blades and experiment to find the best system. I think the SCS18 at 2500 RPM is a better option or two SC48's at 1500 RPM... many possibilities.

You need someone who can calculate how many HP you can generate with your prop + shaft. Remember that you will have losses in bearings and the gearbox!

cheers,
Nick.
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Old 05-10-2009, 15:03   #22
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Leece Neville makes a series of alternators for ambulances and fire engines, which need to put out a lot of amps idling on the job. They have several that will put out 100 amps or more at 1800 rpm, so theoretically only need a 3 to 1 ratio. Coupled with a Balmar or Leece Neville 612 3 step regulator (they're identical, I'm reasonably sure Balmars' is re packaged from Leece Neville) you can program a 45 second delay and get the thing spinning with no load, then slowly ramp up the load. The question is whether at that kind of load you you don't just slowly stop the spinning shaft. I have such a set up, but haven't tried it yet. To many other things to do first.

Best, Bob S/V Restless
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Old 09-10-2009, 13:40   #23
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If you use an alternator like a leece neville then it will use 3 amps at 24v for the field excitement.
This means that you need to be sailing fast enough to overcome this 3 amp negative. So it is not just a case of switching it on and getting power, if the speed is too low you will end up in this case using more power.
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Old 14-10-2009, 18:52   #24
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I just spent the last four days sailing with my newly installed system. Better than my previous attempts in power output, producing 4-5 amps at 4 knots and up to 10 amps at 6 knots, but this is not nearly where I was with the original unit. So I still am thinking the winding is to blame since everything else is essentially the same.

One other problem, the belt rubs against the fan and as even I who fails sometimes to note the obvious, could not help but discern the occasional plume of smoke this caused. But I think a simple spacer will fix this problem.
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