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Old 17-12-2012, 21:42   #16
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Re: Permanent Magnet generator on propshaft

As you work through this, keep in mind the first rule of thermodynamics - conservation of energy.

Whatever energy you draw out of a prop-shaft generator must come from somewhere. In this case, it comes from whatever is powering the boat - presumably wind in this case. Whatever energy you draw out will result in a corresponding slow down of the boat. If you generate 5 hp worth of power, it will be equivalent to running a 5hp motor IN REVERSE while sailing. In addition there is the whole issue of energy losses in every system, and these always work against you. If you don't mind donating some of your forward motion to generating electricity while sailing, then by all means go for it. Just understand that it comes from somewhere and is not free.

Because hybrid cars show an increase in efficiency, many people jump to the conclusion that applying hybrid car techniques to a boat will also yield benefits, but they don't.

Hybrid cars benefit for two primary reasons, neither of which are applicable to boats. The first is that cars operate with highly variable power output. You are constantly accelerating, coasting, going up hill, and going down hill. The result is that the gas engine in a conventional car is sized for the car's max power needs, then mostly run at it's least efficient power output. A hybrid helps level the load on the engine, allowing for a smaller engine operated at a consistently more efficient operating point. The hybrid maintains a minimum load on the engine by applying a battery charge load as needed, and helps skim off the peak loads by kicking in the electric motor to help. None of this exists in a boat which runs at a constant load at any given speed. There is no gain to be had on a boat.

The second efficiency gain with cars is regenerative power. When a car is coasting and/or braking, there is energy being taken away from the car's motion. In a conventional car, this energy is turned into heat and released into the atmosphere. Brakes convert the cars movement energy into heat. In a hybrid, rather than converting motion energy into heat, some of it is converted into electricity and pumped into the battery for reuse later. So instead of throwing away all the energy that your engine produced when you accelerated away from the last stop light, a hybrid recycles some of it as you slow for the next light, then reuses it when you pull away from the next light rather than making your gas engine do it all over again. Once again, this stop and go braking thing doesn't exist in boats, so there is no gain.

Loading up your prop shaft with a generator is the same as using regenerative braking to slow down your car. Just as generating electricity from your car's motion slows it down, generating electricity from your boat's motion will slow it down too.

Just understand, that power come from somewhere.
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Old 17-12-2012, 22:08   #17
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Load shedding on a PM DC generator can be accomplished by simply opening the circuit. Wind generators avoid this as the blades may destroy themselves without some braking mechanism.

Selecting a DC motor or generator is a technical task. You must know the maximum speed and torque you want to handle. The catalog Voltage spec is not helpful.
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Old 17-12-2012, 22:59   #18
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Re: Permanent Magnet generator on propshaft

Thanks Guyfromiowa and Twistedtree for reminding us of the basics.

At the moment I am going thru a whole energy study on shaft alternator using PMA and starting with the basics, before being sold on it.

Re Twistedís caution. Is this a Kinetic- Potential Energy thing when you consider the dynamics of wind and waves acting on a 40 Ton yacht?

My long and heavy 2Ē shaft and heavy prop free spin when sailing normally, so creates quite a bit on momentum that I could not stop by hand

Just like illustration below, as the 40 ton boat gets moving and surges up and down with waves and wind gusts, would the Torque resistance on a PMA shaft Alternator be that significant to my performance?


I am not a racer and given that I motor sail when winds are less than 12 knots, I donít think this is any more of an issue than a dirty bottom.

But I might be wrong??
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Old 18-12-2012, 00:16   #19
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Re: Permanent Magnet generator on propshaft

Exactly right Daddle and this is where I am going thru a massive learning curve.

I am finding good info via PMA manufacturers and Wind Gen Suppliers, but I still need to piece it all together before I can ask some intelligent questions from those with real time experience, based on my needs

Re PMA Torque calculationÖ. this shows how they do it

This is more visual if you get headaches quickly and compares hand torque difference between a 6kw and 1kw PMA


Permanent Magnet Generator for small wind turbines

I think the guys doing this stuff are great!
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Old 18-12-2012, 00:29   #20
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Re: Permanent Magnet generator on propshaft

WindBlue Power has a good FAQ section on PMA hook up and DC regulation
WindBlue Power - The best wind generator parts and PMA Permanent Magnet Alternators on the web
What I have learned so far:

Why you cannot use a Solar or PV Charge Controller for Wind.
For the sake of ease we are going to talk about a 12 volt system for this next section.
As I am sure you have noticed Solar and PV Charge Controllers come in 12, 24, 36, and 48-volt ranges, and you must match the range with your battery bank.
Here's why. Most Solar and PV controllers have circuits that will only work within a certain range of voltage and current/amperage.

For example: Lets say you have a 12v solar panel. It will put out between 0-18 volts DC and up to 3.5 amps (or 50 watts).
Most 12 volt Solar charge controllers are designed to handle up to 20 volts and 50 watts, or 3.5 amps of input power.

Most Solar controllers cannot comprehend voltages outside their range of input power, meaning if they get more than 20 volts of input they go nuts, crazy, wacko, screwball, etc.

A wind Generator can (easily) have a range from 0 to more than 100 volts, and amperage of 0 to 50 amps (on average 2 to 30).
Now if your Solar controller is designed to handle 0-18 volts what do you think it would say (if it could talk) when it gets hit with 25 to 100 volts of DC power from your Wind Generator with amperages up to 50 amps?
Here's my guess at what it would be saying.
1. What in the heck is this?
2. What am I supposed to do with this?
3. And last but not least,,, OUCH!
One other factor to look at on Solar charge controllers is most of them shunt when the battery is charged and that may not be the right solution for your generator. Others open the circuit and let your generator run wild.

You still have to get a wind generator charge controller for the correct battery voltage. And a wind generator charge controller will be designed to handle the wide range of input voltage and amperage from your generator.

An exception to the above are charge controllers such as the Morningstar TriStar 45,

Connecting the Alternator to your Batteries
The alternator can be connected to your batteries in several ways. The most common is to just connect it at the same point you connect your load. But if you are running a higher voltage battery bank such as four 12-Volt batteries connected in series to make 48 Volts you should consider hooking the alternator to just one of the 12 Volt batteries. The reason for this is that the alternator will not start charging your battery until it is spun fast enough to produce more voltage than the voltage of the battery. So for example in a wind setup using our DC-540 model, it reaches 12-Volts at 150 RPM, but it takes about 600 RPM for it to reach 48-Volts. So you can see it would take a fairly windy day to get it turning fast enough to charge a 48-Volt battery bank but only a small breeze to get it to start charging a 12-Volt battery.

We get a bunch of questions asking how do I regulate the voltage coming out of the alternator. The simple answer is you donít. The battery acts as a regulator and absorbs the excess voltage that the alternator puts out. The same thing happens in your cars charging system. If you were to disconnect the battery terminal on your car while it was running, the alternator voltage output would shoot up dramatically, frying most of the sensitive computer equipment on new cars. So as long as the generator is connected to a battery you donít have to worry about the voltage.
which are designed to be used with either wind or solar systems.
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Old 18-12-2012, 03:09   #21
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I'd have to say most of that FAQ is electrical nonsense

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Old 18-12-2012, 03:38   #22
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Re: Permanent Magnet generator on propshaft

give this some thought:

Permanent Magnet Alternator Wind Blue Low Wind

These unit's are great. You may be able to figure out a way to get the speed up via an jackshaft arrangement off your prop shaft. All you have to do is attach two wires to it and run it through a rectifier leading this into at charge controller. It produces variable ac voltage proportional to rpm then the rectifyer converts it to dc which can be handled by a charge controller like the flex-charger Permanent Magnet Alternator Wind Blue Low Wind direct into yor pac. dirt simple.

I;ve built a super robust wind gen from these things and they rock. beats the heck out of the little 400 amp whisper gen type rigs. If your gonna make some power, you may as well make some power. I've had a wind blue PMa on my shop roof for over 5 years with no trouble and have supplemented my shop power with it for my build......it charges all my cordless power tools and the surplus helps top of a little chinese electric car I sneaked over in container to run be back and forth to the coffee shop.

I live in the columbia river gorge and the wind really cranks here sometimes.
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Old 18-12-2012, 03:43   #23
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Re: Permanent Magnet generator on propshaft

sorry for the missing link to the rectifier:

SES Flexcharge NC25A 12 Volt Ultra High Efficiency Charge Controller
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Old 18-12-2012, 03:44   #24
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Re: Permanent Magnet generator on propshaft

oops missed again: Delco Rectifier 10si Wind Blue
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Old 18-12-2012, 04:02   #25
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Re: Permanent Magnet generator on propshaft

Probably the best DIY prop generator would be to use a Fisher and Paykel Direct drive washing machine motor as a generator like many do as a wind generator (just google Fisher Paykel wind generator - there are many websites). No step up gearing required so is very efficient. Can pick up one almost for free in Aus / NZ but for those over the paddock I have seen ads on ebay.
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Old 18-12-2012, 06:20   #26
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Quote:
Originally Posted by daddle
Load shedding on a PM DC generator can be accomplished by simply opening the circuit. Wind generators avoid this as the blades may destroy themselves without some braking mechanism.

Selecting a DC motor or generator is a technical task. You must know the maximum speed and torque you want to handle. The catalog Voltage spec is not helpful.
I am thinking that the load from a hot water heater may be enough to stop the prop in all but the highest speeds thereby reducing drag.
In flying in an engine out of a fixed prop some advocate slowing the plane enough to stop the prop windmilling to reduce drag.
Ideally you could use load coupled with speed to control the prop. When you are pushing up against hull speed I doubt the drag from a spinning prop would be noticed. But I am guessing here.
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Old 18-12-2012, 10:54   #27
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Re: Permanent Magnet generator on propshaft

Quote:
Originally Posted by twistedtree View Post
As you work through this, keep in mind the first rule of thermodynamics - conservation of energy...
Whatever energy you draw out will result in a corresponding slow down of the boat. If you generate 5 hp worth of power, it will be equivalent to running a 5hp motor IN REVERSE while sailing.
True. Conservation of energy is not just a good idea, it's the law! But it's really not that bad. 5 hp would be 310 amps at 12 volts. These systems are not going to be running anywhere NEAR that!

If you can get 5 amps at 14.5 volts, for battery charging, you would be doing very well. That amounts to about 1/10th of a horsepower.

For a sailboat that is barely ghosting along in light winds, of course, having a 1/10th hp engine running in reverse could be a serious slowdown. But a sailboat that's pushing hull speed? That 1/10th hp engine is going to have almost no measurable affect.

I suspect that towing a dinghy will slow you down more than connecting a generator to your spinning prop, and a LOT of people sail around with a dinghy in tow all the time.

On the other hand, this does point out that you probably want to have some way to disconnect that generator when winds are especially light.
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Old 18-12-2012, 11:20   #28
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Re: Permanent Magnet generator on propshaft

The drag from a standard prop (fixed or spinning) is significant. It is the extra drag in generating the power that needs to be considered.
Prop shaft generators will slow the boat down.
However generating X power from the propshaft is not the same as additional drag as as applying X power in reverse. This does not not violate any any of the thermodynamic laws, so the world will not come crashing down. Well not until the 21st anyway
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Old 18-12-2012, 11:26   #29
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For what it's worth: we have a old rebuilt prop shaft generator on our Amel Maramu ('82). It's a little noisy, but very dependable - generates between 2-3watts continuously and spikes up to 4-5 riding down swells

It can't provide all our energy needs - but it's clean and green + reliable source of kinetic energy during passages (aka: sails).

Overall would recommend over a wind generator, yes it's much quieter -- but remember, you can't run a prop generator while at anchor (vs solar and wind). Need symbiosis for charging needs when no sun you have wind, when no wind you have sun etc....we're gonna install a few solar panels in the next year to balance it all out (engine alternator, solar, prop generator, wind>>whisper perhaps etc).

My 2 cents...
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Old 18-12-2012, 11:37   #30
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Re: Permanent Magnet generator on propshaft

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Originally Posted by Pelagic View Post
Curious if anyone has working knowledge of PMAís and how to manage output for a large battery house bank? (1040 AH @ 24v)
You want a DC-DC converter configured to charge your battery bank. It will accept input DC over a wide range and efficiently convert it to the right voltage to charge your battery bank. Make sure the input voltage range for the DC-DC converter covers the full range that your PMA can produce, plus a margin for safety (at the upper end).
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