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Old 30-01-2010, 18:26   #1
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Diesel to DC Motor Conversion

I'm looking into the conversion from my Volvo Diesel to a Electric motor running from 12-14 deep cycle batteries. Has anyone on this worked on, owned, loved or hated a DC drive system. We wont be needing huge range for what we do, but we are looking seriously at this type of power for three reasons

1. Zero engine smell, my wife has a serious health condition which means she cannot be around diesel smells, and i'm sick of scrubbing my engine with a toothbrush to make sure it doesn't smell.
2. greener technology, I'm a greeny so i like the thought of being able to create most of my power through solar and wind and only topping up from the shore power what i cant generate myself.
3. Very low maintenance, from the little i know at this stage the engines are fairly basic therefore repairs are not over kill (ie new brushes, stator etc) and other than routine battery maintenance there is not much else in these systems.

Interested to hear your thoughts

Damien
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Old 30-01-2010, 19:01   #2
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They do it on Subs but man it would take one big battery bank and I do not see how you would get any range.

Even with a Sub they have a diesel to charge back up.

This is only based on what I have seen in moves but even a Sub had limits on how long they could stay under before they would come up to recharge.

The HP differance between Electric motor and a diesel/gas are way different, we used 40hp electric motors on the machines I built at work and the weight per HP is very high.

Just so happens the Machines that I made was used to wash electric/diesel motors before they would rebuild them. the motors came out of very big ships and from what I understand how they work the diesel ran all the time to generate the power for the electric motors, Seen a map one time that had the electric motors under the boat called a power pod they could turn 360 degree.


I hope I help some.

Dutch
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Old 30-01-2010, 20:08   #3
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Do a search for electric drives and you'll find a wealth of information.


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Old 30-01-2010, 20:15   #4
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I've been on a 42' catamaran powered by these. Dead silent, and best part is while you sail, you re-charge the batteries.

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Old 30-01-2010, 20:19   #5
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While I have never done the install on a boat (I have been on a few though), I have built 3 electric cars and 1 hybrid racecar. Electric motors are really cool but they have limited application on boats. The reason that diesel is so good is that it is incredibly energy dense and can be transferred quickly. We don't yet have a cost effective way to store electricity as densely yet and it cannot be transferred nearly as quickly.

I am glad that you have a somewhat realistic idea of the number of batteries you will need. I did a few calculations for a boat using a 10kw output (should push a 35'er along nicely in smooth conditions) and 2 hours of run time and recommended 18 Trojan T-105's. There are many voltages that you can run and these are determined by your components so the exact number of batteries is determined by this. Regarding voltage, the higher it is, the better because your wires are smaller and everything is more efficient. The biggest considerations with batteries are cost (lead acid is the best bang for you buck), weight, and where you will put them.

The correct way to approach this is to look at your needs and then engineer a system around it. Having not seen your boat, I would suspect that you would want 5-7kw continuous output and 10kw(~15hp) peak. Then you will need to decide on a dc or ac system. DC systems have great low end torque but the torque is lower at high rpms when the back EMF is great. AC systems have a more constant torque curve and are more likely to offer the ability to regenerate power while sailing or moored in current. From this you can select a motor and motor controller. One popular motor is an etek. There are a lot of motors out there that would fit the bill and I would recommend looking at what is used in electric vehicles. Once a motor is selected, a controller will need to be selected although most AC motors specify certain controllers.

Then a battery bank will need to be selected. To do this, you should figure out the worst case scenario of how you plan to use the system. If you plan to push into a headwind for 2 hours, then you would need 2 hours* 10kw=20kwhrs of useable energy storage. However, if you never plan to motor for more than 1.5 hours and don't plan to motor when it is rough, something like 1.5hrs*6kw=9kwhrs might be reasonable.

Charging is a big issue for a boat. You will need to plug into shore power to do this, it would take a very very large solar array or many wind generators if you are on a mooring. The battery pack that I quoted above using 18 batteries could be charged off of a 30A plug in about 3hrs with the right charger. The real trick is that you cannot recharge when you don't have shore power. There are a lot of chargers out there, my personal favorite is the manzanita.

Once you have the basics of the system figured out, you will need to figure out how to install it. Gearing is very important and you should match the motor's max rpm with the max rpm of your shaft. Since many of these motors spin 4-5000rpm, you are likely to need a gear reduction of somewhere around 2.5-1. The easiest way to get a gear reduction like this is to belt drive the shaft but that requires at least 1 extra bearing and ideally 2 on the shaft.

I hope that this helps.
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Old 30-01-2010, 20:54   #6
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Quote:
Originally Posted by Sailmonkey View Post
I've been on a 42' catamaran powered by these. Dead silent, and best part is while you sail, you re-charge the batteries.

Solomon Technologies
This is interesting. How did they recharge while under sail? Wind?

Tom
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Old 30-01-2010, 21:04   #7
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Here is one that worked.

Quote:
Originally Posted by tomperanteau View Post
This is interesting. How did they recharge while under sail? Wind?

Tom
re-generative breaking. The prop spins the motor while sailing which can generate power.

Here is a detailed write up of such a system in a Pearson Commander.

Commander 227 - Pearson Ariel Association Forums
Commander #227 (most motor detail is on page 2)
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Old 30-01-2010, 21:06   #8
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While sailing the motion through the water causes the prop to turn. This in turn turns the motor, turning it into a generator!! ......and that's how it turns
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Old 30-01-2010, 21:45   #9
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The OP doesn't say how big a diesel he's looking to replace. Chances are good there will be a need for a generator to help power the system, most likely a diesel powered one, which kind of puts him back where he started.
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Old 30-01-2010, 21:49   #10
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Good write up Klem, I've always wondered about how these systems were set up. Thanks.
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Old 31-01-2010, 08:18   #11
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At the end of the day if you want any range more than getting away from the dock you will have a generator running like telle says. l have seen a few lagoons and custom setups but have not seen a trouble free install yet.
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Old 31-01-2010, 08:31   #12
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The lower the voltage, the larger the DC motor needs to be for the same horsepower. Therefore, in order to not have to have a massive DC motor, you will need multiple numbers of batteries. This would mean a charging system designed around them.

Between a propeller driven motor, solar and wind, you would have one expensive and complex charging system.

They exist, and they are called hybrid systems which in my opinion need a lot more development before they are as practical and cost effective as conventional propulsion systems.
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Old 31-01-2010, 11:34   #13
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Between a propeller driven motor, solar and wind, you would have one expensive and complex charging system.
On the other hand, between the fuel pump, the alternator, the raw water system, the freshwater cooling system, starter motor, and transmission, you would have one complicated diesel propulsion system.

I am contemplating a Atomic 4 replacement in the next few years and electric is one of the options I'm considering. What I've discovered is that the cost and complexity of electric propulsion is roughly comparable to the cost and complexity of a new diesel, at least in the range of power I am looking at. The main difference is that the complexity is in the electric systems, rather than the mechanical systems.

The main penalty from electric is vastly reduced range, probably about 1/10th what you would get from a comparable diesel. Also, electric propulsion optimally requires a larger propeller, and a non-folding one at that, which will reduce boat speed somewhat.

A few more purveyors of electric re-powers I have seen (no affiliation):
Electric Yacht
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Old 31-01-2010, 15:25   #14
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Klem wrote it up pretty well. Electric cars have provided a lot of information as to how to do the conversions. There are certain weight savings by going from diesel to electric, but not enough to totally offset the extra weight of the batteries. I was involved in fielding a car in the 1995 electric car races in Phoenix Az, and learned a fair bit about it working on that vehicle. We stripped that car of every ounce of weight that we could in order to extend the range.

On the subject of charging, A fast charge requires access to 220volt, not usually available dockside. One thing I did see was a pickup truck that extended its range by using a generator set in the bed. It pulled starting power from the batteries and then switched over to a generator for long distances over the highway where the load was more or less constant.

Perhaps removing ballast in the keel and replacing it with racks of batteries might be a way but as mentioned in other posts, lead acid batteries and sea water are a nasty combination. Chlorine gas.

If society keeps going for a while longer, these problems may be whipped but I'm not holding my breath. The rare elements needed for the new batteries is already in short supply.



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Old 31-01-2010, 16:59   #15
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Since one of the diesel smells, a susgestion might be to use an encapsulated generator and an electric motor. That way smells could be kept to a minimum.
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