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Old 23-01-2007, 15:08   #1
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36vdc Motor Bank and 12vdc House Bank

I looked at a 30’ sailboat which had the engine replaced with a 36VDC electric motor. It has 3 12VDC batteries in series to power it, and a 110VAC charger which plugs into shore power to recharge this bank. There was a seperate battery for the house power. All well and good for short trips but for long trips how to recharge the 36 VDC bank?

My idea to make this work for offshore trips was to buy 2 more batteries to create a second bank of 3 batteries wired in parallel for the 12VDC house bank and then use this bank (after it was charged up and wired in series) to become the 36VDC bank for the motor. I would charge the house bank with a combination of a solar panel, a wind generator and some sort of 12VDC portable gas generator, which would sit on deck for use when the wind isn't blowing and the sun isn't shining, and also for redundancy.

Question; My thinking is that it’s better to have just the 3 different ways to recharge 12VDC batteries instead having to find a way to recharge the 36VDC bank as well. So, with that in mind, what is the best way to configure the series / parallel battery connections when switching banks? Let’s assume that the house bank is well charged and I want to swap banks for more motoring. Has anyone seen any kind of multi stage switch which will do all of this – switching a bank of 3 batteries from series to parallel and back again?


Or is there a better way to all this without swapping banks when the 36VDC bank gets low? For extended motoring maybe a better way is to find a portable gas charger with 2 sets of windings which puts out 12VDC or 36VDC and switch it between banks as needed? The problem there is when the 36VDC charge circuit fails, and then the need for bank switching comes into play.
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Old 23-01-2007, 16:47   #2
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The latest Crusing World has an article about a 'hybrid' catamaran made by an African builder which uses the props to turn the motor/generators to help recharge the batteries when the boat is sailing. How cool is that..???

Another thought I had was to rig a generator to a bike on a stationary frame down below. The generator provides the necessary resistance for a great spinning workout.
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Old 23-01-2007, 17:10   #3
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You need to do some math to figure this all out. We have a nice thread on electric an drive Cat. They use a much larger AGM battery bank with diesel genset as well as solar. You need a pretty large reserve to have an electric driven engine. Check this out as this is a real boat:

Electric Main Drive(s)

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The generator provides the necessary resistance for a great spinning workout.
The Greeks and Romans had slaves with oars! You really need to do the math. If you consider you might get 80% conversion efficiency to electricity then back to spinning the prop (I am not seeing this number as possible) this bicycle is a pretty good torture device.
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Old 23-01-2007, 18:31   #4
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Paul, thanks for the link to that thread.
Looks like some usefull info there.

LOL...one man's exercise routine is another man's torture....
As an avid biker it seems like a good way to churn and burn...in the confines of a small sailboat...
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Old 23-01-2007, 18:38   #5
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As an avid biker it seems like a good way to churn and burn...in the confines of a small sailboat...
I've done my share of long hard cycle trips but this one would burn bad. I doubt you could keep a prop spinning.
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Old 23-01-2007, 19:01   #6
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Don't make it complicated like this guy did

Get a wind or solar generator to charge the 36 volt system and simple 20 dollar converter to take the 36 vdc down to 12vdc to feed the 12 volt house needs by passing the a 12 volt battery all together.

however if you want a 12 volt house battery then just put a 12 volt charge controller after the dc converter, once the 12 volt is topped up it will stop drawing from the 36 vdc system.

This going to be my electric plan on my boat, except I am using a 48vdc system for the electric motor.

Matthew
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Old 24-01-2007, 00:28   #7
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I don't know why anyone would seriously consider electric drive. It just simply is not economicaly viable.
Bobola, we also need to know Amp hr ratings of the banks. Voltage is one thing, but the amphrs is more important to work out the requirments of effort in charging etc.

The only seriouse way of deriving 12V from a 36V bank is to use a DC-DC stepdown converter. If you try mechanicaly switching, you are looking at some seriouse switch gear or Relays that would be very expensive and rather cumbesome. Plus if anything ever failed, the result would be catastrophic.

Seriousely, forget electric. It is expensive, you get enormouse loss of energy in conversion. You have limited power available at the prop. You have limited duration. And the weight of battery banks far exceed the weight of an equivilant power output diesel engine. Plus you have to replace those battery banks at say 10yrs if you get a really good run.
A person peddling can develop about 180W of energy. how long that can be sustained for depends on the fitness of the person, but I doubt anyone would keep that up for long. So at 36V, that human genset would be putting 5A back into the bank. 15A if it was a 12V bank. I imagine we are dealing with some seriouse reserve to run the electric motor, so that's a lot of pedling.
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Old 24-01-2007, 01:46   #8
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According to Windstream Power LLC (manufacturers of Human Power Generators) ”... The typical average continuous power that can be generated by pedaling is about 0.166 (1/6) horsepower or 125 watts, more or less, depending on the weight, strength, and endurance of the person pedaling ...”
Human Power Technical Information

Other sources have indicated continuous outputs varying from 0.1 HP/75W (healthy non-athlete) through 0.4 HP/300W (elite athletes).

I know that Bob will pedal somewhere near the upper range, say 0.33 HP/248W, so might expect to produce something over 15 Amps/Hour of cycling. Although this may not represent an adequate prime electrical recharging power source, it would certainly be a significant supplementary source.
Even assuming the 180W/13Amp output Wheels cites, a 13 Amp/Hour recharge is an appreciable incidental benefit of Bob’s “normal” routine - he’s a “riding fool” .

For most of us, the weight & space penalty (of the equipment) won’t be justified by the meager 5 - 10A/H total daily output we might expect to achieve.
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Old 24-01-2007, 09:34   #9
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The bicycle-as-generator idea was intended to be another (less serious) way to squeeze a few amp hours in a battery bank while getting some boat-side exercise.

Alan brought up a good point – overall weight of the batteries. A big downside to my idea of 2 big banks.

However I do like the idea of a portable generator supplying the regenerating power for a fixed electric motor. If/when the generator fails it can fairly easily be removed from the boat and transported to a mechanic’s shop if it can’t be fixed on the boat. A downside is that the generator will probably be gas and not diesel.

The idea works well if motoring was to be limited to moving to and from an anchorage or marina, and there was sufficient solar and wind generating capacity and well insulated reefer if there was even a reefer installed on the boat. Read Dave and Jaja Martin’s logs and they give a very convincing argument against refrigeration of any kind. I tend to agree with them. Take that power hog out of a boat’s overall amp consumption and the electric idea looks even better.

The boat in question is a cheap, old, beat-up 30’ 60’s vintage fiberglass trailerable boat, which the owner started to renovate. I do wish it had a combustion engine of some sort, as I would prefer it actually, but it doesn’t so I am trying to decide how to make this thing work beyond a day sailor. The electric motor may very well be the reason the boat has been for sale for years – asking price is now 6k and it could probably be had for 4.

Mathew, I would like to know more about your boat's electric motor plan.
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Old 24-01-2007, 09:52   #10
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Quote:
I don't know why anyone would seriously consider electric drive. It just simply is not economically viable.
If you look at the thread on electric main drives the boat actually would work quite well (they built it). The uneconomical part really only comes in when the batteries need to be replaced and the price of fuel with increased battery costs add up fast. The AGM batteries really are the proper choice but the cost of replacement is a killer. You would want to buy this boat then sell it before the batteries had to be replaced.

The diesel generator setup really is the right way to go. The whole boat seems well thought out BUT the batteries cost too much. 12 - group 4D AGM Lifelines are not cheap. I have two on my prior boat and they are a really nice house bank.

That is some expensive horse power. Any wind / solar gain is just to deduct from the house battery daily demand. It won't anything left over to recharge the engine capacity. The genset needs to be used for that.

It does mean you can sit for a heck of a long time on the hook provided you don't have to motor any place.
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Old 24-01-2007, 10:46   #11
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My boats electric plan - laugh if you want...

but be nice to me on the forum, I am not suggesting that anyone else do this. This is what I'm doing. I've already ripped out my old tired A4 and sold it for $100.00 just to be rid of it.

Bobla:

I'm using very easy components and over all it should be cheaper than a new deisel or gas install. I am putting an E-tex motor or similar on the exsisting shaft and putting in 8 x 6vdc to make a 48vdc battery bank. The over all weight of batteries, motor, controller should only be about 550-600 lbs... advantage is that it's closer to mid ship. The 410lbs of weight for engine and fuel (fuel tank in tansom) which it is now replacing is closer to mid ship. I can rebuild my engine coompartment for better stowage and the transom locker is now clear of Gas tank and I can put life jackets and bulky light stuff back there.

The gear ratio component and the electric controller will let me regan electric current while under sail, and tidal flows. I should be able to sail for a 4 hours and recharge the battery bank from the 30 minutes of motoring I did to get out of a harbor. The prop will be switched to a fixed 3 blade at a higher pitch a 12x12, instaed of that little 12x8 that basically just churns water. An electric will turn a larger pitch.

I plan on buying a wind generator from KISS that outputs a standard AC current up to 1000 watts and convert that to 48vdc close to the bank for better charging. Then I will use a step down converter from 48 to 12 for house equipment.

Currently the price structure is as follows:
Etek style motor will be 500 to 800
Charge controller with regan is 200 to 400ish
Battery Bank is going to run me 600 to 900 depending on shipping and distributor. I would have to have a battery bank anyway and a standard 12 volt would be about 150.
Wind Generator which I would buy regardless is about 1400 with everything.

So I'm looking at about 2.8-4k total price tag with the additional wind generator.

Now the good news if the motor goes down I can just replace it, if the batteries die after 10 years dito. Controllers are pretty cheap... everything but the batteries can be packed up and sent ups for repair or trade in. Also for cruising I can carry a spare controller and motor for around 1200.00 similar to this package.
Electric Boat Sailboat Kit Mars Brusless motor Sevcon PMAC millipak regen controller

I'm actually using a different system and mine will be a little more expensive. But I like the component aspect of it.

I can also ad a gas or diesel genset... if I want to put it in a another boat I can easily do that myself I can lift everything individually. Heaviest thing is a battery at 56lbs.

For me it's like a really big science project... however if I had a new sailboat and was a weekend warrior and/or still worked a grewling career I don't know if I would have time to mess with it or the desire.

If you are a tinker-er and an DIY then electic conversion may be for you... if you are not then it isn't.

I'm also really frugal about certain things and in 3 years would have spent more on gas than on a battery bank, at 3.00 a gallon this summer it doesn't take long. 100 gallons of fuel a year at 3.00 a gallon is 600 bucks in three years. My battery bank should last about 5 to 10 years. In two years what will the gas price be during the summer? On a personal level do you want to own or rent your power?

But the best part is I can always install a kick plate to the transom and use a 15hp long shaft gasser in an emergency / the hillbilly hybrid . So I'm never without options.

Again I can't stress this enough this is not for everyone and I don't suggest it for others. Also I moore my boat in Provincetown Harbor and lots of poeple here can sail in and off their moorings. So expeirementing with electric propulsion is a little less frieghtening than being in a 3 mile congested channel.

Matthew
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Old 24-01-2007, 11:16   #12
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Mathew,

That all makes sense to me.

When I looked at the old boat near me I was somewhat astounded by all the space freed up in the engine compartment with the electric motor replacement. Extra space could be used for another water tank...etc...

Other benefits of an electric motor over combustion engine; very little noise if any; very little heat generated; fewer holes in the hull; turn the key and go; virtually no maintenance.

Can't agree more on the advantage of the portability of all the pieces.
And the price of it all certainly makes sense.

If I were to replace the electric motor in the boat I am considering the price of a new engine would probably cost more than the boat...!!!
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Old 24-01-2007, 11:30   #13
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But Mathew, you are not factoring in the fuel used in the genset. The replacement cost of the genset. The complexity(expense) of the electronics. The fact that solar and wind will only give you a very small percentage of the required average daily charge (when taken over say a month of available conditions).

Everytime one form of energy is converted to another form, there is a significant loss of energy. Starting with the genset, you are taking a fuel to perform a task of creating rotational energy to drive a Generator. There is a loss due to friction in both machines right off the bat. Then you have the loss of energy due to the fact that the windings also disapate energy as heat and are not truely efficient at creating energy to start with. Then you have the charge controller that connects the electrical energy to the batteries. Then you have the fact that batteries are not so good at taking in that energy, so you have a loss there as well. Then they require more energy in to charge them, than what they return back out and even that has a loss as well. Infact, the battery at rest is even losing energy. It's like having a drip from your fuel tank. Then there is what is lost in the electrical cables. So you have taken one power source and converted it several times to get it to the shaft.
If you had conected the fuel powered engine direct to the shaft in the first place, you would have a greater efficiency.
Then there is the thrust of these electrical propulsion systems. Not big. OK, but not big. So the amount of thrust is no greater than a small lightweight diesel. But the over all weight of the electrical system far exceeds the weight of a small diesel. And the initial set up cost is horrendouse. Way more than an equivilant power output Diesel. In the end the Diesel is going to last many many time longer than the battery banks. So over all cost is such that the Diesel and it's fuel usage is going to be very cheap.
I am not sure why the thought is that the electrical system is cheap. A properly done electrical system is going to be a very similar price and most likely more than a new Diesel engine of equal or even greater power output.
The ONLY efficiency gained in an electrical motor is the fact that the motor is directly coupled to the shaft. The only disadvantage of combustion engines is that they go through a gearbox which creates a loss.

For an interesting electric drive, check out RE-E-POWER
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Old 24-01-2007, 11:33   #14
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Here is how to do the math in a very rough but simple rough fashion.

Take the size of one battery in Amp hours and divide by 2. This is how many useable amp hours at 48 volts you have to work with. If you use more than half capacity at any one time the life expectency of the batteries will diminish real fast. Lets say you use exactly one half you really need to get the batteries back to 100% before the next time you use the engine. The wind generator might do that over a few days depending on the wind so it may not be so bad at all. It's the heading back to port part that will be the issue.

Getting your batteries fully charged in 4 hours of sailing will really be the important component and the one that seems least possible and most variable. The rate of acceprtance on the last 10% will be the problem. As the batteries get full they will accept fewer amps. If you draw down again without being fully charged you are on a slippery slope to a dead battery bank. That will determine if this works for a whole season or just a few times. If you don't top them fully after each use then the ten years could become less than a year.

It's also predicated on a very very low 12 volt demand as you sail as that part is also sneaking up on you too. I realize that the budget is tight but a battery monitor would really help you in this experiment. It's basically like a fuel gage for the batteries measured in amp hours used and amp hour load (- charge or + draw down). I've seen them for 12 volt and 24 volts but you may be able to find a 48 volt one. I have had a 12 volt one on two different boats and they really open your eyes to how you consume electrcity and you always know where you stand. Reading voltage alone isn't so exact. Once you have accurate measurements the math gets to be obvious. You'll get back to the mooring and know net net where you are. When come you back in a few days you see if it is full again. You'll know exactly how many amp hours to get out to sea under various conditions. You'll know when you need the outboard well before the battery bank is dead and you've inflicted damage to the bank and have no power.
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Old 24-01-2007, 15:44   #15
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Bobola:
Did you, or are you close to, buying a (30' trailerable, engineless) boat?
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