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Old 19-01-2013, 02:55   #211
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Re: Electrical Propulsion vs Diesel Propulsion

I'm thinking about converting a Dragonfly to electric propulsion. So far, not a radical idea (Quorning Boats offer their newest model, the Dragonfly 32, with an electric propulsion option). The radical part of the idea is that I'm thinking of locating one battery bank, one DC genset, one solar array, one MPPT controller, and one diesel tank in each ama, so that the vaka is completely free of hydrocarbon fuels.

I realize, of course, that it would not be possible to use the windward genset whenever flying an ama (due to cooling water intake). However, it normally shouldn't be necessary to run a genset when flying an ama and, if an exception might arise, the leeward genset should be available. Gensets would be started only manually, as I would not want a genset to start in an ama that is out of the water.

Tentative specifics:
In (on, in the case of the solar panels) each ama: one 90kg Fischer Panda 4KW 144V DC genset, 45x 40AH (67kg) or 60AH (100kg) LiFePO4 batteries, 100l fuel capacity (up to 82kg), 3x 48V (nominal) or 4x 36V (nominal) solar panels, MPPT controller/charger, auto bilge pump (or two), auto fire extinguisher (with shunt to disconnect DC from the vaka).

Under normal operation, both battery banks (with their respective gensets and solar chargers) would be connected (in parallel, of course) to the 144V DC bus in the vaka but, of course, with breakers (or fuses) both in the vaka and in each ama to disconnect in emergencies or for maintenance. Each 6KWh or 9KWh battery bank would be sufficient (with the other disconnected) to safely operate all systems.

Also connected to the 144V DC bus would be:
18KW propulsion motor
shore charger
space for adding a 115V inverter
watermaker
A/C condensor
cabin heaters
water heater
induction stove

The house bank would be 12V DC powered by a separate solar MPPT controller (solar panels on the vaka) and backed up by a DC-DC converter.

Thoughts? Suggestions? Recommendations? Warnings?
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Old 19-01-2013, 02:57   #212
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Re: Electrical Propulsion vs Diesel Propulsion

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Brilliant sounds like the way to go. Just one more question if that's ok.. I am happy to have only a few minutes of motoring off batteries only, but if I am running large house loads via an inverter from a 288v bank will there be a minimum AH requirement? Or will it be ok having an autostart gen kick in at a certain state of discharge on a small bank?
How will the autostart genset know the state of discharge? One cannot rely on voltage to measure state of discharge with LiFePO4, except near complete discharge.
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Old 19-01-2013, 03:12   #213
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Re: Electrical Propulsion vs Diesel Propulsion

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How will the autostart genset know the state of discharge? One cannot rely on voltage to measure state of discharge with LiFePO4, except near complete discharge.
Sorry I had assumed this was possible.. is it an option with agm cells?
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Old 19-01-2013, 03:16   #214
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Re: Electrical Propulsion vs Diesel Propulsion

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Sorry I had assumed this was possible..
It is possible to measure state of discharge with LiFePO4 cells, but it's not as simple as measuring voltage, which is what most autostart generators have traditionally done. However, rather than measure state of discharge, you might want to measure rate of discharge -- especially if your intention is to have a small bank and immediately start the generator when a heavy load is applied.

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is it an option with agm cells?
You don't want AGM cells. Go with LiFePO4. Why do you want to keep the battery bank small? Weight? Cost? Constrained space?
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Old 19-01-2013, 03:19   #215
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Re: Electrical Propulsion vs Diesel Propulsion

I am not a great fan of autostart generators, but many of the more sophisticated battery monitors / solar regulators will autostart a generator based on the amount of discharge.
The amount of discharge is not based on voltage so would work with lithium batteries.
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Old 19-01-2013, 03:32   #216
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Re: Electrical Propulsion vs Diesel Propulsion

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You don't want AGM cells. Go with LiFePO4. Why do you want to keep the battery bank small? Weight? Cost? Constrained space?
If I go with LiFePO4 then it would be largely cost, in a powercat which would need to run the genset to recharge the batteries anyway the main reason for going electric would be to allow mounting gensets away from the props in a soundproof room
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Old 19-01-2013, 03:38   #217
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Re: Electrical Propulsion vs Diesel Propulsion

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If I go with LiFePO4 then it would be largely cost, in a powercat which would need to run the genset to recharge the batteries anyway the main reason for going electric would be to allow mounting gensets away from the props in a soundproof room
Just be aware that pushing down the capacity pushes up the C factor (charging and discharging) which might impact the useful life. What are your biggest loads? What is your generator output?
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Old 19-01-2013, 04:24   #218
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Re: Electrical Propulsion vs Diesel Propulsion

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Just be aware that pushing down the capacity pushes up the C factor (charging and discharging) which might impact the useful life. What are your biggest loads? What is your generator output?
all theoretical at this point but I would imagine 2x 10-15kw motors and a 20-30kw generator or some combination of 2 generators. That was what worried me about having a generator starting and stopping during long periods of motoring it would just be wasting battery cycles. would there be a way to bypass the batteries when you knew you would be motoring a long way?
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Old 19-01-2013, 04:50   #219
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Re: Electrical Propulsion vs Diesel Propulsion

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all theoretical at this point but I would imagine 2x 10-15kw motors and a 20-30kw generator or some combination of 2 generators. That was what worried me about having a generator starting and stopping during long periods of motoring it would just be wasting battery cycles. would there be a way to bypass the batteries when you knew you would be motoring a long way?
The batteries would be wired in parallel to the generators and motors, so they would be acting as a (beneficial) capacitor. You would not want to disconnect the batteries when motoring. Given your power levels of up to 30KW and given your plan to immediately switch on a generator whenever motoring, I would want at least 5-10KWh of battery capacity online whenever your electrical system is in use. 90x 40AH LiFePO4 cells would give you about 12KWh, so you should be fine as long as you don't choose cells smaller than 40AH (the smallest size made by Winston).
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Old 19-01-2013, 06:24   #220
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Re: Electrical Propulsion vs Diesel Propulsion

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Originally Posted by mcarling View Post
Tentative specifics:
In (on, in the case of the solar panels) each ama: one 90kg Fischer Panda 4KW 144V DC genset,


Also connected to the 144V DC bus would be:
18KW propulsion motor

Thoughts? Suggestions? Recommendations? Warnings?
Just a question,

Suppose the batteries are flat.
Is 8KW of the two gensets enough to "motor" in all circumstances ??
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Old 19-01-2013, 07:52   #221
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Re: Electrical Propulsion vs Diesel Propulsion

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Just a question,

Suppose the batteries are flat.
Is 8KW of the two gensets enough to "motor" in all circumstances ??
Good question.

I believe 4KW should be more than enough to motor into a marina -- even against most tides, and one can normally wait for the ebb if necessary. For making good speed, 8KW is light, but weight and size mitigate against larger gensets. If solar fails to keep the batteries charged during a long passage, regenerative charging should cut the speed under sail by perhaps 0.5 to 1.0 knot.
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Old 19-01-2013, 11:09   #222
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Re: Electrical Propulsion vs Diesel Propulsion

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Octopus, I'll be interested to read your impressions after your current batteries give out if you make the switch to lithium phosphate.

My thoughts exactly!
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Old 19-01-2013, 11:14   #223
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Re: dragonfly configuration

A couple of questions about your proposed dragonfly configuration:

1) Why such a large electric motor? At 750 watts/HP your 18 KW motor is 24 HP, which actually translates to something like 40 HP equivalent given the torque range of an electric. Since you won't be able to generate more than 8KW on an ongoing basis, why the need for such a large engine?
2) Given that you've got 2 redundant generators it seems like you could save quite a bit of money (and weight) by going with a smaller battery capacity. It seems like you should be able to come up with a fairly simple system that would let you run the generator in the flying AMA if the other one totally conked out (I'm thinking something like a flexible cooling water intake hose that you could drop over the side).
3) Given all your electrical loads (induction cooktop, electric heaters, etc) it doesn't sound like you've got enough solar to keep up with your house demands, let alone recharge the propulsion banks.

Out of curiosity, how much do you think your proposed system is going to cost, all told?
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Old 19-01-2013, 11:26   #224
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Re: Electrical Propulsion vs Diesel Propulsion

Quote:
Originally Posted by mcarling View Post
I'm thinking about converting a Dragonfly to electric propulsion. So far, not a radical idea (Quorning Boats offer their newest model, the Dragonfly 32, with an electric propulsion option). The radical part of the idea is that I'm thinking of locating one battery bank, one DC genset, one solar array, one MPPT controller, and one diesel tank in each ama, so that the vaka is completely free of hydrocarbon fuels.

I realize, of course, that it would not be possible to use the windward genset whenever flying an ama (due to cooling water intake). However, it normally shouldn't be necessary to run a genset when flying an ama and, if an exception might arise, the leeward genset should be available. Gensets would be started only manually, as I would not want a genset to start in an ama that is out of the water.

Tentative specifics:
In (on, in the case of the solar panels) each ama: one 90kg Fischer Panda 4KW 144V DC genset, 45x 40AH (67kg) or 60AH (100kg) LiFePO4 batteries, 100l fuel capacity (up to 82kg), 3x 48V (nominal) or 4x 36V (nominal) solar panels, MPPT controller/charger, auto bilge pump (or two), auto fire extinguisher (with shunt to disconnect DC from the vaka).

Under normal operation, both battery banks (with their respective gensets and solar chargers) would be connected (in parallel, of course) to the 144V DC bus in the vaka but, of course, with breakers (or fuses) both in the vaka and in each ama to disconnect in emergencies or for maintenance. Each 6KWh or 9KWh battery bank would be sufficient (with the other disconnected) to safely operate all systems.

Also connected to the 144V DC bus would be:
18KW propulsion motor
shore charger
space for adding a 115V inverter
watermaker
A/C condensor
cabin heaters
water heater
induction stove

The house bank would be 12V DC powered by a separate solar MPPT controller (solar panels on the vaka) and backed up by a DC-DC converter.

Thoughts? Suggestions? Recommendations? Warnings?

All boat designers I have heard about agree:
Keep the heavy stuff centered in the boat as much as possible for best seakeeping and the boat's safety.

I don't know which model Dragonfly for which you are proposing this.
I hope it's at least a DF35 you are talking about with the above.

Think how much the polar moment of inertia is going to punish the rigging, waterstays and akas during a spirited sail in rough conditions! Yikes!
With that much weight out on the lateral ends of the boat, imho you are asking for trouble.

If I did that to my DF1000, it would probably break apart in any elevated seaway.
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Old 19-01-2013, 11:33   #225
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Re: dragonfly configuration

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1) Why such a large electric motor? At 750 watts/HP your 18 KW motor is 24 HP, which actually translates to something like 40 HP equivalent given the torque range of an electric. Since you won't be able to generate more than 8KW on an ongoing basis, why the need for such a large engine?
Perhaps 18KW is too large, but I can imagine circumstances where safety might require 10 knots or more for a little while.

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Originally Posted by susswein View Post
2) Given that you've got 2 redundant generators it seems like you could save quite a bit of money (and weight) by going with a smaller battery capacity. It seems like you should be able to come up with a fairly simple system that would let you run the generator in the flying AMA if the other one totally conked out (I'm thinking something like a flexible cooling water intake hose that you could drop over the side).
I think if one generator totally conks out, that I don't need to fly an ama all the time. I would like to never need to run either generator, but I'm sure there will be times when sunshine, the charge from the last marina, and regenerative charging are insufficient. I've thought about foils on the amas as a source of cooling water, but I'm not inclined to compromise the draft.

You really think that 12 or 18 KWh is a large battery capacity for an all-electric boat? With 1000+ watts of solar panels, it might be possible to get 4-5 KWh on a good day. Enough battery capacity to store 3-4 days' of solar generation makes sense to me. If heating or using A/C, it would be possible to use 4-5 KWh just for a reasonable living temperature.

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3) Given all your electrical loads (induction cooktop, electric heaters, etc) it doesn't sound like you've got enough solar to keep up with your house demands, let alone recharge the propulsion banks.
I expect to do some regenerative charging while sailing, especially on cloudy days.

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Out of curiosity, how much do you think your proposed system is going to cost, all told?
Roughly about $20-30K USD.
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