Sailboat conversion from 14 hp Diesel to 10 Kw 48V electric motor

keimor85

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Hi All,

I'm new to the forum. Have been reading many of the threads on here to educate myself and looking for any guidance. So here is my story. I'm converting my 1979 Cape Dory 30 sailboat from a 14 hp diesel to a 10Kw 48V electric motor (the motor is ordered). I was planning on just using 8 105 Ah 12V batteries in a 4S2P configuration to yield 48V and 210 Ah but @ 60% this would only give me 126 usable Ah with a cost of around $2600. Buying LiFe 105 Ah 12V or 24V would cost may thousands more so that is out of the equation. So now I'm looking at building my own battery with the 3.2V LiFe cells. I'm specifically looking at the Xuba 280Ah cells but the article that was attached to one of the threads say that going with cells over 200Ah for a marine application is not a good idea. I also saw some 200 Ah cell for a very good price as well but they are from Jidian Technology so looking for any feed back on them as well. I have many more question but this is a good start. Looking forward to your replies.
 

keimor85

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Here is my first attempt at the electrical system. I would be replacing the two battery bank with one 48V battery made with 16 3.2 V 200 or 280 Ah cells.Electrical System Design.png
 

mmdb

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Im also thinking of doing conversion of my small 7m semidisplacement powerboat it was diesel 80hp and I'm also thinking about 10 kW electric and go with displacement speeds .and probably go with 16s3p 280ah cells .which electric motor you order ?
 

gearboxlabs

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So thoughts...

Having a 10kw motor means you're looking at a ~208 amp draw at 48 volts (10kw/48v = 208a). With that, you'd draw down a 200Ah 48V battery in about 45 minutes of operation, or about 65 minutes for the 280Ah pack. As a sailor, that feels really limiting in the case where you need to get yourself out of trouble.

What is your planned use for your boat with this electrical system?
 

keimor85

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"Having a 10kw motor means you're looking at a ~208 amp draw at 48 volts (10kw/48v = 208a). With that, you'd draw down a 200Ah 48V battery in about 45 minutes of operation, or about 65 minutes for the 280Ah pack. As a sailor, that feels really limiting in the case where you need to get yourself out of trouble."

I always try to stay out of trouble. Good planning and diligently watching conditions pays off. Having a boat that can sail around the world also helps. I even sail my 30 ft 10,000 lb boat for 8 week with no motor one year.

Yes, you are correct but no sailor ever runs their diesel at max RPMs as no Tesla owner ever runs in ludecrist mode for very long besacue the battery will die in minutes or possibly the driver. As an example my diesel redlined at 2750 but the rule of thumb is run a diesel at ~75% or 2050 with would push my boat at 4.5-5 kms depending on current and relative wind direction. So to push my boat to hull speed (6.5 kms) it would use about 180Ah but if you look at the speed to power consumption curve I will only use about 60 A at 4.5-5 kts. Drop the speed to 3 kts and it only draws 20 A Which means I could run about 10 hours or 30 km. Throw in the solar again and it just increases the hours and distance.


What is your planned use for your boat with this electrical system?

The bottom line is I'm a sailor and the mechanical propulsion is an auxiliary. Last season I logged about 3,000Km less then 30 of those Km were motoring. On an average day I will run the electric motor 10-15 minutes at 5 kms which will use 15-20 Ah. My solar system with array 1 will provide about 32 Ah per day on average if I add the array 2 the average daily Ah will increase to 52. Also my electronic, stereo, etc... will consume about 10-15 Ah per day. So I will see if array 1 will be sufficient or if I need to add array 2.

I will update in the spring.
 

MisterSandals

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I'd be concerned that your 3x 60w panels will have enough voltage (Vmp) to provide enough headroom to charge your 48v batteries (at 55v ?). I guess the question is, is your 63v based on Voc or Vmp?

Some math (use scratch pad for me):
180w / 55v = 3.27a
19ah / 3.27a = 5.8h per day of solar

Does that correspond to this?:
How many "solar hours" of sun do I get per day throughout the entire day at a city near me?

280w / 55v = 5.1a
32ah / 5.1a = 6.27h per day of solar (is this array in a sunnier location?)

280ah / (19 + 32) = 5.49 days to fully charge your batteries operating at 100% efficiency.
 

keimor85

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I believe that the solar panel manufacturer used 5.5 hr per day to come up with the average Ah per day per panel.

Yes, I agree on the three panel array (array 2) only being a at 63V is problematic. The solar panel manufacturer is looking to see if they can up the voltage on each panel. If they are unsuccessful then I will try to add a forth panel to bring the voltage up to 84V.

Per my statements above I will never fully discharge the batteries. As stated on average I will consume 20-30 Ah so it will charge in a day or less.

Lots of good comments but no one has chimed in on my two original questions:

1. Does any one have any input on not exceeding 200Ah cells in a marine application?
2. Does anyone have any knowledge on reputation of Jidian Technology?

I'll add a third question as well:

3. Can anyone recommend a good BMS 48V for marine applications?
 

solarbot

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I'm converting my 1979 Cape Dory 30 sailboat from a 14 hp diesel to a 10Kw 48V electric motor (the motor is ordered) ... the article that was attached to one of the threads say that going with cells over 200Ah for a marine application is not a good idea.
Welcome to the build your own battery club! I know just where you're coming from - I'm looking at my glorious old YSE12 and thinking that sooner rather than later I need to either rebuild or repower. Now I'm charting a course for repower and have likewise concluded that 48v is the only way to go. But I will approach this incrementally by first adding electric auxiliary propulsion, a pair of these:

Caroute S400-48V 180LB Electric Boat Trolling Motor with speed controller 180 Pound Large Thrust Saltwater For DIY

Only when I have solved all the other issues, including battery, solar array and controllers, will I feel brave enough to hoist the old diesel out and bolt on a 10kw motor. That's just me, I applaud you for jumping right into the thick of it. Many of the issues we have to worry about are exactly the same. So...

Solar array. I currently do just fine with a 200 watt array of two compact panels in parallel, with a cheap PWM controller. But this will not do for 48 volts, I will need to go to at least four panels in series. Reason: the solar controllers we use are buck converters, they can only reduce voltage, not boost it. So you need just shy of 60 volts to reach 100% SOC, 3.65v. (16 x 3.65 = 58.4) Four panels can just barely do that, especially in the morning or evening or on overcast days. The other day I saw 16 volts, 1.5 amps in the morning. If I only had three panels I would just be throwing away that precious 24 watts because it would be ten volts shy of the battery voltage.

At high noon you will do better, probably 20 volts, and three panels will be enough to feed your batteries. But for a good chunk of the day it won't be enough. This one is clear: four panels or more to feed a 48 volt system, otherwise there will be large chunks of the day when you get no charging at all.

Battery. I have my own reasons for going with smaller cells, but I would really like to know the specific reasons in the article you mentioned, can you find it again? For me, it is mainly about manageability. Sixteen 280ah cells weigh around 200 pounds, and that is more than I want to wrestle with as a single unit. Also awkward to fit into the odd shaped spaces I have available. My first prototype pack will be 80-100 pounds, roughly 5 to 7 kwh. That will be enough for sea trials of my electric auxiliaries, and also limit my risk during my learning period.

Battery management system. I have pretty much settled on the Overkill 16s: 16s BMS 100a LifePo4 Battery Management System for 48v DIY Batteries

Reasons: the documentation is worlds better than the Daly. In particular, the way this controller handles high voltage cutoff is spelled out clearly: don't disconnect the load, just disable charging. Thank you, that's exactly what I want. The possibility that my boat could shut down entirely just because some cell got fully charged makes me shudder. I can't say for sure that this is what the Daly does, but there's no documentation so how would I know? I just can't live with that.

Another huge reason for going with Overkill: the open source aspect. This is big with me. I want to really know what is going on inside and I want to add computer intelligence as time goes by, because that's what I do. You can sort of do that with good published specs such as Victron's, but maybe not exactly the way I want. And I certainly can't do it with Daly's undocumented black box.

For your project, the Overkill's 100 amps is not enough. But why not go with smaller cells and build multiple packs, each 100 amps? Two packs with 120ah cells should be fine. You can always add more later.

A major benefit of multiple smaller packs is redundancy. Sooner or later a cell is going to fail. With one huge battery pack, you aren't actually dead in the water because it's a sailboat, but close to it. Going to need a tow at least into the marina.

Downside of smaller cells: they cost a few cents per amp/hour more. They require more components - each needs its own controller, fuse and switch. More wires, more assembly. But on the other hand, that's the fun part, isn't that why we're in here? And oh, less than half the price of store-bought. And you can craft the design to fit your boat elegantly.

Battery enclosure. So this is where I get to the fitting elegantly part and it's what I've been obsessing a lot about lately. I've been hoovering up papers and forum threads, trying to answer questions like: is compression really a thing? What about heat dissipation? So I will share some thoughts/opinions/tentative working designs now.

Compression: much internet ink has been spilled about it but little engineering insight is provided. I learned that LFP cells do swell, certainly when stressed and to a lesser but measurable extent in normal operation. For example, your 10kw motor with two 5kwh battery packs will discharge at 1C, full power. Well below the 2-3C rate where swelling seems to be reported in the literature. There is talk of dendrite formation and delamination in cases of extreme swelling. Cells forced apart can stress and damage the terminals.

OK, in all of these cases I don't see how compression actually helps. I do see that fixing cells in position is important, both to protect the terminals and to generally reduce wear. So on to my design.

My battery is going into a dry part of the boat, so a waterproof box will not do much for me other than to take up space, add weight and make the battery harder to inspect. I am uninterested in compression, so I will do away with the tie rods and hefty end plates. Instead, I will fabricate an aluminum box to go on each end of my 2x8 cell pack and build a frame with four pieces of angle stock, bolted to the end boxes. The BMS goes in one of the (open on the outside) end boxes. With this approach I don't put pressure on the cells, but I do fix them in position. That should take care of the terminal damage issue and also eliminate wear due to chafing.

I am still working on details. Thermal dissipation concerns me, however as I have found little to no data to shed light on the question, I think I am just going to build a battery pack and find out. I might put rubber washers between the cells as spacers to let air circulate between the cells. Thermal dissipation is not the only reason for this - it might improve toleration of vibration and it could prevent shorting between aluminum battery cans should holes develop in the delicate looking plastic cover.

Well, I really need to post a drawing. Maybe here, or in show and tell? I do want to get some feedback on my design decisions, and I hope there's something useful here for you. Executive summary: I am building a frame, not a box, a press, or a medaeval torture device.

Legacy 12 volt subsystem. Nearly all of the existing 12 volt subsystem is going to stay: starter motor, cabin lights, electronics, etc. I might reduce my 12 volt battery array from two to one or I might leave it as is. The main change is the solar charging system, it becomes 48 volts. So I need to charge the 12 volt system from the 48 volt system. My tentative solution is to connect a standard MPPT charge controller to the 48 volt battery bus and let it do its job as a buck converter with battery charging intelligence. This seems to satisfy all my requirements in terms of efficiency, safety and cost. If anybody out there has a better idea I would love to hear about it.

inverter. This is where we get serious payback for all the investment in 48 volt systems. The inverter gets a whole lot more elegant. Suddenly, 2000 watts of continuous power is not involving short, scary, thumb-sized cables and massive fuses and the device shrinks to a reasonable size. Yay.
 

gearboxlabs

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I will update in the spring.
I look forward to reading how it goes! I'm personally not ready to give up the diesel inboard, but I am planning on doing my own FLA -> LiFePO4 conversion this year in my Cal 36. Probably a 12V / 280Ah build to replace the two 8D deep cycle batteries.
 

solarbot

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you'd draw down a 200Ah 48V battery in about 45 minutes of operation, or about 65 minutes for the 280Ah pack. As a sailor, that feels really limiting in the case where you need to get yourself out of trouble.
That's right. I am personally aiming at about two hours of pure electric cruising, but for range extension I plan a 5kw diesel generator. Which hopefully I will use only rarely, but yeah, sometimes you need to motor 30 knots and pure electric just won't do it.
 

solarbot

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I'm personally not ready to give up the diesel inboard, but I am planning on doing my own FLA -> LiFePO4 conversion this year in my Cal 36.

It's a gateway drug. Once you have your batteries you will want more batteries. When you have a stack big enough to boast about then you will want to hook a motor to them.
 

keimor85

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but for range extension I plan a 5kw diesel generator
I know of three people that added the diesel or gas generators, two of them have never used it and the other used it once.
 

keimor85

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I'm personally not ready to give up the diesel inboard
I have been there for several years. My diesel was sill running very well with the exception that I was starting to get raw water into the oil last summer. I eliminated all of the simple root causes and finally determined that the water jacket must have finally started to rust through. So I changed the oil every month until I hauled out in early Nov and made the decision to go electric. I'm starting to strip the boat of all diesel gear.
 

gearboxlabs

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I have been there for several years. My diesel was sill running very well with the exception that I was starting to get raw water into the oil last summer. I eliminated all of the simple root causes and finally determined that the water jacket must have finally started to rust through. So I changed the oil every month until I hauled out in early Nov and made the decision to go electric. I'm starting to strip the boat of all diesel gear.
Makes sense. And if I get to the point where my engine is in need of maintenance costs in excess of repowering, I'd totally look at that, too. Up here in the PNW, the weather is fickle. Some days have great wind (this weekend, I went out, 25 knots), some days it's pretty dead. Summer is a lot less windy here.
 

solarbot

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I know of three people that added the diesel or gas generators, two of them have never used it and the other used it once.
Nice data point. I have lots of gear on my boat that is seldom used, if ever, like my fire extinguishers.

Where I sail, a brisk breeze can drop to zero without warning and stay that way for days. Meanwhile there are currents and narrow passages lined with nasty rocks. Without fossil fuel backup I will end up on those rocks sooner or later, or with an embarrassing and expensive tow. Either that or just don't go there, which isn't a solution for me because this is some of the most beautiful seascape in the known universe.
 

keimor85

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It's all about setting up our boats for how and where we use them. What is right for one person may be wrong for another.

I sail primarily in Nantucket sound where there is always wind. The most common forecast in the summer is 10-15 gusting 20 or 25. In the spring and fall it's more like 15-20 gusting 25-30. I sailed 166 days last season and only had to motor in one time. There was still a couple of kts of wind and I was ghosting along at about 1 kt but decided to motor. The furthest I would ever have to motor would be from Nantucket to my home port on Cape Cod which is about 23 miles.
 

Doug

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Legacy 12 volt subsystem. Nearly all of the existing 12 volt subsystem is going to stay: starter motor, cabin lights, electronics, etc. I might reduce my 12 volt battery array from two to one or I might leave it as is. The main change is the solar charging system, it becomes 48 volts. So I need to charge the 12 volt system from the 48 volt system. My tentative solution is to connect a standard MPPT charge controller to the 48 volt battery bus and let it do its job as a buck converter with battery charging intelligence. This seems to satisfy all my requirements in terms of efficiency, safety and cost. If anybody out there has a better idea I would love to hear about it.
I looked at using an MPPT converter to charge a 12V battery from a 48V battery, but I ended up getting a voltage & current limited DC-DC converter and it works well. I have a diode on the output to prevent backwards current from the 12V battery when the DC-DC converter is in standby, though I'm not entirely sure I need it, but for now this is the safe option. It charges in constant current mode up to the set current, then when it reaches the set voltage, it switches over to constant voltage mode. I believe you could operate 2 or more in parallel if you wanted a faster charge rate (I recommend diodes for each). I also have a boost converter from the same manufacturer to charge the 48V from the 12V and that works for the rare occasions where I want that. The diode is critical in this direction though.
 
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