Electric motor conversion

[Qmansailer]

As to the charging side of things, I can run the 12V charger off the inverter, but I also have a conventional alternator that charges an independent AGM battery for the genset starter, as well as the 12V house bank thru a battery combiner. I just kept the 12V house battery bank, because it was easier to keep it than have a 400V - 12V converter on the Li-ion pack. Might change that around when the AGMs have seen their useful life. On the dock of course I can charge both the Li-ion pack and the 12V banks at the same time.
As far as fuel consumption on the genset, the longest run I completed was 18 hours, consuming about 32 gal generating about 12.5KW on average. I’ve rarely done flat out speed runs but at 33KW I hit over 9 knots with electric alone and at about 15KW I maintained about 7.5 knots but had the sails up un a broad reach with about 2 knots of wind. I think I would get about the same 7.5 knots at 22KW without any wind.

[Lost Horizons]

Originally Posted by Qmansailer

As to the charging side of things, I can run the 12V charger off the inverter...

And how is that working for you?

[Qmansailer]

Growleymonster

Very good points on the pitfalls of electric power on a boat. DIY is very challenging for an electric propulsion system on a boat of any size. However, many of the shortcomings change considerably when you use the advancements from modern EVs, such as 400V Li-ion batteries and 3 phase PM AC motors using high efficiency inverter electronics. This goes a long way to mitigate the obstacles for electric drive, currents become tractable and power density is high. Direct high-voltage DC gensets can directly charge Li-ion batteries without any conversion. In addition the power conversions for these modern systems are above 95%, not 85%. But they do cost a pretty penny, and are not exactly a DIY project (but then repowering a conventional diesel is probably beyond DIY for many).

Qmansailor

[Qmansailer]

Originally Posted by Lost Horizons

And how is that working for you?

Fine, why wouldn’t it be?

[Adelie]

Originally Posted by Qmansailer

Fine, why wouldn’t it be?

The way you wrote it implies that you are taking energy from the batteries to run an inverter which then powers a charger to recharge the batteries.

If you actually did that it would result in a net loss of energy from the batteries with no useful work extracted. That lost power would result in heat rejected to the environment.

[Jdege]

Originally Posted by cgm12mgc

We get it, you’re no fan of electric motors.

Anyone who has ever seriously looked at the issue loves electric motors.

• They provide much more power for the weight than internal combustion,
• They put out great torque at very low rpm, eliminating the need for complex transmissions, and
• They are astoundingly reliable - three-phase induction motors go 50,000 hours between maintenance, and then it's just replacing the bearings.

It's not the motors we don't like, it's the damned batteries.

[Qmansailer]

Originally Posted by Adelie

The way your wrote it implies that you are taking energy from the batteries to run an inverter which then powers a charger to recharge the batteries.

If you actually did that it would result in a net loss of energy from the batteries with no useful work extracted. That lost power would result in heat rejected to the environment.

Ahh... I see where the confusion is coming from. I can assure you I understand the laws of thermodynamics very well.
But if reading a little more closely, I have two battery banks, one 400V and one 12V. I use the 15KW inverter attached to the 400V bank to provide AC power to a charger that charges the 12V bank. This supplies all the 12V needs on the boat. I could do this a little more efficiently with a DC/DC converter, but I already had the 12V battery bank, the charger and inverter so this setup was essentially free. The sole purpose is to convert from 400V in the large battery that powers the propulsion system, to 12V for all the rest of the electrical equipment on the boat.
Makes more sense?

[Adelie]

I figured it was something like that, or you were mis-using the word “inverter”. Then again I know people who thought hooking the charger up to the inverter could recharge the batteries and we get folks like that here so I wasn’t completely sure.

[Lost Horizons]

Originally Posted by Qmansailer

Ahh... I see where the confusion is coming from. I can assure you I understand the laws of thermodynamics very well.
But if reading a little more closely, I have two battery banks, one 400V and one 12V. I use the 15KW inverter attached to the 400V bank to provide AC power to a charger that charges the 12V bank. This supplies all the 12V needs on the boat. I could do this a little more efficiently with a DC/DC converter, but I already had the 12V battery bank, the charger and inverter so this setup was essentially free. The sole purpose is to convert from 400V in the large battery that powers the propulsion system, to 12V for all the rest of the electrical equipment on the boat.
Makes more sense?

No, not really. What you are doing is similar to fueling one tank from another tank onboard while spilling a good portion of fuel overboard. It makes just a little more sense than fueling the tank from itself (while also spilling the fuel). By the way, it all has very little to do with the thermodynamics laws.

[NPCampbell]

Originally Posted by Adelie

If you actually did that it would result in a net loss of energy from the batteries with no useful work extracted. That lost power would result in heat rejected to the environment.

Originally Posted by Lost Horizons

By the way, it all has very little to do with the thermodynamics laws.

If I'm not mistaken, this would fall under the 1st law of thermodynamics?

[a64pilot]

Originally Posted by GrowleyMonster

As owner of a DIY electric boat, I will chime in.

Do not delude yourself into unrealistic expectations, with electric. First of all, your HP rating. It is for the upper end of the rated voltage range. For large PMAC motors, i.e. rated 10kw to 20kw, this is usually 72v or 96v. For a small boat it is more common to use a 48v bank for enough reasons to fill a small book. You will therefore probably not see your full rated output power. And if you do, you will be looking at a huge current. Lots of amps. Peukert will kill you when you get up over 200a, that is, if your batteries will support a discharge like that. Talking MAJOR wire size, like 0000. But your bank's capacity rating will not even be a thing, at full power. You could go LiFeP04 or similar, but the cost will blow you away. To keep your batteries charged while discharging such high current, you really need at least a 16kw genset. Solar? Not even a thing, at this power level but I will get back to that.

If your power demands are more modest, and you are quite content to motor at 2kts, you can probably motor indefinitely, with enough solar and a touch of the generator now and then. But this will not work so well stemming a current or seas and wind. Just sayin. A big outboard would be good insurance. Not many full time cruisers have found electric propulsion to satisfy their needs. If those needs are modest and if you can carry a LOT of solar and batteries, that is another thing.

Of course every stage of energy conversion adds more losses. You are using diesel engine to turn a generator. Then you are using a charger to input power to batteries. Then you are using batteries to operate a controller, which sends conditioned power to the motor, which turns a prop, perhaps via a reduction gear. Lets just say that on average every component there is 85% efficient, which sounds sucky but is actually not bad. Lets say you have 6 nominal stages of conversion. You have 85% of 85% of 85% of 85% of 85% of 85% power. So about 37% efficiency, using those made up figures. Obviously, cutting out a few middlemen is a good thing. Here is a novel concept... how about eliminating generator, charger, battery, controller, electric motor, and just drive the prop via reduction gear, with a diesel engine?

Okay that sort of covers most of the cons. Oh, I don't care what kind of turnkey system you get installed. You still need to be something of an engineer to figure out what is happening and what you can do or must do to get the best service out of your EP system. You will need to learn especially about batteries. You think you know batteries? No, not really. Not when it comes to a system that will put so much demand on them.

Now, the plusses, and there are many. First of all if you day sail, and mostly use EP for docking, you can fill your tank so to speak, with shore power. You can probably get by nicely with 8 golf cart batteries from Sams Club. No fuel to spill. No fuel to clean up, or to smell, or to buy or pump. Unless you run that genset. For a bank that size it is feasible to install up to about a 2kw inverter (but also install a smaller one, maybe 300w) for sparodic operation of 120VAC appliances. 1kw of solar panels would see you docking with a full bank, most likely. You have instant ON power. Flip a switch and turn a knob and the prop spins less than a second later, with no warmup. Here is the big one. No minimum idle speed. Most guys don't realize how much it hurts to have to "bump" the engine in and out of gear for very low speed maneuvering. We get used to it. But the first time you approach a dock at 50RPM you will be sold on electric for maneuvering. No more bumping a gearshift. Oh yeah electric is great for single hand tacking, if you have a hardnosed boat that just doesn't tack well. Apply a bit of power with that rudder and around and over you go. Electric drives can be anywhere from pretty darn quiet all the way down to nearly silent or even undetectable topside. No exhaust. No heat. No smell. With a day sailer or weekender, electric is THE way to repower. You may be able to skip the solar, forget about a generator, and just charge from shore power.

It sounds to me like you would be happier with a nice tractor engine conversion like a Beta/Kubota. But you really should go sailing on an electric boat before you decide. I love EP, but I love it for some things, not so much for others.

Can we make this a sticky?

[a64pilot]

Originally Posted by Qmansailer

I’ve been following these discussions on electric propulsion for many years and I’ve learned a lot from the discussions, but I have been reluctant to chime in prior to this because, without hard information, I haven’t felt I could add much to the debate, and, would only add myself as a target for others to push their own opinions. Now that I’ve got some first hand experience, I can hopefully add something to the conversation.

First of all, I am an engineer (in fact most of you have probably owned or used a product that I had a hand in designing at one point), so I do understand “the numbers” and I would argue that there’s plenty of mis-information flying around on both sides of the fence on this one. Second, there’s no definitive answer here, an engineering system, properly designed, meets the intent of the requirements of the intended use. And there are as many intended uses for electric propulsion in the sailing community as there are forum members. What I can hopefully demonstrate is that, for my use requirements, I have been able to apply electric propulsion in a very satisfactory way. It may only apply to me, but it works and I’m very satisfied with it so far.



My set up:

Hull - 43’ Elan GT5 ~ 9000 kgs displacement

Electric Power - 33KW 3 phase AC motor

Batteries - ~ 20KWhr Li-Ion (400V)

Generator - 22KW DC (400V)

Charging - 3KW dockside



With this set up the electric drive is marginally more powerful than the diesel it replaced. I’ve reached a little over 9 knots in pretty flat water, and I can cruise 5 knots at about 10KW. In day-sailing, getting in and out of the marina, I typically use ~ 20% of the battery charge in each outing. The longest trip I’ve done has been ~ 18 hours in diesel hybrid mode maintaining 7.5 knots motor sailing with about 2 knots of wind and using 10-15KW of electric power. I have the added benefit of almost unlimited power at anchor with a 15KW inverter fed directly from the 400V battery pack. I can usually get by on inverter/batteries for a couple of days, and then, it only takes about an hour on the generator to fill them back up again.

Are there downsides - yes there are of course downsides.

- The system is marginally heavier than an equivalent set up of a diesel auxiliary, AC generator, and house batteries, about a 250 kg penalty. I was able to mount all the equipment on the centerline of the boat and minimize the impact to sailing performance. If I could have worked with the hull builder, I would have reduced the ballast, and placed the batteries even lower in the hull to reduce the mass impact, but that wasn’t possible.

- It did take up some room. I essentially had to convert a rear double berth into a single.

- The big one is cost. Many would say it isn’t cost effective. Everyone values everything differently. For me this was worth the money, for others it wouldn’t be. I would say that many people have paid more for a boat than I paid for this all together, and many much less. I could have bought a bigger conventionally powered sailboat for this money, many do, but I wouldn’t get the same satisfaction I get from my boat. To each his own.

The bottom line is, it’s very technically feasible to have electric propulsion on a sailboat. Yes there are compromises and design considerations to take into account. For some it will meet their requirements for other it won’t. I hope this real world example helps to inform the debate.

I commend you for your conversion, and can see many advantages myself.
However it’s I believe well beyond the average person to do, just those voltages alone which are needed for efficiency, require special precautions that many may not know about, or know how to ensure safety.

Eventually a system that is professionally designed and manufactured will become available.

[GrowleyMonster]

Originally Posted by a64pilot

I commend you for your conversion, and can see many advantages myself.
However it’s I believe well beyond the average person to do, just those voltages alone which are needed for efficiency, require special precautions that many may not know about, or know how to ensure safety.

Eventually a system that is professionally designed and manufactured will become available.

Voltage definitely is a big thing. Wiring/electrical standards change a lot when you break the 50v barrier. To keep current manageable, for larger boats, you want to go at least 96v, and for a straight brushed DC or an induction AC motor, twice that. Or more. 400v is definitely not overkill with a big boat and a big motor. One mistake though, and you could be very very dead. You can imagine how big your bank would be, huh? Another reason small boats stick with 48v. Less is less efficient. More is getting into what is regarded as potentially lethal, and a different set of standards. 48v and a BLDC/PMAC motor works nicely for boats up to around 35' and works perfectly for a boat 25' to 30', generally speaking. A bigger boat should go 96v or better. Little to gain, same issues, when you only go up to 60v or 72v nominal. Double your voltage, halve your current, to do the same work. A motor and controller that allow you to triple the voltage, quadruple the voltage, reduce current proportionately. 50v is the watershed voltage. Stay there, or go big. NOT childs play, and maybe NOT for the average DIY tinkerer. 48v is recommended for the shade tree engineer. Which doesn't work so well on bigger boats. A learned electrical engineer is IMHO required for triple digit voltages for a propulsion system. There are few proven turnkey systems with a good and long track record for this level of power. I don't see that changing anytime soon. Not enough market demand. Components aren't cheap. The scale of things is mind boggling. Solar recharging? LiFeP04 batteries? Talking big bucks. Now we are at the point where a diesel is cheaper than electric. A qualified engineer would of course hack electric car technology and repurpose the motor and controller, maybe install 2 to 4 long range electric car battery packs, maybe out of safety concerns upgrade the BMS and add redundant temperature monitoring. On a small boat, you buy a PMAC motor, DIY a belt reduction drive, buy an appropriate controller, fill the boat up with golf cart batteries, optionally hang 600w of solar on bimini and pushpit rails and dinghy davits, and you are good to go for less than half what a diesel would cost. Two completely different paradigms. One demands professional expertise. The other, a pretty smart and handy guy can learn to do himself.

[Lost Horizons]

Originally Posted by NPCampbell

If I'm not mistaken, this would fall under the 1st law of thermodynamics?

In a way of energy conservation, yes.

[Qmansailer]

Originally Posted by Lost Horizons

No, not really. What you are doing is similar to fueling one tank from another tank onboard while spilling a good portion of fuel overboard. It makes just a little more sense than fueling the tank from itself (while also spilling the fuel). By the way, it all has very little to do with the thermodynamics laws.

It’s just a simple engineering trade. I have 20 KWHr of electrical storage at 400V, and I need to supply a few hundred watts of power to the 12V system. I can either buy a DC/DC converter to do that at a cost of a few thousand dollars, or I can use all the existing equipment I already have and lose an additional 10-15% efficiency on those few hundred watts. With 22 KW of generator capacity if needed, those few watts won’t be missed so I went with the latter.
The dictionary defines thermodynamics as “branch of physical science that deals with the relations between heat and other forms of energy (such as mechanical, electrical, or chemical energy), and, by extension, of the relationships between all forms of energy.” so I do think it applies here.