Electric sailboat regeneration question
Reach
Posts: 107
The scenario:
I am converring my sailboat to electric propulsion and in doing so I want to be able to regenerate power while sailing. This would be accomplished by a spinning propeller that is currently attached to a diesel motor. After removing the engine and replacing it with an electric motor the propeller would have two purposes, one to move the boat and the other to create power. Obviously I am aware that electric and fossils fules have almost no comparison in terms of energy density. Yet with my solar array, wind generator and this electric motor I feel Id do fine. In other words this won't be a debate about how negative electric propulsion will be.
Question/s:
As I understand it the battery bank will only take a charge at a given rate, battery's don't like to charge quickly in other words. This being the weak link during a regeneration period. I see it as the motor being able to provide too much power to quickly for the battery's to charge efficiently.
My question is - If i were to select a higher voltage motor and a higher voltage battery bank then the charge time efficiency would increase, true or false? An exaple would be a 48 volt bank vs a 96 volt bank. The 96 volt would not required larger conductors and perhaps I could also charge the bank faster ?
For what its worth I considered super capacitors but as you may know they don't quite have the power denaity as a battery. Unless you know where I can purchase graphene super caps I'll need to use battery's.
I am converring my sailboat to electric propulsion and in doing so I want to be able to regenerate power while sailing. This would be accomplished by a spinning propeller that is currently attached to a diesel motor. After removing the engine and replacing it with an electric motor the propeller would have two purposes, one to move the boat and the other to create power. Obviously I am aware that electric and fossils fules have almost no comparison in terms of energy density. Yet with my solar array, wind generator and this electric motor I feel Id do fine. In other words this won't be a debate about how negative electric propulsion will be.
Question/s:
As I understand it the battery bank will only take a charge at a given rate, battery's don't like to charge quickly in other words. This being the weak link during a regeneration period. I see it as the motor being able to provide too much power to quickly for the battery's to charge efficiently.
My question is - If i were to select a higher voltage motor and a higher voltage battery bank then the charge time efficiency would increase, true or false? An exaple would be a 48 volt bank vs a 96 volt bank. The 96 volt would not required larger conductors and perhaps I could also charge the bank faster ?
For what its worth I considered super capacitors but as you may know they don't quite have the power denaity as a battery. Unless you know where I can purchase graphene super caps I'll need to use battery's.
Comments
good luck
If your hull speed is 3-5kts you can forget producing enough juice to fast charge anything. 48v is a lot for a <30' boat less then 10kts.
San Diego has the best electric sailing associations, I bet you have one locally as well. You'll find lots of people DIY'ing their systems between crossings, and see stuff you've never imagined both high tech and low tech.
The newer battery technology LiFePO4 used in electric cars are much smaller and a lot less weight than the older preferred AGM or GEL batteries. You can also use ~70% of their rated AHr versus ~30% for AGM or GEL. This means you can use a lower total AHr. The net result is the cost is quite similar for the same usable output.
They are also a much easier to transport. I have 2x 255AHr AGMs on my catamaran and they weigh 76kg each!
As for using the engine prop, have you considered that folding props give up to almost an extra knot while folded and sailing on ~30ft yacht. It is over a knot around cruising speed of 5-6kts on my cat. If you are then generating power from the prop I would guess the load would have even more reduction in sailing speed.
I have seen the towable generators used on sailing boats, but I have heard they are often attacked by sharks and the like.
While expensive, an MPPT charger (for solar panels) will extract another ~20% usable energy from your solar panels. Are you able to increase your solar array?? Maybe even a foldable set so that you can unfold while sailing???
It is nice to keep your system below ~60V because there are rules that classify voltages below this as Low Voltage and impose way less restrictions because they are considered less dangerous. It is true the smaller cable is required for larger voltages, given the same power. There are tables for cable size guides vs voltage/current on the internet.
So, I haven't been able to really help with your problem, but hopefully this info helps.
What sorts of electric motors have you been considering?
I dont race my boat she is my home so loosing speed won't matter to me. Heck I tend to sail best when a small craft warning has been issued - I have a very heavy displacement mono hull 32 foot long wit 20,000 lbs of displacement.
More solar panels are of an option, i've maxed out the real estate.
I am using 3 AGM 220ahour 12v batterys and they are indeed heavy but my old girl could carry 6 more without sinking the boot stripe.
I did forget about the 60 volt regulation thanks for the reminder.
I looked over many electrical systems and they all claim regeneration but I hesitate to believe these claims. Reason is, the voltages need to be higher than the battery bank and battery's can't charge to rapidly because of obvious reasons.
Will a dc motor produce more or equal voltage if its spined instead of being powered? I just loath the day the iron jenny is removed but don't want to jump the gun just yet.
Im heading south to New Zealand in 15 months so got to decide on something soon.
The 60V stipulation should also have a current and/or power rating... just saying 60V is like asking how long a piece of string is. Power is a better merit for defining a quantitative amount.
Have you installed LED lighting? Saves heaps. Particularly, change the Nav lights, especially the anchor light that is also often used as a running light.
What charging equipment (brands) do you use?
I have G4 5W halogen internal lighting. When we go cruising again I will replace the G4's with LED plugins <1W. As has been said, you will get a lot less.
What is your current power - presume something like a 40HP Diesel? FWIW when departing NZ, you need a certified liferaft. Presume you will have one anyway.
This will be a great trip. Have you looked at the winds and timing. We were going to do the round-the-world trip with Blue Water Rallies, but with the pirates this has ended
I have some interesting info on my website www.bluemagic.biz and you should also look at www.bumfuzzle.com too.
Personally, I think I would stick with the Diesel for the time being.
Would you mind posting a pic of your yacht?
If you go ahead with this, fit a as large propeller as possible, and one with symmetric propeller blades (forward-reverse equal). Check how much more engine power it takes to increase the speed the last knot to top speed. Approx 50% reaches the water as motive force. I would guesstimate this is around 5 kW for your boat. In re-generation - loosing that same one knot - you can hope to capture 30% of those 5kW = 1.5kW with the propeller, then loose some more (80% eff) in the electrical chain, leaving you with ~1.2 kW charging power. I doubt that this will be too much for your battery bank to manage. Go for lead batteries, weight is no issue in such a boat. They are SAFER, and much more easy to charge/control.
Erlend
It’s great to hear that you lived-aboard I love it and plan to live on the sea as long as I can.
I do in fact have all LEDs on board and use limited devices. I only have a Furno Radar and an "ARM" running Linux that I turned into a chart plotter with usb GPS. I use old style depth sounder that I made from brass hex stock and 100 feet of nylon line. I countersunk a hole in the end of the bass. It allows me to put peanut butter in the hole to bring up bottom soil for anchor selection.
I can stay out on the hook for quite some time with the 660Ahour bank not to mention my 300 Watt solar panel. I also use oil lamps for anchor light and cabin lights. Propane is my cooking fuel for now as I use 2 aluminum 6 lbs bottles that last about a month. I can carry these bottles throughout towns looking for propane without braking my back.
I don’t have a life raft and don’t believe in them. I have outfitted my dinghy as my life raft for many reasons. I decided to trust my life on a boat that I keep maintained daily as opposed to an inflatable that sits in a bag only opened once every few years. My dinghy is multi-purpose, oars, sails and motor.
I will stick to my diesel for a while but I am looking into replacing it and researching alternative systems. I tend to test my sailing skills by not using the motor unless necessary. It’s been a few months now that its been sitting but I do fire it up every 2 weeks just to see if he is still alive.
Erlend,
Thanks for the input I am going to have more questions for sure. I would like to disagree and don't want to use lead battery's only because of the maintenance issues that come with them. I will dive under the boat soon and measure the opening in the rudder for prop clearance.
Ill post a photo of my home soon if you want
About Lead / Lithium - I am not too hung up on which one is best for this purpose, but high-end modern lead batteries are very good and need no maintenance, whereas Lithium batteries are unavoidably some really dangerous firecrackers. That can be sorted by keeping them in fire retardant compartments, sure, but still.
I agree with you about the life raft question - it is kind of a false safety, which further emphesizes that the single most (only) really dangerous situation onboard is a fire. Avoid fires, and you'll be fine. That's why I am a bit weary about Lithium. Have you seen one burn?!
Erlend
Get one in a hard shell for mounting on deck. And get it checked at the correct service intervals.
An inflatable liferaft with a canopy is built to handle much worse weather than your dinghy, and odds are that the weather isn't 'all that nice' if something happens.
For how long do you run the diesel when you test it?
Furno radar?
I hope you mean Furuno, a reputable Norwegian manufacturer. ;-)
I think the smallest 'non-comercial' model draws around 2.2KW. It's probably the single most powerhungry piece of kit on your boat.
The thing about the dinghy in particular is that it simply won't let you survive if you have to leave the boat in rough weather. I know that we wouldn't have made it through fifteen minutes with the dinghy if we would have to leave the boat in some of the (cold and rough) seas we sailed. No way. The raft though, uncomfortable as it can be, is designed to survive being turned over in the sea. (And rough conditions are usually what'll force you to abandon ship - the worst scenario for a dinghy).
We kept the inflatable life raft in a standard easy-to-reach, fast-release setup on the deck. The dinghy was in a davit at the stern, and most of the time we towed the zodiac but sometimes we put it on the deck. It's better to have more than one option anyway.
-Tor
(Edit: I would like to add that many years ago I worked as an operator at a ground station where we monitored, via satellite, emergency location transmitters released from ships, boats and airplanes too far away from being picked up by other means than satellite. That's actually something like 99% of the cases.. Anyway, I've had the pleasure of being able to relay position data from emergencies far out at sea, where people in life rafts could then be rescued. So did several of my colleagues as well. The thing is, the people that survived long enough to get rescued were in life rafts, not in dinghys or anything like that. None. And this reminds me: Get an ELT. It's absolutely essential. Maintain it. Make sure that it'll come with you and won't get lost when you abandon ship. It _will_ be picked up by satellite.)
Another area of interest to me is that one can easily build a custom voltage regulator these days with MOSfets and op-amps. So power generated by ... say alternators ... can be harnessed to charge the kind of battery one finally selects. More source can become available, such as wind regeneration. Most marine lead acid are comparatively deep cycle as one needs to squeeze the most of batteries when in dire circumstances and far from short. Lithium ion and other newer chemistries tend to not tolerate more than 50% discharge in terms of peak voltage.. they suffer irreversible damage. On the other hand, the older lead acid seems to ignore many abuses.
I currently have AGM 2x255AHr and 1x80AHr for the engines. AGM are/were usedin aircraft. They are fully sealed - the battery compartment does not have to be vented - and they canbe charged at 14.2V with a smart regulator. I fitted 2x115A Bosch Alternators with external regulators ( I have a Smart Regulator fot this).
Gel and Lead acid batteries all require venting because of the possibility of Hydrogen emission - very dangerous otherwise.
The newer LiFePO4 batteries seem to now be a better choice than AGM.
Liferaft...
I would recommend you take a liferaft when you start your trip. There are anumber on the market - don't go for too large a capacity over the max crew you will have as they are more difficult to handle with less crew.
And remember, "you step up to a liferaft" which means never abandon ship until your boat is really sinking.
Diesel is quite safe but petrol for your outboard is not. Also becareful with your LPG too.
Learn to do all the enginemaintenance yourself. Take sail repair material and hand needle, twine and wax, and a hand (thimble - cannot recall exact name)
I can give you lots of other info if you like. PM oe email me.
Our cat is a production 35ft. I helpedbuild it and others including the wiring and electronics.
Sailmaker's palm, seaming palm, sail palm, sail needle palm or just "palm". There is also the roping palm, that is a bit more specialized in its use.
You can get high quality palms and other supplies from these guys:
http://rwrope.com
Is it a Westail 32? Or maybe a Thistle?