T-Pain Is On A Boat: Re: [Electric Boats] Re: Batteries for boats, and mobility

Sunday, December 13, 2015

Re: [Electric Boats] Re: Batteries for boats, and mobility

Maybe 80V or so ?

Its a hard question, in some sense.
And whether you are in the US or EU has a lot to do with it.

IF someone sells systems, and they have more than 80V, you get into major legal issues in the EU.
Thus, a manufacturer or kit seller would not want to sell over-80V systems, unless they are very much better technically.

This is one reason high voltage servo drives used to cost a lot.
Then, the chinese dont-care manufacturers collapsed the prices on the market.

I import and use AC brushless servo drives, at 220V AC for example.
Its just like std household mains stuff, and is pretty safe, in truth.

But:
Most boatbuilders probably dont actually know or bother with the electrical issue, atm.
The market is too new, in boats.
No mainstream electric boats, or kits, yet, in the EU, afaik.

Then again:
Looking at boats with major electrical mobility.
You would probably want to have exactly the same systems as in a modern, good, electric car, for the same reasons.
Except that cooling would be very simple, e.g. via cooling plate aka internal keel cooler.

The isssue is basically how much power you use and store, for how long.
Current systems = somewhat inefficient.
Probably about 10-15% losses full cycle, or 85% efficiency.
(Tesla quotes 96-97%. I believe them - after 12 years development. But theirs is a custom controller and motor).

In a 5(-15) kW energy storage system aka battery, you probably wont or cant afford much better, and the electronics are getting cheaper.
In a 90 kW production system, for very little more money or less than todays equipment/kit costs, you could have anything you want.
Thus tesla uses 400 V (== 380V ac, very common).

There are multiple solutions, all technically ok, and often complexity/simplicity/cost may be the drivers.

I think DC systems will evolve, in less than 3 years (available next year, already cheap, I think, from current manufacturers.)
Prices will collapse - just like pricing in dc servos, ac servos, pv systems (high voltage), VFDs, etc did.
For the same reasons.

Current asian manufacturers make really good products, really cheaply.
Inevitably, they will start to make them for the mobility industry as well (autos first, and then kits/forklifts/boats etc).
So, its maybe probable/likely new DC systems will appear.

Already, high power electric scooters and motorcycles are selling in large volumes (hundreds of thousands to millions), and have high exponential growth.

Example:
I swapped my old ac motor for a new ac servo drive, of 2.5 kW (on a cnc lathe).
(AC, 220V).
The new servo drive is about 3x more efficient, accelerates 10x faster.
The exact same situation applies to DC systems vs servos, on similar apps on machine tools == boating use (high traction, high power, harsh duty, low(ish) revolutions.

Since a 12 hp motor drives a 10 m sailboat well ..
Since tens of thousands were so equipped for a long time..
And a 4 hp electric == 12 HP ICE system (at comon 1:3 ratios seen to work well),
Probably a 3-4-5 kW servo system would be the ideal drivetrain motivator. 5kW since the price == same as 3 kW.

At such low powers, battery => inverter => AC motors make sense.

For mainly electric boats, re: sailboat, you would probably
1. want to be able to do 300 miles straightline.
2. accept 120 miles, for reduced cost.
3. use a proper propeller for maybe 15% efficiency gains

Example.
Barcelona - Palma de Mallorca, approx 200 km. Day+night. 111 nautical miles.
5 knots at 3.5 kW.
=> 22 hours.
=> 22 x 3.5 kW = 77.7 kWh.
With a 20% reserve, you would thus want an approx 90 kWh system.

If we accept a 30% reduction in mass over 3-4 years (likely, imho), the 300 kg battery mass is acceptable.
100 l of diesel, engine, auxiliaries etc == 250 kg.
Thus, the mass == equivalent to an ICE system, fairly soon.
(Sole 635 cc 11 kW marine diesel == 100kg, 100 l diesel tanks==100 kg, batteries etc 50 kg).

The biggest potential benefit/issue I think is getting much larger, much more efficient, props on electric sailboats.
Double the surface are, or so.
Excellent docs and youtube from a really smart guy, submarineboat.
He proved that prop shape/type can change efficiency over 300% (small model test, but still) !

So far, I have not seen anything re: props on electric stuff.
Probably exists, but most systems are just copies of old inefficient propellers, in my opinion.

No data anywhere I have seen re: propeller shape, sizes, rpm related to efficiency and electrics.
It obvious that wake, bubbles, cavitation, currents, noise = inefficiency.
Just like a modern motor (ac servo motor example) is very efficient, silent, and does not heat a lot, under 24x7 use continuously vs a std ac motor or dc motor.

It is likely, imo, that the proper solution is relatively much larger props, larger surface areas, much lower rpms.
None of these are commonly used on ICE systems, and thus conventional calcs are not too accurate.

Since ICE => good at 1000 rpm and up (2000 rpm), and electric/propeller => good at maybe 300-600 rpm, I suspect a huge potential improvement.
Note that a 30% efficiency improvement is => 30% systems cost, or 3000-5000-15000 $ potential savings, depending.

On 12/12/2015 14:54, Bob Moriarty moriartybob@yahoo.com [electricboats] wrote:

A real newb question:

What sort of DC voltage would you expect for the 2018-2020 time-frame batteries for a 10M, 5Kg sailboat?

--Bob Moriarty

1975 C&C 33-1 (10M)