Please help me decide LiPo/A123 (electric outboard)

[Bazaki]

Hi there,

I've been reading alot the last few weeks about different kind of packs.
My mission is to build an Electric outboard with 15KW to get in plane with a inflatable boat.

I want to use following setup :

http://www.plettenberg-motoren.com/UK/Motoren/aussen/Predator37/Motor.htm 1000 euro
http://toprc.eu/jeti-spin-300-opto-d 500 euro
8x Turnigy 6S 5000mah to make one 12S 20ah 570 euro
Second hand broken 10HP Yamaha outboard 200 euro

But I want to sail this boat with my wife and daugther also and putting so many Lipo's together could be dangerous. Although I would store them in a metal case which can be thrown out of the boat.
I choose the Lipo because they are very cheap and I have really good experience with them, cheaper than A123 ( I think )the problem is the charging, to buy several good chargers a 1000 watt power supply would cost about 1000 euro. And a lot of work to charge each single pack.

As a "project" it's fun to watch and monitor Lipo's being charged but as a daily used boat to go out with the familiy it would be nice to have a plug and play battery pack which is easy and safe to charge and handle.

I have seen affordable 48v 20Ah A123 packs, but usually with a BMS that handle only 100A (totall pack).
And my theorie was, if a Lipo will be dead, I can replace it, if I have a stock A123 48v 20ah pack and 1 cell is dead, how can I replace this one cell ?

I'm looking for some advice, just to let you know, I don't want to sail on 15kw the whole time, just use it sometimes. 5kw will be enough and only for a few minutes.
Any other ideas for my setup maybe ? I didn't order anything yet !

Thanks !


( EDIT ! : With the A123 packs, I just mean a stock 48v pack, other kinda brand is also fine, as long at it is a safe pack )

 

[memy]

Sorry to rain on your idea but.
A 20AmpHour 48V battery has 960watt hours. To provide a 15kw peak the pack needs to provide peak amps of 312 amps (if the battery voltage did not sag below 48).
That’s 15C discharge so A123 or decent Lipo is viable, however the fun would last about 4 minutes before battery is flat.
Even pushing a boat with (2.2kw) with perfect efficiency gives you about 25min run time. Use a efficiency of %80 = 20min.

Boats at planning speed need high power to maintain. To get a boat on plane with two adults and two kids regardless of hull design will take a fair bit of power to maintain.

The motor and controller you have referenced are not really suitable there appears that there is no performance data available but at the end of the day there is not enough mass to sustain decent power without elaborate cooling. Google the "Brushless Etek Motor" as there are outboard conversions using this motor.
Or a bit more out there is to use the Model: HPM5000B -- High Power BLDC Motor From http://www.goldenmotor.com/
I say "out there" as I have yet to see anything on the web about this motor been implemented in anything.

 

[Lock]

...to get in plane with a inflatable boat.

An inflatable anything is usually not a good idea performance-wise... ie the flex in the hull eats energy so however you power the thing you will need more of it (power.)
Why an inflatable? Just happens to be what you have on hand? When you say "sail" you don't mean *under* sail ie with a cloth sail and spars some of the time?
tks
Lock

 

[Bazaki]

With sail I don't mean to say sailing in the wind. Just "drive" on the water with a boat and electric motor.
An Inflatable since they are very light and have a flat and stiff bottom. I think it's perfect to get early in plane.

http://www.youtube.com/watch?v=SrqqvDiNyYY
They did the job already!

The 15kw I will only use for a few seconds just to make a very fast start out of the water.

At our lake everybody is cruising there boats with a 800 watt motor, with about 5 km/h.
The max distance on the lake is only 1km, so I need my power only a few minutes and I charge in my garden which is on the same lake.

The golden motor is too weak I think, I prefer an overkill of speed so I can give less throttle.

I agree that my RC setup is small and can't handle the heat so good as a bigger EV motor, but maybe I can make it watercooled.

So I really need a 15kw motor, but not too heavy.

But what about the batteryquestion ? I only can find 48v packs with a BMS that can stand 100a burst and normal 60a.

 

[BMI]

You might find the attached article on electric boating to be of interest.
View attachment watts up.pdf

 

[Jeremy Harris]

Bazaki,

When you asked a similar question on the electric kayak thread (here: http://endless-sphere.com/forums/viewtopic.php?f=7&t=14640&p=223673#p223673) I gave you an answer that pointed out some of the limitation of using electric propulsion on fast boats. You've had further advice above, pointing out that you'll need a LOT of battery capacity and reinforcing my point that an inflatable is a bad idea, as they are inefficient and need a lot more power than a properly designed hull.

You need to get the boat sorted first, before you even think about the propulsion system. Look for the lightest possible hull you can get, with a shape optimised to plane on very little power (take a look at some fast dinghy hulls for ideas). Then you can start looking at designing and building an electric propulsion system, but bear in mind (as I've already pointed out to you) that using an outboard leg and gearbox will be very inefficient, as it will have a lot of internal drag and it's unlikely that the gearbox ratio will be OK for a powerful brushless motor, like the Predator.

You say that you need 15kW, but how have you worked that out? Do you know the resistance curves for your hull, at the range of weights that you're likely to be operating at? There's a lot to be gained by working out what you really need, before charging off and assuming that you need a very expensive, very powerful, Plettenberg brushless motor.

If you're intent on spending that much money on the electric propulsion parts, then why not just buy a Torqeedo motor? ( http://www.torqeedo.com/en/hn/home.html ). They are pretty efficient and may do just what you want on a nicely designed hull. Take a look at some lightweight ply hull designs, they will be cheaper, more efficient and lighter than an inflatable, meaning that you'll get better performance, need less power and hence a smaller battery capacity.

Jeremy

 

[Bazaki]

Thanks for the replies !

The Torqeedo has too less power, the stock 11 KW outboards will cost about 8000 USD.
The budget I want to spend is about 4500 USD incl batteries and charger.

Another boat with less weight is a good idea and a better hull also......

But look at this: http://www.youtube.com/watch?v=FT4m-c1UnMY&feature=related

Now let's remove the petrol engine and put a big ( brushless ) E-motor on top of the shaft with same RPM's with 10-15KW. ( no gearing, K/V of predator 37 should be perfect )
What part wouldn't work out ???

( Please forget the duration, 4 minutes full throttle is good enough, later I can add another pack in parrallel )

 

[Jeremy Harris]

That video was using a 7.4kW motor, about half the 15kW you mentioned earlier as being what you wanted. If you decided to use a decent hull, then you could probably get this sort of performance on about 4 or 5kW.

Matching the motor, reduction ratio and prop to the hull is critical to getting good performance and efficiency with electric power. You have to understand the very different torque/rpm characteristics of an electric motor, compared to a petrol or diesel engine. The compromises that lead to sub-optimal prop sizes and gearbox ratios on outboard motors just aren't there with an electric motor. For example, an electric motor won't "bog down" from a standing start, so a larger diameter (and higher efficiency) prop can be used. This will need a bigger reduction ratio, or slower rpm motor, to work well,

The prop diameter, pitch and rpm are highly dependent on the hull drag, so you really do need to know the characteristics of the hull before you invest time and money on something that most probably won't do what you want.

I started my boat project thinking just as you have, that I could use an off the shelf prop and a simple right angle gearbox leg. I've learned the hard (and expensive) lesson that making an electric system work well needs a good understanding of the hull characteristics. Only when you have this can you decide what motor, battery, gearbox ratio and prop will work well.

Sorry to sound a bit negative, but I'd hate to see you spend a lot of money on stuff, only to be disappointed with the outcome.

If you want to make something that's inefficient, but probably OK for short duration use in an inflatable, then I suggest you look at a cheap experimental solution, using a $400 brush motor (like the Mars), an old outboard leg, a $200 Kelly 200 amp brushed controller and four relatively cheap golf cart type 12V lead acid batteries, wired in series. It won't be elegant or efficient, but it would be as cheap as it gets for this power level and relatively easy to put together It might well do what you want. at the very least you'd get a good feel for the sort of power you really need and the way that electric propulsion places different demands on the prop, gearbox etc.

Jeremy

 

[Bazaki]

Thanks for the helpful information ! Good work !


I already have this 6.5KW brushless Turnigy 130KV motor from hobbycity, it's new and I don't use it. Maybe this a good motor to experiment with.

Just mount the whole thing together and see what it will bring us.

Could a Kelly brushless controller also work with a Turnigy brushless motor? I mean it is a motor for the RC, and the Kelly kinda controllers are not.

 

[cell_man]

I have seen affordable 48v 20Ah A123 packs, but usually with a BMS that handle only 100A (totall pack).
And my theorie was, if a Lipo will be dead, I can replace it, if I have a stock A123 48v 20ah pack and 1 cell is dead, how can I replace this one cell ?

I'm looking for some advice, just to let you know, I don't want to sail on 15kw the whole time, just use it sometimes. 5kw will be enough and only for a few minutes.
Any other ideas for my setup maybe ? I didn't order anything yet !

Thanks !


( EDIT ! : With the A123 packs, I just mean a stock 48v pack, other kinda brand is also fine, as long at it is a safe pack )

If you referring to the cells that are currently available on ES, then they come come with whatever BMS you require. Just needs to be requested and ordered in. Packs supplied will use screw terminals so should be no problem to change a cell if it's required. Far safer than RC type Lipo, much better lifecycle, similar or better performance, similar or better energy density and similar price. 15KW is quite possible for bursts but it would require higher currrent and less volts due to sag on a 16s 1p pack 20Ah pack. A BMS by Ggoodrum maybe your best bet at that kind of current level, but if you're happy to run RC Li Po without BMS, then why not LiFePO4. I suppose at least on a boat you won't have far to throw a Li Po pack if it goes up in smoke :lol:

 

[Jeremy Harris]

Thanks for the helpful information ! Good work !


I already have this 6.5KW brushless Turnigy 130KV motor from hobbycity, it's new and I don't use it. Maybe this a good motor to experiment with.

Just mount the whole thing together and see what it will bring us.

Could a Kelly brushless controller also work with a Turnigy brushless motor? I mean it is a motor for the RC, and the Kelly kinda controllers are not.

An RC brushless motor that is rated at 6.5kW on the Hobbycity site probably has a real rating in a non-RC aircraft application of perhaps half that, if you're lucky. They may, just, peak at the Hobbycity rating for a few seconds, but they won't sustain a few minutes at that power without cooking, especially when they are used in an application where there isn't a lot of airflow through the motor (even with airflow, they won't sustain the Hobbycity rating, in my experience).

For example, I tested a 2.8kW rated brushless motor on a home made outboard leg, driving a fairly heavy 16ft boat at around 5kts and it got pretty darned hot. According to the Watts Up I had hooked up it was running at just over 500 watts, but it got too hot to run for more than a few minutes at that power. There is no way that it would have run at 2.8kW for more than a few seconds without burning out. For use on a boat you need to be able to sustain a pretty high power level for a reasonable length of time. Even just the four or five minutes that you're looking for is going to get one of these small motors hot, if run at anything close to it's rated power.

The Kelly brushless controllers can be made to work OK with bigger, slower turning, brushless RC motors. You just need to fit Hall sensors to the motor (as quite a few of us here have already done).

By all means experiment with the Turnigy motor you have, just don't expect it to perform like an 8 or 9hp outboard. You may well get away with running it with a cheap high current RC ESC, as a boat prop presents a load proportional to the cube of it's rpm, so doesn't need a high starting torque. I bought a couple of Swang Hobby 120 amp controllers that have turned out to be pretty tough and they only cost around $40 or so each.

Jeremy

 

[liveforphysics]

Jeremy- I run 100amps @ 100v through the big hobby city motor. The current quickly drops off fairly quickly as RPMs increase of course, but I've not burned a motor up yet. I'm only giving it this sort of power with a very small duty cycle though (unlike a boat that is 100% almost always), unless I'm climbing a long hill or something, in which case the motors do get hot, but they also heat up the giant heatsink they are bonded to, which has a pair of CPU coolers and fans attached to keep things cool.

The fast electric hydroplane guys run 3-5kw for 100% duty cycle through RC motors smaller than what we use, and often burn up controllers (even the water cooled ones), but rarely burn up a motor (which are water cooled also of course).

 

[Bazaki]

I've followed your bikeproject and read the whole topic, amazing cool !!

The 6.5KW it just to play around and see what happens, the Jeti Spin Opto 300A has a thermal protection and overload protection, So I can take the risk to push the Turnigy motor to the max !

I expect about a 4 HP outboard motor performance out of the Turnigy. If the setup runs fine but not fast enough I'll order the Predator 37 15KW.

About the Ggoodrum cells, is this a nickname ? or brand ? How to find it ?

 

[cell_man]

I've followed your bikeproject and read the whole topic, amazing cool !!

The 6.5KW it just to play around and see what happens, the Jeti Spin Opto 300A has a thermal protection and overload protection, So I can take the risk to push the Turnigy motor to the max !

I expect about a 4 HP outboard motor performance out of the Turnigy. If the setup runs fine but not fast enough I'll order the Predator 37 15KW.

About the Ggoodrum cells, is this a nickname ? or brand ? How to find it ?

Ggoodrum makes a BMS and there are threads in this section about it. I supply some rather special cells and again there's a thread in this section about them and something in the for sale section too. Think RC type li po performance with none of the drawbacks.

 

[Jeremy Harris]

Luke, you've hit the nail on the head with the mention of duty cycle, this is the killer for a boat motor. As you rightly say, a boat is going to load the motor at a high average power, something these small motors can't sustain, as they can't get rid of the heat fast enough.

I mentioned on another battery thread the ratio of peak to average power that road vehicles use; typically the average power is somewhere around ten percent of the maximum power available, less for really high performance stuff. I measured the power that my old Prius used, it was around 12 to 13hp average over the three years I owned it, yet the maximum power was over 100hp. Boats run at high continuous power, it's not uncommon for them to run at a continuous 70% or more of full rated power for long periods, which is way more than a car or motorcycle's 10% or so.

These small RC motors can only deliver loads of power for short periods before they start to get hot. I was a bit surprised just how hot my TowerPro 5330 got when running at a continuous 500+ watts, although not having a good airflow running through the motor probably made it worse. I suppose it should really have been that much of a surprise, as, assuming that the motor is around 85% efficient, it would have been trying to get rid of about 75 watts or more, which is asking a lot from such a small case.

In the case of the bigger Turnigy motor, at it's "rated" 6500 watts it will be trying to get rid of nearly a kilowatt of heat if run at it's "rated" power, which is why I maintain that these ratings are just mythical numbers, plucked from the air by the manufacturers. We know that a big bike hub motor, rated at much less than 6.5kW, will overheat when run at maybe 2 or 3kW continuously, so a motor that's less than a quarter the size can't hope to get rid of twice as much heat.

Jeremy

 

[liveforphysics]

When these motors are bench tested by a manufacture, it's always just driving a prop, blowing thousands of cool air across the motor. You would be really amazed at the power a tiny inrunner motor powering a ducted fan in an RC jet can handle. 2-3kw into a motor 30mm around and 90mm long and has bad efficiency is not unheard of, and it works out because it's got a constant 150mph stream of incoming cool air rushing past it when it's running. Same with a hydroplane, when its' up at speed with 2-3gal/min of water flowing through that case, I've heard they actually reach a point where they de-mag the magnets, or the controller blows, but the motors are virtually impossible to kill from power. With a boat, you're sitting on an unlimited supply of a fantastic heat conducting and absorbing material that is almost effortless to passively transfer on a moving boat. Might as well use it to your advantage IMHO.

[youtube]VgqT0-PocQ[/youtube]

But yes, I do agree that manufactures just pick a number they think could be in the ballpark. Some companies and/or customers do decent testing with various props and voltages though. When running a prop, they measure counter torque on the fixture the motor is mounted on, and RPM with a laser tach, and this gives them a mechanical power number, which is easy enough to take measured electrical power input and find efficiency. It's really interesting to look at the measured results from various prop/voltage combos. The same motor may be 80% at a given voltage/prop, and when swapped for a different setup, that same motor might be in the low 90% range, which would mean it's got over double the power handling ability of course, just from a better voltage/prop choice.

 

[Bazaki]

I totally agree with the heat issue, A bike , or anything that "roll's" will take less avarage power than a boat.

That's why I want to use an overkill of power. Like the 15KW Predator and use only 5kw of real power and maybe 10kw for 30 sec.
View attachment Naamloos.jpg

My distance is only about 500m, but I want to get there as fast as possible. With 10kw I hope I can reach 40km/h so that would take 45 sec. to get there.
Normall familly cruising speed will be 5 km/h with about 0,5kw. But just to cross the middle of our lake in 45sec. would be fun !

So I will never use full power for longer than about a minute. at the shaft of the motor I will install a FAN, and another stand alone fan for when running the motor.


http://www.youtube.com/user/FreEdl63#p/u/15/2E32KLzAoDs I've had a lot of contact with this guy, he is using two of the smaller predators 30.

 

[Jeremy Harris]

Luke,
I agree that high speed forced air cooling makes a big difference, as does water cooling. Apart from making the motor survive, they also get more efficient if kept cool, due to lower winding resistance, which is one of the reasons for me fitting my motor in an underwater pod. I'm toying with the idea of filling the pod with very thin oil, to keep the seal lubricated, provide a hydrostatic balance at the seal to make it less likely to leak and to aid heat conduction from the motor to the case. What I'm not yet sure of is the amount of drag the spinning rotor will create. I've smoothed the inside of the rotor with high temp epoxy, and turned it to a smooth internal finish over the magnets, so hopefully this will reduce the viscous drag a bit. I need to try it and see, maybe by just dunking the motor in a can of oil and seeing how much the unloaded current increases.

Bazaki,
You may be very surprised to find that it most probably won't take anything like 0.5kW to drive your boat at just 5km/h with the family on board. I easily powered a pretty heavy 16ft boat, with two on board, at nearly twice that speed on around 0.5kW. My current project boat will use less than 100 watts to do 8km/h with two people on board; in fact the target is to get it to do this speed on around 70 to 80 watts. The secret is all in the design of the hull, get that right and the power needed drops a great deal, making everything a lot simpler.

Jeremy

 

[gestalt]

Growing up on the puget sound we used hydrofoils on our 16' alluminum smokercraft. Just by using small foils on the hull and on the four stroke 48 evenrude outboard got us somewhere in the neighborhood of 15% fuel efficiency increase. More and more I feel that hydrofoils are the key to making e-boats viable.

 

[Jeremy Harris]

I tend to agree, anything that reduces the hull wetted area will make a difference in viscous drag pretty much in direct proportion to the reduction in wetted area. Similarly, anything that reduces wave-making resistance, like lifting the hull clear of the water, makes a huge difference in high speed drag.

What surprises me is just how little attention has been paid to efficient hull design. It seems that the ready availability of powerful engines has made hull designers lazy; they just fit a big engine to overcome the gross inefficiency in the hull design. Some of the most efficient hulls were designed hundreds of years ago, most of the poorest have been designed in the last fifty years. It's about time that we paid as much attention to efficient hull design as has been applied to efficient cars over the past twenty years or so.

Jeremy

 

[Bazaki]

This is Denny from Kayo Battery Co., Ltd. Nice to talk with you on our web messenger. As per our talking you are requesting 24V40AH LiFePO4 battery pack with Max continuous discharge current of 312.5A for your boat application. After confirm with our engineer I am glad to tell you that we can make the battery pack to you request.



To meet your requirement we will have to make some change on the BMS of the battery, so the lead time for your first order will be longer, about 40 days. Following is pricing information for your reference:

Model: KFL2440
Voltage: 24V
Capacity: 40AH
Dimension: 235*236*190mm
Including BMS
Max continuous discharge current: 350A
Unit price: USD788.2 FOB Hongkong
MOQ: 10 pcs
Payment: 30% down payment and balance before shipment




This pack should be fine too I think. 48v 20ah should be the same price I think. And they just can change and adjust the BMS and it can handle 350A

 

[Jeremy Harris]

If you only want to run the motor for a few minutes (I think you said 4 or 5 minutes earlier), then why not just go for a couple of cheap 12V lead acid leisure batteries? They would be much, much cheaper than any lithium battery, not need a BMS, could be charged with any cheap car charger and would easily deliver the very high current that you think you need, for the short run time you're looking for. Even a really cheap leisure battery will happily deliver 400 to 500 amps; if you wanted something a bit more robust and sealed, take a look at something like the Hawker or Optima AGM type batteries. I have a small Hawker PC680 sealed motorcycle battery sat by my desk as I type this (it's the starter battery from my old aeroplane). It cost about $100, weighs around 7.5kg, is sealed and will work any way up, delivers 680 amps peak or around 400 amps continuously and has a capacity of 16Ah. Two of them, or maybe a couple of slightly bigger batteries of a similar type, might well do what you want for a lot less money and hassle than a lithium battery pack.

Although lithium batteries have some advantages, lead acid still pretty much has them beat if you want very high current for a short duration. I had this discussion a short while ago with a chap who was building an electric hill climb race car, where we concluded that if you want short duration, very high power, then lead acid still has the edge over other battery types.

Worth considering for your project.

Jeremy

 

[Bazaki]

True ! But I don't like the weight. I've been thinking of 4 Optima Yellow TOPs. I already have 2 of them( see winch video ).
That would be 80KG and for a future bike-project I can't use them either. The Lipo pack is perfect but the number of charge/decharge cycle is a bit low I'm afraid. If I am really going to use this boat every day once or twice a day during the summer than the Lipo's will be used about 200 times in 4 months.

And 200 times is about their lifetime ?

And about the motor, I have been thinking. if this really is going to work out fine like I hope it is working than I need more lipo packs for longer duration. But this 1.9kg 15kw brushless can still handle the 10kw for about half a minute ? Every half a minute I have to take care for a good cooling down. So A bigger stronger motor with even more power should handle this longer than half a minute. So I agree with your statement from last week !

http://agnimotors.com/95_Series_Performance_Graphs.pdf

Like this one, It is still not too heavy to lift it up and it should handle 10kw without a problem. If I still would have power problems I can increase the voltage to 72v for an extreme power output !

How does this sound ? I can't find other 11kg motors that have a power output of 15kw or more.

 

[curious]

While this is OT I second the suggestion for hydrofoil for high speed cruise. Then optimize the displacement hull for really low power/low speed cruising.

Do not start from spending big $ on large lithium pack !!! Make sure everything works, do all power measurements and hull/motor experiments with a cheap battery. One minute run time is plenty to acquire multiple power/speed points and then design your battery system accordingly.

 

[Bazaki]

Well, the boat shouldn't be the problem. A 340cm Inflatable is the choice, I've seen so many video's of these boats with 5-10hp. That has to work out.

The setup would now be a Agni 95 motor and a Kelly controller.

About the battery pack and charger, I was thinking about the following:

9x Turnigy 6s 5000mah making 18s 3p = 66,6v 15.000mah
A Zivan NG3 72v charger to charge the above pack at 2C, so it will be full in half an hour. ( very handy, I could charge at other locations near the water )
The charger would be overkill, but if everything runs fine I could make buy another 9x 6s 5000mah.

And balance each 6s 3p with a balancer.

I would then have 66,6v 30.000ah and could be charged in one hour.
A I charger 206b could charge at 300watt and balance also, that would be nice, but if I really have a big pack. then 300watt each charger would go too slow.


Question: A lead acid battery which say 12v 100ah would have 100ah when decharged with 5a for 20h
Decharger with 100A would give a result of about 50ah or less, right ?

What about a Lipo pack ? They claim 6s 5000mah. but when does it have 5000mah ? Decharge at 1c ? what about 10c or 30c decharge ?