Motor for 18ft Electric boat

[GijsW]

Hi everyone!

Together with a couple of friends I am converting a small 18ft canal boat (about 750 kgs unloaded) to electric.
We hope you can provide us with some help in the motor selection.

The required motor power is roughly 1.5 kW constant, with peaks up to 3 kW. The propeller shaft rotational speed is max 800 rpm.
We are planning to use a belt transmission (ratio obviously dependent on the motor, but probably around 1:3 - 1:4).

For us, it most important that the motor runs at a high efficiency at low powers (400-1000 W), and that the motor has a long lifetime (a couple thousand hours).

We plan on DIY'ing a LiFePo4 battery pack. We can cheaply get 3.2 V, 90 Ah cells, but these are 2 kg/piece which limits the maximum voltage of the pack since the battery has to be portable. Therefore, the max system voltage is 48 V, though lower would be better.

Currently, we are considering this (BLDC synchronous) motor:
- Golden motor HPM3000B 48V 3kW (https://www.goldenmotor.com/)

There is a performance curve of the motor on the website, but that is at max power. What would happen to the efficiency curve of the motor when lower powers are required? I ask this because we would have to select the gear ratio, and are wondering how to size that so that the efficiency is as high as possible when cruising at low speeds (while retaining peak power at max speed). Is the efficiency curve for BLDC motors roughly constant relative to torque, or more relative to rpm when the controller limits the power? My best guess was that it would be pretty much constant to torque, but will shift a bit to the left (so higher efficiencies at low torques) but I am not sure.

Also, would it be a good idea to undervolt the motor? Say we put in a 36V battery pack and run the motor on 36V instead of 48V. How much lower would the power and efficiency of the motor be? We would still be able to use the same controller, right?

If undervolting is not too bad for efficiency but only significantly lowers power, could we also run one of the following motors on, say, 36V? If their output power drops by half, that wouldn't be a issue for us.

- QSmotor QS138 72V 3kW (http://www.cnqsmotor.com/en/article_read/QS%20138%203kW%2072V80KPH%20Mid%20drive%20motor%20with%20new%20appearance%20belt%20design/869.html)
- LMX motor 60mm 72V 3.1kW (https://lmxbikes.com/en/drivetrain/138-moteur-lmx-60mm-2018.html)

Ideally, we would find a high efficiency motor which we can run at 24V, get peak powers from of 3 kW for under €750 including vat and shipping to the Netherlands.

 

[amberwolf]

While it is for a different purpose (bicycles), the http://ebikes.ca/simulator may help you see how the various parts of the system are interrelated, and how voltage vs winding vs load, etc., affect efficiency, speed, etc.

Read the whole page first so you know what everything is and does, and then setup a bicycle system with one voltage setup on System A, then a lower voltage setup (proportional to the difference between the "intended" voltage of the motor you're looking at vs the voltae you want to use it at), and play with different loads, etc, to see how things are affected.

YOu can then setup different systems to see what effect each thing has on the outcome.


Sorry I don't have any direct answers for your questions, but hopefully the above will help get you started.

 

[john61ct]

Thunderstruck is a great source for OTS kits

 

[GijsW]

Thanks for the replies!

The simulator is incredibly helpful. It appears the efficiency is proportional to the torque (it does go down a bit for lower voltages).
When throttling the motor, the max efficiency goes down, and the max efficiency point is found for lower torques.

We are probably going to go with the 3 kW golden motor with a 36 V (12S LiFePo4) battery.
The max output power should be around 3.3 kW, which is enough for us.

For the controller, would you recommend the Golden motors VEC-200 or something else (like a kelly controller, which are also cheaper, like the KLS4812S, https://www.kellycontroller.com/shop/kls-s/)

Thunderstruck is a great site indeed, unfortunately it does not ship to the Netherlands

 

[GijsW]

Oh, one more question.

I was under the impression that brushed dc motors were quite inefficient (around 60-70%)
Now I'm seeing some PM brushed DC motors with 90% peak efficiency (motenergy for example).

Would these be a good option as well? And what efficiency would forklift motors roughly get?
They go for around 100 bucks (example: https://www.machineseeker.nl/jungheinrich-f14-25/i-4387933)
Am I correct that these are series wound motors? Are they less efficient than the motenergy PM brushed motors?

Help would be much appreciated!

 

[Dui ni shuo de dui]

Hi,

I'm not sure what is exactly the objective for your project. What is this boat intended use? I'd guess low speed cruising in the canals?
Also, why do you seem to care so much about efficiency?

Since your budget seems to be relatively low, I would try to save money on the powertrain as much as possible and use it for the battery. The motors you chose are valid choices, but they are totally overkill regarding what kind of performance you said you wanted. I'm pretty sure these can take 15 000watts peak easily (provided you got the right controller and battery of course).

So, the idea would be to find a second hand 10 inches hub motor, since they are widely available and you can probably find some second hand motors for really cheap (not sure in the netherlands, but here in China a used 1000Watts motor can be found for around 20 Euros). Hundreds of millions of these motors have been used all around the world, shouldn't be too hard to find.

Given the intended use you described (1500W continuous and 3000W peak), basically any 1000-2000W rated hub motor will be able to deliver reliably that kind of power, so don't bother buying some expensive stuff. A 1000W rated hub can even be able to take 5-6000Watts peak, with loads of torque (so you can use a bigger propeller while running at lower RPM).

You'll be able to gear it up or down to make it run at its optimal efficiency rpm if you want, just need a chain/sprocket or a belt system. Sure it will take a tiny bit of efficiency, but money saved on the motor turns into money invested in the battery, which is, in my opinion, the smart move to do.
So, basically, instead of focusing on your motor efficiency, I suggest you to focus on your battery quality and size. Good cells will last longer, will have less internal resistance (hence, much better efficiency), will give you more power and reliability. Also, the higher the voltage, the higher the efficiency, so actually if you care about that you should run at higher voltages, lower amps. Won't matter much at that kind of low power though, I'd just go with more capacity, it's a 750kg boat, not sure space is your primary concern, you can probably fit a huge battery in there if you want (unlike in our motorbikes :wink: )...

The only drawback I see is that fitting a hub motor in a clean/good looking way might be a little bit more challenging. But you can offset the motor from the propeller shaft and put it in some convenient place, hide it inside some covers... Just be creative!

Hopes this brings an interesting perspective. Whatever you decide, good luck on your build!

 

[amberwolf]

There are some boat motor conversions here on ES (and elsewhere) that use hubmotors to drive a chain or belt that then drives the motor shaft. IIRC one of them was an outboard motor conversion by Bazaki, but I'm not sure. It's in the Watercraft section of the forum somewhere.
https://endless-sphere.com/forums/viewforum.php?f=39

 

[GijsW]

Thanks for the replies!

The intended use is indeed low speed cruising in canals, though it should be able to do around 9-10 km/h with headwind and 8 people on board for shorter periods of time.

The reason I care so much about efficiency is that the batteries are to be charged at home, meaning we have to carry them to and from the boat every time. Higher efficiency results in less battery weight.
Also, we're going to spend almost 2 grand on batteries, so a higher efficiency drivetrain will partially pay itself back by saving on batteries (10% higher drivetrain efficiency saves about E 200.- in batteries).

I like your ideas about using a hub motor. However, it does appear there is less availability here than in china/US. 1000 W hub motors go for around 100 euros. I can get a 3 kW golden motor for E 375.- including shipping and taxes, which also seems like a good option (mounting will be much easier). The boat currently has an inboard diesel (with engine compartment) so mounting is no issue, but I want it to have a professional look so potential resale (in a couple of years) will be easier.

Could I use the KLS6018N (https://www.kellycontroller.com/shop/kls-mn/) kelly controller for the goldenmotors 3kW motor? Does anybody know what exactly the difference is between the KLS-H and KLS-N controllers? Or any suggestions for better controllers? What I like about these controllers, is that I can program it so that the potentiometer throttle can also be used to reverse.

Thanks again!

 

[alpine44]

Don't forget to take a look at the belt driven alternator starters ( BAS) from some hybrid vehicles out of a junk yard aka car recycler. You can get battery, power stage, and motor from there. All you have left to do is to connect a Lebowski or vesc brain to the power stage (or hack the OEM's CAN protocol) and build a reduction drive that ties into your boat's propeller shaft. The other advantage is that most of the hybrid vehicle stuff is water cooled, which is ideal for a boat.

As far as the weight of the portable battery is concerned, you can always break the battery up into smaller modules that are connected in series when in the boat. That's how large electric vehicle packs are assembled. (Do NOT connect multiple modules in parallel unless you fully understand the ramifications.)

Also take a look at the calculators at boatdiesel.com to double check how much power you need for your hull and what the ideal rpm are for your propeller.

 

[memy]

Am I missing something here, if weight is an issue why use lifepo4?

 

[Hillhater]

If money is tight, you ought to consider a brushed motor system. At your power levels and casual use application, a brushed motor would be fine.
Controllers are cheaper, systems are simpler, problems easier to find and fix.
Maybe look for a old electric golf cart motor and controller.
Efficiency is a theoretical distraction, you can gain 20% run time simply by tweeking the speed down a couple of km/hr. Or cleaning the bottom of the boat hull !

 

[john61ct]

Dutch canal boats have no access to mains power hookups?

 

[GijsW]

Thanks for the suggestions guys!

We wanted to use lifepo4 since they are fire-safe, cheap, have insane lifetimes, are quite tolerant to higher operating temps and are easy to assemble (large 90ah cells). However, we just decided to go with 'regular' 18650 lithium cells in order to achieve higher voltages and a lower weight. We'll assemble 20S packs (pcb protected, and bms of course) for 72 V operation.

The 72 V opens up paths to other motors. We're probably going to go with either the 1000 or 2000 W (QS90/QS128) QSmotor with a Kelly or Sabvoton controller (I read that the Sabvoton has a bettery overall build quality, and I like that you don't need restarts between adjusting settings, but I haven't figured out whether or not it has joystick mode, which is a must).

About the brushed motors, I have no objection to using them in general, but I can't really find setups much cheaper than going the bldc+controller route, so I figured I'd just spend a little bit more on a bldc system. Also, our budget is not that restricted. For instance, the QS90+controller would be around 450 euros including shipping, which would be fine.

And about waterside power hookups in Amsterdam: Unfortunately they don't exist, which is quite ridiculous considering non-electric boats will be banned from the city center from 2025 onwards.

 

[john61ct]

so they will!

LFP cheap?

I would really advise sticking to that rather than the much higher fire risk with other chemistries.

There are tiny cylindrical cells in LFP, but 60Ah cells much easier to build from, very easy size to carry, maybe 40Ah if smaller / weaker humans involved.

I reco CALB, GBS, Sinopoly or Lithium Werks (A123).

Hard-cased prismatic rather than DIYing with bare pouches.

 

[amberwolf]

If you do want to go with non-LiFePo4 cells, then for the size of pack you need, especialy for somethign that has to be transported frequently, I would recommend using stuff like EV-grade large-format cells. Some can be found used, like old Nissan Leaf packs (scrapped from totalled cars; there's a fair number of types to choose from out there, but these are bolt-together so easy to reconfigure), or new cells, like teh EIG NMC cells Jimbob01 is selling over in the for-sale-new section here on ES (he's in teh UK).

These are more likely to be more firesafe than 18650s (without special cooling depending on the loads you put on them and the specific cells you use), and MUCH easier to assemble into large packs.

 

[GijsW]

Ok we went with LiFePo4 after all .
Bought a little spot welder and a bunch of 32700 LiFePo4 6Ah cells.
Going to assemble a 24S5P pack first. The idea is to make multiple packs, but if the LFP turns out to be too heavy we could opt to switch to NCA/NMC for our next pack.
That will depend mainly on real consumption of the boat (which will decide how many kWh's we'll need).

We also decided to go with the 120H 2000W QSmotor. The peak power of about 4.5 kW will be a bit extreme and unneccesary, but also fun! We're gonna put a video on youtube of the conversion process and finished result. I'll post a link here when it's done (in about 2 months). I'm just trying to decide on the motor controller now. The Kelly controller KLS7212N (60A continuous 160A peak) seems to be powerful enough. Or do you guys think we should go with the more powerful KLS7218N?

Thanks all!

 

[CobraJet]

If money is tight, you ought to consider a brushed motor system. At your power levels and casual use application, a brushed motor would be fine.
Controllers are cheaper, systems are simpler, problems easier to find and fix.
Maybe look for a old electric golf cart motor and controller.
Efficiency is a theoretical distraction, you can gain 20% run time simply by tweeking the speed down a couple of km/hr. Or cleaning the bottom of the boat hull !

Can you recommend a brushed controller. Needs to have reverse.