Boat trolling motor efficiency

[jag]

Has anyone taken a Minn-Kota or other brand trolling motor apart? Are these usually cheap brushed motors? Or nicer brushless?

I have a 16" Folboat Greenland, with rudder and foot steering. I was hoping to take the lower end of a trolling motor and integrate into a custom made rudder. Hoping for stealth and decent efficiency.

 

[BMI]

Minn-Kota and similar trolling motors have a very low overall efficiency of less than 20%.
Torqeedo motors have a much higher efficiency of around 50%. A Torqeedo motor will provide double the run time/range per charge compared to if you were using a Minn-Kota or similar trolling motor.
You might want to check the efficiency curves and technical info on the Torqeedo website here-

http://www.torqeedo.com/en/hn/background-knowledge.html

I hope that helps!

 

[jag]

Minn-Kota and similar trolling motors have a very low overall efficiency of less than 20%.
Torqeedo motors have a much higher efficiency of around 50%. A Torqeedo motor will provide double the run time/range per charge compared to if you were using a Minn-Kota or similar trolling motor.
You might want to check the efficiency curves and technical info on the Torqeedo website here-

http://www.torqeedo.com/en/hn/background-knowledge.html

I hope that helps!

Thanks for the link. The torqueedo web page is indeed much more informative than that of other trolling motor sources.
The definitions and conditions used for their efficiency calculations are still not crystal clear. I think the conclusion is right however. The typical trolling motor propeller does not look hydrodynamically efficient. Inside may be a cheap DC brushed motor. (still wondering about this. Nobody cannibalized a trolling motor?)

I had planned to cut the shaft off a regular trolling motor, then mount the lower unit with 10" or so of shaft left on it to the regular rudder system of my kayak. Now seems like they have already thought of this:

Doesn't come cheap though. So I have to think if my dozen or so uses/year motivates spending
(quoting http://kayakfishingblog.net/?p=60

Price slaps ya in the face at around $1800 US.

When a regular Minn Kota Endurance 30 can be had for $99 at Walmart.

Now with a Starnberg, location that should not come as a surprise. these were the haunts of Kaiser Ludvig and other dignitaries in centuries past, and is now where the superich retreat from the hustle and bustle in Munchen. While you can take a public transportation there (S6 towards Tutzing), I was unable to afford even lunch... Here's their webpage image of Starnberger see with the alps in the background.

If you are in the area don't miss it! Chiemsee is also nice. I lived and worked near Ammersee for a year. Not as spectacular views, but far more affordable. http://www.cs.rochester.edu/u/jag/vw/gen/pops/popul.htm

 

[BMI]

The Torqeedo Ultralight kayak motor is the latest motor available from Torqeedo and with an overall efficiency at the prop of over 50% is the most efficient motor also.
If you can afford to buy one you certainly won't regret the quality and performance the motor provides.

I am involved with several larger electric boat projects at the moment which will be powered by Torqeedo motors. One of these boats has solar panels fitted and the power of the sun provides enough electricity to provide two hours of free motoring per day.

 

[gilnet]

not sure to what degree of excellence you're looking for.I heard of people screwing around w/the minkotas for ebike motors a few yrs back.probably a reason aint heard anything since.But every boater in minn. and wisc has one.I started seeing many in late 70's.they made many models,some real expensive.$5-600.big dough back then.So there are probably some old workhorses out there in flea marketville cheap.Never heard anybody complain about the pricier ones.most people I know used them everyday backtrolling for walleye.they were the must have christmas gift so many got little or no use.Our company used them for premiums/promotion gifts and unloaded warehouses full in the hayday.have seen many a canoe on "no motor"lakes on the boundry waters using them.

 

[jag]

not sure to what degree of excellence you're looking for.

After some thought, I'll probably go with something inexpensive first to see how much actual use I can get from it. I already have plenty of NiCd batteries from the eBike hobby, so I only need a trolling motor lower end. I can buy a new inexpensive Minn Kota, or buy a used one, and harvest the lower end. Then drive with either the Minn Kota controller, or an eBike controller.

The one trolling motor lower end I saw on eBay had two thick wires + some smaller going to it. That made me think (old ones) are likely just brushed motors. The torqueedo is obvioulsy a brushless and geared.

Some trolling motors are 5 speed, How is this implemented? Different wirings brought out from motor?
Others are "infinite speeds", which probably means a PWM controller.

Now from the web page reading I've learned that for a boat the prop efficiency difference is more crucial than the 10% or so difference between a good brushed and brushless. The trolling motors for fishing have weedless props. Probably not the best efficiency. Torqueedo sells just the prop if I can find a cheaper lower end to upgrade. Of course the prop may be just as expensive as a whole Minn Kota.

Should eKayaking become a major pastime I can always upgrade from the $100 initial experiment to a Torqueedo later.

 

[John in CR]

I have one of the lower unit only trolling motors from ebay. Yes it's brushed, and the multiple wires are for the different speeds. With the price of those torqueedo's, just save the $ and buy some extra batts, because you're right on that it's all in the prop. Trolling motor props are for thrust and cutting the weeds, not for moving most efficiently.

John

 

[GGoodrum]

Hobie is now offering a Torqeedo-based option for their kayaks. It is a slick setup that comes with two mounts, one in place of the rudder and the other replaces the pedal drive up front. These are very slick setups, but cost as much as the whole kayak.

I've been looking at the regular Torqeedo setups as a replacement for a small outboard on a dinghy, but they are just way too expensive ($2k+...). The only thing that sets them apart from other, less efficient electrics is that they use a brushless motor. They have a Lithium pack, which also drives up the cost of some models, but nothing special about them. If I had better mechanical/hacking skills, I'd love to modify a outboard with a blown engine and put in something like a couple of AstroFlight 3220s and power it with a 12s6p 44V/30Ah LiPo pack.

-- Gary

 

[jag]

Hobie is now offering a Torqeedo-based option for their kayaks. It is a slick setup that comes with two mounts, one in place of the rudder and the other replaces the pedal drive up front.

An integrated rudder/motor like this is pretty much exactly what I had in mind making.

It is nice there is a commercially made version, but no way I'm paying 2k. More likely I'll take the lower end of a $100 trolling motor (like this Minn Kota Endura 30) and graft it to the rudder mechanism:

 

[BMI]

Hobie is now offering a Torqeedo-based option for their kayaks. It is a slick setup that comes with two mounts, one in place of the rudder and the other replaces the pedal drive up front.

An integrated rudder/motor like this is pretty much exactly what I had in mind making.

It is nice there is a commercially made version, but no way I'm paying 2k. More likely I'll take the lower end of a $100 trolling motor (like this Minn Kota Endura 30) and graft it to the rudder mechanism:

Of course not everyone can afford the performance and efficiency of more than 50% efficiency delivered at the prop for the Torqeedo motor compared to the overall efficiency of the Minn Kota at barely 10%.

 

[jag]

Of course not everyone can afford the performance and efficiency of more than 50% efficiency delivered at the prop for the Torqeedo motor compared to the overall efficiency of the Minn Kota at barely 10%.

No doubt the Torqeedo has superior engineering design, and will perform better in general. It may not always be a 5:1 ratio advantage though. This graph is provided by Torqeedo and would seem to show that the Torqeedo is vastly superior to in particular the low power "competitor". However, it fails to mention anything about how it was measured. If it was an actual test on a boat that boat may have been to large for the smaller of the competitors.

An interesting piece of information can be gleaned from the table at the end of this page (I couldn't figure out how to insert the html code for the table in the post)
http://www.torqeedo.com/en/hn/background-knowledge.html
For the gas outboards they measure the propeller efficiency alone, and the values suggest that the superior efficiency of the torqeedo is mainly a factor of the propeller, not so much the other components. For a larger boat one usually tries to match the propeller to the boat for maximum efficiency, but unfortunately for us interested in efficiency for a small boat or canoe/kayak, that is not common with small motors.

Again, details on how the experiment was conducted are missing in this table. For a somewhat complete picture graphs of thrust and efficiency for both different speeds and input powers would be needed.

So overall Torqueedo does a better job of presenting their product than other trolling motor manufacturers, but it is still not as good as e.g. the information we have for ebike motors.

 

[blisspacket]

The MinnKota is brushed. It is also bushed. I'm referring to the armature which runs in bronze oilite bushings. A single ball in the armature shaft at the front bears against a steel surface on the housing. Thats their thrust bearing. The forward bushing is selfaligning.
I had an armature that I put in the lathe, spun it, found a wobble on the open end, pushed and straightened it; pushed again and introduced another wobble. Apparently there was a hairline crack in the shaft somewhere under the windings. This is a 1/2" shaft. I bought the motor used so no idea of its history or how that might have happened.
PulseWidthModulation controls some of these motors, I think good for 60 amps at least on their 24 and 36v motors. The PWM's I think are the only good component, and worth scouting for as an inexpensive (relatively) item. Their 3X model does not have electric reverse (motor rotates at least 240o) and so has a more simplified electronic pwm.

 

[jag]

So I ended up buying a cheapie Minnkota Endura 30 trolling motor. Only $100. The thing is heavy, but that matters less in a kayak or boat. So far I'm glad that I only spent $100, since I haven't been using it much anyway. Most places I kayak here in the Canadian rockies national parks don't allow any kind of motors so not even electric.

Jeremy Harris pointed out that one way to increase efficiency of these trolling motors is to replace the prop with a RC prop adapted to the boat. Another improvement would be to replace the resistance based speed control with a cheap PWM from a scooter or similar.

 

[chvidgov.bc.ca]

http://www.lightperformanceworks.com/lpw-kayak-products/kayak-power-system.html

The linked site has an off the shelf relatively inexpensive kayak trolling motor which is premade to work with existing rudders...
I'll be curious to hear about your work jag, as I have a Greenland II folbot as well..

 

[jag]

http://www.lightperformanceworks.com/lpw-kayak-products/kayak-power-system.html

The linked site has an off the shelf relatively inexpensive kayak trolling motor which is premade to work with existing rudders...
I'll be curious to hear about your work jag, as I have a Greenland II folbot as well..

That's more or less what I planned to make eventually. From their pics they might very well be using exactly the same Minnkota Endura motor.

However, so far the only thing I made is a crossbar that fits across the rear of the cockpit on the Folbot GII. Sorry, kayak is packed up for the winter so no pictures possible.

My other insight was (after I got the motor) that the lakes here in Alberta are so small that there's really not much point with a motor. In BC that would be a different thing of course.

Another idea I wanted to try is to try to convert one of the small Cute 108 hub motors y just putting propeller blades on it and (somehow) sealing it for underwater use. The 10:1 reduction gearing and big prop blades should give really good thrust. Now I guess I have to look for a job in BC so I can live by the coast again...

 

[chvidgov.bc.ca]

Hmmm...i wonder if there is a way of coupling a prop to a hub motor like the Cute with really strong rare earth magnets operating through a waterproof motor enclosure...have to put on my thinking cap for that one...

 

[EVTodd]

I have been thinking about this quite a bit myself.

I currently have a canoe that I use a trolling motor on all the time for fishing local canals and small rivers. I love the setup and it works great but I've always hated dragging a huge battery around.

My thought was to pick up a cheap trolling motor, gut the motor and mount an outrunner in it's place. Just a simple direct drive.

After doing a bunch of reading about Torqeedo's products I'm pretty much set on picking up one of their props and modifying it to fit. You can get one for around $85 or so. Crazy expensive for a piece of plastic but if they work that good I'll do it.

A couple of lipo packs in a waterproof box... Man, it would be nice to have a lightweight setup like that.

 

[blisspacket]

Lipo batteries might be fine. I'll stick with the NiMH batteries that are culls from a Prius battery rebuilder in Sanford NC. I currently have 108 of his 6.5 amp 7.2volt Panasonic batteries. I used them on a MinnKota with a Torqeedo prop, and now on a Torqeedo 801. The batteries require a NiMH charger and there aren't that many around that have the capacity to charge them rapidly. I've been impressed that I can leave them in the garage for a month without tending to them and they don't discharge, even when indiscriminatly tied in a 4s3p configuration. Clincher was the $3 per battery, delivered at my doorstep. I have both the three bladed Torq prop and their smaller 2 bladed prop, and it's hard to establish valid comparisons, but I'm a believer. Especially coupled to the brushless Torqeedo motor, it's an efficient propulsion system.

 

[chvidgov.bc.ca]

I'm building a sailing canoe these days, and I've just aquired a Minnekota PWM 40thrust ("EnduraMax") for backup propulsion on calm days and for salmon trolling. I'm going to try running it on two of my 48V Lithium ebike batteries using a DC DC 48 to 12V converter for golf carts, which is supposedly rated for 30Amp output. I doubt continuous. I hope it will work, if I don't max the motor out for long at a time. The runtime should be AWESOME compared to AGM, not to mention the much reduced weight. At first, I thought I would build a big 12V headway battery, but figured the efficiency loss of the convertor might be ok given the advantage that I could use my existing packs etc.,possibly even pulling the boat to the water with my bike.

 

[gogo]

I'm building a sailing canoe these days, and I've just aquired a Minnekota PWM 40thrust ("EnduraMax") for backup propulsion on calm days and for salmon trolling. I'm going to try running it on two of my 48V Lithium ebike batteries using a DC DC 48 to 12V converter for golf carts, which is supposedly rated for 30Amp output. I doubt continuous. I hope it will work, if I don't max the motor out for long at a time. The runtime should be AWESOME compared to AGM, not to mention the much reduced weight. At first, I thought I would build a big 12V headway battery, but figured the efficiency loss of the convertor might be ok given the advantage that I could use my existing packs etc.,possibly even pulling the boat to the water with my bike.

Wouldn't it be better to replace the Minn Kota controller with a 48V brushed motor controller and trim the throttle signal to restrict the output to 12V max? Feeding a PWM 12V Minn Kota controller with PWM power from the 48V to 12V golf cart converter seems unwise and a bit inefficient. 48V brushed controllers may be cheaper than the converter.

 

[chvidgov.bc.ca]

I'm not sure what you mean when you say the converter is PWM. It just produces plain old DC 12V at a max of 30 amps, with 90% efficiency, and provides it to the EnduraMax PWM controller. The power isn't PWMed by anything other than the Minnekota controller. If I limit my end wattage to 250w using just the throttle alone it should be straightforward I think. 20Ahr of 48V lithium should be equivalent to maybe 150Ahr of lead acid AGM given the Peukert effect on the lead which would probably only put out 80 amphrs. I should be able to run that motor for days at only 5 amps coming from the lithium which is only .25C, which is transformed to 20 amps at 12 v out of the converter - my canoe should be able to do 3 knots at that wattage which is my target top speed. Its a displacement hull and will only do 5 knots max anyway, so it would take a stupendous amperage to get it over 4.5 knots. I hate to take apart a brand new motor like that - and I'm more excited by the sail rig anyway which will be awesome - just need to sort my leeboard/ex-snowboard I might put a different prop on the motor too, later. See how it goes. I imagine your idea would work as well - either way I need to be careful not to suck too many amps with my throttle setting, as I understand it.

Thanks,
Chris.

 

[gogo]

I'm not sure what you mean when you say the converter is PWM. It just produces plain old DC 12V at a max of 30 amps, with 90% efficiency, and provides it to the EnduraMax PWM controller. The power isn't PWMed by anything other than the Minnekota controller. If I limit my end wattage to 250w using just the throttle alone it should be straightforward I think. 20Ahr of 48V lithium should be equivalent to maybe 150Ahr of lead acid AGM given the Peukert effect on the lead which would probably only put out 80 amphrs. I should be able to run that motor for days at only 5 amps coming from the lithium which is only .25C, which is transformed to 20 amps at 12 v out of the converter - my canoe should be able to do 3 knots at that wattage which is my target top speed. Its a displacement hull and will only do 5 knots max anyway, so it would take a stupendous amperage to get it over 4.5 knots. I hate to take apart a brand new motor like that - and I'm more excited by the sail rig anyway which will be awesome - just need to sort my leeboard/ex-snowboard I might put a different prop on the motor too, later. See how it goes. I imagine your idea would work as well - either way I need to be careful not to suck too many amps with my throttle setting, as I understand it.

Thanks,
Chris.

I'll admit that I may be in over my head on the technical aspects, but I'm fairly sure that a DC 48V to DC 12V converter is a buck converter. Buck converters use PWM to achieve the voltage conversion and have an induction coil to smooth out the output voltage ripple. If your buck converter doesn't smooth out the voltage ripple well enough, it may output 'dirty power', or a harmonic, that doesn't play nice with the Minn Kota PWM controller.

You would also be avoiding the inefficiency of double PWM stages and the induction coil in the 48V to 12V converter. Since you are feeding coils of a motor, you could just use a brushed motor controller as a buck converter that has variable output of 0V to 12V.

You wouldn't need to take apart the lower section of the Minn Kota. You would just be substituting a 48V brushed motor controller and its throttle for the 12V Minn Kota controller/throttle.

I don't know how well DC to DC converters smooth their voltage ripples, but you may be risking damage to your Minn Kota controller by feeding it 'dirty power'.
View attachment 2064986_Endura_Max_40.pdf

 

[chvidgov.bc.ca]

Hmmm...that's interesting - I kinda knew that DC-AC inverters could produce either "dirty" or clean sine-wave AC, but I didn't know that DC-DC might have the same issue. I guess I will have to do some more research if this is a risk to the motor. Its the Rumsfeldtian "don't know what I don't know" that will get me. From what I understand, using a 48V controller would be risky if you ran the throttle too high, as the amps sucked by the motor will increase exponentially at the the higher prop RPMs of voltages over 12 - risking the motor, which could be produced if you throttled too high on the 48V controller. In my concept, the motor wouldn't be asked to run at anything over 12 volts, although I might need to limit the throttle to protect the DCDC converter.

 

[gogo]

I believe you can limit the output voltage of a brushed motor controller by altering the 'control signal', or voltage from the throttle. Others would have to advise how to do that, as I've not done it myself. You would achieve the amp limit by choosing a suitably large controller with the desired specification.

I forgot about the need for reverse. I'm not sure how to implement that with off the shelf brushed controllers.

 

[chvidgov.bc.ca]

It turns out that the DC DC converter runs the motor flawlessly from my 48V Headway pack...

http://endless-sphere.com/forums/viewtopic.php?f=14&t=66653#p1014187