Trolling Motor & Battery Advice Required

Discussion in 'Electric Propulsion' started by StormUK, Feb 24, 2021.

  1. SolGato
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    SolGato Senior Member

    Exactly. I see a lot of talk about voltage and wattage, but not enough focus on amperage when it comes to designing an electric propulsion system.

    As I mentioned before, you size your battery bank based on the capacity of the battery. This capacity rating basically states how many amps over a period of time a battery can continuously deliver that amperage without damaging it.

    Motors are then rated for a Max Amp draw.

    As voltage increases, a motor will use less amps to deliver the same power (basically).

    So, a 12V motor at full throttle may take 50A to push a boat, whereas a 24V of the same size would use 25A.

    This is one of the main advantages of going with a higher voltage system, a few of the others being that you can produce more torque at the higher voltage, and you can use longer wiring or smaller gauge wire.

    So instead of thinking about power/wattage, I like to focus more on amperage because that what you want to track going into and being pulled out of your battery bank.

    Ideally, you want to consume as few amps as possible during typical use giving you the greatest possible range. With every component there is a loss in efficiency, so matching components and using the most efficient components will result in better overall performance.

    Another important thing to remember when talking about Watts and sizes of motors and their equivalency to ICE motors, is an electric motor will consume X amount of watts, but then deliver less of those Watts in power. The more efficient the motor, the less power loss. So when someone says it’s a 1000W motor, is that what it uses, or puts out under load? And how many Watts does it take to move your boat at a reasonable speed? Most manufacturers don’t share this kind of data, but some do. Until you do real world testing, you can only make a best educated guess based on as much info as you can collect.

    Designing or finding a motor to adapt for electric propulsion is the easy part, the hard part is controlling the motor. When people say I burned up my motor, they more than likely had a component failure in the motor controller. With new motors using electronic relays and other components, current and heat are the things you have to worry about. Current and heat are directly related to Amperage. Most components are spec’d to be working within their operating value range, but when you start experimenting with props or you get stuck in the mud, or you reduce the gauge or lengthen your wiring, failures can occur. Most manufacturers don’t leave a lot of headroom, they could but rarely do because every penny they save adds to the bottom line. You see a lot of people taking pancake motors and various AC motors and adapting them to lower ends of outboards that experience a lot of controller failures. It’s not easy to regulate and control a motor for use in a boat and have it work reliably, safely, and with longevity.

    In the case of Portacruise hot rod modding his 12V motor, he carefully monitored the Amperage to make sure he wasn’t overloading the components. Most Brushed trolling motors aren’t going to care much about Voltage. In the case of MK motors, internally they are more or less the same. They use thrust bearings and rubber seals, so you may see more wear on those components due to the motor turning at a higher RPM, but it doesn’t surprise me that he didn’t see any signs of damage due to over-volting. He eliminated the factory motor controller and substituted one that could handle the higher voltage. What you do not want to do is supply excess voltage to the stock controller.

    Plus a 12V motor would have wiring capable of handling higher Amperage than a 24V equivalent, so you don’t need to worry about significant resistance or burning up wires.

    And I assume Portacruise that you were powering a lightweight craft, and not a gear loaded planing hull Bass Boat?

    Another industry to look at with regard to electric propulsion of small craft is the ROV industry. They make some very powerful brushless motors for ROV’s that are very efficient and universally adaptable.

    For example, for a couple hundred dollars you can buy a brushless 5” motor (BlueRobotics T200 for example) that will run up to about 24V and put out 11lbs of thrust using about 30A spinning up to around 4000RPM. These little motors are potent and efficient and can power a small kayak, skiff, canoe, etc.. Manufacturers make even larger ones for big ROV and submersible Craft.

    And then of course there are the motors being designed for foiling boards which are ridiculously powerful for their size and reach mosquito buzzing like RPM’s thanks to high voltage and amperage and drive gearing.

    Hopefully I haven’t gone too far off topic here on this thread and some of this info is of interest and value to others. There’s are lots of options out there, some better than others, none the perfect option for all. The main thing to keep in mind is to build for your needs and habit of use while taking into consideration the “unlikely but possible” scenarios. If you do that, you will probably spend more time enjoying the wind (more like slight breeze) in your hair cruising under electric power, than troubleshooting or being towed in due to a failure.
     
    Last edited: Apr 24, 2021
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  2. portacruise
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    portacruise Senior Member

    SolGato, Do you think the flooded blue robotics motor can match the efficiency of a motor that is spinning in air like the electric paddle, if everything else is equal? Because of the viscosity difference between Water and Air, it seems like there would be a lot more friction for an Armature that spins @ 4000 rpm in water compared to air?
     
  3. SolGato
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    SolGato Senior Member

    Two completely different animals the ROV Thruster and the EP Paddle, but I would guess if you had two identical motors with one submerged and flooded and the other above the water and air cooled, the air cooled motor would be more efficient because it doesn’t have the friction of the water like you suggested. But then there is something to be said about liquid cooling in order to increase efficiency and reliability.

    One of the reasons my brushless motor manufacturer places their controllers in the motor housing is for cooling purposes. On top of that, they embed them in a thermal potting like material to seal them from condensation and draw heat away from the components.

    FYI, never got any serious data from EP, but the BlueRobotics company being a robotics like product have all the data you’d ever want about their motors with regard to efficiency, thrust, power, etc.. Lots of graphs and data to study on their site. People are building some pretty serious ROV’s with them based on hard numbers and their technical data.

    Before Covid, I had reached out to them after purchasing a pair of their T200’s and asked if they had any plans to develop an even larger motor and they were in the testing phase of something larger with more thrust that could handle more voltage and amperage. I think unfortunately they had to hit pause on development, but I’m looking forward to see the specs of what they come up with.

    Take a look around on YouTube. You should be able to find videos of people who have adapted them to canoes, kayaks, etc.. Even a few who have made underwater diving fins and my favorite, the guy who mounted them directly to a paddle.
     
  4. SolGato
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    SolGato Senior Member

    BTW, this is the kind of data I was able to get from my motor manufacturer. The fact that they have logged this data tells you they are pretty serious about product development. And if I remember correctly, the tests were performed under load pushing a small inflatable dinghy with two passengers on board.

    Since we’ve talked about PWM in previous posts, have a look at the efficiency values based on Amperage and Watts in/out. It’s pretty easy to see where my motors operate most efficiently. This is the “sweet spot” that I mentioned that I try to operate in that I’ve tuned and matched my components for, drawing about 30A.

    Although the manufacturer has experimented with different props and wasn’t able to safely make a substantial increase in speed, I think with my efficient Catamaran hulls I should be able to swing a little bigger higher pitched prop based on my max amp draw under load with stock props.

    So I have purchased a few Torqeedo props and modified their hubs to work with my motors to test this. I will be monitoring amps under load using my BMS, and since my boat uses dual independent thrust motors, if both are set to match one another in RPM, any difference will be quite noticeable. One issue, Torqeedos Run Clockwise and my motor’s run Anti. So for testing I’ll be running one motor in reverse.

    I have to say I was surprised at how undersized the prop shaft, and more importantly the shear pin is on similar size Torqeedo motors to my motors. No wonder they are notorious for shearing pins! I have to wonder if it has something to do with them using the planetary drives from the power tool industry in that it limited the shaft diameter, and thus the shear pin.
     

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    Last edited: Apr 27, 2021
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  5. portacruise
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    portacruise Senior Member

    Another thing I look at when trying to find just the efficiency of just Motor Part on its own, is the no load draw. Some Motors draw as little as four watts over a range of voltages operating in air, whereas submerged motors of similar rating may draw 20 or more watts, due to the seals, waterproofing, etc. which is required. Of course, that is more important if you're operating a small power system, compared to a large one.

    Second thing is the hydrodynamics of the motor setup itself. I would think it is preferable that the prop operate in as little undisturbed water as possible from appendages front and rear. Generally, a trailing shaft motor has a smaller appendage profile, which greatly reduces some of the disturbance caused by brick in front or behind design submerged Motors. Prop spinners front and rear to smooth the flow would seem to be helpful, where it is possible to use them.

    Of course, degree of hull streamlining and propeller shape /size considering motor output are also important, and have to be tweaked to synchronize and optimize the overall efficiency of the whole system.

    Hope this helps.
     
    Last edited: Apr 27, 2021
  6. portacruise
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    portacruise Senior Member

    For those that are operating their Electric Motors around weeds and/ or gelatinous types of algae, there may be complications when using open /flooded blue robotics type thrusters. That is because of the possibility that plant matter or small Aquatic Life can be inhaled into the mechanism causing overload if there is a jam, or loss of efficiency because of fine deposits gradually accumulating inside. Clearing these types of impediments so that someone can continue on their Journey might be considerably more time consuming compared to conventional propeller systems.
     
  7. Kayakmarathon
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    Kayakmarathon Senior Member

    One human powered boat (The Cavitator) set its record speed using a fan blade in air rather than a prop in water. The fan blade did not cavitate like a prop; so it was more efficient. I've designed brushless DC motor controllers for both fluid and air circulation systems. For the same voltage / current / wattage range, fans had a much greater RPM than pumps.
     
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  8. portacruise
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    portacruise Senior Member

    Water props can also be efficient, maybe more efficient if designed to work properly with the whole system.

    From : What foil profile(s) does the MIT Decavitator (or similar vehicle) use? https://engineering.stackexchange.com/questions/36667/what-foil-profiles-does-the-mit-decavitator-or-similar-vehicle-use

    Also other sources.



    "The principal examples of HPV solo hydrofoils are Flying Fish and Decavitator. There were several incarnations of both craft. Flying Fish won in the match race, but Decavitator's air prop let it exploit a rule permitting up to five knots of wind during the record attempt. The record was set running downwind in 4 knots, giving the air prop an efficiency boost."
     
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  9. portacruise
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    portacruise Senior Member

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  10. SolGato
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    SolGato Senior Member

    As I mentioned, holding and maintaining a higher voltage, especially when under load, is one of the big benefits of lithium batteries that many people don’t talk about or understand.

    BUT, when you use them with motors that have controllers designed for FLA, you could overload the components as manufactures like Minn Kota rarely use over valued components.

    So when you have say a 24V Lithium bank, it could hold a voltage of 27V under load with very little voltage sag, whereas a FLA battery will immediately drop to a lower resting voltage when under load and continue to drop as it delivers power over time.

    Minn Kota’s motor controllers are designed around this voltage sag and expect to see voltages closer to 25V or less.

    One more caveat, if you have solar power and a charge controller integrated into the system, you have to be very careful to make sure your MPPT settings are kind to your motor controller, otherwise your motors could see 30V+ when the solar is in Bulk mode.


    In general, LiFePo4 is a better Lithium battery to use with motors originally designed for FLA.

    With regard to their warning about Amperage, Lithium batteries have a Max Charge and Discharge rating. A lot of the more affordable batteries on the market are limited to a 50A Max discharge by the internal BMS. A lot of Minn Kota motors are rated at pulling more than 50A Max, so this would cause the batteries BMS to disconnect.

    Remember that this same value also limits how quickly you can recharge said battery.

    So if you have a 100ah capacity battery with a 50A Charge/Discharge rating, technically you can run it at its Max Amp draw for 2 hours, and if you had a big enough charger, replenish it in a little more than the same amount of time.

    Again, this is where going to a higher Voltage system makes sense. By increasing Voltage, you cut Amp draw in half for the same size motor. So a 12V motor that pulls 60A, might pull only 30A at 24V.

    This is why companies like EPropulsion have gone to a 48V architecture with all their motors. By going with a higher voltage, they can drastically reduce the Amp Draw which gives them better range and increased thrust for the small capacity of their integrated batteries.

    For example, their Spirit motor will run for 1hr 15min at full throttle and is rated at a 20A Max draw. So if you work that math backwards, their battery has a capacity of about 25ah or so. Most full size Lithium batteries are good for about 100ah, so you could theoretically extend your range by 4X with an auxiliary full size lithium battery. And commendably, Epropulsion easily allows for the use of auxiliary batteries, unlike their competitor Torqeedo.

    Also if you look at the voltage specs of that motor, you’ll see it can handle voltages as high as 60V even though it’s a 48V motor. This is to allow for the additional input voltage voltage from a Solar Charge Controller which can be used while operating the motor.

    With the way things are going, I wouldn't be surprised if Minn Kota doesn’t come out with a line of motors “optimized” for use with Lithium batteries as more fisherman start moving toward Lithium for their house batteries to run electronics, accessories, etc..
     
    Last edited: May 20, 2021
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  11. portacruise
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    portacruise Senior Member

    PC: Ok, that is 48v x 25 ah = 960 watt- hrs.

    PC: Full size at the standard 12v x 100 ah = 1200 watt - hrs. Using a very inefficient dc-to-dc up converter would be needed to get you to 48 V, so I must be missing something, if someone is able to get 4x the range (960 ah x 4 hr = 3840 wh required vs. 1200 wh) with a single full size lithium battery. Unless four of the standard batteries will be in series to get 48v, but that will mean a lot more weight, a lot more volume, and a lot more cost vs EPropulsion 960 wh 40v battery...

    PC: Yes, gives the purchaser the purchaser the ability to shop for their own batteries and more freedom to design.
     
    Last edited: May 22, 2021
  12. SolGato
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    SolGato Senior Member

    I didn’t mean a single battery, but a bank in series for 48V.

    Yes, batteries are expensive and large batteries are bulky, but most bigger boats have the room for a bank of batteries, and for what most of these electric outboard companies charge for their integrated battery, you could buy larger capacity 3rd party batteries and at least double your range.

    For example, EPropulsions battery is $900. You can buy 4X 100ah 12V LiFePo4 batteries with a built in BMS and 100Ah Charge/Discharge capacity for $2000, or 2X 24V 50Ah for the same.

    To get the same range that 100Ah bank offers, you would have to buy 4 EPropulsion batteries at close to 2X the cost.

    And that bank of 100ah batteries will likely have a much better lifespan, certainly greater than the 500 charge cycles I believe E states in their specs.

    Also, the bank would have the ability to recover much faster with enough solar feeding them as they could technically handle as much as 100 amps.

    I find fast charging and recovery of the bank to be key when you are on the water all day.

    And don’t forget LiFePo4 batteries are actually a lot lighter than most people think. Mine are smaller and weigh less than half the FLA’s I ran for the last 4 years, and they deliver more Amp Hours while maintaining a higher target voltage.

    My point was simply that if one is going to invest in an electric outboard, it would be wise to choose one that has a lot of flexibility of use and the ability to integrate additional power sources.

    Personally, I don’t like being locked into an integrated system that requires buying additional batteries from the manufacturer in order to extend run time, which is why I commend EPropulsion for allowing the use of a 3rd party battery bank as an auxiliary or even primary battery.

    In fact I have confirmed with them that you don’t even have to have their integrated battery attached in order to power the motor, so if your battery goes bad like a lot of them did on Torqeedo customers, you won’t be forced to upgrade or buy a factory replacement, unless of course you want to retain portability.

    As you said, this gives the owner a lot more freedom.
     
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  13. portacruise
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    portacruise Senior Member

    Thanks, that makes sense compared to buying another Spirit battery.

    Probably the cheapest way to greatly increase range is by switching to the best model airplane prop and streamlining appendages where it is needed, as listed in the link of post number 12. Just about any trolling motor with wide and or multiple blades, or cages (kort nozzle mostly insignificant) around blades can be improved significantly by using the ideas in that link, IMHO. The electric paddle motor uses that very efficient approach, while turning a nice profit on cheap replacement props by packaging props with a module containing part of the lower unit. But existing model airplane props have their limitations; when used for primary propulsion of heavy or high power boats they can deform or break.

    Any luck with your experimentation using torquedo props?
     
  14. SolGato
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    SolGato Senior Member

    Haven’t had an opportunity to test props yet. Hoping to get on the water this weekend for some baseline testing using stock props and new LiFePo4 batteries.

    BTW, I see Haswing is now offering a bigger 24V motor that has a 3-blade prop that looks very similar in size and pitch to Torqeedo offerings. I’m going to try to get info on it. With any luck, it’s a little different with specs somewhere between a trolling motor prop and Torqeedo’s props giving yet another option for testing.

    A few years ago I 3D printed a test prop out of PLA at a low resolution with a hub that accepts swappable blades of different pitch and length. I never finished designing a method for securing the blades, but the concept still has merit for honing in on a optimal design that once determined, could be printed as a solid unit using HDPE. I might have to dig it out of a box if I’m not happy with the results of modifying and trying factory designs.

    E7E4BA33-C2C1-4E8A-A1C1-BE55F654230D.jpeg
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  15. Jeff in Boston
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    Jeff in Boston Senior Member

    Nice propeller! Next year I expect I will be buying a "5hp" Haswing trolling motor for my project unless a better alternative comes along.
     
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