Trim motor amps

Discussion in 'Outboards' started by cmaas, Feb 13, 2023.

  1. cmaas
    Joined: Sep 2007
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    cmaas Junior Member

    Does anyone have an idea about how much current a trim motor on a Yamaha 25 four stroke outboard uses? Or any similar trim motor will do. I'm working on an ICE to electric outboard conversion and want to make sure my dc-dc voltage converter can handle the loads.
     
  2. Heimfried
    Joined: Apr 2015
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    Heimfried Senior Member

    I'm very interested in what you are doing and did, because I'm building a solar electric katamaran (21') for recreational use. It will start with very low power (2 trolling motors 1,4 kW each).
    Regarding your question I can't provide an answer, sorry. What is a trim motor? Which voltage is your source and which voltage after DC - DC conversion? What boat in what conditions will you drive with the converted outboard?
     
  3. alan craig
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    alan craig Senior Member

    You will definitely need a wattmeter to test and set up your electric outboard so use that to measure the current for the trim motor ( I presume trim is the angle of the propeller relative to the transom).
     
  4. fallguy
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    fallguy Senior Member

    Typically, the fuses are 20amp for most small trim motors. What you can do for design if you already have the motor is test it by trying weaker fuses in the tt circuit. The heaviest draw is at the start up, so it should be easy to check and mess with. Look for the tt relay which is a small black rectangular thing you'll hear when you hit the button. From there trace the wires to find the fuse which should be waterproof in line. Then try to go 25% lower and see if it'll make it. I would not go super low because the draw may change a bit for any small issues like weeds on the prop.
     
  5. cmaas
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    cmaas Junior Member

    IMG_0072 (1).jpg
    My boat is a 6m foil assisted powercat. Here is a picture of an early test of the unfinished hulls using a Honda 20 outboard. We are in fairly protected water. Waves over 1m would be rare. 18kW motor battery voltage is 72v converted to 12v for loads like trim motor, motor coolant pump, running lights, etc. A trim motor powers a hydraulic pump that tilts the motor.
     
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  6. cmaas
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    cmaas Junior Member

    Your are right. Motor/controller/battery gauges are on the way. In the meantime, and before I can set the system up, it would be great to know what the loads will be on the 12v system.
     
  7. cmaas
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    cmaas Junior Member

    That's a good idea, thanks. I see a 20amp fuse on there now so I'll try stepping down from there. My guess is about 15a start up amps. I have a 20a DC-DC converter and it would be nice to use that. It may be a little on the small side though.
     
  8. Heimfried
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    Heimfried Senior Member

    Thank you cmaas.
    An hour or so I found out, what a trim motor is for. Looking up such motors to be sold there weren't given any electrical data (power intake). I consider this not a good sign for guys (like you and me) whith (only) electric propulsion depending on the power capacity of their batteries.

    I think these trim motors are mostly designed to assist a more or less powerful ICE engine and its alternator provides electricity to waste with. So designers had far more interest in a motor cheap to build or buy than a motor with high efficiency.
     
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  9. fallguy
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    fallguy Senior Member

    The four stroke motors came with one flaw. They are currently and probably will be always, heavier.

    Lifting even a 35hp two stroke requires an assist bar for all but the strongest fellow.

    And yes, cheap is the way. These motors are actually a pain for many of us. They draw down a start battery quite a bit. If you leave the landing and lift the motor engine off, you draw, get home and lower to put in garage, lift up to the lake entry; it can actually be quite a draw in total..
     
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  10. SolGato
    Joined: May 2019
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    SolGato Senior Member

    What RPM will you be able to achieve at the output shaft of your electric motor?

    I ask because the biggest drawback of converting an outboard to electric is the gear reduction in the lower end which isn’t necessary for a lightweight electric performance planing hull application.

    On the DC to DC converter, I would go bigger if you also plan to run a bilge, NAV lighting, USB charge ports, etc.. The inrush load the trim and bilge accessories would draw alone can spike the cheaper DC to DC converters with low duty cycles. The brand name stuff like Victron has specs that can be relied on if you find you are cutting it close.

    If you add solar with an MPPT, the smaller Victron units come with a handy Load Output feature that is current limited depending on MPPT size, and is able to be switched on/off remotely or set to a schedule.
     
  11. cmaas
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    cmaas Junior Member

    This motor's max rpm is 5000. About 1000rpm slower than the ICE. 4000rpm should get me close to my target 18 - 20 knots.
    This is my current gas/electric conversion. 3500rpm at the motor shaft is about the 'sweet spot' for speed (12 knots) vs power consumption
    DSC_9987 (2).jpg
    Thanks for the thoughts about the DC-DC converter. I think you are right that it's a bit small.
     
  12. SolGato
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    SolGato Senior Member

    That’s Gizmo, yes?

    Such a cool boat!

    I mentioned the gear ratio issue because your new build looks the part speed-wise, but it sounds like you won’t have a problem reaching your goal.

    Out of curiosity, do you find there is a point where your hulls approach their hull speed at the same time the foils are reaching their lift speed that necessitates extra power to get it on plane, or is it pretty much a smooth transition?

    I ask because maybe in the case of your designs with the foils you are taking advantage of the gear reduction like a traditional planing hull.

    I’m going to be building X2 electric outdrive legs of my own design for my new electric power Cat with 1:1 gearing and have pondered whether I could use the existing daggerboard cases to mount some sort of foil assist just to smooth out the ride, reduce wetted surface area, and increase efficiency.

    Also if I may, how is stability once on plane? Being smaller boats I imagine weight shifting must come into play and “everyone must please remain seated”?

    Thanks for letting me pick your brain.
     
  13. cmaas
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    cmaas Junior Member

    The foils create some lift as soon as they start moving and by the time Gizmo is doing say 5 knots the hulls are lifted a fair bit, reducing hull drag. Though of course the foils create their own drag, but not as much as the decrease in hull drag. The Hobie 18 hull shape isn't the slipperiest thing out there but they are long and skinny and so don't really have a wave imposed hull speed. The transition from low riding to flying is unnoticeable unless you're watching the water. I do use full power to reach flying speed quickly then throttle back once up.

    The new boat does have planing hulls and there is no discernible speed hump through the speed range. The first tests were done with only a stern foil so the boat has alway run dry from the step aft. I had hoped, for simplicities sake, to not use a midships main foil. That worked fine when the boat was light - we could easily reach 18 knots with the 20hp Honda - but with the addition of 800 lbs of water ballast, to replicate the finished boat weight with passenger and batteries, the performance suffered horribly. We could only reach 13knots. The addition of the midships foil brought our speed back up to 18.5 knots.

    Both boats are surprisingly stable in pitch. In Gizmo an adult can wander from near midships back to the transom to look for weeds without much change in pitch. The new boat seems the same in pitch and roll. Those planing hulls don't want to get pushed deeper at speed. Gizmo is not so stable in roll and needs a fair bit of aileron applied to stay level if someone moves out onto a hull.
     
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  14. SolGato
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    SolGato Senior Member

    Thanks for the info. All very interesting.

    I’m sure it’s complicated and that there’s a lot to it, but do you think in general that the daggerboard cases on a performance sailing Cat might be strong enough for the loads created by an assist foil on a powerboat conversion?

    I would think the cases would see much more loading with a sail rig, but admittedly I have no foil experience, and I can only go by what I’ve seen.

    For me draft is very important, so the idea of being able to use a drop in case to deploy the foil versus a permanently mounted foil makes more sense.

    Thanks
     

  15. cmaas
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    cmaas Junior Member

    Maybe. The loads are very different. On a sailing cat the load is almost all lateral. On a foiler most of the load is up trying to lift the boat. It would be interesting to know if the A-cat guys beefed up their daggerboard trunks when they first starting messing around with foils.
    The foils swing back to retract on both of my foilers. A lifting trunk is fine too but can cause more damage if you hit something hard.
     
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