---In electricboats@yahoogroups.com, <smasterson2@...> wrote :
Hi,
I've been following your thread for a while. I fully understand what your trying to do and why. You are trying to optimize your performance in hope to maximize your range.
I don't know. I already know that according to the numbers, I should be using a reduction ratio of 3:1 or a bit less. But I had a 2:1 gearbox installed. I bought a 3:1 unit to try, and I took a hit of several percent on RPM/watt. So I was going to put the 2:1 gearbox back in. Then I thought hey, it might not work, but let's try direct drive. It SHOULDN'T work. But the 2:1 shouldn't be more efficient than the 3:1, either, so lets try it, says me. And I did.
The motor definitely did not overheat. It stayed cool to the touch. The controller just didn't like running at over 100 amps. Probably some setting in the configuration. I have to borrow a windoze computer to make changes because Kellys configuration app does not run on a Linux system.
I realize that the 14" prop would seem to be too much here. The thing is, why then, do I spend fewer watts per RPM at direct 1:1 than at 2:1, and fewer watts/RPM at 2:1 than 3:1? Well, I just don't know. All I can do is look at the empirical data and go by what it tells me.
Yes, in fact I generally operate at very low power levels when entering and leaving my slip. I just can't think of any good reason to run faster than 2 or 3 knots, actually. I know, some folks are just in a hurry. When I am on my boat I am already at my destination before I even get going. But the 200RPM benchmark is just an arbitrary test point while tied to the pier. No particular reason.
Believe me, I know all about being wrong. And I may be wrong now. But I am just going by the data.
But now the bad news. The thrust bearing I used does not grip the shaft securely enough. Sounds like the rotor is rubbing on something (hope not the stator coils) so I am putting a halt to this experiment for now, until I get or make a better thrust bearing. I have other pressing projects like leaks and faulty bilge pumping system and I want to rewire my DCDC converters properly since I am not going to maintain a separate house bank any more. And time is running out, I need to go back to work soon. After my next job I might do some more experimenting along that line. Meanwhile I don't want to trash my only big motor. I wouldn't worry so much if it was one of my 5kw motors.
Here's the problem I'm wrestling with. At 5 amps, the ME0913 has a torque constant of .75 Nm or .55 Ft Lb. If your spinning your prop at 200 RPM and it is a direct 1 to 1, if I understand correctly, at .55 Ft Lb, 200 RPM, you will be making about .021 HP.
The motor definitely did not overheat. It stayed cool to the touch. The controller just didn't like running at over 100 amps. Probably some setting in the configuration. I have to borrow a windoze computer to make changes because Kellys configuration app does not run on a Linux system.
I realize that the 14" prop would seem to be too much here. The thing is, why then, do I spend fewer watts per RPM at direct 1:1 than at 2:1, and fewer watts/RPM at 2:1 than 3:1? Well, I just don't know. All I can do is look at the empirical data and go by what it tells me.
Yes, in fact I generally operate at very low power levels when entering and leaving my slip. I just can't think of any good reason to run faster than 2 or 3 knots, actually. I know, some folks are just in a hurry. When I am on my boat I am already at my destination before I even get going. But the 200RPM benchmark is just an arbitrary test point while tied to the pier. No particular reason.
Believe me, I know all about being wrong. And I may be wrong now. But I am just going by the data.
But now the bad news. The thrust bearing I used does not grip the shaft securely enough. Sounds like the rotor is rubbing on something (hope not the stator coils) so I am putting a halt to this experiment for now, until I get or make a better thrust bearing. I have other pressing projects like leaks and faulty bilge pumping system and I want to rewire my DCDC converters properly since I am not going to maintain a separate house bank any more. And time is running out, I need to go back to work soon. After my next job I might do some more experimenting along that line. Meanwhile I don't want to trash my only big motor. I wouldn't worry so much if it was one of my 5kw motors.
Here's the problem I'm wrestling with. At 5 amps, the ME0913 has a torque constant of .75 Nm or .55 Ft Lb. If your spinning your prop at 200 RPM and it is a direct 1 to 1, if I understand correctly, at .55 Ft Lb, 200 RPM, you will be making about .021 HP.
I can see it moving water at 100 amp, because at 100 amp, we are now talking about 11 Ft Lb and spinning the motor at 1,000 RPM, you'll be making a little over 2 HP. If you overheated the motor, it clearly shows that you are overloading the motor with too large of a prop, almost twice the size it should be in my estimation if your quest is to avoid a gear reduction. If you are getting only 2 HP and your using a 48v system, it illustrates how inefficient that 1 to 1 ratio and 14" prop set up is making that motor.
That motor's sweet spot at 48v is around 2,500 RPM. It is rated to run at 125 amps all day long without breaking a sweat. If your headstrong on using the 14" prop, it's 2.5 to 1 reduction for 2 blade, 2.75 to 1 for 3 blade and 3 to 1 for 4.
Have you taken the boat out of the slip at 200 RPM? Is it your intention to maintain a 200 RPM prop speed?
Maybe I just have everything wrong about what your doing. I've been wrong before.
Scott
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