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Old 01-07-2013, 01:39 AM   #1
Theplum
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Default Prop for ac eletrical motor -different application

Hey Guys,

Been browsing your forum here and have learnt quite a bit. My application is a bit different, where I am using a motor to push water in a fish tank, using props/parts that you guys uuse in the rc world. Since I am trying to match up a RC prop to my motor, I was hoping you might be able to lend a hand.

I have been quite successful so far, though am attempting to fine tune my project, which is where I have hit a stumbling block.

1. I am unsure if I can find te RPM of my motor, without a tachometer (if not, I will just order one). I Believe the one number I am missing is if the motor is one pole, two pole, etc.

2. With the rpm of the motor, i am not sure how I co-relate my plugged in motor to your battery powered motors.

The motor is your typical pond motor, where a sealed magnet turns and spins a prop which is on a magnet shaft. It consumed approx 120 watts/hour, 60 hertz.

Thank you for any help you can lend.
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Old 01-08-2013, 04:21 PM   #2
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I'd ask the RC Boat guys.. I imagine a "water/boat prop" would be better than an "aircraft prop", wouldn't it?
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Old 01-08-2013, 06:03 PM   #3
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Originally Posted by Dr Kiwi View Post
I'd ask the RC Boat guys.. I imagine a "water/boat prop" would be better than an "aircraft prop", wouldn't it?
Hi kiwi

I tripped over an article (don't have it handy) where they were stating that essentially the design could be used for either application.

I am using the largest boat prop, ("Diameter 70L mm(2.76"), Pitch 1.4x70=98mm or 3.86") so looking to move to something larger like an airplane prop to achieve more flow, as it is turning this with ease it seems...


rated pump at 160W is consuming 121W regularily, so concerned that the RPMS might be higher leading to unnecessary wear on the motor.
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Old 01-08-2013, 06:26 PM   #4
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Wow 2.76 Dia!! I Used to have a impeller type "prop" inside a tube it was 0.75" dia. in 75 gal. tank. How much water you trying to move? Tank?? or pond??

cr
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Old 01-08-2013, 06:41 PM   #5
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lol

yeah - its a 1000 gallon tank. I have about 3 others just short of 1000 gallons, so this application will be duplicated in those as well.

i have some purchased pumps that move a 6000GPH, and this is dwarfing them!

fish love it - but i think the pump can produce more, and i worry that since the watts is 121 as opposed to 160w, that the RPM's might be too high.

I attempted to reach out to the company to find the manufactured RPMs, as I think that is relevant (maybe not) but they are not of any help so far.
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Old 01-08-2013, 06:52 PM   #6
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That is too cool. You have any pics showing your setup now? It would give us a better idea to what you have now. I agree with Dr kiwi that an impeller boat type might help you move more water with lower rpm.

I used to have several 20" pacu and fire tiger oscars, they would fight so much at dinner time just a blast to watch!!

btw....freshwater or saltwater

cr
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Old 01-08-2013, 07:44 PM   #7
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it is good advice - I might have to do more research and find a larger impeller for boats - just unsure how to do the proper calculation for a "non-battery" electric motor.

yeah - its a bit of a disease. I am sure it is the same in your hobby... once you get the bug, you can't stop.

I will try to dig up some pictures - I have some of me in the tank - measures 8x4x4
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Old 01-08-2013, 07:47 PM   #8
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sorry - freshwater.

Rays, piranhas, puffer fish,
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Old 01-08-2013, 09:27 PM   #9
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Originally Posted by Theplum View Post
lol

fish love it - but i think the pump can produce more, and i worry that since the watts is 121 as opposed to 160w, that the RPM's might be too high.

I attempted to reach out to the company to find the manufactured RPMs, as I think that is relevant (maybe not) but they are not of any help so far.
also you said

The motor is your typical pond motor, where a sealed magnet turns and spins a prop which is on a magnet shaft. It consumed approx 120 watts/hour, 60 hertz.


This is an AC motor you are using, The motor will run at the designed speed, controlled by the frequency of the input power (60 hertz) There is no physical connection between the spinning magnet on the output and a spinning magnet on the other side of a plastic wall ( most little pond pump motors work this way,) or it could be simple magnetic induction through the wall. If you over load the motor, or in my case the pump sucked in a piece of wood and totally stopped for about 2 days, there is no harm.

Too big a prop or impeller may slow down the output shaft, but there should be no harm to the motor.
Too small or no prop or impeller, the motor will just spin freely, doing no harm to itself.

Dave R, Proud PGR rider.
When you have flying skills like mine,
You become a master at repair.
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Old 01-08-2013, 09:51 PM   #10
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Originally Posted by Wildflyer View Post
also you said

The motor is your typical pond motor, where a sealed magnet turns and spins a prop which is on a magnet shaft. It consumed approx 120 watts/hour, 60 hertz.


This is an AC motor you are using, The motor will run at the designed speed, controlled by the frequency of the input power (60 hertz) There is no physical connection between the spinning magnet on the output and a spinning magnet on the other side of a plastic wall ( most little pond pump motors work this way,) or it could be simple magnetic induction through the wall. If you over load the motor, or in my case the pump sucked in a piece of wood and totally stopped for about 2 days, there is no harm.

Too big a prop or impeller may slow down the output shaft, but there should be no harm to the motor.
Too small or no prop or impeller, the motor will just spin freely, doing no harm to itself.
hmmmmmm

Thank you for the response.

I had thought that damage could occur as I damaged a pump in the past that i modified, though you are correct, that one was DC, not AC.

so - no damage can occur, that we think, the only difference is whether the prop is producing optimum flow or not.

I am hoping that by figuring out the RPMs of the motor, i will be able to find information from you RC guys where you have already figured out what propeller works best.

that was my theory anyway....

i suppose I could maybe try different weighted items in a tank and track the distance it moves the objects, along with the width of the flow.
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