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Old Jan 13, 2011, 08:23 AM
Registered User
South Africa
Joined Dec 2010
62 Posts
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Thrusters draw too much power!

Hey all
Just tested my thrusters, they create huge amount of thrust
One problem: at 5v they already draw 20amps each
Is there anything i can do to use a higher voltage , was planning on 12v and lowering the amps somehow?
(so higher voltage, low amps instead of low voltage, high amps)
So rather high voltage and low amps? How could i do this if it is possible
Because for 4 20amp thrusters,lights,camera ect I would need a BIG battery (too big...)

Thanks
Philipp
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Old Jan 13, 2011, 09:51 AM
Registered User
Aberdeenshire
Joined Jan 2011
30 Posts
What's the maximum voltage your motors will take?

What's their full load power? In watts?

In simple terms Watts = Volts X Current (ohms law)

If they are designed to withstand more voltage you can increase it, but your ESC (if you have one) will have to be rated for the increased voltage too.
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Old Jan 13, 2011, 10:15 AM
Registered User
South Africa
Joined Dec 2010
62 Posts
The maximum voltage is 12v. Couldnt find data sheet on the motors but they didnt get hot at 25amps so they probably have about 250-300w (i think)
I want to increase the voltage but decrease the amperage though, is this possible or are the 2 always directly proportional?
Thanks
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Old Jan 13, 2011, 10:57 AM
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Aberdeenshire
Joined Jan 2011
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Yes they are roughly proportional, if you increase the voltage the current should go down.
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Old Jan 14, 2011, 12:36 AM
NeverAgainVolunteerYourse lf
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Australia, QLD, Regents Park
Joined Mar 2007
3,733 Posts
If you double the voltage you will, with the same prop, double the amps and quadruple the power because you double the rpm. Its the propellor that is creating the load, it takes 4 times the power to drive a prop at double RPM.

You will only halve the amps on this setup if you keep the RPM of the prop the same by gearing down.

It sounds like you either have too high a KV motor or the prop is too large for the motor.

To use higher voltage you need to lower the KV of the motor, either by selecting a different motor or reducing Kv with a gearbox.

What prop and motor are you testing?

Nick
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Old Jan 14, 2011, 04:02 AM
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Aberdeenshire
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Probably worth noting too that a low RPM large prop will provide more thrust at the kind of speeds an ROV moves than a small high RPM propeller.
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Old Jan 14, 2011, 10:08 AM
Registered User
South Africa
Joined Dec 2010
62 Posts
Just figured out the prop im using is a racing prop since it has a high pitch
its 45mm and not sure about the pitch,(maybe like 35-40 degree when you look at it)
If i switch to a larger prop with lower pitch like this one
http://www.alwayshobbies.com/Boats/R...4-Threaded.ice
Would that prop cause a smaller load (less amps being used)? since it has a much lower pitch or will the added surface area even it out again?
Also if i have a high kv motor then a lower pitch prop would generally be better correct?
Thanks
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Old Jan 14, 2011, 11:23 AM
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Aberdeenshire
Joined Jan 2011
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At the prop end you'd want to go for a smaller prop with a less aggressive angle to decrease the current.

You could always run the motor more slowly via speed control but the amount of thrust would then be lower.
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Old Apr 18, 2011, 10:12 AM
Straight up is all I ask
Fairfield Ct USA
Joined Apr 2002
2,323 Posts
As far as power consumption is concerned Diameter is most important . What takes power is screwing the blades through the water . Pitch wont matter much to you for a few reasons . First is that most props for models are square in pitch with the acceptation of racing props. Meaning a 45mm dia prop will usually give you a 45mm pitch , a 3" diameter prop will have a 3" pitch .
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