need help with designing a small propeller pump

[Frank De Block-BurijParticipant @frankdeblock-burij61943]

Well, yes, I want to move the water, not the boat.

I am preparing an aquaponics project.

aquaponics is the breeding of fish and plants in a closed system, all very ecologic. See my website http://www.aquaponics.eu for more details.

 

To move the water around, we need small pumps.

I have calculated that commonly used centrifugal pumps are very inefficient: an efficiency of 3% is an achievement.

 

The reasons for this are multiple: poor design, the fact that centrifugal pumps are designed for much higher heads (say 30-40 meters) than we need: on average, we need only 2 meters head.

 

In my research I have found that for these heads, propeller pumps are much more efficient. Unfortunately, there are no small propeller pumps available on the market.

 

So I will try to build my own.

 

What are the requirements?

-12 volts (so the pumps can be battery operated and serve as emergency backup in case of power failure).

-flow somewhere between 10 and 20 l/min.

-2 to 3 m head

-simple on/off operation

-standard, off the shelf motor (see 

http://www.johnsonmotor.com/)

 

please help in choosing the propeller and calculating the motor.

 

Frank 

 

[Frank De Block-BurijParticipant @frankdeblock-burij61943]

[Dave MilbournParticipant @davemilbourn48782]

Frank

Have you seen these? Link here

The motor is only 7.2v but that shouldn’t be a problem. 

Dave M

Edited By Colin Bishop on 12/11/2009 10:48:37

[60wattParticipant @60watt]

http://www.the12voltshop.co.uk/Shop/water-and-plumbing/pumps/reich/

 

http://shop.ebay.co.uk/i.html?_nkw=Reich+pump

[JC Uknz 1Participant @jcuknz1]

My need is for bow thrusters so I got myself a couple of windscreen wiper pumps.  12 volt required which I work with in my boats.     I doubt if they would like continuous running if that is a requirement of yours?  I know it is fun making things for oneself but when the Asians make them so well and usually cheaply ???

[60wattParticipant @60watt]

Frank’s project seems more about cost capitalisation of power equipment design.

 

I used to do that myself can see that there is a crucial piece of data that he missed out.

It may be that continuous usage means a few watts of power saved is worth much more than the pump(s) purchase cost.

[Frank De Block-BurijParticipant @frankdeblock-burij61943]

 Thank you, Dave, for the tip:

I found the
manufacturer of the bow thrusters, had a phone conversation with them
and they are going to send me some equipment to experiment with.

http://www.raboesch.com/

 

60watt, reich pumps are centrifugal pumps, not propeller pump

but they are cheap, very reliable and may possibly be used for bow thrusters

 

<<Frank’s project seems more about cost capitalisation of power equipment design.

 

indeed, like you say, in continuous usage, the price of the pump is less important than power consumtion

 

would love to find an asian manufacturer of small propeller pumps

 

frank

[60wattParticipant @60watt]

Inputting your pressure head and flow rates into the Power = Pressure x Volume/second equation gives you 3.4 to 13 watt.That is within the capability of many small coreless motors on 12 volts.

 

Coreless motors, will give efficiency peaks of > 80% where the iron cored motor you get with the bow thruster will probably not be >60% at best.

The peak efficiency point of a coreless motor is much nearer the motor free running speed than the typical 80% for an iron cored motor.

 

A rough equivalent for size,power and rpm of the iron cored motor variety would be a 385 while the motor you would get on the bow thruster is a more powerful 400 with the same dimensions as a 385 but with a much higher torque.(suits a bigger prop than 385)

[Frank De Block-BurijParticipant @frankdeblock-burij61943]

thanks, 60Watt,

your calculations correspond with mine

but what is a 385 and a 400?

probably a reference of some kind to a motor

would that motor be right for continuous usage?

what would be the right prop choice?

what would be the right rpm?

 

frank

[60wattParticipant @60watt]

RE385 http://www.mfacomodrills.com/motors/385.html

Available from all model suppliers and RS components

More from Mabuchi

 

400 7.2volt Graupner Speed 400 7.2V (1794)

 

An industrial design for continuous usage would have an ac motor as brushless dc motors are only just becoming common.I only dealt with large ac motors so I can’t give you the lifetime of a brushed dc motor.The limitation is brush wear and not temperature as the power losses at 6 watts output can be maintained continuously by a 385/400 motor.Another issue is coreless motors use metal brushes for low friction and I don’t know how that affects lifetime.

 

The prop determines the rpm and power output of a motor so there must be a starting point,of course.

I started with the power on 12 volt and picked a 385 on that basis.

From there, and with a similar known motor, you can roughly calibrate a prop in terms of load torque and you will get there in one or two tries at most.

In model boat terms, a 20-25 mm small pitch and blade-area (for high rpm) suits a 385.

 

I am suggesting you use a coreless motor as the absence of iron gives them a higher peak efficiency.

You can get these from surplus motor suppliers but a search of RS components is bound to turn up a coreless motor at the right power,though pricey.

This will help you understand motors but coreless motors have a maximum efficiency of around 80% and at closer to the Y-axis.

[60wattParticipant @60watt]

I said they were expensive Ironless motors .The pdf data is useful,though.

Here is a surplus one MF859 from surplustraders

My prop estimation is for 1:1 ratio but a bow thrustor does not work on that ratio.

 

It would be easier  to save power by replacing lights with LED lamps. 

[Frank De Block-BurijParticipant @frankdeblock-burij61943]

60watt,

whaw, what a weath of information

will need some time to work through it

thanks a lot

can I come back to you later for more aid?

frank

[60wattParticipant @60watt]

Apart from the tip about coreless motors,most folk here know 385 and 400 motors so any of them with O-level physics could have helped.

I’ve already seen the piece on your website so why not keep it there?

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