Help me find the right DC motor / driver

[friogatto]

I am in search of a DC motor and controller/converter for standard home 120v. Here are some of the requirements.
Speed adjustable (future timer/driver controller)
Approx 1000 RPM - Max 2000 - min stop
For trial purposes up to 3000 rpm
Compact as possible
Maintenence free
continous duty rated
sealed if possible but not manditory
Trying to keep cost down.

I have no packground in electronics so I will be digging around here to learn more and reply as best I can. Some of the details are still being worked out with the impellar and housing unit but I thought I would start asking questions and learn as I go.

This will be going in a saltwater environment. It will be moving a 1 1/2" diameter X 6" tall squirrel cage type impellar running 24/7. Enough torque will be required to start the impellar without to much wear on the motor.
I am new to this forum and know nothing about DC motors so any suggetions would be great. Especially +'s and -'s of particular motor features.
Thanks

 

[itsmoked]

Hi friogatto,


More detail please!! There may be a "cooler" solution but I need more info.

 

[friogatto]

What type of details do I need to help you help me? I don't know what specs DC motors have so I don't know what I should be looking for.

 

[bklauba]

If it is 24/7 app, the most common forms of DC motors, which have brushes, might not be the best choice from a reliability standpoint. There are brushless DC motors, ( a bit complex for a motor novice )but there is a simpler solution (which maybe is itsmoked's "cooler" idea).

It is possible, in fact, rather easy, to use an inexpensive inverter that could be powered with 120 VAC, single phase, to power a 230 VAC 3ph motor. (See kbelectronics.com)

Such motors come in a wide variety. A 2 pole version, which would normally turn about 3500 RPM, if comnnected directly to a 230 VAC, 3 ph line, would span your speed range of 1000 - 3000 RPM, using such an inverter. (1000 would be the minimal speed, not just from your req'ts, but also due to excessive heating that would occur if running much below.)

What are the power/HP requirements? The impeller mfr. could help you with that.

BK

 

[sreid]

I suggest a Variable Frequency Drive (VFD) and a 3 phase induction motor. Automation direct is selling a 1/4 HP drive/motor for $200 and this may be a good starting point for you to experiment.

Usually, the drive is placed in a protected environment perhaps in a NEMA box remote from the motor. For exposure to a sea salt environment you may have to use something like a stainless steel washdown motor.

 

[itsmoked]

Yeah bklauba, that's where I was going. As I mentioned in another post around here I run an aquarium wave machine with a VFD in my living room. It's run it's cycles for 6 years without a single hitch.

 

[itsmoked]

friogatto, THis is what I'm talking about. One of these running a regular small three phase motor.

http://web5.automationdirect.com/static/specs/gs1drives.pdf

These are $165. You won't touch a DC drive for that. Nor a DC motor.

Hey, I addressed two posts with one link! TaDA!

 

[friogatto]

Thanks for all the replies. I dug through your links but it's hard to figure out what I need.
Does anyone have a link to a "crash course" on Motors so I can ask more specific questions?
Is there a way to find what kind of HP I'm going to need to run this thing? Maybe a math equation or something.
Also, it's not required to be a DC motor. It just has to spin the same way every time and push a huge impellar at aprox. 700 rpm. It also needs to be quiet and continous duty.
Is there a way to gear it down so I use a smaller hp motor?

Oh, and is there a way to post pics here so you have a better idea of what I am talking about?
Thanks

 

[itsmoked]

friogatto; There are some standard equations that we can help you with by applying them correctly.

Sadly I don't believe there is a way to post pics here...

Often people post them to a public viewing site then provide the link to it. This works pretty well and a lot of peeps do it. There are many of these sites out there and they are free.

It would be great if you could get us pics.

If not, we need a lot more detail.

 

[friogatto]

Link to Reef Central that gives a little more detail to my illusions.

http://www.reefcentral.com/forums/s...66658&perpage=25&highlight=eddie&pagenumber=2

 

[friogatto]

Oh, and remember that I am planning on this impellar being 8" tall with a 2-3" diameter

 

[itsmoked]

friogatto:

I took a look at your circulator. Should be interesting.
Especially from my point of view with my 165Gal marine aquarium. Couple of thoughts. I have lost three fish over the years to pump/circulator suction ports. How are you going to keep the wildlife out of this?

You will not want to spin this thing faster than about 100RPM if that! Otherwise you will suffer severe bearing, flexing problems. This means you can probably gear it like the one in that guys garage and use a shaded pole motor. You will want a fan on the other end of the motor shaft too.

If I were to do this I would look for a gear drive output shaded pole motor. I have used them for many projects like this.

But first I would build the squirrel cage and its mounts then twiddle it with my fingers to get a feel for the speed and how hard it would be to turn. You will find that you want it to turn MUCH slower than you first think. Once you figure this out you can use a CORDLESS variable speed drill to mess with it. Then you can wrap a string around the shaft and pull it with a spring scale/fish scale. Using the diameter of the shaft and the scale reading you will be able to figure out the torgue required and the speed (RPM).

Then you can hunt for the correct motor.

 

[friogatto]

Very good ideas, thanks.
I'll get to making the impellar and test it out. I have something similar to what I want but need to make some adjustments.
I'll post when it's complete.
itsmoked,
There will be a guard across the bottom to keep critters out. I too have lost many snails to pumps.
My concern is if the impellar will be able to suck water up 6-8" to supply it.
We'll see.

 

[TomG33]

Friogatto,

I also read your circular. Interesting idea. I agree with itsmoked, You are going to have to turn this thing very slow to get the gentle agitation you are looking for. I would suggest that when you build the prototype, make the blades removeable and start with say two opposite each other and try it, adding in Blade pairs as you go (keeping it symetrical for balance)
The design you show is optomized for air flow, not water flow, May i suggest you make the "Blades" much wider, say 2/3 the radius with a 1/3 radius gap in the center.

the power you are going to require is a function of how much water you move and how fast you move it. I am sure you do not want "fish Soup" so I am guessing slow gentle stiring with a couple of blades may be all that you require, Maybe no faster then 4 or 5 seconds per revolution.

Do a test run with a hand crank handle and then work out what speed the thing needs to be turned at, to achieve what you want to achieve.

At this speed A "Direct Drive" (meaning no intermediate gearing)is impractical as your motor would be trying to deliver a lot of torque at a very low speed. (Cooling a slow turning motor also has it's own problems)

I would suggest you do the rounds of some hobby shops and see if you can find some gearing units that you can install between your motor and the "Stirrer" I think i have seen some that you can pull apart and adjust the gear ratio. so you can fiddle with it to find what ratio works best.
Remember that the output at the slow speed side will require a lot of torque so you will need to look at the design to see if it is built accordingly.

I agree with all the other people that replied in that you should forget DC and use a small shaded pole ac motor such as found inside your washing machine. (maybe a motor out of a small fan would be closer to the power requirement)

This is my two cents worth

Tom Grayson

 

[itsmoked]

Friogatto, TomG33's comments are right on about the actual cage. Large blades. Very slow. Probably 4 blades total will do the trick, (start with two). Water is very, very, different from air. That's why ships don't have squirrel cage fans under them but instead just a few big blades.

If you use an air type blower the water will just circulate around each individual blade. Never actually any where else! The large blades allow the energy to be imparted into a larger volume of water so the large chunks can acutually separate and move away from the blades.

 

[mmasu]

Friogatto
i'm just a novice looking to learn from this forum, but one suggestion i do have is check ebay for the motor and driver - i've picked up both ac (1 phase and 3 phase) and dc gearmotors brand new for probably less than 0.10 on the dollar - drives too(both dc and inverter)