powerful stepper /brushless motors up to 12Krpm 750+W

[Simon]

The downside of  a proprietary, private system is that you can't find much help for it in a forum, you have to actually know what you are doing.

So far people have been quite helpful and i've gleaned some useful information from this discussion.

Why?  Because that is what will provide the airflow you need with the current blades?  Can those blades be run at those speeds?  Saying you need a "10krpm fan" is like saying you need a "48 pin MCU", it's verging on meaningless unless you provide a whole bunch of context.  (Same goes for the wattage rating frankly)

the fan being driven has been specifically speced, it just needs driving. The power rating has been given in relation to the speed required, what is so out of context ?in effect I've practically specified a torque if you do the math. Measuring the torque required to turn a bearing is not something you do with a mechanics torque wrench

Jesus Christ on a cracker.  Do you mean you guys might run it all the way through a single work day, or similarly short period of time?  Are you trying to run it for months on end?  And when it fails, what are the implications of it not running?

no it won't run for more than a few hours but then that is enough to eliminate any possible use of something that can take a higher load for a short period. whatever is used needs to withstand it's specs for prolonged use not run up and run down again.

Taking off some plastic blades and replacing them with heavier metal ones sounds safe.

yes but when you have a motor that has a controller specifically designed to start with the torque required to turn a light plastic load it sort of doesn't like it when you put a metal pullet on it and use it to belt drive another pulley at a higher speed with a metal impeller on it particularly when the controller of the motor is designed to detect clogging f the original fan and not try to run the motor full blast and burn it out.

[strangelovemd12]

So far people have been quite helpful and i've gleaned some useful information from this discussion.

Yeah, there has been a lot of gleaning in this thread.

the fan being driven has been specifically speced, it just needs driving.

So someone built/designed/sold/picked a fan for you to use, saying "This will meet your requirements when spun at 11krpm,"?  Alright, that's what I'll go with.

The power rating has been given in relation to the speed required, what is so out of context ? in effect I've practically specified a torque if you do the math.

Information provided:
Around 10krpm
Please show you how one would "calculate the torque".  Make some guesstimates based off of your "750w" requirement?  It will depend on fan diameter, mass, system resistances, etc.

Measuring the torque required to turn a bearing is not something you do with a mechanics torque wrench

You missed my boat.  I was saying that since you had trouble starting the system it would be handy to find out how much energy was required to crank the shaft when cold.  A torque wrench is a quick and dirty method that has served me well many times.

no it won't run for more than a few hours but then that is enough to eliminate any possible use of something that can take a higher load for a short period. whatever is used needs to withstand it's specs for prolonged use not run up and run down again.

Awesome, this is the sort of info that's needed.  Obviously we were never looking at just tossing a starting motor on there, even if it would get you the 750w consumption you want.  Nor do you need a proper extended up-time motor.  Just a continuous duty 1.2 service factor 10krpm unit.  Dime a dozen.

yes but when you have a motor that has a controller specifically designed to start with the torque required to turn a light plastic load it sort of doesn't like it when you put a metal pullet on it and use it to belt drive another pulley at a higher speed with a metal impeller on it particularly when the controller of the motor is designed to detect clogging f the original fan and not try to run the motor full blast and burn it out.

I understand, you want your improvised system to spin harder faster longer.  Reading this thread I pray that you guys are big fans of cotter pins and Loctite.


Something like this might work:

http://www.grainger.com/product/2M191?gclid=CLDCuf3BirsCFZFxQgodvQ8AiA&cm_mmc=PPC:GooglePLA-_-Motors-_-Definite%2520Purpose%2520AC%2520Motors-_-2M191&ci_src=17588969&ci_sku=2M191&ef_id=UfKNxwAABdCufJqv:20131129172604:s

Requires 120v, easily achieved from your car batteries and a boost converter.  Looks like 10krpm@SF1, but easily derated for 12k.  40*C ambient rating mean you probably wont need cooling at SF1.2  (Also, notice the brush life?  Things like this are why running for a workday and running for an extended period make a huge difference.)  Is it powerful enough?  Who can tell.  You could certainly talk it into drawing 750w though.

[Simon]

I understand, you want your improvised system to spin harder faster longer.  Reading this thread I pray that you guys are big fans of cotter pins and Loctite.

Oh yes we are. What we need is more power. our 500w motor will not run quite fast enough and is uncertain on startup due to the way it's controller is configured and stops if it decides we have overloaded it so we want more power margin (as derating will give better durability) and control over the controller so that we can configure it for what we want.

i note your suggested motor states an rpm range of 10'000 - 20'000 and being a dc brushed motor I guess that are around 10-12000 rpm we are looking at 50% power which is 1/2 Hp where are we are looking for 0.8-1 hp (around 750W of power usage)

[Simon]

another option of course can be a motor with integrated gear box to increase speed, of course we don't want the gearbox failing

[strangelovemd12]

i note your suggested motor states an rpm range of 10'000 - 20'000 and being a dc brushed motor I guess that are around 10-12000 rpm we are looking at 50% power which is 1/2 Hp where are we are looking for 0.8-1 hp (around 750W of power usage)

Guessing sucks, read the datasheet.  Actually, read a lot of things.  Reading is fun.  I'll make that motor draw 1kw@0rpm if you really want me to.
And yeah, motors sometimes come with integrated gearboxes.  Was this not being considered before?   

Please just tell me you're working on an amphibious vehicle so that I can just laugh off the stress.  (Silence means "yes")

[Simon]

well there was no obvious datasheet but there's a catalogue page and yes it says full load speed 20-100% so if i may guess again they are saying that it will retain it's full power down to 20% speed.

another requirement is that they obtainable, we don't want to develop a system around a motor only to find that the motors are no longer made.

i honestly don't know what sort of vehicle this is. We don't work on the actual vehicles only supply subsystems for them and i'm not that deep into this project just looking at motors for them.

[strangelovemd12]

another requirement is that they obtainable, we don't want to develop a system around a motor only to find that the motors are no longer made.

Call Grainger.  Nice folks.

[G7PSK]

I assume from the speeds being talked about that we are talking about some form of radial rather than axial fan unless you have something akin to the front end of a gas turbine. So how much air flow is required  ? cubic meters a minute at what pressure, given that you can go to a fan supplier and they should be able to list your options.

[Simon]

if by radial you mean something akin to a centrifugal water pump yes. It's an industrial high pressure air blower, cast impeller and housing with it's own bearings.

[free_electron]

And if you read the brushless motor page it describes a stepper type motor with built in controller and says about as much:

"Brushless motors may be described as stepper motors; however, the term stepper motor tends to be used for motors that are designed specifically to be operated in a mode where they are frequently stopped with the rotor in a defined angular position. This page describes more general brushless motor principles, though there is overlap."

lemme guess .. crappypedia ?

a stepper motor has poles that line up with the rotor.
a bldc does not ! if a bldc rotor has 8 poles the bldc stator has 9 ! a bldc is always driven by a 3 phase current. a stepper motor not.

[strangelovemd12]

I assume from the speeds being talked about that we are talking about some form of radial rather than axial fan unless you have something akin to the front end of a gas turbine. So how much air flow is required  ? cubic meters a minute at what pressure, given that you can go to a fan supplier and they should be able to list your options.

I've tried this form of logic, it seems to be a nonstarter.

[Simon]

I don't know what air flow specs are required, I told them to use a vacum motor but between it being brushed and high voltage they weren't having it and it may not even of done what they wanted. I will inquire further on monday about that as an option as if it would work it would really simplify things but I think preference is on a brushless motor as there are less mechanical parts to worry about.

[SeanB]

You do get 24V vacuum motors, commonly used in commercial wet extractors as a safe vacuum which will not shock even if it gets wet. About the same power as a mains motor, and about the same life.

[Simon]

same life ? because I'd be awfully worried about that amount of current being commuted on those brushes at 24V. There are 110V vacum motors and at the end of the day it won't be too hard to get 24V to near 100V using a H bridge and voltage doubling twice or a proper inverter. I think the concern with brushed motors is also the emi emmisions but I'll explore the possibility on monday

[SeanB]

I have had them run for over 5 years used daily ( about 2-3 hours a day) and they are cheap, about 40 pounds each as generic spare motors. Took one out last weekend that died, it did about a decade of work, and had worn the brushes down to springs, along with the commutator being about 3mm thinner where the brush ran. Aside from that and noisy bearings the motor was still fine, just really dirty. Easier to replace than put new brushes and bearings in.

[Simon]

any idea where to get them ?

[SeanB]

Any place that sells white goods spares to the trade, look in your yellow pages. Bosch, kArcher and WAP are units that are using these, though they tend to use a 36VAC motor inside, so as to still have a  SELV  rating even when wet.

[Simon]

Yes I've just googled and seen them all over the net and looking just like a unit i used at 240V so we are already familiar with the basic type but we will need look at the power, I've seen a 500W one. Monday I will contact the people I got my 240V one from and see what they have.

[SeanB]

If you need more than the single one can flow and have the space then use 2 in parallel with equal length and bend ducting on inlet and outlet to allow them to share the load. Used on commercial machines to get the flow rate up. you also get 2 stage units that have 2 series impeller units that give extra suction within a single housing.

[Simon]

yes I had considered that and i suppose it adds safety margin in redundancy. the one i used in a hand drier is 2 stage and there are 3 stage ones too.