The RPM of Dyson DC04 vacuum motor and more....

[royp]

TL;DR

Does anybody know the typical motor rpm of a reasonably powerful vacuum cleaner? Specifically, same for Dyson DC04?

Hello,
I have got an integrated motor-fan unit of a Dyson DC04 vacuum. I don't know the motor speed (could not find from the manufacturer) but I guess, it must be well in excess of 10,000 rpm. Here is an image:

https://www.espares.co.uk/product/es1562476

Now, I want to fit an axial, blower fan (4 blades; around 20cm diameter) to the extended shaft (could be seen in the image) - at the opposite end of the centrifugal fan . If the motor is switched on now, both the fan will rotate and probably, the axial fan will run the motor speed down.

Will it blow up? I mean: will it affect the performance of the motor? Damage/burn it? Your valuable opinion will be very welcome.

Many thanks,

royp

 

[jrmichler]

Adding extra load to a motor will reduce the RPM, which will increase the current, and thus the heat. While the motor internal heat increases, the airflow over the motor decreases due to the lower RPM. More heat plus less heat removal = hotter motor. If the motor gets too hot, it burns up. You see this as smoke coming out of the motor. You can run a motor under overload conditions for a short time, typically a few seconds, without doing too much damage if you shut it off before it gets too hot.

Very few 8" diameter fans are made to run at speeds over 2000 or 3000 RPM. If it's a fan made of thin stamped aluminum sheet, it's definitely not designed for high speed operation.

If you want to do this sort of experimentation, it's a good idea to monitor the power consumption of your motor with a power monitor such as a Kill A Watt: http://www.p3international.com/products/p4400.html. When the power drawn by the motor exceeds the nameplate rating, you can expect to see smoke. And make sure that if a fan blade breaks off, it cannot hit anything important, such as you.

 

[royp]

Adding extra load to a motor will reduce the RPM, which will increase the current, and thus the heat. While the motor internal heat increases, the airflow over the motor decreases due to the lower RPM. More heat plus less heat removal = hotter motor. If the motor gets too hot, it burns up. You see this as smoke coming out of the motor. You can run a motor under overload conditions for a short time, typically a few seconds, without doing too much damage if you shut it off before it gets too hot.

Very few 8" diameter fans are made to run at speeds over 2000 or 3000 RPM. If it's a fan made of thin stamped aluminum sheet, it's definitely not designed for high speed operation.

If you want to do this sort of experimentation, it's a good idea to monitor the power consumption of your motor with a power monitor such as a Kill A Watt: http://www.p3international.com/products/p4400.html. When the power drawn by the motor exceeds the nameplate rating, you can expect to see smoke. And make sure that if a fan blade breaks off, it cannot hit anything important, such as you.

Many thanks for your precise and very useful advice, jrmichler . I am actually experimenting with designing a propulsion system where high suction (like a vacuum motor-fan) is necessary. I probably can 'afford' a smaller axial blower at the other end - for this purpose. So, given my constrains, can you please advise me on the choice of an axial, blower fan in terms of diameter/material/number of blades etc., which can sustain such high RPM? Or for sustainable and stable system, another centrifugal fan must be used?

 

[Rive]

For this kind of RPM you should consider using a model aircraft propeller. Those (should) have a rated RPM and an RPM-power curve.
Fitting that with the motor datasheet (if that exist) you might get an idea about the stable RPM of your system.

By the way, I think you should get/borrow some equipment to regulate the input voltage of the motor, so you could 'map up' the RPM-power curve and stay within the limits.

The cooling of these motors depends on the original fan, so you must not remove that by any chance.

 

[royp]

For this kind of RPM you should consider using a model aircraft propeller. Those (should) have a rated RPM and an RPM-power curve.
Fitting that with the motor datasheet (if that exist) you might get an idea about the stable RPM of your system.

By the way, I think you should get/borrow some equipment to regulate the input voltage of the motor, so you could 'map up' the RPM-power curve and stay within the limits.

The cooling of these motors depends on the original fan, so you must not remove that by any chance.

Many thanks, Rive - for the valuable suggestion!

 

[hutchphd]

There are ducted fans for electric radio control "jet" aircraft. I would look at them. They look, not surprisingly, like the input fans on high bypass turbofan engines.
I believe the axial design is better suited to high flow low backpressure than the radial.

 

[royp]

There are ducted fans for electric radio control "jet" aircraft. I would look at them. They look, not surprisingly, like the input fans on high bypass turbofan engines.
I believe the axial design is better suited to high flow low backpressure than the radial.

Many thanks, hutchphd for suggesting electric RC aircrafts. I was not very aware of them and have been going through. They are quite powerful but probably limited by the battery. As regards to the axial vs. radial, I have a feeling (based on the literature) that raidals can 'pack' more suction (pressure difference) as they house more 'blades' in a given diameter/circumference and can achieve more rpm with relatively low power input.