Thread: JET 2HP Dusty - bother modding?

I have one of these DC designs amongst my DC collection - They are an old design, not very efficient and don't think it's worth modifying.

My 2HP modification (see sticky in this forum) relies on having an impeller exit area approx equivalent to a 6" round duct but this impeller has a round 5" exit and will requires a major rebuild of the impeller to make it a 6" exitc so it is a limiting factor against modification
BTW they are not really baffles but deflectors to set up a semi cyclonic action in the chip bag. They are best left alone if you want this unit to act efficiently.

So I've delta-ed the motor, hooked up a Huanyang VFD, set the output freq to 50 Hz and the motor runs very slowly (but smoothly) with only 38V on the output. I've not used this particular drive before - is there a setting that needs tweaking for this kind of load?

Aaand to answer my own question, this VFD came setup to drive spindles, so the max motor freq was 400Hz, and the thing puts out a voltage that's proportional to the Hz to Max Hz ratio.

Setting the max motor freq to 50Hz fixed it.

Originally Posted by RustyArc

Aaand to answer my own question, this VFD came setup to drive spindles, so the max motor freq was 400Hz, and the thing puts out a voltage that's proportional to the Hz to Max Hz ratio.

Setting the max motor freq to 50Hz fixed it.

Just out of curiousity, how do adjust the motor frequency?

Originally Posted by davesmylie

Just out of curiousity, how do adjust the motor frequency?

Firstly it has to be a 3Phase motor.
To run a 3phase motor from single phase power the motor must be configured to delta and connected to the mains power via a box of eletrickery called a Variable Frequency Drive (VFD)
VFDs are usually programable and one of the settings that can be altered is the output frequency.

Rusty Arc, You may be able to run the motor at 60Hz and get 20% more flow.
Whgen you do this you should watch the current because the higher frequency may draw too much power and overheat the motor.

Originally Posted by BobL

Rusty Arc, You may be able to run the motor at 60Hz and get 20% more flow.
Whgen you do this you should watch the current because the higher frequency may draw too much power and overheat the motor.

I should sort out some way of measuring the airflow, then I can find out if them affinity laws are true

Originally Posted by RustyArc

I should sort out some way of measuring the airflow, then I can find out if them affinity laws are true

A simple way to measure changes to flow indirectly is to measure the Static Pressure (SP) in inches of water column of your setup.

1) Make a water column manometer
2) Block and seal the DC inlet.
3) Attach one side of the manometer to the sealed inlet and measure the SP
4) use the chart below to determine the max airflow
The red slanted lines are the duct size in inches.
Start on the horizontal axis with your measures SP and proceed vertically upwards till you strike the MINIMUM ducting size in the path of the air flow and then make a right angle on the graph and proceed to the LHS axis and read off the CFM.

Not seeing a whole lot of SI units there

Cheers though. I'll give it a try.

Originally Posted by RustyArc

Not seeing a whole lot of SI units there .

If I could find a graph with SI units I would post it.

I did find a graph with SI units with the pressure in Pa but then you'd have to convert mm or cm of water to Pa.

Originally Posted by BobL

but then you'd have to convert mm or cm of water to Pa.

That isn't the most difficult conversion. 1mm is approx 10Pa.

Originally Posted by RustyArc

That isn't the most difficult conversion. 1mm is approx 10Pa.

I spent all of my life working and teaching with SI except when it comes to air flow. The specs for the fans and filters we used in our labs were mostly imperial and so I worked with Imperial. Only when I had to communicate with students/engineers/colleagues or at conferences about air flow did I convert final results to SI, except once when I gave a presentation in Denver.