roots blower as an air mover??

[1960FL]

Beetle,

There are many VFD out there that will do single to three phase conversion and offer you good control over the motor. You will obtain much better control running a 3 phase motor which can be had cheep in the US if you look.

Rick

[Beetle]

finding a 3 phase motor is easy.....what about the VFD??? vfd is all new to me. i can put single phase in and get 3 phase out?? thats cool!! i just looked on E BAY at VFD's and it's all pig latin to me..................

[Tony]

Yes, you can get a variable frequency drive that will run from a single phase, but usually the largest VFD you will be able to find will be rated around 3 Hp.
The reason being, at 3Hp the current draw will be about as much as you can reasonably expect to get from a single normal wall outlet in most countries.

The rather strange power distribution system in America is absolutely unique world wide.
Nowhere else in the world can so much power be drawn at 220 volts across only one phase.
That is why very large single phase VFD's are simply not made, they could only ever be used in the USA.
There are other technical reasons too, three phase power is much more efficient for many things, and a very big VFD supplied with three phase input power can be made smaller and more power efficient, but up to 3Hp that is much less of a consideration.

The convenience of being able to plug in a small low power VFD into any available wall outlet has made small single phase input VFDs very popular.

The advantages of using a VFD for your flow bench will be:

At turn on, the speed can be automatically ramped up eliminating any initial power surge or belt slippage.
Because there are no huge power surges, you can run right up at the maximum available rated mains current without fear of nuisance fuse blowing or breaker tripping.
The airflow can be controlled by motor speed with very precise control.
The motor only needs to run fast enough to do the job, minimum noise, and minimum power consumption.
Induction motors have no sparking brushes that burn up or wear out, they are also silent and very long term reliable.
Three phase Induction motors, especially large ones, are readily available at very low cost.
A VFD will regulate motor speed precisely, sudden jumps or changes in mains supply voltage will have absolutely no effect at all on the set motor running speed.
A VFD can run a motor faster than it's rating plate speed, as well as slower, so pulley drive ratio to the blower becomes far less critical. You can still get full rated motor horsepower at much increased motor speed.
Motor direction can be reversed, and with a roots blower, that very neatly solves the problem of reconfiguring the flow bench direction for blow/suck.
A VFD can be connected to the Forum automatic test pressure controller, to provide a constant precise test pressure over the full range of flow from absolute maximum right down to zero totally blocked flow.

Only disadvantage is the initial cost of a VFD, but these are now becoming much more common, and the cost is rapidly coming down.

[1960FL]

Here is an example of a phase conversion VFD,

220/240 VAC single phase in and max 5HP 17 amp 3 phase out

A little pricey at first but at $600 US it is not far off the price of 8 good vacuum motors and it is far mor versitile. And it has alot of nice features like PWM and other control input functions.

Rick

[Beetle]

thanks for the link Rick...now i know what to look for.....

[Tony]

Rick, if you think that $600 is pricey, the same thing in Australia would be a steal at a thousand dollars more than that.
US and oZ dollars are just about at parity at the moment.

It stuns me when I hear Americans complain about the cost of things, when the exact same items cost two or three times as much in most other countries.
You guys just don't realize how lucky you are.

In most places around the world these days, gasoline is more like ten US dollars a US gallon.
Yet I hear Americans saying that five dollar gasoline in the US will lead to riots, and the complete economic death of America.

[jfholm]

Rick, if you think that $600 is pricey, the same thing in Australia would be a steal at a thousand dollars more than that.
US and oZ dollars are just about at parity at the moment.

It stuns me when I hear Americans complain about the cost of things, when the exact same items cost two or three times as much in most other countries.
You guys just don't realize how lucky you are.

In most places around the world these days, gasoline is more like ten US dollars a US gallon.
Yet I hear Americans saying that five dollar gasoline in the US will lead to riots, and the complete economic death of America.

Tony,
That is exactly why we are so often referred to as "The Ugly Americans"

John

[Tony]

John,
Our uglies are more ugly than your uglies.
We can beat you at anything.

[jfholm]

John,
Our uglies are more ugly than your uglies.
We can beat you at anything.

Tony,
That made me LMAO as years ago I dated an Aussie girl who was over here for a while. She said she liked the American guys because the Aussie guys were always too busy trying to out do each other and did not have time for the girls. She also gave me an Aussie to American dictionary so I would know what the heck she meant when she talked about her Wooley Jumper and her Bonnet and yawning in technicolor. She was a hoot. I have always wanted to come to Australia since then. Love you guys down under.

John

[Tony]

That all seems very true John, from what I have heard. Aussie girls really do like American guys.

I have never been to America myself, but we are constantly bombarded with Hollywood and the whole American cultural thing.
Aussies in my generation grew up on a strict diet of "I love Lucy" "Leave it to Beaver" and The Mickey Mouse Club. You cannot get any more American than that.

American women seem to be far more demanding, assertive and aggressive than Australian women.
It really amuses Australian guys to learn that a typical American husband entertains his buddies out in the garage. Whereas the women rule the house.

As a result, American males seem to be far more polite, thoughtful, and much less dominant than the rude aggressive, competitive beer belly Aussie male.
So to an Australian girl, an American male looks like a pure gentleman compared to an Aussie brute.

And to an Aussie brute, a stuck up spoiled demanding American female is just insufferable.
All they want to do is get married, give you hell, get a divorce, and financially clean you out.
At least that is how it seems.

So here we have the perfect solution to the worlds problems.

American women can get their divorce and/or become lesbians.

Australian women can go over to America, find husbands and both can then be really happy.

Those beautiful sexy Asian women that are even less demanding than ours, can come to Australia and be really happy over here, and make us Aussie brutes really happy too.

I believe this is actually very slowly happening................