Motor CFM @28"

[Tony]

Using one Kemo module plus a potentiometer is a fairly low cost simple and practical solution for an entry level flow bench.

Trying to combine multipes of these creates a host of potential problems you could well do without.
Also the cost multiplies, especially if you start blowing up these modules, as is quite likely.
They are not very robust, and motor faults will very likely also kill the Kemo module.

A six motor bench would definitel;y benefit from one of Bruce's well proven motor control systems.
It will work much better than the Kemo, with fewer quirks at the high and low ends of the adjustment range.
It has a fully mains isolated ten turn potentiometer that runs on a low (and totally safe) dc voltage.
It will have a massive power rating that can easily cope with as many motors you have the available power to run.
If each motor is individually fused, a failed motor will blow the fuse and the much more robust power controller will be pretty certain to survive the mishap.

Six 1600 watt motors is 9.6Kw, or 40 Amps at 240v.
That is a LOT of power and you need something pretty solid if its going to do the job reliably for a long time.
Save up and buy something decent.
It will probably save you money and a lot of frustration in the long run.

And if you later decide to upgrade to fully automatic depression control, the PTS pressure controller just connects straight to it.

[rwdford]

Some good points there Tony, I just went with the Kemo controller since I know someone using one to power 4 motors probably averaging 1200W each, I imagine the max watt's and amps would be with the motors under full vacuum and no airflow, I believe 1200W is more likely to be the max power consumption at 40" water but time will tell, I have the electronics so I will use them and see how it goes since a lot of other people seem to be using them, the PTS power controller sounds very good, I will see how it goes and if I have any trouble I can always upgrade now that I know it will work with EU power

Many thanks

[Tony]

If you already have the electronics, then it is logical to use what you have.

There are a couple of ways you could link three modules to operate together off one control potentiometer.
The "cleanest" way would be to buy three of the Kemo isolation modules that allow an isolated dc control voltage replace the potentiometer on each module.
You can then run all three (or more) Kemo power modules from the dc output of a single potentiometer.
The power modules remain electrically isolated from each other, and from the control potentiometer (for safety) and the power modules could be run off different mains phases if required, or all from one single phase.

If you are a bit more adventurous on the electrical side, those Kemo isolation modules almost certainly use a fairly special type of opto isolator, one which has a light dependent resistor on the output (actually a JFET).
Just that, and a couple of resistors.
You could make your own isolation modules using an H11F1 opto isolator for probably only a couple of Euros.
I can go into that a bit more deeply if that idea interests you.

The entirely mechanical way, would be to link three control potentiometers arranged in a triangle, with a light drive belt and three large diameter pulleys.
It sounds a bit red neck, but its a practical, simple low cost solution.

I don't like the idea of directly connecting three Kemo modules at the potentiometer connections.
It should in theory be possible, but if one module develops a fault, all three are likely to blow up spectacularly.

[Tim]

After long searching...
http://stores.ebay.com/Mainline-Electro ... 34.c0.m322

[rwdford]

Thank you for the replies and ideas

After a little more testing I have found that the motors will not trip a 5A fuse each, even drawing over 80" vacuum with the chamber sealed and also starting the motors straight to full power they will still not trip a 10A fuse (2 motors)

So what I have found is that the motors are actually more efficient since they draw 1200W max, a bit of false advertising with the 1600W claim but this is a good thing as the controller is rated for 16A continuous, feeding 3 motors is no problem and 4 may also be possible

I also tried a 5A fuse feeding 2 motors and I could get 30" vacuum before it went, so at 30" vacuum each motor draws 600W, and 1200W each at maximum vacuum over 80", I am thinking at 50" with a large orifice the motors will draw 3.5 to 4A each / 840 to 960W (no sense being able to go to 80" vacuum and ideally a breaker switch should cut out at say 50" or less at the motor)

Also about the variable speed, I can use two controllers and 3 motors per controller + stereo lin pots (one channel for each controller) to control all of the motors at the same time no problem and I believe 8 motors would also be run this way with sensible max vacuum levels and 2P 15A to 16A breaker switch feeding each controller with a good sized heat sink and cooling fan, a very inexpensive solution for up to 530CFM @28" and a 30A 240V power supply

After thinking it through I am going to control 4 motors with 2 controllers, and have the other 2 motors on switches + 2 check valves

This way I will be able to get around 270CFM @28" with the 4 motors and up to 400CFM with all 6

[Tony]

That sounds like a very good solution.

Those motors probably will draw much closer to 1,600 wats at full voltage, and full unrestricted airflow.
Any back pressure actually reduces mass airflow, and motor current.
It sounds counter intuitive, higher differential air pressure drawing less shaft power, but its true with a centrifugal blower.

Run any vacuum cleaner and block the hose. The motor will definitely be heard to speed up.
If you ever do blow a fuse, it will probably be while running the bench flat out with just an open test hole.

[SSR]

Is the best motor to fit not the one with the biggest wattage? What about a 2200w ? Not for the one which is adjustable I know.

Slightly O/T, but in Europe we are facing a ban on vacuum cleaners which are too powerful, yes really:

https://uk.finance.yahoo.com/news/vacuu ... 40275.html

In the short term there is no cause for worry, but long term it will mean powerful motors will be harder to find

[rwdford]

That is interesting about cfm vs amps draw Tony

I tested the 2 motors connected to mains power with a 10A fuse, with completely unrestricted flow and also with completely closed off flow, nothing will blow the 10A fuse even straight to full power so the max watts per motor is certainly 1200 max each, the 1600W advertised must be just for sales

What I did notice is when testing at 45" and then completely closing off the flow the motor rpm's rise significantly as you said and it reaches a point when I can hear the air flowing back and forth through the motor as it reaches over 80", not a test I would ever recommend doing but the chamber I am using is super strong and just wanted to test the limits of these parts

Interestingly the guy I know running 4 motors from 1 controller is using a single 13A fuse, he says if the motor rpm's are increased gradually all works fine but if he starts the motors with the pot set too high the fuse needs replacing

I am pretty sure the max load is when the motors are started from 0 to full power, as for where it is when running at full speed you are likely right that it is with unrestricted airflow, I will do a little more testing to see what the max amps are under different conditions



Very large motors could work but they would need testing to measure CFM @44" vs amps and voltage, these motors cost about £40 each and flow 66CFM to 68CFM each @44" depending on max voltage input, Lamb motors probably flow 15% more on average but they seem to be harder to find in Europe, the cost would likely be close to double after import duty and postage, but maybe worth it for long term use

Any idea what amps and volts Lamb motors draw with 44" at the motor under full power and what the CFM is at 28" + 16"?

[Tim]

https://www.google.fi/webhp?sourceid=ch ... 96.3.703-2
Pick link (xls) Results - Tractorsport . If i understand rigth this good xls is made by bruce. Domel 496.3.703-2 is one of best candidate 9 motors setup with 3 power contol. Domel not anymore publish their motor data...

[Tony]

Is the best motor to fit not the one with the biggest wattage?

What eventually limits most of us is the power available from the mains.
The general idea is to try to get the most air for the least amps.

When testing and comparing motors, the figure of most interest should be CFM per amp at around 44 inches depression.
Sometimes that can be found in a published specification, sometimes you need to test and measure this yourself.

Motor wattage is of no real significance, because size has nothing to do with efficiency.
If the motors are a bit small, you just run more of them, and still end up with a lot more air for the same amps.

Cost comes into this as well, the larger motors are always more expensive, often hugely expensive.
Typical expected efficiences fall into the range of around 8 to 16 CFM per amp for 220-240 volt motors, and about half that for 110-120 volt motors.
Good motors can supply TWICE the air of junk motors, so its well worth looking into.

The problem is, that a source of good surplus motors may suddenly become available, and all be completely sold out in a just few months.
So the motor supply situation is constantly changing.
There are some really good small motors out there, and some pretty good big ones too.
And there is also a lot of highly priced junk.
Price and size are not reliable indicators of efficiency.

A particular motor may be more efficient at much higher or lower depressions, and be pretty average at around 44 inches where we like to run ours. Others peak very nicely in efficiency at around 44 inches and might be ideal.

Its all a bit of a lucky guess unless you do some research.
Any serious effort you put into sourcing some pefect motors at the flow bench planning stage will be amply rewarded.