Thread: VFD install summaries

Originally Posted by BobL

Depends what they're used for.
When HYs were half the price of Powtrans I ended up installing 7 of them on various basic machines in my shed and have installed another 4 elsewhere.
The oldest ones are now 6 years old - none have failed and have done a great job at protecting motors when I did something silly.
I wouldn't have used a HY on a higher end machine, or recommend using them in a high use facility.
These days I would go strait to the Powtran as they have more features and are well priced.

It's great that they all still going

Being a Sparky i stick to "approved" equipment, and i take care to wire according to our regulations. That's the reason i don't recommend some drives...

Originally Posted by ericks2

Being a Sparky i stick to "approved" equipment, and i take care to wire according to our regulations. That's the reason i don't recommend some drives...

Sure that makes sense - especially as you have to sort of guarantee the installation..

Originally Posted by BobL

Sure that makes sense - especially as you have to sort of guarantee the installation..

Obviously i am not responsible for what people add to an installation or plug into a power point. In my case it's not an issue cause i only do Industrial maintenance, breakdowns and installations. However i have seen some scary things people do re mains power

Originally Posted by ericks2

Obviously i am not responsible for what people add to an installation or plug into a power point.

I was referring to VFD installations that you undertake.

Originally Posted by BobL

I was referring to VFD installations that you undertake.

Thanks i understood you meant that

Bob
On a Metalwork forum (american) there is reference to Inverter Quality Motors for use on VFD equiped machinery (lathes & mills). From what I can understand these motors are better equiped to handle prolonged operation at lower & higher frequencies. Do you know what constitutes an inverter quality motor, are they available in Au and are they worthwhile?
thanks
Ron

Originally Posted by ronboult

Bob
On a Metalwork forum (american) there is reference to Inverter Quality Motors for use on VFD equiped machinery (lathes & mills). From what I can understand these motors are better equiped to handle prolonged operation at lower & higher frequencies. Do you know what constitutes an inverter quality motor, are they available in Au and are they worthwhile?

Ron, you basically nailed it.

I'm not that familiar with these motors and the following is basically what I know.

A standard 50/60 Hz 3P motor is built to run efficiently at these frequencies.
Above and below these frequencies they cannot produce full power.
Below these frequencies the power is proportional to the frequency.
This is compensated for by using a vector drive VFD but that does not fix the issue completely.
Another issue since most motors are self cooling at low frequencies motor cooling becomes inefficient and can lead to probs - this can be addressed by independent or load sensitive fans.

Above 50/60 Hz the power drops of slowly until 150 - 200Hz where the frictional forces start to kick in and the motor runs out of puff.

Inverter rated motors have been available as spindle type motors as used for CNC for some time and are increasingly available in other formats.
As well as being made with magnetic characteristics that suit a wider speed range these motors are better balanced and use better bearings so they can run up to 24k or even 30k RPM.
For these high speed motors the heating problems are addressed by water cooling but this can be a PITA.
The non spindle inverted motors used on machinery usually have constant torque between about 5 and 75 Hz which makes them ideal for mills and lathes.
At the other end of the speed range bear in mind you shouldn't spin the mechanicals on most machinery past their top mechanical geared ratings anyway

I haven't seen non-spindle inverter type motors for sale in Australia but I haven't been looking too hard because my motor budget typically is around $50 and I'm using these mostly on budget level machines .
When available inverter motors are not that expensive on eBay, used ones go for $100 for small ones, ~$250 for 1.5 - 2kW.
If you have the readies or a $2000+ mill or lathe I'd say its worth it.

Thanks Bob
I run both wood and metal home worshops. Fortunately I havle both single and 3 phase available which makes more VFD’s available at good prices
Several of my machines are VFD equipped using mainly AB drives.
My problem is my vertical bandsaw, a Woodfast 19” which has been converted to 3phase using a 3hp 4pole flange mount TEFC motor and an old style AB 1315 non vector VFD.
I use this saw for both wood and metals including steel. As you know to cut steel the sfm is quite low and I need to run the motor as low as 10-15rpm which is a problem with both power and cooling. Fortunately most of my steel cutting is of quite short duration and sofar over-heating doesnt seem to be a problem.
I think the best (ideal)solution would be to replace the motor with a 6 pole inverter model and a modern vector control VFD. The 6 pole motor would not require as low a frequency for the required band speed and hence have more power.
Couldnt find a ready source of 6 Pole 3hp 3 phase motors when I first did the conversion.
Hence my interest in Inverter quality motors if I need to purchase a new motor. Do you think just updating the VFD to a Vector VFD would be sufficient. Since I am quite comfortable programming AB drives I would probably stick to something like a AB Powerflex 70 which are available 2nd hand reasonably cheaply on ebay and seem to be bullet proof.
Cheers
Ron

Originally Posted by bueller

Just need to order some motors for both of them now, they’ll both be getting WEG W21 units, going to place the order later on today if I get the time.

Hi bueller
The way you mentioned the WEG W21 motors made me think there must be something special about them.
What is it that makes you specify these motors
Thanks
Ron

Just decent quality for not a huge amount more than the no name motors from China. Industrial use mainly but they have a decent selection of smaller HP motors as well.

Just to clarify/amend my previous post.
The power and torque curves for VFDs can be a bit confusing.
The diagram below shows some power versus frequency curves for VFD motor combinations.

First lets look at theoretical power and torque
The black line represents the theoretical response of a 3P induction motor - the speeds below 50Hz are usually constant torque, while for frequencies above 50Hz its usually constant power.
Since power is basically torque x speed the region below 50Hx is in theory a constant torque region (blue line) - the reason the power increases is because speed increases.
Above 50 Hz, the power is constant but as speed increasing this actually means the torque is dropping as the speed increases.

Now lets look at the practical (non-vector drive) this is usually called V/F drive.
The green line shows the typically power curve.
Nothing happens until you get enough torque to get things going. On my WW lathe (1 HP motor on an HY non-vector drive VFD) nothing happens until it gets to ~10Hz.
Torque and power stay low until ~ 20Hz before it its it starts approximating a theoretical motor.
Above 50Hz the power drops off slowly at first but above about 150Hz it will really start to drop of

Now lets look at the practical vector drive VFD driven motor - orange curve
At less than 50Hz a vector drive VFD will boost the current at low speed to provide increase torque which provides more power
On my MW lathe with budget level vector drive VFD and budget level motor the slowest it will run is ~2.5 Hz but at that speed I can stop it by hand - at 5Hz I have no chance of stopping it. Of course it depends on gear ratios etc but that gives you an idea of what to expect
Above that it will not do much more.

Screen Shot 2018-03-03 at 1.31.57 pm.png

In principal all motors can deliver constant torque below 50Hz but in practice most need more juice below about 15 Hz than a basic V/F drive can deliver at those speeds.
An inverter type motor will operate closer to theory than a general motor but if you really want a boost at low speed then using a vector drive will make more of a difference even with a basic motor.
A combo of the two will probably be even better.

I don't see how you can get a 1450 rpm motor running anywhere near 10-15Hz using a regular V/F VFD.

Even using a 6 pole motor is only to drop your base speed to ~1000 rpm at 50Hz.
Seeing as you need 10-15 RPM this means you will end up in the <1 - 1.5 Hz range.
A good Vector drive VFD will struggle with this and an inverter motors won't add much more to this.

I reckon the best use of any $$ is to purchase a small dedicated metal cutting Band saw.
They have so many advantages over upright BS, the main one being that you start them running and walk away - when they finish cutting they turn themselves off
The no-hands cutting is heaps safer.
Cutting lube can be use to greatly extend the life of blades
They are slow enough to cut SS and other hard steels.
But best of all, I really dislike swapping blades - a 10-14 TPI bimetal blade on the metal cutting saw cuts just about everything and saves a lot of time .

Thanks Bob for your comprehensive reply. I now better understand how a vector drive functions at low hertz. I am sorry but I made a typo in my previous post when I put 10-15 rpm when I should hve typed 10-15Hz. This does work at the moment but the saw has very little power at this frequency.
Your suggestion of a dedicated horizontal saw is correct and I already knew this in the back of my mind but was hoping to get away with what I have mainly for space reasons.
PS Another problem with a vertical saw cutting both steel and wood. Cant use my dust extraction when cutting steel. Have to leave extraction off for a period after cutting to ensure no hot metal to ignite my sawdust bin. Fortunately my saw is usually fairly clean of sawdust to start with the Clearview connected
Cheers
Ron

10-15Hz is doddle for a vector drive - the only issue you might have is overheating with extended use, especially because a Vector drive provides more current at low revs so the motor will get hotter - you could always attach a 6" computer fan on top of the motor. I did this on a motor I had plans to run at 15-25 Hz but I never got around to using it.
A vector drive at 10-15Hz should give you the same power as the drive does at around 20-30Hz, so about half the available motor power.

Originally Posted by ronboult

PS Another problem with a vertical saw cutting both steel and wood. Cant use my dust extraction when cutting steel. Have to leave extraction off for a period after cutting to ensure no hot metal to ignite my sawdust bin. Fortunately my saw is usually fairly clean of sawdust to start with the Clearview connected

Actually you can - this is what I did for my metal linisher.
Basically its a fire proof chip catcher made from a 20L drum which incidentally was used to hold raw alcohol (cutting that open was another story)
The corrugated ducting is made of aluminised mylar used in stope top ventilation hoods. This stuff is moderately heat resistant.
The chip catcher will prevent pieces of hot metal and sparks from getting into the PU flexy and then the DC.
With the light off at night you can see if any sparks get into the PU flexy outtake but have yet to see a single spark make it around the corner

I also tested injecting sparks direct into the PU so I could see how far they got and they never got further than about a metre.
I think the large airflow rapidly cools the sparks.
This is especially the case for Al being cut with a TS.
The chips come off as little shavings that are razor sharp and very hot - but once again the rapid air flow and tumbling action cools the chips and small pieces of Al off very quickly so I don't use a chip catcher.

IMG_1615.jpg
IMG_1616.jpg

IMG_1617.jpg

IMG_1618.jpg

I don't need to use this setup on my MW BS because I use flood lube/coolant which stops metal dust from getting into the air.
I use it mainly when sanding, cutting, polishing and grinding.
Total capture efficiency is lower than wood dust because metal dust is much denser than wood dust and tend to evade capture, but somewhat like wood dust the bits that are large will drop out very rapidly from the air and they hot the floor and become nuisance value - again its teh fine dust we need to worry about.

My particle counters shows general fine metal dust values can be quite high when doing things like metal sanding, cutting with a grinder, using a wire wheel to remove rust, or using a Scotch bite wheel.
On the plus side even the fine metal dust hangs does not hang around anywhere near as long as wood dust does.
General ventilation also comes in handy.