Thread: VFD for 3 Phase Mini 30

Hi Gorris,

First up... welcome to the Forum!

You already have it pretty much correct, the VFD's function is primarily to provide a 3 phase output, you get the speed control as an added side benefit.

First, the single phase incoming mains is rectified to produce straight DC, which then drives IGBT's to produce a 3 phase output, the reason for not wanting switching between the motor and the VFD is to avoid sudden load changes that could damage the VFD, at least that's the theory..

Second, since the existing machine controls are no longer doing anything, the usual practice is to rewire the start/stop/e-stop switches to control the vfd.. in the case of the e-stop it's normal to have a latching contactor upstream of the vfd, and the e-stop unlatches the contactor dropping power.

Hope that clarifies some of your questions.

Regards
Ray

Ray has given you some good info.

Originally Posted by gorriss

. . . I was told DON'T SWITCH LOAD SIDE OF VFD or I will blow it up. Not 100% sure what that means (I guess don't switch machines on/off while VFD powering them?) Just after some ideas about the best/cheapest way to set this up.

When using a VSD the standard power switch on a machine is usually deactivated and the VSD unit (which has switches on it) is used as the motor switch and speed control. If the power to the VSD is turned off the machine reverts to a safe state so there's no problem with the machine starting to move when the power to the VSD is restored.

For a multi motor machine a single VSD can be used but what you would need is a switch (or set of interlocked switches) which switches off the power to the VSD before the VSD output could be switched to a different machine.

There's probably already some kind of switch out there but one way to do this would be to wire a 24V retic solenoid power supply into the same circuit as the VSD power. ie if VSD is powered the solenoid is active and it latches shut a small door behind which is the switch to disconnect/connect the VSD to different machines. To access the "switch the machines switch" you would have to turn off the VSD power. I kind of like that - could be worth having a crack at doing this.

One downside of using a single VSD to power multiple machines is that you would have to learn how to program and run different programs to provide the machines with different operating parameters ie different frequency/spped ranges etc.

760/440V? Whats that?

I run two machines off one VSD with a 4PDT center off switch. The fouth pole is a control wire that doesnt allow the machine to be "on" when the vsd is switched to it.
If I switch the vsd from one machine to the other while one is working I guess it would depend which contact opened first as to what would happen, but on my head be it.(the vsd is on coasting stop so I guess it could be switched from one machine to the other as soon as the stop button is pressed)

Given what these machines seem to go for and guessing that there are only two motors. If the motors will run on 240V I think I'd be going with 2 VSDs.

Stuart

Thanks for your replies. I thought I would get email notification of any posts but I didn't, hence my late reply. I have got my head around the way VFDs work a bit better now. I am planning on still having one VFD for the 2 motors, since they are identical and normally run at the same speed. Mainly I only want to vary the speed on the spindle moulder motor. Anyway, correct me if this is wrong, but this is how I plan to do it. Basically I will disable all the controls on the machine itself. I will put a 2 way selector switch on the machine itself, which will be connected directly to the VFD and then to the two motors. So the switch is always directly connecting one and only one motor to the VFD. Obviously you would never touch this switch while the machine was running (why would you want to anyway?). I will be happy to switch the machine on and off directly from the VFD so I don't believe I need to wire anything else?

Is this doable, or have I got it wrong.

Cheers
Graham

Actually I just re-read your posts. So the VFD ITSELF has to be powered off before changing the selector switch? Does that mean even if the machine is not running? I would have thought the VFD could be powered on but as long as I don't have it driving anything I could switch the load?

Originally Posted by gorriss

Actually I just re-read your posts. So the VFD ITSELF has to be powered off before changing the selector switch?

That's what the manuals say

Does that mean even if the machine is not running?

Correct

I would have thought the VFD could be powered on but as long as I don't have it driving anything I could switch the load?

Nope - the manual says VFD MUST be off.

Thanks Bob. My other option is to put a single phase motor in for the fixed speed functions, and just use the 3 phase plus VFD for the spindle moulder. The extra cost of single phase motor is much less than another VFD.

Graham

Just to disagree with Bob.
My understanding is only the output of the VSD must be off for switching.

(from memory) My manuals say "no swtiching" and leaves it at that. Which manual are you talking about Bob?


Cost would depend on what VSD you plan on using. You can get 3hp ones off ebay for around $140. Though they are 240Vinput/output. I still dont understand your 760/440 volt comment? If the motors cant be rewired for 240V your options become more limited.

Stuart

Hi Stuart

The 760/440 motors are the originals in the machine. I can't use them unless I get 3 phase on at my house, so I plan to replace them with 240V 3 phase motors and VSD. The VSDs I have been quoted on are $550 - $650 (The cheaper was a Teco). Can you give a link to the $140 ones? Are they OK?

Graham

Originally Posted by Stustoys

Just to disagree with Bob.
My understanding is only the output of the VSD must be off for switching.
(from memory) My manuals say "no swtiching" and leaves it at that. Which manual are you talking about Bob?

You are correct - The Huanyang VSD manual says this

Do not install any switch component like air circuit breaker or contactor at the output of the inverter. If any of such components must be installed because of the requirements of process and others, it must be ensured that the inverter has no output when the switch acts.

My SAJ VSD manual effectively says the the same thing but in a version of Chinlese that led me to believe the VSD had to to be turned off.

Thanks for the clarification. It sounds like my plan will work then. On a slightly different note. The current spindle moulder motor has a 100L frame (bigger than the 90L models I want to buy). It only has a bigger frame because it is a 4 pole dual speed motor. The problem is the 100L has a 28mm shaft and the 90L has a 24mm shaft. My existing motor has a 150mm x 45mm belt pulley. Can I use a sleeve to mount this pulley on the smaller shaft or do I need a new pulley? If so, any ideas where or how much? I am in WA.

Cheers
Graham

Hi Graham,

Thats what I thought you meant..........who uses 760 3 phase?(or are they what I would call star start delta run motors?)

You dont say what hp you need.
this is the first 3hp cheapy I found
PROFESSIONAL 2.2KW 10A 220-250V 3HP VARIABLE FREQUENCY DRIVE INVERTER VFD t7 | eBay

Of course if you get two you'll likely be able to get them a little cheaper. I bought 4 for $125 each delivered but that was over a year ago now. There are many sellers. They are all still working but most dont get much use. Many others on the forum have them, I am only aware of one that has gone up in smoke.

Just to had to the confusion. At your price of $550-$650 what may work for you is a Teco from the UK that has been modified for 240V single phase input - 415V 3 phase output. I have one. Its the one I switch the output on in fact. Working fine so far, I doubt I would go this route again but it could be an option for you.


Stuart

Hi Stuart

I didn't think you could get a VFD that did 240V single phase to 415 3 phase? That would be a great option because obviously I can keep my existing motors - cheaper all around and less work. So it works OK for you. What sort of motors do you have? I have heard that VFDs can damage older motors. Apparently you should preferably use inverter rated motors? My motors are probably around 1980 vintage.

Graham

PS Both motors are 3hp aprox 2800 RPM.