Variable Speed AC Controller

Hello Steve

I took a look on the Grainger web site. The model that you are considering is good for 1hp. You may consider the 5JJ62 (1.5hp) at $171 or even the 253G-200E (3hp) at $219. They are not a lot more money and a lot of the makers seem to have indicated that 1hp was not really enough for them.

It may be a good idea to contact the manufacturer to get their opinion. My (limited)experience is only with AC drives.

The manufacturer's web site is http://www.dartcontrols.com

Phil
 
I looked in the Grainger catalog and those work only with PSC (permanent split capacitor) or Shaded pole motors. There is only one 1 HP PSC motor in the grainger catalog, and it's a two shaft ac fan motor. PSC and SP motors have low starting torque and are used on fans, etc. Capacitor start motors have a can on the outside that hold the capacitor and won't work with these controllers. I would guess that your grinder is capacitor start. Oh well, I was excited too.

Steve
 
I think you will find these do not work with capacitor start motors that we typically use in the shop. These are for AC motors like a router or hand drill that do not use a capacitor. They are more like a reastate (sp).



Regards
 
Check out eBay. I picked up a Cutler Hammer model AF91 a couple weeks ago. It is rated for 3 Hp which works perfect for my 2 Hp Burr King.

I got it for $76.00 plus $14.00 shipping. It is brand new and came with the owners manual. Also it uses 220V - 240V single phase as an input and cranks out your 3-Phase needed to drive the motor.

There is alot of good stuff on eBay. Do alot of searching and be patient. Cross reference what you see on Ebay with the manufacturers website to make sure you are geting a good deal. Don't get auction fever. :)
 
Here's what I got back from Dart Controls:

Yes as long as it is not a capacitor start motor.
Click to expand...

That's what you guys said. There isn't a visible capacitor on the motor case. However, I'm at work and can't inspect under the base.

I'll do some more investigating, but I'll bet it is a capacitor start. Still, there's hope.

Steve
 
Anyone know how these things work...? I mean the operating principal...i.e. Variable frequency? variable voltage?, pulse width modulation..?

It makes me go hmmmmm!

-Rob
 
Mine works on varying the frequency. The read out on the display is set to show Hz. It can also be set to show motor amp draw, or scaled to read your actual sfpm. Luckly, when the Hz is 60 my sfpm is 6000, even easy for me to do that conversion in my head.:)
 
Your VSD should be at least 1.5 times the hp rating and should be used on a inverter rated motor or you will burn up the motor quicker.Now it may last quite awhile if your not a production type maker, but just letting you know.Also most VSD's work on 3 phase motors with single or three phase input.The varible part comes in by changing the standard 60 hz (50 hz overseas) to say 10 hz for slow speed to say 80 hz for high speed.Motor torque stays virtually the same thru the range.VSD's are very voltage picky as any significant drops in voltage will cause a VSD to trip out under load.They should be on a dedicated circuit in the house.Hope this helps some. Dave:)
 
The Sears 1hp unit does have a capacitor.

Bummer 1.

I asked the tech at Dart Controls if there is some other option and got this response:

No, there are no options that you can do. The motor is made to run at full speed.
Click to expand...

Bummer 2.

Steve
 
Hi
You can add a potentiometer to the dart to make it variable.
I dont know where or how, but I have one that is modified like that!
 
One of the limiting factors of operating a single-phase motor on a VFD is a mechanical device intrinsic to most, not all but most, single phase motors. A mechanical centrifugal switch. The centrifugal switch operates off of motor rpm's. It opens and closes to take the start winding of in and out of the circuit and is attached to the motor shaft in most cases. When trying to run these motors on a VFD you experiance a bunch of problems trying to start or run the mtor at slower than full rpm's. 02 worth mike
 
Did you see the picture of ???'s (dang, forgot his name) shop.

He did something cleaver. He hooked the unused end of the shaft on his grizzly to a slower motor. Then he runs the grinder part using the stock motor as nothing more than a shaft.

I wonder if that's hard on the original motor?

I have a 1750 motor laying around, I guess I could try that.

Trouble is I still want a KMG and don't want to spend any money that won't be used to that end.

Steve
 
Hi Steve,
I am in the same boat as you. I wanted to slow down my Sears
grinder and found that I could not do it,( variacs ect. will
burn up the motor). I decided that I have had it with this, and
have decided that I will get a real grinder with variable speed.
This is what I have learned so far. I bought a 2HP 3 ph 220v ac motor.
I will need a vfd that can supply the continueous 6.4 amps. The vfd(
variable frequency drive) will have to be rated higher than 2HP
because I only have single phase input, which puts out less amps. (The vfd will only drive a 3 phase motor). The higher rated vfds are
a lot more expensive. It is hard to win. I am still not sure which
vfd I will need to buy to make up for only using 220v single phase.
 
The standard capacitor start motor as stated has a start winding conected to a capaciotr to shift the phase angle to start the motor, the centrifical switch cuts out at about 75% full load speed depending on the motor the centrifical force will hold the switch out even at less than 75% full Load speed but it would probably vary with each motor. The wasy to work out the motor speed is
rpm = 60(seconds)x hz (freqency 50 in aust I think 60 for you)divided by pairs of poles - 5% slip in the fields. (insert to 10 and 80 hz figers into the equasion and that is why it goes faster or slower)

here the pairs of poles gives us 3000 to from memory 850 rpm most common 1440rpm without changing frequency.Motors are wound to a specific number of poles and that is what they run at.
Don't worry about the calculation the speed should be stamped on the motor. I have not been working as an electrician for 15 years so its a bit rusty. Also that long ago the electronics required to change the frequence (hz) was way to expensive. The above is just to give you an idea of how variable frequence contollers work and basically why if you look at the speed of your motor take 75% of it that is as slow as you will get before the capacitor start and centrifical switch start to give you real problems. capacitor start motors have good starting torque that is why they are most commonly used.

More over motors are designed for a duty rating and cooling factors some have internal fans fitted. If you just hook up a controller to just any motor and it is not well designed you will let the smoke out. We all know they run on smoke because if you let it out they stop working.

Please don't be dicouraged by this I am just being my usual cautious self not wanting anyone to burn out their motors on a lets see if it works approach. Speak to the maker give him all the information stamped on the plate on the side of your motor and let him tell you if it will work. (remember 15 years since I did this for a liveing)in those days variable was only for 3 phase and DC. elcetonics has come a long way since then particularly price has plumited.
Good luck
 
Thanks Reg Ellery for your information. I am still trying to
make sense of it all. I have a response from one of the vfd drive
makers and they say that a 3 phase 4 pole motor rated at 1800 rpms
will give 600 to 3600 rpms. Note however that at 3600 it will only
have 1/2 the torque that it will have at 1800 rpms. I have been trying
to get in touch with Reliance to check on my motor, but by the time I
get home from work it is too late. I bought the motor cheap, however if it won't work, it wasn't cheap enough! As someone said, if you go
with DC, the controllers are cheap and the motors are expensive. If you go with Ac, the controllers are expensive and the motors are cheap. So far, it looks like none of it is cheap!
 
save your money for the KMG, rob's a great guy to work with, he put together a var, disc grinder for me and i have one of his proto type rotary paltens for the hardcore machine. you will still find lots of uses for the sears when you upgrade, i have a coote and a hardcore and will add a kmg some day. its great to have a back up machine and as you develop you pattern of procidures you can leave them set for each chore.
 
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