Question for those running a KBAC 27D.

Not to hijack this thread but let me ask you this john, I'm about to get a vfd for that surface grinder I just got.
I've pretty much decided on an IP20 Teco 2 hp, the reason I'm going with this is for the digital read out with variable hertz-speed read out.
$186.00 delivered, verses a digital read out nema 4 going for North of $400.00

What I'm concerned with is over speeding the spindle without a digital readout on a surface grinder, of course I'm putting it in a enclosure with a fan. on a vfd like the KBAC27D, I don't see how to judge the spindle speed on a surface grinder without maybe going by amp draw on the motor or some kind of optical reader- for lack of a better term....
I hope...and think I'm going down this road right.
Also, something I've read about is the electrical pulses pitting motor and spindle bearings using a vfd, although I suppose that's on equipment running 24-7 day in and day out.
 
bladegrinder said:
Not to hijack this thread but let me ask you this john, I'm about to get a vfd for that surface grinder I just got.
I've pretty much decided on an IP20 Teco 2 hp, the reason I'm going with this is for the digital read out with variable hertz-speed read out.
$186.00 delivered, verses a digital read out nema 4 going for North of $400.00

What I'm concerned with is over speeding the spindle without a digital readout on a surface grinder, of course I'm putting it in a enclosure with a fan. on a vfd like the KBAC27D, I don't see how to judge the spindle speed on a surface grinder without maybe going by amp draw on the motor or some kind of optical reader- for lack of a better term....
I hope...and think I'm going down this road right.
Also, something I've read about is the electrical pulses pitting motor and spindle bearings using a vfd, although I suppose that's on equipment running 24-7 day in and day out.
Click to expand...

I agree. A digital readout is super handy. Most VFDs display output frequency. It may be just as easy to get a digital tachometer if you want to see the actual shaft RPM. But knowing the max frequency will give you a good idea of the motor speed like you say.

Don’t worry about pitting in the bearings, etc. I’m still on my original el cheapo Ironhorse motor on my grinder. It’s going on 7 years now.
 
John Wilson said:
nerd alert... (file under: you'll be sorry you asked)

How a VFD makes 3 phase variable frequency from a fixed frequency input:

The output of a VFD is created inside the VFD on the power board. Sounds like an obvious statement, but it's not The distinction is that the VFD is not modifying what comes into it. It is changing what comes into it and creating something entirely different and sending it out. The input AC comes in and gets turned into DC Voltage on the power board. Just Voltage. Not current. Just a big pile of DC voltage sitting there waiting to be used. Then the control board takes over. The control board is the brain which controls the Power Board, where all the real work is done. On the power board, there are IGBTs (Insulated-gate bipolar transistor) which is a fancy way to say a remote-controlled On/Off switch. There are two of them connected head to tail so that when #1 fires, you get a big positive square wave as it turns on and off again. Then it's reversed mate fires, giving you an equal but opposite negative square wave. As this repeats, you have Alternating Current in the form of a square wave. How fast these IGBTs fire is how the VFD creates the output frequency. How tall the square wave is determines the voltage and the peak to peak distance between the waves is the Hertz. These VFDs are referred to as "Volts per Hertz" because they do vary the voltage with the frequency. It's a less expensive design with looser control tolerances, but it's an ideal way to run fans, pumps, and grinders- basically anything where you don't want herky-jerky motion and don't need to start and stop on a dime.

Getting three phase from single phase:

Imagine that your three phase VFD is what I described above. It just has three channels. Phase A comes in, gets turned into DC Voltage sitting on the power bus A, then the control board tells the output IGBTs how fast to chop it up, and you get a Variable Frequency output. Ditto on Phase B, and Phase C.

Well, the cool thing is once it's DC, you can do whatever you want with it. Heck, you have all this DC voltage sitting there on the DC Power Bus. The VFD can route that wherever it wants to. So it takes all the input AC and turns it into the combined DC Power Bus. Voila. That's how it turns single phase into three phase: it has a big DC Bus that feeds all three output channels. But this isn't free. You can't put out more than you take in, so the output is derated a bit (the average amount of total output can't be more than the average amount of total input).

The KBAC's aren't the only drives that do this. It's a pretty common feature on industrial VFDs. However, what's cool about the KBAC is that it will run off 110VAC and give you 230VAC out. But that's why it's limited to 2HP. You run out of 3 phase output pretty quick when you're trying to feed it with 110V single phase. It's really putting out about 1-1/2 HP when you do this and it's only possible because it's being used on a belt grinder which doesn't work very hard at all (compared to what VFDs do in industry).
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Nikola Tesla was right...DC is better.
 
Wouldn't the 3 inch wheel have a faster surface speed with the same rpm? If needed , just place a dumbo alert on this post. I can't be offended !
 
I'm with Jesse. Way before VFDs became readily available, I ran my grinders on 180V/3hp DC motors and controllers. The rpms on both motors was only 1240rpm..... and when I put a smaller drive wheel on to try to speed it up, there wasn't enough power..... I could literally stop the motor/trip the breakers. When I switched to 3ph motors and VFDs..... the heavens opened, and the angles were singing!! :) Well, not literally, but there was that much difference!
 
Chris Railey said:
Yeah...That was an egg head joke. A reference to the battle between Edison and Tesla. Sorry, sometimes only I get me.
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i LOL’d

AC is so much better (thanks, Nicola) but until VFDs came along DC was vastly more versatile.

The starting torque (and torque response to slip) in an AC motor is unreal. VFDs have changed the world immeasurably. I used to do a lot of work in the midwest in heavy manufacturing. There were still huge plants built around DC. I think they paid as much to the power company for Power Factor Correction as they did in power consumption. Imagine pounding giant slugs of copper through a tiny orifice... that’s how you get copper pipe. It’s brutal. I used to watch the process and imagine every TV around for miles getting fuzzy.
 
A couple comments on Rob Fink's excellent review of setting up a KBAC controller:
- I've found having a reversing switch to be helpful if you want to use the grinder for knife sharpening.
- Having an On/Off switch is important on a KBAC 27D (as his description shows). If I recall correctly, the basic KBAC 27D doesn't come with an On/Off switch (I could be wrong on that). While in the On position the controller seems to emit a substantial of AM radio interference. I haven't found that to be an issue with KBAC 24D.
 
A follow up comment - I just noticed in Fink's setup description there is this comment under the "Min" speed control pot setting.
"It is recommended to set this so that the grinder is still moving slowly as a reminder to the operator that the unit is in the "run" mode until the switch is placed in the "stop" position."
I disagree, that seem like a poor idea. For instance, when I'm putting on a new belt, I will often start the controller in the On position, and the speed control set to zero so that there is no belt movement. Then I gradually increase speed to make sure that the belt is tracking properly before increasing the speed. I suppose having a Zero speed setting with a moving the belt could work, but I want to control the speed all the way to zero movement.
 
MTBob said:
A follow up comment - I just noticed in Fink's setup description there is this comment under the "Min" speed control pot setting.
"It is recommended to set this so that the grinder is still moving slowly as a reminder to the operator that the unit is in the "run" mode until the switch is placed in the "stop" position."
I disagree, that seem like a poor idea. For instance, when I'm putting on a new belt, I will often start the controller in the On position, and the speed control set to zero so that there is no belt movement. Then I gradually increase speed to make sure that the belt is tracking properly before increasing the speed. I suppose having a Zero speed setting with a moving the belt could work, but I want to control the speed all the way to zero movement.
Click to expand...

I completely agree with you on this.
 
MTBob said:
A couple comments on Rob Fink's excellent review of setting up a KBAC controller:
- I've found having a reversing switch to be helpful if you want to use the grinder for knife sharpening.
- Having an On/Off switch is important on a KBAC 27D (as his description shows). If I recall correctly, the basic KBAC 27D doesn't come with an On/Off switch (I could be wrong on that). While in the On position the controller seems to emit a substantial of AM radio interference. I haven't found that to be an issue with KBAC 24D.
Click to expand...
Without me reading that set up stuff by Fink, why is the off/on a good thing?
 
tkroenlein said:
why is the off/on a good thing?
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The main reason I mentioned this is because of the AM radio interference while the unit is powered on (again, apparently only on the 27D model). The other reason is that I like to shut off power to electronic equipment in my shop to protect it from power line surges or similar events that can harm electronics. I just checked Amazon and, indeed, the basic 27D unit does not come with an on/off switch (nor a Fwd/Rev switch).
 
MTBob said:
The main reason I mentioned this is because of the AM radio interference while the unit is powered on (again, apparently only on the 27D model). The other reason is that I like to shut off power to electronic equipment in my shop to protect it from power line surges or similar events that can harm electronics. I just checked Amazon and, indeed, the basic 27D unit does not come with an on/off switch (nor a Fwd/Rev switch).
Click to expand...
Gotcha. I unplug mine when not in use. A disconnect would probably be handier.
 
After running my grinder for three days on my generator I can confirm the crappy power supply in my shop must be the problem. The grinder runs a lot stronger now and does not bog down when it used to bog down. Hopefully, it will only be a couple of more weeks until I get my sub panel installed. I now understand you can burn up stuff using it on insufficient power. I thought 110 was 110 but naw. Better read up before you start messing with these fancy grinders and such...
 
Chris Railey said:
I now understand you can burn up stuff using it on insufficient power. I thought 110 was 110 but naw. Better read up before you start messing with these fancy grinders and such...
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Yep. Just ask Eddie Van Halen. He burned up a bunch of amps. He used a variac (a transformer with a knob you use to turn the voltage up / down). He’d crank the voltage down until the amplifier circuit was unstable. Great sound...cooks the amp.
 
Chris Railey said:
How did he get the volume with the voltage so low?
Click to expand...

You get the sound you want from one amp/speaker and then mic it. Feed that mic back into the PA and send it out through all the other speakers. That's how it was done back in the day. Now there's effects for everything.

Nerd alert: The "fuzz" tone that every single rock guitarist uses now via a pedal, came about by accident. Marty Robbins was recording in 1961 and the bass amp lost a tube. The result was a fuzz tone, and it sounded great. The studio engineers debated on re-recording because they couldn't isolate the sound to get rid of it, but Marty wanted to keep it. Everyone loved the sound. In 1964, Dave Davies of the Kinks slashed amp speaker with a razor blade to mimic the sound on "You Really Got Me". A guy had been working on a "fuzz tone" pedal ever since 1961 sold it to Gibson. When the fuzz sound took off so did his pedal. Keith Richards used the fuzz pedal in 64 to record "I Can't Get No Satisfaction" and the fuzz pedal became a staple.

So every rockstar since 1961 has Marty Robbins to thank.
 
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