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Re: [TCML] Variable RSG



Hi Miles,

Your sync motor sounds as John said, a hysteresis type. This type of motor will sync, but it will sync at a different spot each time you apply power. Even to capacitively alter the phase will not allow it to phase at the same position. For this you need a salient pole motor and physically grind flats on the rotor to force the motor into sync operation or a non-hysteresis type off the shelf motor.

To do this electronically, capacitance needs to be variable. I'm not up on Johns phase controller, but if C is variable, then it should work. Or you could switch in run capacitors after the motor is started up. Maybe experiment with this. The only way I ran sync was to grind flats. I then set up the stationary electrodes on an arm which moved "really slow" along the curve of the disc with a slow dc gear motor. A lot of work really. I probably would have been better off going with John's phase controller, but then I already had this up and running at the time and I also simply wanted to see if I could do it.

Take care,
Bart

miles waldron wrote:
Bart,

I hate to be a pest, but is there an electronic way to ajust the phase of a
syncronous motor? I have a nice two horse power motor does not reach
synchronization at the same place, by experiment with a phosphor lamp. So I
need to be able to tweak it around without physically rotating the motor, or
the contactors.

Science !

Miles Waldron
678-557-7737



-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
Of bartb
Sent: Wednesday, April 09, 2008 12:53 AM
To: Tesla Coil Mailing List
Subject: Re: [TCML] Variable RSG


Hi DC,

The only "problem" I have noticed is if I vary the potentiometer too quickly. Like trying to get from 60Hz (full motor rpm) to say 120Hz within a quick turn of the dial. If this is performed too quickly, a motor fault can occur, generally a voltage or current fault. There are settings within the VFD to help compensate. One of the most basic settings is the accel and decel time. For example, I typically set ACC (acceleration) to 3 seconds. Thus, from where it is to what speed it is going, it will calculate and attempt to get to the new speed within the 3 second window. Many times, it will get there sooner (if the load is low and the new speed is not that far off), however, if you move the dial too quickly a fault can occur. The trick is to gradually turn the pot up to increase speed, then there's no problem. With higher HP, this issue is less apparent.

I know how you like those high rpm powerful cars! This VFD experience actually turns your coil into a screaming machine. Heck, attach the pot to a gas pedal and it will literally simulate a high performance engine as you "varoom" the pedal. You've heard sstc's with audio modulation, well, this is similar but far more barbaric! You've seen people who have stood in the midst of a coil for the first time? Well, put this kind action into the coil and they will literally run out of the garage (heads in their hands). Very amusing! But it's all about bps variation at the will of your finger tips.

I've had no problems with the proximity. The closest distance for me is about 12 feet from coil to control cabinet. My VFD is in a steel grounded cabinet. The only thing out of the cabinet is the cable running to the motor (3-phase, so 3 wires plus 1 wire for ground) and of course the pig. In my case, the cable is shielded which may help (or may not). I haven't tried it without the shielded cable. The cable I picked up free. At a customer site I saw a bin of cable (to be thrown out). It was waste from a Siemens Railroad application. Red, Black, White, Green, 14 awg, and shielded. It was perfect for this VFD. Anyway, I picked up a couple 20 foot lenghts. If a VFD does go into a fault, it can be set to stop or to freewheel. In my case, I let it freewheel, but I also use a PLC to control the main contactor. If a VFD fault does occur, it sends signal to the PLC and the PLC opens the contactor removing power. Thus, I am never in a situation where the rotary slows with power to the coil. It is always at full power and a perfect status, or there is a problem and no power is allowed. Just a safety thing I put in place because it was really simple to do (and I had the parts on hand).

I haven't had any issues with RF or magnetic fields from the coil. These VFD's are built for industrial applications. For example, at work we have 3 massive lasers that cut through 1/2" steel, massive punches, CNC's galore, robot welders, brakes, and all the industrial noise you can imagine. VFD's are built specifically for this environment. Some VFD's are better than others. The ABB brand is used in industry everywhere. SquareD (Telemechanique) and Fuji are two other brands that are very rubust and have greatly improved over the years. Telemechanique (Brazil is where it started) was completely revamped several years ago. Location, engineers, all changed. They improved quite a bit from their early years. There are some brands not so good and have little experience in the industry (TB Woods is one of the brands I will not use. Experience with their VFD's and a particular discussion with the engineers left a horrible taste in my mouth. Wow, the quantities they could have seen!).

Take care,
Bart

DC Cox wrote:
Bart

Have you had any problems with the VFD setup being affected by the RF or magnetic fields under the primary coil, eg, in the base when the RSG is placed? Especially with DRSSTCs with their extremely high primary currents and fast switching speeds producing large pulses in controller wires, etc.

Does anything kick back into your controller causing full speed lockon, or do you use some filters of some type between the RSG motor and the controller which is usually at a remote location?

Dr. Resonance






On Tue, Apr 8, 2008 at 8:07 PM, bartb <bartb@xxxxxxxxxxxxxxxx> wrote:

Hi Scott,

I meant to reply to your thoughts about Grainger, but deleted the email and emptied trash. So writing this under and new subject.

Anyway, yes Grainger does have some decent prices. But, for AC speed control, price is HP dependent (even at Grainger). If motor is under 1/4HP, you can pick up a speed control for $34. But for something like a 1HP motor, you head to the $170 range minimum. I use a 2HP Baldor myself. This of course gets even more expensive for speed control. Even at 1HP, your already at VFD prices. The motors themselves are cheap and 3-phase is likely the least expensive. For DC motors, the price can get very high in the 1HP range. This is where eBay comes in real handy.

Adam and myself are using a VFD to control a 3-phase motor and vary speed with a simple potentiometer. My Altivar31 2HP VFD is expensive at $300 each off the shelf. No matter how you slice it, as HP is increased, variable speed will cost a bundle between the motor + controller if purchased as new (even at Grainger). I think eBay is still probably the best way to beat these enormous prices.

BTW, I should let everyone know I have a brand new (in box complete with 375 page manual) ABB 3HP VFD for sale which list in the $500 range. I'm letting it go for $200. P/N is ACS350-01E-09A8-2, 1-phase 200 to 240, 21A and 3-phase 230V out, 9.8A, 0 to 500 Hz variable frequency. I haven't used it and I don't know any of the details. Should not be too difficult to figure out.

I also have a used 2HP SquareD Altivar 31 VFD for sale for $125. Works perfect! Don't have the p/n handy, but it's 1-phase 200-240 in and 3-phase 230V out with 0 to 500 Hz variable frequency.

If anyone wants these, they should contact me at bartb@xxxxxxxxxxxxxxxxx I will also offer a money back guarantee that these VFD's are "both" in new working order. In order to use these VFDs, it is necessary to pick up a 2HP or 3PH 3-phase motor for them (as appropriate to the VFD HP rating). Check eBay. Sometimes these motors can be found for around $50. I have only one spare 1HP 3-phase motor on hand, but it doesn't match these particular VFD's. However, if you come across a VFD or speed controller requiring a 1HP, 3-phase motor, I will sell it to you for $50.

BTW, for those that don't know, Leeson (major motor manufacturer) just announced that they are off to Mexico to build their motors! Cheaper labor I guess.

Take care,
Bart
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