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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