[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: Contactor question

Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>

Hi Jonathon,

Not really all that complicated. Sorry, but no paper work on it. Just kind of threw it together on a Saturday.

http://www.classictesla.com/temp/cab_outer.jpg

http://www.classictesla.com/temp/cab_door.jpg

http://www.classictesla.com/temp/cab_inner.jpg

It's nothing complicated. I simply installed a 24 VDC power supply and PLC on the inner door of the controller cabinet and mounted the VFD and contactor to the bottom of the cabinet. PLC simply handles audible alarms for start up, errors, etc.. and handles the contactor. A din rail mounted relay drives the contactor (24 VDC coil). The PLC is programmed with a few basic error routines for the PLC itself and the rest is simply "energize the coil based on inputs" and "de-energize based on errors". The VFD converts the 1 phase to 3 phase for the motor. It also outputs an error signal when necessary. That signal is routed to the PLC as an input. Thus, the PLC will cause the contactor to open if the VFD takes a dump (if it did die, the RSG would start slowing or possibly break to a stop. So I want the VFD itself to disengage power).

The other misc. signals into the PLC are the key switch and dead man switch. Once everything is ready to go (key on, PLC ready, VFD up to speed and error free) the dead man switch then energizes the contactor. I then usually turn up the voltage about 1/2 way and then give it a little ballast (variac on top is current control and variac inside is voltage control). If outdoors, I can adjust V and I for best power. I have a 30k pot and switch wired to the input control of the VFD. They simply increase/decrease motor speed or change rotational direction. Their located at the top right corner of the cabinet.

For a while, I ran 8 preset speeds via binary PLC programming (rotary switch controlled), but the variable pot was just more fun. Note, all these are one-hand adjustments as the dead man switch is in the other hand at all times providing the signal to the PLC. My dead man switch is actually a Cobra CB Mic. Simple handheld switch that only needs to switch a signal (not power). It just worked out for a nice handheld switch which I had lying around and the coil cord was a plus. The program is such that the contactor would open even if the PLC itself had an error. So far, I haven't experienced a problem there.

The setup actually proved out the VFD error signal on the 4th of July. I ran the coil full open for several minutes and at one point, the VFD errored, which immediately shut off the contactor and removed power to the coil before I could release the dead man switch (it was faster than I was). I got a little crazy with the speed adjustment and turned it up too fast which caused an over voltage error. It's hard not to do that when your having that "varoom" sound added to the sparks. It was simple enough to reset and get going again.

These particular toys I spec in at work and use everyday. Thus, it was easy to simply add to the controller cabinet for the pig powered coil. The VFD was an old obsolete unit that has been laying around a couple years. It's a SquareD Altivar 28 for 2HP 3-phase motors. I have grown to appreciate SquareD components, especially the VFD's. Even the PLC is SquareD, although IDEC sells it to SquareD. I just hate IDEC's Octal system program. SquareD took IDEC's simple PLC and made it better with a simple program (software is a free download!). I use MODBUS for comm via USB port. However, the serial is easier to install. The SquareD Altivar 31 is even better than what I'm using and has 16 preset speeds and is physically smaller. But, we actually use those now, so no free lunch there.

Take care,
Bart

Tesla list wrote:
Original poster: Kidd6488@xxxxxxx
Sounds like a heck of a controller? Do you have some details/ pics / schematics on this? Either on here, or just email to me if you dont think people will care...

Jonathon

In a message dated 8/15/05 1:53:37 AM Eastern Daylight Time, tesla@xxxxxxxxxx writes:

Hi David,

Yes, I know well what your are thinking here. But, the contactors do
not all make or break at the same time. Thus, the last in line to
open will see the "full" load for that brief moment. (Inductive loads
are nasty on contacts of any size). Likely, this particular contact
will always be the "slow one" and it will eventually weld closed if
opened and closed during a load, which is the key to it's use.

I use a 50A contactor. It is controlled by the PLC and will open if
the VFD has an error or for a few other reasons (dead man switch
open, key off, PLC glitch, etc.). This is "error" mode and is the
only time the contactor would actually open during a load. During
normal operation, I always have the contactor on before putting V and
I into the tranny. The contactor I use has had no problems so far.
IMO, 30A is a bit small for these swinging pig loads. Even 50A
ratings I would consider risky.

Take care,
Bart