generator field controll

dexter2 · Aug 25, 2013

Hi,
I want to controll a generators field using my PLC. (S7200)
The Analog output on the PLC's range is 0 - 10V and the generators field requires 0 - 24V. The generators field draws almost 80W so an opamp is not going to work.
Any suggestions?

Lancie1 · Aug 25, 2013

You could use a variable speed DC motor drive, one with the proper output and a 0-10 volt input signal.

The Dart Controls Low Voltage DC Drive, model 65E10E36 accepts a 24 VDC or 36 VDC power input, has a 0 to 24 (or 0 to 36) VDC output, 360 watts at full voltage, with a miliampere or DC voltage input signal.
http://www.dartcontrols.com/product-guide/battery-pwm-dc-controls/65e10/

The Omega Engineering Model OMDC-123D-C-5 has a 36 VAC input, 0 to 30 VDC Output, rated for 5.5 Amps DC out, or 165 watts. The only problem is that it only accepts a 4 to 20 miliampe signal input. http://www.omega.com/pptst/OMDC-125.html

There are plenty of other brands with similar DC drives made for small motors.

shooter · Aug 26, 2013

a DC speed control like the ones in portable drilling machines could work, also a model RC car is doing this.

BobB · Aug 26, 2013

Do not fiddle about - use a voltage regulator that is designed for the job. You can either lock it in on a fixed voltage or drive it up and down with a PLC analogue output.
Not worth the bother of mucking about with a PLC.
http://www.basler.com/

V0N_hydro · Aug 26, 2013

if you really want to do this yourself build/buy a fully controlled rectifier that will have output voltage controlled by PLC.

Mickey · Aug 26, 2013

BobB said:
Do not fiddle about - use a voltage regulator that is designed for the job. You can either lock it in on a fixed voltage or drive it up and down with a PLC analogue output.
Not worth the bother of mucking about with a PLC.
http://www.basler.com/

Bob has the answer, save yourself a whole lot of grieve and do it the right way.

BobB · Aug 28, 2013

Biggest issue I see with people trying to re-invent the wheel is you waste so much time mucking about that the 'expensive' cost of the right gear pales into insignificance when you take into account the time wasted, and worse still, 3 or 4 other jobs you could have been working on.
It is quite funny - working for yourself and being so busy you do not have any time as well as any time you save means you can be working on another job and making more money soon makes the cost of 'expensive' equipment inexpensive!!!!!

Lancie1 · Aug 28, 2013

Dexter is using an S7-200, a PLC that is obsolete but a few are still working in school PLC training labs. Also the "generator field" is only 80 Watts. These facts suggest to me that this is not a utility or industrail application, but a training exercise with certain parameters about how the task must be done. So far I guess we haven't hit on the right answer.

Robert Richter · Aug 30, 2013

I would suggest a generator field controller like Basler (in no way associated with them). However, if you want to control it yourself, I would suggest a high speed output card with PWM or PPM over analog for your fields. From this PWM signal, find a DC optical isolation cube and provide proper flyback protection. I would think the inductance on a field winding to be so high that PWM would be a better route than true analog.

dexter2 · Sep 25, 2013

thanks for all the sugestions. I ended up using a PWM chip with a MOSFET and a free weeling diode over the generators field and using the PLC's analog output as the input for the PWM chip. took me about a day to build and works like a charm.

generator field controll

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