Question for Phil

Mark Williams

Nov 28, 2000
Hey Phil,

Could you ask the engineers if it would be possible to use a VFS7S-2015UP
as a controller for a heat treating kiln? It is listed as a 7.5 KW. Is this actual wattage? Or could it actually put out more ?

I would be nice to use the variable output IF the unit can accept a feedback from a K Thermocouple, but that could be asking too much. Maybe either a D/A converter could be used as the input interface?.

Could the output be set up to control a solid state relay?

Just REAL curious.


Aug 27, 2004
What you smokin' Mark????

Although I'm not Phil, everybody knows that you can use the Froitenheimer Model BR549 in order to change the angle of the dangle. That is unless you use the Skrebitz 101 to enhance the heat of the meat.

You really have to do some mathematics............ As you know, that the square of the hair divided by the heat of the meat and multiplied by the angle of the dangle equals the cube of the tube. With these simple formulas, you shouldn't have any problems.

If I can be of additional assistance, please let me know.

Jul 11, 2003
Mark Williams said:
Could the output be set up to control a solid state relay?

Yes. With that much inrush amps you'll need a relay of some kind, Mark.


Oct 29, 1998
Hello Mark

Using a drive for such an application is probably overkill. It would also take a lot of work to adapt the drive to an application that it was never designed for. If you want finer control of the temperature, try seting the upper and lower limits closer together on your oven controller.

The motor drive has a three-phase output. Does your kiln have a three-phase input?

The control algorithms in motor drives that I worked on in the past expected the load on all three output phases to have equal loads. If they sensed that the loads are unequal, the drive tripped out. I doubt that you will be able to dissable such a trip function since it is expected that the connected motor presents a "balanced" load if it is working correctly. I will have to ask on Monday if the Toshiba drives do this too (I strongly suspect that they do).

The 7.5 kW rating is the total output power of all three phases. You will have to draw the same amount of power from each output phase (see above).

I think that the VFS7 series have digital outputs so you can control a solid state relay. I don't think that the analog inputs for any drive would work with a thermocouple since the thermocouple will need special ciruitry to energize it and then to amplify and linearize it's output. The digital inputs of a typical motor drive is not meant to work with anything like an A/D converter. When they do have to use an A/D in the system, the A/D is connected to a host computer (PC). The PC runs software (usually custom written) that processes the A/D data and sends commands to the drive via some communication channel such as RS-232 or RS-485. With that many pieces of equipment and so much power running around, there is a high potential for a lot of electrical interference that will screw up either the thermocouple input and/or the communication channel.

If your oven temperature is swinging a lot, it is probably due to the response time of the oven. Reaching way back to the thermodydamics classes that I barely passed, I would have to say that the temperature swing is related to the wattage of the heating elements, the thermal mass of the oven's interior and the rate at which heat escapes from the oven (how well insulated your oven is). In general, high values for each of these parameters will increase the amount by which the oven temperature will swing, I think.

I hope that this helps.

Take care.