Wood Heating
System Design
Control Logic
Software Design
Electrical Schematic
Simple system w/ storage
Domestic Hot Water
Heat Storage
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System Components
User Guide
Programming Guide
Failsafe Design
Sample Application
LM35 Sensor Assembly
Pinout Info
Poor Man's VS Circ
Plastic Pipe Collector
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Connecting a Variable Speed Control Unit

The Variable Speed Control Unit is typically mounted next to the device that's being controlled in order to keep high voltage wire lengths to a minimum. There is a light gauge cable connecting the Variable Speed Control unit to the Variable Speed Breakout Box that's typically mounted next to the NFCS. This cable uses a standard RJ11 connector on the NFCS end and is hard-wired to the control unit. The example photos here are for a benchtop demo and use standard appliance line cord for the high voltage (115vac) wiring. Actual installations would typically use armored BX cable or a code-compliant equivalent.

Configuring the Control Unit

Dip Switches

The heart of the Control Unit is the 'Nimbus' manufactured by Control Resources. In the NFCS application, it's configured to be controlled by a 4-20ma signal. The DIP switches should be set according to the picture at the right - switches 1,2 and 7 on and the rest off.


There's also a jumper which needs to be installed on the two pins nearest the edge of the card. This photo is courtesy of Smokeless Heat in Pennsylvania. They use the NFCS with an interesting Swedish boiler, and have quite a bit of experience with the Nimbus variable speed controller.

The Nimbus is a quite sophisticated device. There is a complete manual available from Control Resources.

Connecting Power and Load

The Control Unit requires connection to both 115vac and the load that is to be controlled. These connections are made as shown in the photo below, The load is to the left and is connected to the red and black wires at the left end of the row of wires (when viewed as shown). The next two wires (black and white) are connected to 115vac power.

Connecting the Control Signal

The last connection that's required is the control signal from the Variable Speed Breakout Box. This signal will be provided via an RJ11 cable (typically flat 4 conductor). If the standard 4 conductor color code is used, the signal is on black and yellow, corresponding to pins 1 and 4. If six conductor cable is used, the control is on pins 2 and 5.

The black wire (pin 1) is connected to the purple wire on the control unit, and the yellow wire (pin 4) is connected to the gray wire. Because the signal wires are so small, use cable ties to tie the signal wires to the control unit wires as shown.

Hooking up the whole system

A complete variable speed setup consists of several components:

  1. The NFCS controller (of course)
  2. At least one temperature sensor
  3. A variable speed breakout box
  4. A variable speed control box
  5. The load to be controlled

The setup shown below is a demo for closed-loop (PID) control. It has an additional sensor for room temperature. The 'Lamp Shade' sensor is held in place with a clip. The goal of the system is to vary the 'heater' (light bulb) to hold the lamp shade at a specified temperature.

The first step is to connect the breakout box to the controller. Variable speed output is present on connector number 6 which is yellow on later model NFCS controllers. A standard Ethernet (Cat5) cable is used to connect the NFCS to the VS breakout box.

The VS breakout box can drive up to four variable speed controllers. In this diagram, a single VS control box is connected to the first channel of the VS breakout box.

The load is also connected to the VS control box as described above. In this example, the load is a lamp and the VS control box output is wired to an outlet box. This is a convenient setup for testing as it's easy to see the lamp change brightness as the variable speed control adjusts the power level.

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