Vermont Energy Control Systems

Practical monitoring and control for the real world

Variable Speed Control

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 Vesta controller. This cable uses a standard RJ11 connector on the Vesta controller 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

A picture of the dip switches in the Nimbus

The heart of the Control Unit is the 'Nimbus' manufactured by Control Resources. In the Vesta controller 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.


A picture of the jumper in the Nimbus

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 Vesta controller 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

A picture of the wiring 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

A picture of the wiring 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.