AC Circuit	AC PCB (single sided)

AC Board

The AC board consists of a PCB mounted encapsulated transformer, a solid state relay for AC switching, a fuse and some discrete components.

What are the links for and why are two fuses shown? Starting at the primary side of the transformer jumpers 1-4 allow for 120 or 230V mains input. If the transformer you use only has one primary winding no links are required.

Although two fuses are shown only one should be fitted.
Fuse F1 is used if the switched output is to be driven directly from the non isolated mains; a conventional heater or light bulb for example. Use the fuse in the F2 position if you prefer an isolated switched output, ideal if you are using resistance wire or low voltage heating pad.
In the latter case the transformer would need to have a secondary rating sufficient for the load. The transformer specified has a 2.5A secondary @ 12V.

  The board is designed to use an encapsulated toroidal transformer. Apart from the fact these tend to have the higher amperage they also provide better regulation and lower electrically induced noise.

Although not shown on the schematic, for safetys sake a double pole mains rated switch should be connected between the mains inlet and transformer primary.
Link 5 connects one of th MT terminals of the SSR to either non isolated mains or the secondary of the transformer. The SSR MP240/120D4 contains a zero crossing circuit for minimum mains interference and a built in snubber network for inductive loads which helps to prevent voltage spikes when the internal triac switches off.

JP5 is the low voltage signal input from the controller board, and JP6 is the 12V AC output that connects to the power in of the controller board. R8 is the current limiting resistor for the internal LED of the SSR.

Back to DC board	 Back to climate main page