TrolMaster DSD-3 Switches Equipment That Wants a Dry Contact
Many dehumidifiers, HVAC units and commercial controllers accept a simple contact closure instead of switched power. The DSD-3 gives a TrolMaster controller that kind of output. Inside is one relay with both a normally open and a normally closed contact, so you can pick the logic each device expects. It is dry contact only, which means it passes no voltage of its own and acts purely as an isolated switch. The contacts are rated 1A at 250VAC or 1A at 30VDC. The module takes its power and data from the controller over a single RJ12 cable. In the controller menu it can work as a temperature, humidity, CO2 or timer device. The front panel has Auto, Add/Reset, On and Off buttons for local control. It snaps onto a standard DIN rail, which suits a panel or a TrolMaster controller cabinet. The box includes 0.5 ft and 4 ft RJ12 cables and a 4-pin terminal plug.
Wiring the DIN Rail Dry Contact Station Into a Panel
Connect it to the controller's device port, then press Add on the module. A pop-up on the controller confirms that the station has been addressed. The 4-pin terminal adds local override without touching the controller. Shorting the ON SWITCH pin to ground forces the relay closed, and shorting OFF SWITCH forces it open. Momentary or toggle switches both work for those inputs. The ON LIGHT pin puts out 12V at up to 50 mA while the relay is closed. That is enough for a 12V DC LED on the panel door, wired with its anode to ON LIGHT and cathode to ground. If manual switching does nothing, check that the switch wiring to GND is tight and actually completing the short. Label each module on the rail with the device it drives so troubleshooting stays quick. Keep it in a dry enclosure, since it is rated for 32 to 104°F and must not get wet.
Key Features
- NO and NC Contacts: One relay offers both normally open and normally closed terminals to match the equipment's logic.
- Isolated Dry Contact: The output carries no voltage of its own, so it interfaces safely with external control circuits.
- Four Controller Modes: Run it as a temperature, humidity, CO2 or timer device from the controller menu.
- External Switch and Lamp Terminals: Wire ON and OFF wall switches plus a 12V status LED to the included terminal plug.
- DIN Rail Mount: Snaps onto standard rail inside a panel or TrolMaster controller cabinet.
Technical Specifications
| Specification | Value |
|---|---|
| Part number | DSD-3 |
| Relay | 1 relay, NO and NC contacts, dry contact only |
| Contact rating | 1A @ 250VAC, 1A @ 30VDC |
| Input | 12V, 0.1A via RJ12 |
| Controller modes | DST (temperature), DSH (humidity), DSC (CO2), DSP (timer) |
| Indicator output | 12V DC, max 50 mA when relay is closed |
| Mounting | DIN rail |
| Operating temperature | 32–104°F (0–40°C) |
| Operating humidity | ≤90% RH |
| Unit dimensions | 4.84 × 2.33 × 1.38 in (123 × 59.3 × 35 mm) |
| Package dimensions | 5.51 × 3.54 × 1.97 in (140 × 90 × 50 mm) |
| Gross weight | 0.44 lbs (0.20 kg) |
| Package contents | DSD-3, 0.5 ft RJ12 cable, 4 ft RJ12 cable, 4-pin terminal plug |