Dimmers for 12V DC circuits are relatively simple, but one common misconception is that two-way dimming circuits will work—they don’t. In this lesson from the EXPLORIST.life Mobile, Marine, and Off-Grid Electrical Academy, we’ll dive into how 12V dimmers function and why two-way dimming fails.
Dimmers and 2 way Dimmers – VIDEO
Tools & Equipment
For this demo, we’ll be using a Blue Sea Blade Fuse Block. There are several types of fuse blocks available, including models from Progressive Dynamics, Blue Sea Safety Hub, and Tiger Expedition UFO 200. While the specifics may vary, the connection method is essentially the same. You’ll also need a distribution hub—such as the Victron Lynx Distributor—to bring power from the battery, but we’re going to focus on the connections to the outlets for now.
Safety First
Before starting, always make sure your power is off. In this demo, we’ve already pulled the fuse from the fuse block to ensure there’s no power running through the wires while we work.
Wiring a 12V DC Dimmer
A basic 12V dimmer is quite simple, with only three wires:
- Positive Input: Comes from the 12V fuse block
- Positive Output: Goes to the lighting circuit
- Negative Connection: Connects to both the light’s negative terminal and the negative bus
Different brands of dimmers may have slightly different wiring configurations, so always refer to the manufacturer’s instruction manual. In our example, the wiring is as follows:
- Red wire: Connects to the 12V fuse block (positive input)
- Black wire: Connects to the lighting circuit (positive output)
- White wire: Connects to both the negative fuse block terminal and the negative wire for the light
After wiring, the dimmer operates as expected:
- Turning the knob left switches the light off
- Turning the knob right switches the light on at full brightness
- Adjusting the knob in between provides smooth dimming control
The Problem with Two-Way Dimming
Many people want to install multiple dimmers in different locations (e.g., by the camper van’s front door, near the bed, and at the driver’s seat). However, this does not work. Here’s why:
Two-Dimmer Wiring Example
In an attempt to create a two-way dimmer circuit, we wired the system as follows:
- Dimmer 1 (first switch):
- Red wire: 12V fuse block (input)
- Black wire: Dimmer 2 input
- White wire: Negative bus
- Dimmer 2 (second switch):
- Black wire: Light positive terminal
- White wire: Negative bus
What Happens?
At first glance, it seems to work:
- When both dimmers are at 100%, the light turns on fully.
- When both dimmers are at 0%, the light turns off.
However, problems arise when adjusting the brightness levels:
- If Dimmer 1 is set to 50% and Dimmer 2 is at 100%, the light gets unstable.
- If Dimmer 1 is at off and Dimmer 2 is dimmed, the light flickers unpredictably.
- The system fails to properly dim because each dimmer operates independently, unaware of the other’s setting.
Why It Doesn’t Work
Imagine both dimmers acting like water valves:
- If both valves are fully open (100%), water (power) flows freely.
- If both are fully closed (0%), no water flows.
- But when one valve is partially open and the other is partially closed, the balance is unpredictable—sometimes water flows, sometimes it doesn’t, creating an erratic effect.
In electrical terms, the dimmers interfere with each other because they’re trying to modulate the voltage independently. This causes conflicting signals, leading to erratic dimming or flickering.
The Right Way to Achieve Multi-Point Dimming
If you want to control dimming from multiple locations, you’ll need a software-based system like the REDARC TVMS Rogue. This system allows for:
- On/off control from multiple locations
- Dimming control from multiple locations
- A touchscreen interface for centralized control
- App integration for smartphone control
While more expensive, the REDARC TVMS Rogue eliminates the electrical conflicts caused by multiple manual dimmers and provides seamless operation.
Conclusion
For a simple one-location dimmer, a basic 12V dimmer switch works perfectly. However, two-way dimming using manual dimmers does not work due to electrical interference. If you need multi-location dimming, consider a software-controlled solution like the REDARC TVMS Rogue.
For more advanced tutorials on 12V electrical systems, check out our Branch Circuits Playlist in the EXPLORIST.life Mobile, Marine, and Off-Grid Electrical Academy!
