Hi! Complete beginner here — hoping someone can help me calm down a little.
I just installed an rbdimmer 4A module to control a 100W incandescent bulb in my dining room. Everything works perfectly — the dimming is smooth and the light looks great.
But after about 10 minutes of running the bulb at full brightness, I noticed the module feels warm to the touch. Not burning hot, but definitely noticeably warm. I pulled my hand back pretty quickly because I wasn’t expecting it.
Is this normal? I’m coming from a background in interior design, not electronics, so I have zero intuition for what’s safe and what’s a warning sign. The module is mounted inside a junction box with the cover on, and I’m worried about heat building up in there.
Should I be concerned? Is there a temperature where I should definitely turn it off and call an electrician? Any advice would be really appreciated — I just want to make sure my house isn’t going to catch fire.
Don’t worry Wendy — what you’re experiencing is completely normal TRIAC operation. Let me explain why.
A TRIAC isn’t a perfect switch. When it conducts, there’s a small voltage drop across it (called the on-state voltage, Vt). For the BTA16 used in rbdimmer modules, Vt is approximately 1.2V. This means a small amount of power is always dissipated as heat inside the TRIAC itself.
For your 100W bulb at 230V:
Load current: I = P / V = 100 / 230 ≈ 0.43A
TRIAC power dissipation: Pd = Vt × I = 1.2V × 0.43A ≈ 0.52W
Without a heatsink, the TRIAC’s thermal resistance to air is roughly 70°C/W. So the temperature rise above ambient would be:
ΔT = 0.52W × 70°C/W ≈ 36°C
If your room is 25°C, the TRIAC case temperature would be approximately 61°C. That’s warm to touch — you’d instinctively pull your hand back — but it’s perfectly within the component’s safe operating range.
The 4A module comes with a small heatsink in the box — make sure you’ve attached it to the TRIAC. With the heatsink installed, thermal resistance drops significantly and the temperature rise will be noticeably lower.
General temperature guidelines:
- Below 60°C: completely normal, nothing to worry about
- 60–80°C: acceptable, but verify your load is within the module’s rating
- Above 80°C: something is wrong — reduce load or add a heatsink
At 100W on a 4A-rated module, you’re well within specs. The module can handle up to approximately 920W (4A × 230V), so your 100W bulb is only about 11% of its capacity.
Thank you so much, both of you — you explained it so clearly!
Vincent, the math really helps put it in perspective. Knowing that 100W is only 11% of what the module can handle makes me feel a lot better. And I just did the touch test — I can hold my finger on it for a few seconds without any problem, so it sounds like everything is fine.
And oh — I just checked the package and there IS a little heatsink in there that I completely missed! I’ll stick it onto the TRIAC right away. I’ll also make sure there’s a bit of space around the module inside the junction box. Right now it’s not packed tight, but I’ll double-check that no wires are pressed directly against it.
Thanks again — this community is incredibly helpful for someone like me who’s learning from scratch!