DIMMER SWITCH PROBLEM

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Forum Name: Lights, Neon, LEDs, HIDs
Forum Discription: Under Car Lighting, Strobe Lights, Fog Lights, Headlights, HIDs, DRL, Tail Lights, Brake Lights, Dashboard Lights, WigWag, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=63127
Printed Date: May 05, 2024 at 4:37 AM

Topic: DIMMER SWITCH PROBLEM

Posted By: waynehuff
Subject: DIMMER SWITCH PROBLEM
Date Posted: September 22, 2005 at 11:33 PM

Today I wired up two 12v 55watt lights for night fishing on my boat and I want to be able to controll them with a 12v dimmer switch. I used a (car interior light dimmer switch) which worked for about a minute, then it started heating up and smoking so I had to disconnect it. I don't know how many amps this dimmer switch can handle, all I know is that it is a 12v switch and came out of an old car(don't know the model of the car, it was given to me). Can anyone tell me what the problem might be and how can I tell how many amps the switch can handle by using a meter? Thanks for any info.....

Replies:

Posted By: Velocity Motors
Date Posted: September 23, 2005 at 8:02 AM

A dimmer switch works where at full it will be 12 volts but when it dims, it will slowly ground out to 0 volts ( absolute ground ). This is why it started to smoke on you.

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Jeff
Velocity Custom Home Theater
Mobile Audio/Video Specialist
Morden, Manitoba CANADA

Posted By: waynehuff
Date Posted: September 23, 2005 at 10:23 AM

I know it goes to 0 volts and thats what it would do. It's when I left the dimmer at full 12v when it started getting hot. I think the dimmer switch can't handle the amps the lights pull. I may be wrong thats why I'm asking if you know how to check the dimmer switch with a meter to know how many amps it can handle. I know that two 55watt lights = 110watts and that means I need a dimmer switch that will handle 9.5 amps. So how do I use volt meter to determine how many amps my dimmer switch can handle?

Posted By: ff-mike
Date Posted: September 23, 2005 at 11:03 AM

You can't- the only measurable attribute of a resistor is the resistance. There is no straight rating for current, they have a maximum wattage, which is a function of the voltage and resistance.
The dimmers are designed to dim maybe a dozen sidemarker lamps- so may be rated ~50 watts. Maybe you could use for each lamp. Another possibility would be to use a simple transistor amplifier using a 2n3055 power transistor
posted_image

Should work, not tested.
Make sure you use a heatsink with this, as it will get nice and toasty, and is rated at 115 watts. This will draw at most 6 watts from the dimmer, well within specs

Posted By: waynehuff
Date Posted: September 23, 2005 at 12:37 PM

humm...sounds like a solid option to look into. What about using the 9.5amp dimmer switch I found? it should handle the ~110watts needed, right? they are only about $39.00 bucks.

Posted By: ff-mike
Date Posted: September 23, 2005 at 2:49 PM

First, I'll correct my mistake- the dimmer would get at most 3 Watts.
RadioShack shopping none the less ....
3W Rheostat $3.99
Transistor $2.29
And then just get a heat sink

Posted By: waynehuff
Date Posted: September 24, 2005 at 9:32 AM

Thanks Mike,

I understand what your ideal is and how it would work, I just would'nt know where to begin putting it all togeather. I'm not an electrician just an average bear who knows somewhat about electricity. I love doing this kind of stuff but never had no schooling on it. I wish I had your knowledge.