Router speed control to light dimmer

More than a year ago I was approached by an independent filmmaker about light dimmers. The problem fo them was how to get affordable light dimmers to control the film lighting. I was told that many independent non-commmercial filmmakers use a HarborFreight router speed control to dim the lights used for moviemaking. The reason is that they are are cheaper and far heavier (15A) than building our own from a 600W house lights dimmer. The problem with these router speed control devices is that they do not dim down enough to turn the lights off. They also don’t quite go to full brightness but that is a minor problem as they have a switch that bypasses the electronics and provides full power.

HarborFeight43060

After some discussion I got one of these units mailed to me to see if there is a way to modify those to work as better light dimmer.First thing I did was to open the device to see how it was built out. Based on what I saw the circuit was pretty close to a traditional light dimmer. And there seemed to be also some adjustment trimmer for some adjustments. Looked promising.

Harbor_dimmer_open

The nest task was to test the device. The problem that those are designed to operate 110-120V AC 60 Hz power has a slight problem to me. In Finland the mains power is 230V AC 50 Hz. Getting real 120V 60Hz power and finding 120V AC light bulbs is hard here where I live. I got one 120V lamp with the router speed control device so I had suitable lamp. Getting real 60 Hz power would involve some expensive power converter or using 12V to 120V AC true sinewave inverter or something similar that I did not have at the moment. So I decided to do my first testing with 110V 50Hz power that I get easily with a suitable voltage conversion transformer (I used fully isolating transformer for safety).

I did some testing. I found that the controller trimmer potentiometer controls how dim the output can go. I was able to get lamp very dim. Here is the picture of the dimmer electronics with a well insulated screwdriver adjusting the trimmer (there is a hole on the circuit board that gives access to the trimmer). Well insulated screwdriver and isolation transformer powering the whole circuit makes it possible to do ajustments with live circuit pretty safely when you know what you are doing. I mailed the results back to person who sent me the router speed control and he tested the results with real 60 Hz power (they worked).

Harbor_dimmer_adjust

The adjustment instructions: Set the potentiometer lowest setting. Then adjust the trimmer so that you get as dim light as possible without noticeable side effects. When you set the trimmer to too low setting, turning potentiometer will cause the output to be completely off (lap turns off). When dimmer reaches this full iff state, the dimmer potentiometer need to be turned quite much (one third or one fouth) until the light turns back on, quite bright already. The ideal setting I think would be that the lowest dimmer potentimeter setting would just set the bulb to be just barely on (lamp filament dark red and does not make much light), so you have always full control range from it to full setting without problems.

In this way a relatively cheap router speed control device is converted to a relatively inexpensive high power light dimmer.

39 Comments

  1. Janakiraman says:

    Sir,
    I need to know abt your dimmer system for NVG lab and whether it is compatible or not.

    Reply
  2. Irondog says:

    Tomi,

    Thanks! I use these controls on some motors, but noticed that sometimes I could not slow thing down enough. Your tip on the internal pot that could be tweaked was very useful.

    Cheers!
    Mark

    Reply
  3. jean says:

    I fully true!!! I think your site is nice !!! thanks for the story

    Reply
  4. Schummie says:

    Hello Tomi,

    thank you for your post about the Router Speed Control.
    I’m searching for a longtime for a 220v router speed control.
    My question is off this speed control also useful is for 220v?
    The factory says yes, see http://www.nb-dazhong.com/enprosoall.asp?mmm=3&sele=19&text=19&fl=Various
    I hope you can help me.

    Thanks Schummie.

    Reply
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  13. BN says:

    maybe a bit off-topic, but then again dead on
    i just moved from europe to canada and brought my router.. stumbled upon this blog and i instantly knew why it wouldnt work, and how to fix it. europe uses 230v 50Hz and canada uses 115v 60Hz, combining two out of phase live wires makes 230v, now that was the easy part… the router still wouldnt work right. the moment i saw the picture of you adjusting the potentiometer it hit me… thats what i have to do, now it works like a dream. Thank you

    Reply
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  32. Larry Holmes says:

    There are a couple of simple modifications you may make to this speed controller to solve the problems you are experiencing. These modifications.are not difficult for a technician to do but they may be too much for someone who does not know how to solder, how to add and remove components on a circuit board, and now to test his work to.be certain it works properly AND SAFELY! This post is old, however,week so it will be no trouble to share my results with you, as long as you ha e the technical skills I’ve me ruined if this “problem is still an issue needing to. be fixed in more useful manner, I can send instructions to you by email or postal mail. By coincidence, I am about to apply these modifications to the exact same controller from Harbor Freight. Next

    Reply
  33. Larry Holmes says:

    Thank you for this excellent article. I am an electrical engineer,so I am always interested in articles about practical issues and their solutions. I often find that articles written about subjects such as this one are either poorlywritten, technically wrong, or both! This article is accurate without being hard to understand, which means the author has the skill and experience to recommend this procedure and he emphasizes safety, which is EXTREMELY IMPORTANT for anything which plugs into the mains, which carries enough power to be VERY DEADLY if not handled with respect. BETTER TO HIRE A TECHNICIAN IF YOU AREN’T CERTAIN YOU CAN SAFELY DO THE MODIFICATION! That being said, my sincere compliments to the author!!!

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