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Hercpilot

Dimmer/Potentiometer Question

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A potentiometer will work however it will be quite hot, depending on current. Also, again depending on current, it will need to be quite large.

 

A PWM type dimmer is a much better solution.


Adrian Smart

Cozy IV #1453

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I think the unit in the diagram runs at about 80 hz. It wouldn't hurt to shield the unit in a box

 

Waiter


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Yes indeed that will work, however DC motors are generally switched very rapidy. This high frequency switching may cause noise in your COM. Being that it is only 410Hz I think it will be fine. I am used to motor speed controllers in the kHz range.

 

It's basically the same as Waiters suggested circuit (A couple of 555 timers firing a driver). Fixed Freq (astable 555), varied Duty Cycle (monostable 555).

 

Try it, and if it is noisy swap out a few components to bring the Freq down. It's pretty simple.

 

Another addition I would make is a switch to go full brightness (even a pot with an internal switch). That way you get 100% DC as opposed to the circuits max of 99%. Now you could have the switch power the MOSFET permanently or you could have the switch carry the lamp current, effectively 'shorting out' the dimmer. That approach would extend the life of the MOSFET, as it wouldn't be running at 100% load when not required to dim.


Adrian Smart

Cozy IV #1453

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Here is a screen capture of that circuit in a simulator (with my added switch). Gets about 7A max on the dimmer into 100 watts of globes, and 8A with the switch closed. Controls down to about 3A so you have a brightness range of about 40% to 90% with the dimmer. You'll get 100% with the switch. With some mods you should be able to get <40% if you so require.

 

post-1445-141090162683_thumb.jpg


Adrian Smart

Cozy IV #1453

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Controls down to about 3A.

Whoops made a mistake. Create the connection from R7 to Q2 emitter and it controls down to 850mA. Much better. Top end no change.


Adrian Smart

Cozy IV #1453

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My added switch is labelled J1 in the simulator. It connects the lamps to ground in place of the MOSFET. This could be added to the circuit quite easily (even externally).


Adrian Smart

Cozy IV #1453

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