# Current Divider Assistance

1. Dec 29, 2009

### GPT

Hello all,
I'm attempting to create a dimmer circuit for some lights Id like to install in my room. Ive attached the diagram below.

Heres the problem: When I increase the resistance of potentiometer 2, for example, to decrease the current lamp 2 receives (thus dimming the lamp) the other lamps brighten. I want the other lamps to maintain their luminous output at a constant level dependant upon the amount of resistance of their respective pots.

Bear with me (this is my first circuit) but I dont understand why this is happening.

Two Questions
1) If the resistances of all the other pots remain the same, the same amount of current should flow through them, no? Why are they getting more current?
2) What are potential solutions to this problem?

Glenn

Edit:
Here are the parts I'm using on the breadboard:
-12v battery; 12v, 60mA mini indicator lamps; 10k ohm, .5W pot; 300ohm, .5W resistor in series with lamp and pot

These are the parts Id like to use in the finished circuit:
-12v transformer (wired to mains); 12v, 35W MR16 halogen lamps, appropriate pots and resistors

#### Attached Files:

• ###### setup.jpg
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Last edited: Dec 29, 2009
2. Dec 29, 2009

### Staff: Mentor

If you measure the output voltage of the transformer as you vary a pot, does it vary? That would explain why the other bulbs change when you vary one pot. It would be because the output resistance of the transformer is not negligible in your circuit.

3. Dec 29, 2009

Actually his trial version uses a battery, even more likely candidate for internal resistance I'd say, especially if the battery is "tired".

By the way, what about safety on the transformer version - need to be sure of the transformer rating, and with 35W lamps those "appropriate" pots may run a bit warm.

4. Dec 30, 2009

### GPT

By run a bit warm, do you mean warm enough to be a fire hazard, or too warm to touch?
Is there a formula I can use to calculate the heat dissipated by the pot and its accompanied fixed resistor?

5. Dec 30, 2009