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Halogen light circuitry 12vac

Halogen light circuitry 12vac

(OP)
Good Afternoon

I have a broken halogen light fixture that came with a CNC milling machine that I'm trying to fix. I did some troubleshooting and found that that the problem is somewhere in the transformer circuitry. Purchasing a replacement seems to be a ripoff and the workers like the light.

Attached is a picture of the circuit board that is used in the lamp. To the right are 3 wires for L,N, and G. To the left are 2 wires that get connected to the bulb. You can also see the transformer on the left side of the circuit board. The transformer is labeled 120-12-55 which I'm guessing is 120vac in, 12vac out, 55hz.

I did a google search for "12vac halogen lamp transformer" and got many results for transformers in the 20-30 dollar range for 120vac -> 12vac. Would connecting power directly to one of these transformers and connecting the bulb to the stepped down voltage output work? I'm just concerned because there are all these circuit board components between the 120v and transformer. Would all of this be included in the "20 dollar halogen lamp transformer" ? Or am I buying just the transformer. The lamp has no dimmer, just an off/on switch which is in series with the bulb leads.

The bulb:
h3 halogen
12vac
55w
It seems that they're also used in cars.


Thanks for your help

RE: Halogen light circuitry 12vac

"The transformer is labeled 120-12-55 which I'm guessing is 120vac in, 12vac out, 55hz. ... The bulb: h3 halogen 12vac 55w ..."

The "55" on the transformer must mean watts, not Hz.

Light bulbs are not critical. You simply need a source of nominal 12 volts with at least 55 watts (about 5 amps).

RE: Halogen light circuitry 12vac

PS: I recently purchased a 12v / 5A (60w) switching PS intended for LED strips off eBay for $8.70 delivered. It seems to work fine.

RE: Halogen light circuitry 12vac

The supply is far more than just a 115V step-down transformer to a 12V halogen light. The circuit board appears to be a switch-mode power supply, and the transformer will be a custom designed for the supply, and is not the likely component that has failed.

A halogen light that is run straight from a step-down transformer, or the rectified output of a step-down transformer will actually go from zero voltage to SQRT(2)*12V at 120times/sec for 60 Hz input. Some older halogen and newer ultra-cheap lights use this arrangement but it shortens the bulb life. A 12V lamp power supply that provides a constant 12V will insure longer bulb life.

RE: Halogen light circuitry 12vac

Halogen lamps are not very sensitive to type of power. They will run 12v AC at any frequency or DC. The switch mode power supply that I took apart in my college days operated at 20 kHz that varied in amplitude from zero to about 12v at 60 Hz (so no capacitor was needed). The 20 kHz, of course, allows a very small transformer to work.

RE: Halogen light circuitry 12vac

(OP)
Thanks for all your help

I managed to find a 60 watt 12vDC ac/dc adapter and it worked with the light. I didn't realize that light bulbs can be either ac or dc.

RE: Halogen light circuitry 12vac

They last longer on AC because there is no migration of metal ions as there is when a DC supply is used. Not a practical consideration in most applications because most failures occur at switch-on.

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