# Resistor to trick 12v transformer

1. Jul 22, 2010

### Joel2010

Hi guys, new here. I was wondering if anyone knew of a way to trick a 12 volt transformer into seeing more load. I have these lights http://www.lowes.com/pd_172832-2496...=/pl__0__s?newSearch=true$Ntt=tiella$y=0\$x=0" and it won't light them. If I put back in 1 of the 20 watters it works.
So what I need to know is, would something like this work? https://www.amazon.com/Parts-Express-Ohm-20W-Resistor/dp/B0002KR4HU"
Any help would be greatly appreciated.

Last edited by a moderator: May 4, 2017
2. Jul 22, 2010

### turbo

If you check out motorcycle accessory catalogs on-line you will see lots of gadgets to add load to lighting circuits so incandescent bulbs can be replaced with L.E.D. arrays. Perhaps one of those would fit your application.

3. Jul 22, 2010

### Joel2010

Any idea how many ohms and amps I'd be looking for?

4. Jul 22, 2010

### Staff: Mentor

I don't understand what you are asking. Are the LED light modules rated for 12Vrms (AC), or do they expect 12Vdc? You don't "load" the output of a transformer to get the LEDs to turn on....

Last edited by a moderator: May 4, 2017
5. Jul 22, 2010

### Joel2010

It doesn't say if they're ac or dc.
What I'm saying is they leds work as long as there is one incandescent bulb (4leds, 1 incandescent) in the line but don't if I take it off so it seems the transformer wants to see a little more load. ?

6. Jul 22, 2010

### Staff: Mentor

No, that doesn't seem to be what is going on. What is the AC voltage with nothing connected (transformer open circuit voltage)? What is it with just the LED load? And with the added incandescent?

What is the part number of the LED light module? You should be able to find specs on it somewhere.

7. Jul 22, 2010

### Joel2010

Ok, with nothing it was .1 volt ac, with just leds .2 vac, add one incandescent 6.7 vac.

The only info I have on the leds are in that ebay link. There were no specs with them. Hong Kong!

8. Jul 22, 2010

### turbo

The need to do load-balancing in vehicles is generally related to the function of relays and flashers in lighting circuits, IIR. If you were going to replace a simple switched lamp with LEDs (brake light, tail light, etc) there would be no modification required.

9. Jul 22, 2010

### Staff: Mentor

No, not right. The unloaded output from the "12V" transformer should be over 12Vrms. When fully loaded, it should come down to about 12Vrms.

Try checking the voltages on the DC scale. Maybe the transformer has an output rectifier and filter?

10. Jul 22, 2010

### Joel2010

I opened it, it says 12vac 105 watts. Readings are the same. Doesn't make much sense.

11. Jul 22, 2010

### Staff: Mentor

Could you maybe shoot a couple pictures and post them? Also, were you able to track down the datasheet for the LED light assemblies?

12. Jul 22, 2010

### Joel2010

If I short it real quick, the leds light up. Is there a safe way to short it all the time with a resistor or capacitor or something?

13. Jul 22, 2010

### Staff: Mentor

No, something is not getting hooked up correctly.

14. Jul 22, 2010

### turbo

OK, a suggestion... incandescent bulbs don't care about polarity, but LEDs sure do. If the circuit is set up to reverse-bias the LEDs, they won't illuminate. I don't know why replacing one of the incandescents in the circuit will allow LEDs to illuminate, but just a thought.

15. Jul 22, 2010

### Joel2010

Here's the whole thing then a closeup of the transformer. I can't find any other info on the leds. There's no numbers on them at all.

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16. Jul 22, 2010

### Joel2010

I don't get it either but the leds work perfectly as long as there is an incandescent in there.

17. Jul 22, 2010

### Studiot

It says electronic transformer on the label you posted.

This means it is probably a switching mode power supply, not a conventional transformer. These do need sufficient load resistance to operate.

Are your lamps in series or parallel?

18. Jul 22, 2010

### turbo

Good catch!

19. Jul 22, 2010

### Joel2010

Parallel so my total for the leds is only 6 watts. They are 1.2 each. The extra 20 watts gets it all going. That's why I'm trying to add a load.

20. Jul 22, 2010

### Joel2010

Guess I could hide an incandescent in the wall lol. Not