Resistor to trick 12v transformer

[poor mystic]

Hi
I have an excellent test-equipment design I want to share with you because it will enable you to track down your fault.
It needs parts : 2 of 12v filament lamps; a mounting arrangement for the lamps, and a probe. Oh, and red and blue paint.

Connect the 2 lamps in series, and connect the series circuit to the battery which is supplying the circuit under test. Connect the probe to the joining between the 2 lamps.
The 2 lamps glow weakly as soon as they are connected. If the probe is touched to a part of the circuit at positive voltage, one of the lamps will glow. Paint this one red. Paint the other lamp blue.
Keep this test equipment forever! You will soon find faults like the one described in this thread using your 2-lamp tester!

 

[sophiecentaur]

Could it be that the leds are self-biasing themselves off in some way as charge is only flowing one way through the circuit? Foggy thinking on my part, here, but I seem to remember something of the sort happening in another context.
You could try connecting one of the led units the other way round which would stop this happening as current could then flow in both directions through the transformer.
If it works then I was right - otherwise I wasn't!

 

[zgozvrm]

Besides the fact that it is an "electronic transformer" (i.e. ballast), it also states:
Soft Start
Overload
Short Circuit Protection
Auto Reset
For 12V Halogen Lights Use Only

Correctly-biased LED's probably look like a short circuit to this device, therefore causing it to shut itself down.