DC-DC Converters

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electricity_bill

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I have bought a few of the DC-DC voltage reducers and they don't seem to work. I am using a 12V AC supply and want to power some LEDs at 3V DC. I have connected the AC supply to a bridge rectifier and then to the voltage reducer. I cannot seem to get the voltage reducer to change the voltage and even with nothing connected they get extremely hot to the point where a burn is imminent. Any ideas?
 
The last time I used a DC-DC step down device, which is rather recent, I think the polarity may be important. But since my short term memory is in the tank, don't quote me. After the bridge rectifier converts AC to DC doesn't it put out + and - ? If so, then check your DC-DC step down device. It may be labeled for + and - input.
 
electricity_bill said:
I have bought a few of the DC-DC voltage reducers and they don't seem to work. I am using a 12V AC supply and want to power some LEDs at 3V DC. I have connected the AC supply to a bridge rectifier and then to the voltage reducer. I cannot seem to get the voltage reducer to change the voltage and even with nothing connected they get extremely hot to the point where a burn is imminent. Any ideas?
Click to expand...
LEDs are all about current, not voltage, or so it has been pointed out on this forum many times, I also understand that the correct current at AC will light an LED, but I am sure one of the real experts will give you some details.
As for your voltage reducers, the voltage will only reduce on the output with a load, so at no load, very little change.
 
electricity_bill said:
I have bought a few of the DC-DC voltage reducers and they don't seem to work. I am using a 12V AC supply and want to power some LEDs at 3V DC. I have connected the AC supply to a bridge rectifier and then to the voltage reducer. I cannot seem to get the voltage reducer to change the voltage and even with nothing connected they get extremely hot to the point where a burn is imminent. Any ideas?
Click to expand...
Why have you duel posted this !!!!
 
To the OP:

Post a photo, or two, of your setup and list the parts you are using..
It sounds like a possible wiring error, might be the problem?

PhilP
 
Madman said:
The last time I used a DC-DC step down device, which is rather recent, I think the polarity may be important. But since my short term memory is in the tank, don't quote me. After the bridge rectifier converts AC to DC doesn't it put out + and - ? If so, then check your DC-DC step down device. It may be labeled for + and - input.
Click to expand...
On DC equipment, polarity is usually important.
 
You mention a bridge rectifier but have you added a capacitor across the dc output of the rectifier?
 
As soon as you add a capacitor to the output of a bridge rectifier the voltage goes up. A/C is a pulse and the 12 volts is a average of the voltage. Multiply the expected rectifier output (the diode bridge will drop the voltage by approx. 6/10th volts or even 1.4 volts depending on the type diode bridge used. Now multiply this voltage by 1.414 for the 'real' DC voltage when adding a storage capacitor. This is another good reason that I suggest the CL2 N3 current control device as voltage does not matter, just use 20ma leds. Note the CL2N3 does not need resistors and works for changing DC voltages and keeps full brightness at low speeds. I only use the 3 volt type leds with the CL2N3.
 
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