Diode Holders Problem with 13.8v transformer - power supply to 12v halogen lamp?
I have a 13.8 volt regulated DC power supply (Maplin) which gives 5A continuous, 7A 50% duty cycle and 9A surge.
I have connected this directly to a bulb holder to power a 12v 50W halogen 6.3 bulb.
The problem I am having is that when I switch the power on to the transformer and light that nothing happens, but if I then remove the connecting wire to the transformer from the light and tap it on the terminal a few times it starts to work and stays on for however long. This happens every time.
The circuit is very simple and has been tested, the transformer is kicking out 13.8v so I thought it could be a faulty diode in the transformer that cause the problem. But, today I got it exchanged with Maplin for a brnad new one and the same problem exists.
Any ideas as to what could be causing this?
Many Thanks
Your transformer is intended as a car battery charger and not for passive loads like a lamp. My guess is there is some active circuitry in the box that is determining the charge on the car battery and the lamp is confusing it.
It is possible that a high value capacitor in parallel with the lamp may trick the charger. Worth trying if you have such a capacitor, but don't go out and buy one.
Keyrazy LED's 12 Volt Pre wired LED's Lexus is300 is 300
Interference/crackling on a transmitter microphone?
I have just modified an FM transmitter, it has an inbuilt mic, but i decided to add an extra Jack in case i needed to add an external one. I added the Jack wires to the mic input, so it has two mics in one input lead, and added a switch to the original mic to stop a mix in signals. The system does work, the Original mic works a treat, but the added mic has a crackling sound, unless I hold the lead, or touch the Battery holder, I presume that I am grounding it by doing this, the original mic does not need any grounding to work, do not know why this is happening, I thought of adding a diode to the negative lead, but am not sure, does anyone have any ideas?
Thanks Mick
Also the 2 mics are the same, and how could I screen the wires?
The added mic works fine, I have tested it on a computer
Crackling normally comes from a poor contact, so normally I would suggest you try cleaning the jack socket and / or switch.
However, what you said about the crackling going away when you touch parts of it makes this doubtful. It could be high frequency instability in the microphone pre-amplifier because you are using a different type of microphone, or it could be picking up RF interference because you have not screened the mic wires properly, or you could be getting feedback from the transmitter output back to the mic input.
If this is an electret capsule type mic, you should be aware that these have a small amplifier built into them which takes DC power from the 2 wires. Therefore it has to be connected the right way round. Try reversing it.
Things you could also try:
Make sure the mic lead is screened correctly.
Connect a small value capacitor (~100pF) across the microphone.
Put ferrite beads on the wires to the microphone.
Edit:
The cable to the mic should be single screened or twin screened cable. It has one or two wires inside surrounded by a screen of foil or thin copper wires. Make sure the screen is connected to circuit ground, which is probably the battery negative voltage.
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