Problem with 13.8v transformer - power supply to 12v halogen lamp?

Question

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

Answer 1

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.

Answer 2

the cold halogen would draw 12 times the current that it would at operating temperature (3800 degK/290 degK). the power supply is not only regulated but must have over-current foldback as well. sparking the load heats the halogen filament, increasing its resistance to the point that the foldback (about 9 amps) can work normally. you can put a glo-bar thermistor in series with the halogen to limit the start up surge current.



you don't really need the fancy dc power supply. the halogen will run just fine off the 13.8 vac transformer by itself.

Answer 3

Put extra capacitor is a stupid way and would not help to solve your problem. The failure came from your computer power supply. Its 12V could not produce enough current and it shut off while you overloaded it. You need to buy a car battery charger that can produce more than 10A current to meet your heating requirement. Or use 12V car battery as its power source.

Answer 4

Hmmm. 13.8V supplying a 50W load pushes 3.6A. The start-up surge can be 10 times the steady value for a lamp. This is for a very brief time but must be long enough for your p.s. to trip.