deffective electronic transformer?

greets

I bought a step down step down electronic transformer Horoz HL 372 http://www.horozelektrik.com/en/components/transformers/hl-372.

220/240VAC to 12VAC

it doesn't seem to function properly. If no bulb or load is connected to the output the out voltage is pretty much zero. If e.g. I connect a 12v 5w halogen bulb the voltage goes up by a tiny bit, still under 1 volt. With a 12V 35W bulb connected the out V goes up to ca. 2/2.5 volts and the bulbs lights up but very dimly. Does this mean that the transformer is defective, if so what could be the cause? For me that's a weird defect, it either works or it doesn't.

thanks for your input

p.s. the only thing that the instructions say is that the distance between the output and the light bulb has to be greater than 200mm. I connected the bulb with a longer cable, ca. 300mm.

That's not a transformer. It's a ballast for a florescent lamp. You'll be hard pushed to get any decent current out of it.

nope it's not a ballast. It's a transformer with mains input and 12VAC on the output just like it says on the package and instructions.

Are you sure it's not an inverter? (Made to step UP from 12v to 220v)

Have you measured the resistance across the input leads and across the output leads (whilst disconnected from the power, of course)?

Can you show us a pic of the label?

hi

I get infinity resistance on the input and about 0.5 Ohm on the output leads.

What happens if you use a 150 w load ?

If the input resistance is infinite and its a transformer, its a burnt out primary winding. However if its some sort of switch-mode supply, that could be normal.

Photo of the label?

it is a switching PSU, so infinite is normal.

I connected a 80watt load, the output voltage went almost up to 6V.

Could it be that this psu can deliver 12V only if a load ca. 150W is connected to it? Although that would be strange.

The label is in attachment in a post above

Thats what im thinking, could be an old design.
I recall early swithcmodes doing that .

Boardburner2:
Thats what im thinking, could be an old design.
I recall early swithcmodes doing that .

hmm, I bought this thing a week ago.

If this thing can only give me the rated output voltage at max output power it’s pretty much useless.

What i cannot remember is if it was a particular topography, or a fault condition.

Really a question for an electrician who used to use them.

I’m going to say it’s probably defective.

Some switching supplies do require a minimum load, but it should be less than 1% of the rated current. And in most cases, the minimum-load resistor will be pre-installed on the board so you don’t have to worry about it.

p.s. the only thing that the instructions say is that the distance between the output and the light bulb has to be greater than 200mm. I connected the bulb with a longer cable, ca. 300mm.

I’d just guess that’s to keep it away from the heat from the light bulbs.

It cant be a switching type power supply if the output voltage is AC. Has to be a conventional transformer type.

Its on a site selling lighting accessories, a 12V halogen bulb will work on DC as well as AC...

I took it apart (pics attached).

measured the resistors, none are blown, all the diodes also seem to work fine. Don’t know how to test the two big caps in circuit. The two transistors have 13007ED written on them, I reckon they are analogous to http://www.onsemi.com/pub_link/Collateral/MJE13007-D.PDF

I also have a smaller (60W) electronic transformer (from another manufacturer), the circuitry looks identical to the defective one, just on a smaller scale. It works but only when a load is connected, e.g. a 12V 10W halogen bulb, if nothing is connected I measure pretty much 0 volts on the output and it buzzes. If the bulb is connected I measure around 12Vac and the buzz goes away.

So I guess these types of PSU’s can sense if a load is connected and the first one (150W) has a problem with that part of the circuit, it does not sense properly if or what kind of load is connected.

I connected a 80watt load, the output voltage went almost up to 6V

What did you use to measure your voltage? I think we have established you don't have a transformer but a switcher of some sort. They are no doubt using it to drive Landscape Bulbs and I suspect the 12V is a square wave, thus the name AC. Not really what you want. It's kinda neat, and maybe you could trace it & hack it. Not many foils on the board, just big ones.

What did you use to measure your voltage?

An analogue multimeter.

It’s kinda neat, and maybe you could trace it & hack it.

I think I’m gonna do that, it’s probably similar to this one:

http://sound.westhost.com/lamps/elect-trans.html

quote from the above page:

Most electronic transformers will not function with no (or light) loads. For example, a 60W unit will typically need a load that consumes at least 20W before it will function normally.

So I guess my 150W transformer is working after all, just needs a high enough load.

naut: So I guess these types of PSU's can sense if a load is connected and the first one (150W) has a problem with that part of the circuit, it does not sense properly if or what kind of load is connected.

Correct. Note in your diagram, "T1A" of the excitation transformer is in series with the output transformer, so if there is no load, there will be very little current driving the output transformer and there will be insufficient feedback.

The buzz is the "kickstart" DIAC (DB1) circuit oscillating (at a lower frequency); if/ when the main circuit actually starts, D5 inhibits this.

mauried: It cant be a switching type power supply if the output voltage is AC. Has to be a conventional transformer type.

All electronic power supplies for Halogen lamps output high frequency AC.

A typical power supply will have a circuit very close to this: http://goo.gl/Z8wgaM

// Per.