electrical load question

Factual Questions
1

My question is probably an easy electrical theory issue but I’m not electrically-inclined.

Suppose I have the following:
() two (2) incandescent lamps: 12 volt a.c., 50 watts each
() transformer: 120 volt a.c. input, 12 volt a.c. 2 ampere output

After attaching the lamps in parallel to the transformer output and plugging in the transformer what happens?

(A) the lamps lights up normally;
(B) the transformer overheats and burns out;
© the lamp filaments heat up a bit but nothing else happens;
(D) something else.

My understanding of this situation is that (B) will occur but I don’t know why. What say ye, oh SDMB experts?

2

Each lamp is 50W, so in parallel, they are 100W.
Your transformer is rated at 24W (12 * 2), so yes, B is probably the correct answer.

It’s also possible that the transformer may just overheat, and the lamps might glow very dimly, but a burnout is more likely.

3

IANA electrician

Watts = Amps x Volts

So 12 volts and 2 amps = 24 watts.

Your lamps will glow dimly. ‘C’

4

The answer is (D) fuse blows.

Because you did provide a fuse, right?

5

yeah D, your appropriately sized fuse/circuit breaker will blow.

if not eventually B.

6

The amperage rating on a transformer isn’t a limit on how much current it can deliver; it’s how much current it can safely deliver. If you put a low-resistance load on it, like those two light bulbs, it’ll just try to deliver more and more current, until something breaks.

7

Agree with above – transformer is unhappy, and probably eventually expresses that unhappiness by overheating or otherwise breaking.

But if this is based on actual equipment, I’d be interested to find out about those bulbs… 12 V AC power? 4+ Amp bulbs? Just curious as to what they’re for.

8

There are a wide variety of high-wattage 12v halogen lamps.
Here’s an example.

9

NEVER OVERLOAD A TRANSFORMER.

Max load is set by the current, due to its thermal characteristics… how much current can it handle before something gets too hot.

And so the correct answer is B, the transformer overheats.

A thermal fuse is a good idea for a transformer… If you are unsure of the situation , attach a thermal fuse to be sure it never gets too hot.

10

No fuses.
Depending on the construction of transformer.
Transformer design voltage 12 volts and 2 amps, with a 8.3 amp load. There will be a decay of voltage and if it drops low enough the lamps will not even light may flicker. If the decay voltage is only a volt or two the lamps will light. But in either case the transformer is running around 400% of load so it is going to get very hot in a short time. It will probably let the smoke out of all the wires.