I have a bulb that currently uses a 120V primary to 6V secondary transformer. The load is a 30Watts. I would like to know what transformer I could use to power 8 bulbs (6v 30W each) ? Thanks. How can I calculate that?
Assuming you wire the bulbs in parallel. You need a similar transformer (6v secondary) but one that is rated at 240 watts (or a bit more), 40 amps. Note that the current will be 40 amps and will need quite a heavy wire, #4 or 5. You could also put the bulbs in series, and would need a 48 volt secondary, still at 240 watts. You would have problems of any series string, if one bulb goes out, they all go out. You can also use parallel series combos, 3 pairs, or 2 strings of 3 each as a compromise. edit. Later thought of another alternative that may help. Get a transformer with a 12vCT 240W secondary. Wire like you would 2 phase house wiring, 3 bulbs to each outside terminal, and all 6 to the CT. This means the wire only has to handle 20 amps and can be smaller, and you will not have the series string problem. 12VCT transformers are fairly common. Or if you can find it, and the wiring is still a problem, get a transformer with 2 secondaries each of 12VCT at 10 amps.
