If you have two 12 volt transformers and if we connect their hot wires together does the voltage become 24 or 12 volts?
There is actually a phasing to the transformer windings. If you connect them in series with the phases adding (both hit + 12 at the same instant) you get 24 volts out. If you connect with the phasing wrong (one hits +12 while the other hits -12) and put them in series the output will be zero volts (and they might overheat). If you connect them in parallel with the right phasing you will get 12 volts and the amperage will add to give you the sum of their amperage. If you connect in parallel with the phasing wrong you will get zero output voltage (and the danger of overheating). If the transformers do not make their phasing clear put a voltmeter on the output and briefly turn on the primary while seeing if you get zero or the voltage you want. If the phasing is wring swap the wires of one transformer around and check with the meter again.
