Network transformers are used as sources of alternating voltage in various equipment. When making homemade devices, it becomes necessary to select a transformer with suitable parameters. Before measuring the output voltages, it is necessary to find the primary winding so that the transformer can be connected to the network.
Necessary
- - Powerful light bulb in the cartridge;
- - multimeter.
Instructions
Step 1
Examine the transformer carefully. On some transformer models, the windings are signed on the top layer of insulating paper and the corresponding terminals are labeled. CCI transformers are completely filled with a green compound, they are also called military transformers. They write a brand on them, which is in the reference book for such transformers, and number the conclusions of the windings. Finding the primary winding of a transformer from an amplifier or low-voltage power supply is quite simple - it is made with a wire of a smaller section than the secondary winding. You can find the primary winding of a low-power transformer from devices by measuring the resistance of all windings. The winding with the greatest resistance will be the primary winding.
Step 2
Powerful multi-winding transformers of the TAN type were used on the old lamp equipment. The resistance of their high-voltage windings differed insignificantly, and by the value of the winding resistance it was impossible to unambiguously judge which winding is the primary one. To find the primary winding of such a transformer, measure the resistance of each winding and write down the values obtained on paper, also note the numbers of their terminals. Those windings whose resistance tends to zero are low-voltage windings designed to power the filament of the cathodes of radio tubes. The remaining windings can be examined by applying voltage to them.
Step 3
Connect a powerful 220V electric lamp in series with the investigated winding of the transformer and connect the resulting electrical circuit to the network. With a multimeter set to AC voltage, measure the voltage across the transformer winding. After that, turn off the power and examine the other windings. Record your results on paper. When examining the windings, be careful not to switch windings while the mains supply is on. When applying voltage to a winding, do not touch the terminals of other windings, as the corresponding voltages are induced on them.
Step 4
Make a mains cable with a fuse holder, install a 1A fuse.
Step 5
From the records made, find the winding that had the highest supply voltage. Connect the transformer with this winding to the network by connecting a multimeter in series, switched to the current measurement mode. If the no-load current does not exceed 30-50mA for 200-300W transformers, it is possible that the primary winding is found correctly.
Step 6
Disconnect the mains supply, disconnect the multimeter from the tested winding, switch it to the volmeter mode. Measure the mains voltage and write down the resulting value on paper.
Step 7
Measure the voltage across the found cathode windings. If at a mains voltage of 220-225V it is 6, 25-6, 35V, then the investigated winding is primary.
