Transformers that operate specific devices should be matched to the specific voltage on the device that the manufacturer specifies.
The key is the door bell specification. They typically run on a 24 VAC transformer. You can certainly hook it up and try it with 9 volts, but it probably won't work as intended. 24 Volt transformers are relatively cheap.
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Low voltage lighting is famous for getting over heated. With the lower voltage more current flows to get the equivalent wattage output you would find in a 120 VAC circuit. For a similar wattage bulb in a 24 VAC system you draw 5 times the current and higher currents generate more heat. The most common problems in low-voltage lighting systems are poor wire connections, too many lights on one transformer and wire that is too small for the load. It is usually recommended to re-tighten all connections in a low voltage system after a period of time.
The transformer size is calculated by using the load current that is required on the secondary side of the transformer. This secondary current is multiplied by the secondary voltage times 1.73. This total is then divided by 1000 to give you KVA. KVA = I x E x 1.73/1000.
The recommended voltage input for a 24 VAC transformer is typically around 120 volts.
You can use a transformer with a turns ratio of 24:5 to convert 24 VAC to 5 VAC. This means the primary winding has 24 turns for every 5 turns on the secondary winding, which will step down the voltage proportionally. Make sure the transformer is rated for the appropriate power and frequency.
Transformers that operate specific devices should be matched to the specific voltage on the device that the manufacturer specifies.
The key is the door bell specification. They typically run on a 24 VAC transformer. You can certainly hook it up and try it with 9 volts, but it probably won't work as intended. 24 Volt transformers are relatively cheap.
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48*2.2 = 105.6VA
Low voltage lighting is famous for getting over heated. With the lower voltage more current flows to get the equivalent wattage output you would find in a 120 VAC circuit. For a similar wattage bulb in a 24 VAC system you draw 5 times the current and higher currents generate more heat. The most common problems in low-voltage lighting systems are poor wire connections, too many lights on one transformer and wire that is too small for the load. It is usually recommended to re-tighten all connections in a low voltage system after a period of time.
To increase a 4.5 VAC supply to 5.5 VAC, use a transformer. To increase a 4.5 VDC supply to 5.5 VDC, you'd need a boost converter.
To change from 120 V AC to 24 V AC, just connect it up to an appropriate transformer. To convert 120 V AC to 24 V DC, you'd need a transformer followed by a full-wave rectifier and filter capacitors.
Transformers voltage ratings are typically at full load. For instance, A 24 VAC, 10A transformer will have a terminal voltage of 24 when it is feeding 10 amps to a load. Since the transformer windings have some resistance, the transformer designer has to wind the transformer to put out more than 24 volts, since some of the voltage will be lost, dropped across the resistance of the secondary windings. But, according to Ohm's law, the voltage dropped across a resistance is proportional to the current (E=IR). If we take away the 10A load, there is no current, and therefore no winding voltage drop! The excess voltage the designer built in now appears at the terminals. This is the no-load voltage. In my example above, when we remove the 10A load, the output voltage of the transformer might rise to 26.4V. We would say the no-load voltage of that transformer is 26.4V The ratio of full-load voltage to no-load voltage is called the transformer's "regulation factor". It is calculated as: (no-load voltage - full-load voltage) / full-load voltage * 100. Ours is: ((26.4 - 24) / 24) * 100 = 10%.
The small transformer (at the back of the enclosure) has a single centre-tapped secondary. The voltage across the entire secondary is 28.8 VAC, or 14.4 VAC across each half, as measured with a 3.5 digit DMM on my working sample of this receiver. The primary appears to be configurable for either 120 or 240 VAC.
The transformer size is calculated by using the load current that is required on the secondary side of the transformer. This secondary current is multiplied by the secondary voltage times 1.73. This total is then divided by 1000 to give you KVA. KVA = I x E x 1.73/1000.