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NORA Oilheat Technicians Manual

Transformer Wiring Chapter 9 Ignition Systems Chapter 9—Ignition Systems 9-5 Step-up transformers are used for ignition purposes on oilburners. Generally, it will be found that ignition transformers are made up of 90 to 100 turns of fine wire in the secondary coil to one turn of stout wire in the primary coil. In the example, you will note there are 60,000 turns in the secondary and 690 turns in the primary coil, a ratio of about 90 to 1. In Figure 9-3 on following page, we can see what the ignition transformer looks like with its outer case removed. As voltage increases, amps decrease This is a good time to explain a most important characteristic of transformers, see Figure 9-2. The rule: If the voltage (E) flowing out of a transformer is increased, the current, or amperage (I), is always decreased proportionately. For instance, if the voltage is doubled, the current will be cut in half. In the case of the transformer in our example, the primary voltage of 115 volts is increased 90 times to 10,000 volts in the secondary coil, where the current flow (I2) is 23 milliamperes, which is 23/ 1000ths of one ampere. Although not shown in the example, the current flowing in the primary coil can be determined by multiplying .023 x 90, or about 2 amperes, which is average for ignition transformers. This can be proven in the field by checking amperage in the primary circuit with an amperage meter. Moisture proofing It is important that both the primary and secondary coils of the ignition transformer Figure 9-2: Transformer wiring Warning! All high voltage circuits, especially AC circuits, are potentially hazardous. Depending on the size of the person, contact area and time, and voltage characteristics (magnitude, frequency, and path), electric shock can occur and cause bodily damage, burns, or death. Use extreme caution at the input or output end of an ignition transformer! Iron Core Primary E1 = 115V1 Magnetic Field Secondary E2 = 10,000 V I2 = 23 ma


NORA Oilheat Technicians Manual
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