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NORA Oilheat Technicians Manual

Drawbacks to iron core ignition transformers An ignition transformer does just what it claims to do—it transforms voltage. There is a single copper winding on the primary side for every 90 to 100 windings on the secondary side and that is how it transforms voltage. This becomes a problem when input voltage drops. For every one volt you remove from the primary side, you remove ninety volts from the secondary side. The ignition of the atomized oil is not a result of the spark, but rather the result of the heat generated from the spark. Remember, the ability of an ignitor to ignite oil depends on more than just high voltage; it depends on arc output as well! Spark heat energy = voltage times current. You must provide between 600-700° Fahrenheit to ignite atomized No.2 fuel oil. 9-8 Ignition Systems This translates to approximately 9,000 volts and about 19 MA short circuit current. A 10,000 volt 23 MA transformer only has a small margin of error built into it, and can be a problem. A few facts • Ignition transformers are insulated with tar. Tar can melt with heat and the tar oozes from the transformer and typically deposits on the combustion head assembly, making for a nasty clean-up. • An ignition transformer’s tar-covered windings are susceptible to moisture infiltration. Moisture infiltration will cause an immediate shorting of the component. • Electrical consumption with an ignition transformer is typically 80 to 100 watts of electricity. This is the approximate equivalent to a 100 watt light bulb turned on over the burner when the transformer is running. • Finally, ignition transformers deteriorate over time. During this deterioration, they cause delayed ignition problems that worsen until, finally, the transformer can no longer light the atomized oil. Transformer testing Over the years, there have been many and various methods of testing transformers. Regardless of the method used, one thing must be kept in mind and that is to be sure the transformer has the correct input voltage to the primary coil. This is very important because the output of the transformer is relative to the input voltage. In other words, if the input is down by 10%, the output will also be 10% lower. Note: 9,000 volts by itself is not what is required to ignite oil; 9,000 volts is considered sufficient to create an arc across the air gaps between the electrode tips normally used in oilburners. The secondary current flowing through the arc heats the air and lights the oil. The important factor in creating an arc is voltage; the important factor in igniting the oil is current. This is why Underwriters Laboratory (UL) requires 10,000 V ignition transformers to have a short circuit current of at least 19.5 MA (11.6 MA across a 1/8" air gap). Most 10,000 V ignition transformers our industry uses are rated for 23 MA. Chapter 9 Ignition Systems


NORA Oilheat Technicians Manual
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