How is a transformer selected?
Four decisions, taken in order, that narrow the choice to the right isolation transformer.
An isolation transformer connects each light or sign to the series circuit, so it is chosen to suit both. The load sets the power rating, the circuit current sets the primary rating, the secondary must suit the lamp or LED it feeds, and the location decides how the housing must be built.
The flowchart only narrows the choice. The final transformer is confirmed against the design for rating and primary current, insulation level and connectors, and against the standard it must meet.
Frequently Asked Questions
Q1How is an AGL isolation transformer selected?
By working through a few decisions in order: the load it must carry, the current of the series circuit it connects to, the type of load on its secondary, and where it will be installed. The result is then checked against the data sheet and standard.
Q2Why must the transformer rating match the load?
A transformer that is too small is overloaded and runs hot. One that is far too large runs lightly loaded, with poor efficiency and extra magnetising current, which adds load to the series circuit regulator. The rating is chosen to suit the fixture or sign, with the margin the design allows.
Q3Why does the primary current matter?
The transformer is connected in series with the circuit, so its primary must be rated for the circuit current and carry it at every brightness step. Most AGL series circuits run at 6.6 A and some use 20 A, so the circuit design decides.
Q4Does an LED fixture need a different transformer from a lamp fixture?
The secondary must suit what it feeds. A lamp load and an LED driver load behave differently, so the secondary rating is chosen for the actual load, and the manufacturer confirms that the transformer and fixture are compatible.
Q5What should be checked before the choice is final?
That the rating, primary and secondary values, insulation level and connectors match the design, that the housing suits the location, and that the transformer meets the applicable standard. The manufacturer's data sheet and the standard decide.
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