Transformers - Chamberlain LA500U Troubleshooting Manual

TRANSFORMERS

Transformers are used to change incoming voltage to a different outgoing voltage. A transformer
has a primary side (incoming voltage) and a secondary side (outgoing voltage). The primary side
connects to wires from the main power source and the secondary side outputs the new voltage
created. In commercial gate operators, the secondary side is generally 24 Vac. Read the markings
on the transformer to determine the primary and secondary voltages. Transformers are rated in
VOLT Amps (VA). A transformer can only pass the rated amount of electricity from the main
power to the secondary side. Be careful not to overload the transformer. Verify the amperage
rating on all devices connected to the 24 Vac side of the transformer including devices attached to
the control board. Multiply the Amperage rating for each device by the voltage needed to run the
device.
EXAMPLE FOR CALCULATING AMPERAGE DRAW
Below is an example of text for a label that could be placed on accessory devices:
Output Rating...5 AMPS 28VAC or DC Max
Power...24VAC @ 30ma
The "Power" rating is required. The transformer's secondary side is 24 VAC and the transformer is rated for 20VA. The example accessory above uses
30 milli-amps, which is .03 Amps. Multiply the volts being used (24V) and the amps (.03A) to get the VOLT Amps (VA) used by the accessory
(24Vx0.03A=0.72VA). That leaves (20-0.72=) 19.28VA left for other accessories (photoelectric sensors, loop detectors, etc). Once the total VA exceeds
20VA, the operator may experience failures. For operator setups requiring multiple accessories, calculate total VA draw and upgrade the transformer if
necessary (40VA transformers or greater are available). The output rating is how much electricity the accessory is able to have pass through it. This
number is useful when determining if an accessory will properly function long term with the operator. The output rating has nothing to do with the
required amount of electricity to make the accessory function.
TYPE OF TRANSFORMERS
Plug-in Transformer
Toroid Transformer
Block Transformer
BASIC TROUBLESHOOTING
4
24 Vac
(Example: Block Transformer)
MODELS
LA400U, RSL12U, RSW12U
LA500U, CSL24U, CSW24U
CSW200U, SL3000U, SL585U, SL595U
COM COM
120 120
240 240