LiftMaster RSL12U RSL12U Troubleshooting Guide Manual - Page 5

BASIC TROUBLESHOOTING 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. 24 Vac COM 120 240 EXAMPLE FOR CALCULATING AMPERAGE DRAW Below is an example of text for a label that could be placed on accessory devices: (Example: Block Transformer) 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 MODELS LA400U, RSL12U, RSW12U LA500U, CSL24U, CSW24U CSW200U, SL3000U, SL585U, SL595U 4