Tech Tip: How To Setup and Use Latching Contactors from AutomationDirect

Latching contactors are great for those situations where you can't guarantee reliable coil power to keep the contactor engaged. Maybe the equipment is in a place with frequent brownouts or maybe it will be used in a part of the world where you just can't count on steady reliable power. Or maybe you just want to control motors with pulses from momentary switches instead of having to hold power on the coils. Latching contactors are perfect for all that. Just engage the contactor by applying power to its coil. Then a mechanical device that doesn't require power holds the contactor in that position so when the pulse goes away, the contactor stays on. Another contactor is used to release that mechanism when its coil is energized with a pulse. This contactor controls the motor, and the power poles on the other contactor are left un-connected. So simply by adding a second contactor and a mechanical device between the two, you can now use a single pulse to turn a motor on and another pulse to turn it off. Here's a live example using some WEG mini contactors. This contactor will be our primary that controls the motor. If I push this green button, you can see by the test button the contactor engages as long as I hold the button down. This contactor will be our latch release. When I press the RED button it's engaged, but again, only as long as I hold the red button down. When I release the red button, it dis-engages. Now if I add this latching bar, when I press the green button the primary contactor engages, but when I release the coil power, look ... the contactor stays engaged. This mechanical bar is holding it there. Pressing the red button applies power to the second contactor which trips the mechanical latch and allows the primary contactor to disengage. One more time -- I engage the primary contactor with a pulse to its soil, then trip the mechanical latch by sending a pulse to the second contactor. That's it. Using latching bars like this gives you a quick and easy way to control motors with pulses of power to the coils from a PLC or even just a couple of momentary push buttons like we did here. And notice that you can still add aux contacts or even surge protection with the bar installed. Cool. The only catch is you can't use this latching bar with a contactor that has a low coil power consumption coil -- they simply don't have enough power to drive all of this hardware. Which explains why I was using 120 VAC coil contactors in the demo -- If I had used the 12 or 24 volt low power consumption coils, it wouldn't have worked. Here are the part numbers that were used in this demo. As always, if you have any questions, please don't hesitate to contact AutomationDirect's free award winning tech support during regular business hours - they will be happy to help you out. And don't forget to check out the forums. They aren't monitored regularly by Tech Support, so don't post any support questions there -- but there are lots of very helpful folks that hang out there that will offer all kinds of friendly advice and suggestions.