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This crane uses a "Lifting Magnet Controller" which requires:
1) A maintained ("latching") contact – closed when the magnet is lifting or holding the load,
open when it is (or will be) dropping the load.
2) One momentary contact for each: "Fan" ("Dribble"), and "Drop".
Client wanted to use his existing Magnetek "Flex EX 12" remote controller to do this.
Client wanted both Lift and Drop to each require two different pushbuttons, because the operators were wearing heavy gloves and "they were accidentally turning the magnet on".
On the remote, six existing pushbuttons were being used (Up, Down, Left, Right, Forward, Reverse), which left six "spares".
I worked out how to do this using four pushbuttons, leaving two for future use:
I installed four "ice cube" DPDT control relays on a DIN rail, as shown.
"R1" is energized whenever the "Magnet" pushbutton is being pressed
(connected to contacts in the remote receiver).
"R2" is energized whenever the "Off" pushbutton is being pressed.
"R3" is energized whenever the "On/Off/Start" switch is being turned to "Start".
As wired, "R4" is energized whenever the "Magnet" pushbutton is being pressed and the "On/Off/Start" switch is being turned to "Start" (i.e. both R1 and R3 on), and after that stays "latched" on by the holding contacts on R4. ("Lift Mode")
Also, "R4" is de-energized whenever both the "Magnet" pushbutton and the "Off" pushbutton are pressed at the same time (i.e. both R1 and R2 on). ("Drop Mode")
(The magnet control power supply is 120 VAC, via terminals "GX1" and "GX2" in the Magnet Controller.)
During "Lift Mode", R4 connects the Magnet Controller terminal "M11" to the "Lift" terminal. This causes the Controller to energize the electromagnet.
When starting "Drop Mode", R4 opens the connection between terminals "M11" and "Lift". The Controller does not yet de-energize the electromagnet...
In "Drop Mode", the "Fan" ("Dribble") pushbutton connects terminals "M11" and "Fan" – while connected, the Controller gradually lowers the voltage to the electromagnet.
In "Drop Mode", when the "Drop" pushbutton is held while turning the "On/Off/Start" switch to "Start: terminal "M11" is electrically connected to the "Drop" terminal. This causes the Controller to totally de-energize the electromagnet.
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