If I understand this correctly we have an overhead crane that is powered by 480 volts.
This crane has two 12 volt direct current electric motors that operate an air compressor and a hydraulic pump.
The operation of the crane and both the compressor and hydraulic pumps are controlled by a pendant that hangs from the crane which the above drawing is supposed to be of.
Well I am going to leave this one alone as I just don’t see the crane lifting and lowering with only two wires to the motor controler but will ask why these tanks that are designed to be buried underground must be handled so delicately? Are they not reinforced by some sort of rebar?
Only the hydraulic pump and leveling system are in this picture, and a 480V turn motor and the compressor and control pendant were added as my work continued.
Ultimately, I installed a cord reel to bring 480V down to the hook and power everything on the beam from there.
Last edited by leejosepho; 06-16-2010 at 10:03 AM.
Cool Dude and thank you for the explanation. I was having a hard time with the pendant and thinking it controlled the crane as well as the beam.
I can also understand the pulling of green concrete in only 12 hours of pour. Having done some work at a similar plant I suppose I was thinking of your plant being like the one I did service work at. There they had break away molds that were opened in the yard.
Contactor coils do NOT like less than their rated input voltage (which may be a range). The contact ratings of the contactor power leads are a maximum, and using lower voltages (and current) on them than specified won't be a problem. Some motor designs will work and just run slower if you drop the voltage, some will burn up. If you are using DC contactor coils, you want to install a diode across the coil with it reversed, so during normal operation, there is no current flow (i.e., it is blocking the flow and not acting like a short across the relay coil - IOW, put the cathode on the plus side of the coil and the anode on the minus side). Then, when it is de-energized, the coil's induced voltage will be drained off, and not cause the thing to chatter as the spike decays. If the coil is big enough, there can be enough current generated when control power is removed to cause it to momentarily re-energize itself. the diode prevents that and lenghtens the life of the relay contacts for minimial costs.
Important note - I'm not a pro
Retired Defense Industry Engineer