| Vicegrip |
05-31-2006 04:09 PM |
Sorry to hear that. I have had 4 contactors stick on auto lifts at HBL. They run all the way up and go into lock out but the cars can't hit anything. No harm but freaks out the mechanics!
There is an easy way to build and install a 100% cutoff system on the beam. Feel free to contact me for info. Home Depot and Grangers stuff and an afternoon to install working slow. Same as manufacture methods or better. I am right around th corner from you in Falls Church.
Anything less that feed power cutoff will not protect you from switch or contactor welding. A switch or contactor can weld and stick from simple bad luck, a motor overload or from bumping. Hitting the UP switch while the motor is coasting down can cause the motor to attempt to restart while the centrifugal start switch is not reset this causes high inrush amps and can weld a switch or contactor. The breaker can trip and when you reset the unit now runs uncontrolled. This is not an unheard of or real unusual thing to have happen.
I would not use the lift before installing a self built or factory purchased feed power lock out system. (Duh, as if you planned to) If the lift does not use a contactor that is controlled by the UP button I would add a 2X or 4X rated contactor. $30 or so and 20 min of wiring inside the control box to do. You can also as a solid state timer to prevent bumping. It can be set to lock out the control switch for 3 or 4 seconds after up cycle. $20 or so and installed inline with the switch to contactor wiring. A good contactor might help with the breaker tripping problem if the push button switch closes slow and one leg drags. A small unfused service disconect at the controller might make for better sleep too. Lift gos apeshit you pull the switch. No help if you are out of the room but the overhead device will catch that.
As to the 70 amp and the 20 amp tripping together. The 70 might be closer to full cap than the 20 or the legs might be miss match loaded. If the 70 has badly mismatched loads on it that can make it sensitive as well. One leg of the split phase has more draw and trips out or pulls the entire breaker open. Test for amp draw on each leg as well as each branch down stream.
A high inrush load can cause the 70 to trip first as well. Sometimes the unit or device protector breaker will trip and as it does the panel or sub panel will trip as well. Unless this happens often there is little to do other than testing amp draw and matching the loads to the system. 70 tripping before the 20 I would test the loads on the 70 and replace the 20. 20 amp 2 leg breakers are cheap.
Anything can fail and often when you least or most expect it. Good build and redundant methods can prevent the less odd happenings.
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