Motor Circuit Surge Surpression
Motor Circuit Surge Surpression
(OP)
Dear all,
We have a temperature limit switch that controls a 1/6 HP single phase motor/fun. This limit switch is 1/2HP rated according to the product sheet, however, it failed (welded and shut) due to arcs across the contacts caused by inductive kicks. I am wondering if there is a practical solution to avoid it happen? Would a MOV across the main circuit help?
Thanks a lot,
JJ
We have a temperature limit switch that controls a 1/6 HP single phase motor/fun. This limit switch is 1/2HP rated according to the product sheet, however, it failed (welded and shut) due to arcs across the contacts caused by inductive kicks. I am wondering if there is a practical solution to avoid it happen? Would a MOV across the main circuit help?
Thanks a lot,
JJ





RE: Motor Circuit Surge Surpression
It this in a very wet or damp location?
Any special environmental concerns such as trace amounts of ammonia, SO2, H2S or other nasty gasses?
Is this in a dusty or dirty location?
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Motor Circuit Surge Surpression
RE: Motor Circuit Surge Surpression
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Motor Circuit Surge Surpression
Diode type surge suppression is often for the coils. I want to find something good for this main circuit. Any thoughts?
Thanks.
RE: Motor Circuit Surge Surpression
RE: Motor Circuit Surge Surpression
A good quality 2 HP rated switch should have no issues with a 1/6 HP motor.
The switch may be poor quality and reaching the end of a short life span. Normally a temperature switch that is HP rated will have some type of snap action. Temperature switches are slow acting and need some type of snap action mechanism. If the snap action becomes inoperative the switch may open or close too slowly and the motor current may start an arc that destroys or damages the switch.
I doubt very much that there will be any kind of destructive surge associated with 1/6 HP motor.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Motor Circuit Surge Surpression
Thanks a lot.
http://files.engineering.com/getfile.aspx?folder=5...
http://files.engineering.com/getfile.aspx?folder=5...
RE: Motor Circuit Surge Surpression
The switch is closed.
There is the standard 6~8 times inrush to start the motor.
The switch opens again during the inrush.
Instant weld.
Because the switch is trying to interrupt the starting current it thinks it's trying to interrupt a much larger motor.
That is an abnormal function occurring because the mechanism that is actuating your micro-switches is screwed up in some manner. Sometimes it's because the mechanical jolt of starting is mechanically feeding back to the structure or mechanism. Sometimes it's because of a bad adjustment. Sometimes the thermal sensing medium has leaked out somewhere. Often fools have set the open and close temperatures way too close or the hysteresis of the switch mechanism is dead or missing.
The solution is to repair or flat-out replace the exiting temp switch system with something new.
Google: "refrigeration temperature switch" and pick one that makes sense for your application. You might need knob adjustable or screw adjustable.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Motor Circuit Surge Surpression
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Motor Circuit Surge Surpression