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Darkwood
If your talking about suppression devices then its to absorb the spike created by the collapsing magnetic field when the coil is de-energised.
Read this http://www.sprecherschuh.com/library/techdocs/get/TECH_Surge_Suppression_109.pdf
Read this http://www.sprecherschuh.com/library/techdocs/get/TECH_Surge_Suppression_109.pdf
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Darkwood
Have to disagree i believe he is on about an old practice of fitting a small indicator lamp across the coil as a resistive suppressor ... i work in panels with 50+ coils in them that's a lot of panel mounted indicators on the front ...
Connecting lamps for contactor status indication direct across the coils of relays and contactors is a practice i avoid i always use plc output or auxillary relay contacts to do the job so as to avoid any flickering of lamps during normal operating conditions.
I fit them when i can but because i use DC and require instant drop-out i sometimes have to find alternative methods due the delayed drop-out effect fitting suppressors to DC relay coils has..... they can be a pain in the butt sometimes when you require fast switching.
but will we ever know approx 1 post every 6months i think we will be waiting a long time for the OP's response.
Connecting lamps for contactor status indication direct across the coils of relays and contactors is a practice i avoid i always use plc output or auxillary relay contacts to do the job so as to avoid any flickering of lamps during normal operating conditions.
I fit them when i can but because i use DC and require instant drop-out i sometimes have to find alternative methods due the delayed drop-out effect fitting suppressors to DC relay coils has..... they can be a pain in the butt sometimes when you require fast switching.
but will we ever know approx 1 post every 6months i think we will be waiting a long time for the OP's response.
Last edited by a moderator:
S
silva.foxx
Totally unsure why. I'd suggest a better practice would be for the contactor to switch a supply to an indicator to confrm the contactor has switched. I dislike using a PLC to switch an indicator lamp unless its part of a light-stack unit to inform Ops.
I'd not heard of that method before, I've always used diodes across DC coils.
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Darkwood
Agree nowadays .. its old hat and you didn't have the mass manufactured cheap suppressors many yrs ago ... i bet the bloke who told him was trained by an old hat or is himself due retirement.
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Darkwood
My reply is slightly biased as ive just done a 1 indicator with multiple tasks i.e. solid light, slow pulse and fast pulse to notify machine stop saved loads in space and materials.
K
Knobhead
OK you saved on space. The space you have to worry about is the space between the operator’s ears.
I tried various multifunction flashing indicator lamps and gave it up as a bad job years ago. Given two options the average operators brain goes in to overload.
One reason against an I/L across a coil is the inductive spike will simply blow the lamp. As SF said, it doesn’t really give a true feedback, the lamps OK, pity the coils burnt out.
To the OP, are we talking AC or DC coils?
OK you saved on space. The space you have to worry about is the space between the operator’s ears.
I tried various multifunction flashing indicator lamps and gave it up as a bad job years ago. Given two options the average operators brain goes in to overload.
One reason against an I/L across a coil is the inductive spike will simply blow the lamp. As SF said, it doesn’t really give a true feedback, the lamps OK, pity the coils burnt out.
To the OP, are we talking AC or DC coils?
Thanks for all the responses chaps. Just to clarify, the coils are AC. I think the most valid reason not to do this is that the lamp will not give a true indication of the contactors status i.e. if the coil goes open circuit. Where ever possible I try to use a separate auxiliary on the contactor for indication. Plus as has been mentioned, the lamp will be subject to spikes reducing it's life.
P.S. I may be getting on a bit but I'm a good few years off retirement.
P.S. I may be getting on a bit but I'm a good few years off retirement.
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Darkwood
I did use a solid state plc output to do the I/L pulsing so had no issues thus far and yes can only agree with the operators thinking power but this was so simple to understand i went with it-
The lamp comes on if the punch machine trips the coiler drum that is what is monitored this winds the punched wire and is run through a slip belt so is always tensioned and can naturally slow its winding speed as the coil fills and the circumference increases, so simple rule was
Lamp - solid light (coiler stalled - wire jam)
Lamp - slow pulse (underspeed - wire feed issues)
Lamp - fast pulse (overspeed - wire broken)
Ive fitted 4 so far and seems a system both operators like as before they had to work out why the machine had shut down which wasn't always obvious.
It's sounders where I work, there is a different pitch/pulse rate for various conditions, machine fault, reject, slow loading etc. the most annoying is every 90 seconds while a body traverses a walkway, the only one that can't be mistaken is E. stop when every sounder in the area goes off!
When I was an appprentice in the 70's saw a sparky wire a 240V drill across phase and earth (3ph board) to save using an extension lead from nearest socket!
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