Mag switch mystery problem

Maybe I am losing my mind or there is a simple explanation? I installed an automatic system to turn on and off the coolant as needed on my cold saw.
The mag switch in my cold saw turns on the coolant pump and is linked to micro switches to cut power or enable power to the mag switch coil. The problem is that the switch does not turn off when the power is cut to the coil?
When it happened initially I was so surprised I thought I had done something strange with the wiring but there was no voltage to the coil. The kicker is that it will shut off eventually or sometimes right away which would be normal operation. It is random but sometimes works better than at other times.
I changed the switch to an identical one and at first I thought the problem was solved but it too started to do the random shut off.
I tested the voltage at the coil and it is definitely off but coil is still pulled in and motor running. Switch is 208 volt 3 phase with a 110 volt coil.
So any ideas? I have never seen this with any other mag switch in 40 years of running electric tools.

Is it wired correctly-especially to the coil?
You are saying the coil is still energized & pulled in even though there is no power to it?
Pics and/or a sketch of the wiring will be needed to help.

Yes, I am saying the coil has no voltage when tested but is still pulled in and the motor is running.
Sometimes it works correctly and shuts off immediately and sometimes there is a delay, could be a few seconds could be a full minute. It is random and very annoying.
I will take some pictures of the wiring and test again just for fun.

I doubt your problem is wiring, sounds more like a sticky switch. Is it old? Did you get it NOS? The stickiness could arise from armature wear resulting in ferromagnetic particles in the air gap. Alternatively, ingress of oil or water could cause similar effect. A new switch no doubt would fix your problem.
EDIT: just reread your post & noted you've replaced the switch ..duhh. I guess it IS possible one bad switch replaced with another? Is the replacement one new? Not up to the current draw? Could be partial/intermittent welding of the contacts. Maybe your saw is drawing more current than usual for some reason such as heavier work or a motor fault?

M. Moore said:

Maybe I am losing my mind or there is a simple explanation? I installed an automatic system to turn on and off the coolant as needed on my cold saw.
The mag switch in my cold saw turns on the coolant pump and is linked to micro switches to cut power or enable power to the mag switch coil. The problem is that the switch does not turn off when the power is cut to the coil?
When it happened initially I was so surprised I thought I had done something strange with the wiring but there was no voltage to the coil. The kicker is that it will shut off eventually or sometimes right away which would be normal operation. It is random but sometimes works better than at other times.
I changed the switch to an identical one and at first I thought the problem was solved but it too started to do the random shut off.
I tested the voltage at the coil and it is definitely off but coil is still pulled in and motor running. Switch is 208 volt 3 phase with a 110 volt coil.
So any ideas? I have never seen this with any other mag switch in 40 years of running electric tools.

Click to expand...

a new switch/contactor that at first works correctly and later starts misbehaving is a strong sign of dirty and contamination
therefor mechanical sticking
another mechanical problem can arise from the switch not being rated for the current it is applying and interrupting
this will result in the contacts burning and trying to weld together, thus holding the contacts mechanically

if the switch is in an enclosure and is not exposed on the machine contamination is not likely
there are solid state electronic controls that even tho they are not passing current they leave a residual voltage on the circuit which is not enough watts to energize the coil but can hold an already magnetized armature in the energized state
i.e. the contactor will remain closed

another option is the circuit you designed is receiving a back feed of power from another source that you did not anticipate when you designed/added the circuit
how are you measuring the coil when you say it is off?
where do you place your volt meter leads?
are you certain you have selected the correct meter setting when you measure?

i assure you that you are not losing your mind lol
sometimes it is not the fault of the electrical system, it is mechanical
electricity is not magic, there is always a reason for it's behavior
you just have to find it
this is what is called trouble shooting/diagnosing

If a magnetic switch is a contactor or relay, check the gap between the coil and the armature. If the armature contacts the iron core of the coil, residual magnetism may keep the contacts closed for a short time. A coil voltage higher than rated for the coil may aggravate this condition. Increasing the return spring tension may also help open the contacts.

Bob
WB8NQW

Thanks all for your replies. The switch is old as there were two together as a reversing setup. I tried the first one and now the second is doing the same thing. It is in an enclosure on the back side of the machine, quite clean there so not a dirt problem.

If I give the enclosure a little tap it usually shuts off so a mechanical/residual magnetism problem is the most likely. I have just never seen this before and I have wired quite a few start/stop remote switch stations successfully in the past with no problems.

If there is a wiring problem the switch either stays on and won’t shut off or it won’t start at all.

I am now inspired to have another go at this and either fix it or change it to another switch. ( also used)

Here is the switch. The red/black control wires go to the micro switch and then to a shutoff switch in series. With the cold saw in the fully up position the micro switch is open so no coolant. As the saw starts down the coolant comes on, repeat as needed.
The main shutoff is needed or the pump would be on all the time when I park the saw with air pressure off and blade in the fully down position.
Testing the switch in the horizontal position it works perfectly, on off
quickly as it should function.

I mistakenly wrote 120 volts for the coil but it is 208 volts.
The heaters are a bit big for the motor at 1.8 amps and the motor is only 0.7 amps. Not too worried about overload for the coolant pump.
I just tested it again in the normal mounted position (vertical) and it works perfectly. Maybe complaining about it here publicly shamed it into working properly? Is there a hair pulling out emoji?

now that you bring up vertical position ,,, read on that switch carefully
it may not be intended for horizontal use
some of the old ones are not, vertical only
which could mean it does not have as good a disengage system as you may need
new ones dont usually care either way

also, as old as it is , it may be worn badly enough that it is sticking mechanically

if it opens when you bang on it, you diagnosed it already.
no head scratching, puzzlement, hair pulling or posting here needed.
dirt, partially fused or damaged contacts, weak spring, or all three.
if that's the "new" one, not too surprising its sticking also.

if that's never happened to you before in 40 years of running electric tools, you are either very very lucky, or haven't used many tools,

Over the years I've encountered several contactors that developed magnetized laminations. No springs, but depend on gravity and vertical installation. Perhaps disassembly and the use of a de-magnetizer would fix the issue, never tried it.

The springs in the coil feel fine when hand tested. The contacts are not great, dirty and pitted some. There is an unused set on the left so I can swap those and see if it helps. I think I still have the twin so I can probably get another set of unused contacts.
When mounted it is in the vertical position.

M. Moore said:

The springs in the coil feel fine when hand tested. The contacts are not great, dirty and pitted some. There is an unused set on the left so I can swap those and see if it helps. I think I still have the twin so I can probably get another set of unused contacts.
When mounted it is in the vertical position.

Click to expand...

dirty and pitted contacts could be the problem, depending on the size of the pits.
are there also bumps where the opposite contact meets a pit?
if either the bumps or pits are greater than 1/16" , they are trying to weld together, one day they wont come apart.

Really old contacts were made of a special silver alloy, and could be lightly dressed to keep them running.
new ones have a coating on the surface, once that starts showing pits they are done, replace only.

I replaced one of the contacts with a new set and then gently cleaned the other two. Tested fine so we will see if that continues.
I put the same system on both of my cold saws and it is a really nice feature. Can‘t imagine a saw without it now.
Thanks for all the positive and helpful responses.