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What kind of switch is this? Has a "heater"?

wulbert

wulbert

pfm Member
Not audio, so my apologies for the off topic. I'm baffled though and there are people on here who know about old stuff.

An ancient band saw, gifted to me, has an "MEM" branded toggle switch on it. When moved to the "On" position the switch box itself emits a vibration and noise. The motor is nice and smooth and quiet but the switch makes a loud buzzing noise. I've never seen a switch that vibrates and makes a noise. What is going on?

The switch will not stay on, previous owner rigged a bit of string and weight to keep it in the "On" position. Since the switch is labelled "Off", "Reset" and "On" so I'm assuming the switch has a relay of some kind and is either broken or not happy and is trying to switch off.

The weird thing is that the switch contains a slot-in "fuse"-like part with a metal "element". This part can be levered out like a traditional fuse. On the back of this part it says "HEATER" 25SPH "Switch Off Before Removing". Why would a switch for a band saw have a heater?

The switchgear is clearly ancient and so is the rubber power cable. I'm wondering what to replace the switch box with, in order to use the saw safely. Any ideas on what this is?




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It’s a part of a thermal overload relay. The motor current passes through the element which heats up in proportion to the current flowing. A nearby bi-metallic strip will open if the overload set point is exceeded, usually set at the motor’s rated full load current.
This in turn will mechanically trip the switch to the off position in this case I think. Usually the bi-metallic strip will break an electrical control circuit but this looks simpler. Would need to see the inside to be sure.
 
Johnjo said:
It’s a part of a thermal overload relay. The motor current passes through the element which heats up in proportion to the current flowing. A nearby bi-metallic strip will open if the overload set point is exceeded, usually set at the motor’s rated full load current.
This in turn will mechanically trip the switch to the off position in this case I think. Usually the bi-metallic strip will break an electrical control circuit but this looks simpler. Would need to see the inside to be sure.
Click to expand...

Thank Johnjo ( and others). So this is to protect the motor from being overloaded, correct? E.g. someone stuffing a large piece of timber in and jamming/slowing the blade and working the motor too hard. There's no load on the saw motor at present, because it has no blade fitted.

I can't yet understand the vibration/noise but maybe the bi-metalic strip is producing it, or perhaps a relay.

So, to replace this safety feature I just need to find a safety switch which will cut out at the correct current? Motor says "FL Amps: 4.8" which I'm guessing is for Full Load Amps: 4.8. The motor is rated at 550 Watts output so around 2.3 amps max when its working normally.

Think I'll just advertise it as "Free to a good home" spares or repair.
 
The motor could be noisier without load as the load may pretensions against a bearing /bushing, or failing that it could just be goosed, unbalanced due to corrosion.
 
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