NVR switch buzzing

[walks]

Hi all,

Probably a silly question from a newbie, but should an NVR switch on a bandsaw buzz when the machine is switched off?
It doesn't always and if you wiggle the buttons it comes and goes.
Probably nothing to worry about, just thought I'd seek the wisdom of you guys.

Thanks in advance.

Andy

 

[NetBlindPaul]

Is the machine off at the wall, or local isolator, or just not running as in stop button pressed type of off?
Really either way it should not buzz, but, if it is, the reasons could be different depending on the answers to the above.

 

[CHJ]

....Probably a silly question from a newbie, but should an NVR switch on a bandsaw buzz when the machine is switched off?
It doesn't always and if you wiggle the buttons it comes and goes.
...

I have a NVR type unit from an Austrian piece of equipment that hums/buzzes whenever there is mains power supplied to it.
The holding solenoid is permanently powered via the Stop (Push to break) Button and in its rest (no mechanical load) position against the solenoid core the armature buzzes.

The Power to Device (output) contacts are made by the On Button which mechanically latches contacts to the armature when actuated.

Hit the Stop Button or switch off power at source and the Mechanical Latch of the On Button contacts is released, opening up the output contacts. The design of the On button is such that it has to be physically returned to OFF before it will engage the output contacts again, an alternate to having a mechanical latch on the Stop Button.

Rather a poor design, saves on a set of coil contacts but means that if power is not isolated at source the coil in the NVR is subject to mains power and attendant heating and a possible out of hours fire risk if you don't isolate shop power.

So basically in answer to your question is yes they can, dependant on design, but not the Norm for the majority of units where the holding coil is only powered when you push the start button.

Does your Bandsaw have a rotary On Switch that latches On, could be indicative of a unit with permanently powered coil as above.

 

[walks]

Hi Guys, Thanks for the replies.
The switch only buzzes when it is on at the wall but the machine isn't running. When I switch it off at the wall the buzzing stops.
It is a 2 button type switch not a rotary.
The Bandsaw is the SIP 10inch saw if that helps anyone.
Thanks again.

 

[CHJ]

It is a 2 button type switch not a rotary.
The Bandsaw is the SIP 10inch saw if that helps anyone.

Is the switch this pattern (On another SIP BS) ? If so it should not in itself buzz as the coil is wired across the output terminals and only energises when the switch is made.

The switch although mounted in the semi sealed pillar and fitted with a splash cover does fill up with sawdust as the rear case is not completely sealed and has holes in the top.

 

[CHJ]

Having looked at a 10" model image I see that the NVR shown is a different pattern to the above so may well be constructed differently internally.

Only suggestion is that with machine disconnected from power source, is to undo the two fixing screws and pull the switch out and have a look at the connections to see if the coil is permanently energised when power is applied, as this is the only thing I can suggest that may be buzzing if it is a similar mechanical latch system to the one I previously described.