NVR switch failures ... why?

[Eugene]

I seem to be a jinx where NVR safety switches are concerned; one look at me and they die .

In the last few years I've had three expire on my table saw, and the latest one to take the hara kiri route lasted two weeks on the Myford lathe. The supplier (Axminster) bless them, have offered an FOC replacement, so that's good, but what causes these things to fail? In all cases the relay gave up the ghost, ie the "On" switch refused to stay in.

The tools are in and around my garage / workshop which was professionally wired for domestic supply some 5 years ago. The feed lines come quite a long way from the house distribution board (also new), say 20 metres underground to the kennels and another 20 metres underground from there. Could there be some sort of problem with the feed that knackers up the relays? Or are they just cheap crap from furrin' parts?

Eug

[DavidA]

Have you measured the voltage coming in at your machine ?

Dave.

[philf]

Could there be some sort of problem with the feed that knackers up the relays? Or are they just cheap crap from furrin' parts?

Eugene,

You're probably right.

I made my own NVR for my lathe using a normally open start switch, a normally closed stop switch and a relay to latch the supply. It's simple to wire and the plug-in relay is easy to replace if necessary.

I've never had a problem with it unlike the Chinese? NVR on my T&C grinder which packed up after about a month and I replaced it temporarily with a plain on/off switch about 5 years ago.

Phil.

[Eugene]

Have you measured the voltage coming in at your machine ?

Nope, nor do I have the means to do so. What would be the implications of low / variable voltages for the life of the relay as opposed to i's function?

Eug

[awemawson]

The imported far eastern NVR switches do seem to be very flimsily made in comparison to MEM and other older brands, but I suppose that's the way the world has gone 

When I've built my own machines, or re-built industrial stuff without some form of NVR I've done like Phil and used an appropriate Red & Green pair of buttons and a contactor with a latching n/o contact. All a bit more robust.

[hermetic]

From your description of the fault it sounds like the relay pulls in, the machine starts, and stops again as soon as you release the start button? If this is so it sounds like the holding in (maintaining) contact is not making. Is this something you can get inside or is it all sealed? Pics? Went to fit a new NVR starter on my mates 3 phase ingersoll rand compressor, he took me to his local electrical wholesaler, and we got one, £45-00 plus the vat................made in India, worked ok and still is working, but a very small plastic enclosure that made wiring the thing very difficult. Found them later on Alibaba, fob price for the starter is $4-00 each.

[John Swift]

the budget no volt release switches are nothing like the direct on line starters we think of

if  I have interpreted  the diagram correctly the coil is wired across the output  of a 2 pole switch

the green start button pushes the  switch  closed and the solenoid then holds it closed until
you force it open by pushing the red stop button 

thinking of the early  demise of the switch
 if the mains is too low at the end of the 40 meters of cable
the solenoid may not hold the contacts closed with enough pressure to ensure they make a good low resistance connection



    John