Broken NVR Switch

[Daniel.l]

I recently picked up a free performance power table saw. I couldn't say no really as it was free and he told me about the switch.
So I picked it up and the switch was broken you could press the button and it would start but as soon as you released your finger it would stop. So I took the nvr switch apart and there was a spring that kept popping out of place every time I reassembled it anyway the plastic parts eventually crumbled so it's knackered now.
The original nvr switch has 6 pins see image
Can I swap this for a 4 pin or would I be better off buying a 6 pin. I can get one for £25 pounds on Amazon just worried the same thing will happen. I have a 4 pin and gave swapping them a go but it didn't work kept tripping the breaker
Anyone have any ideas?

 

[eribaMotters]

Unless you know what you are doing, then I'd chicken out and play with a 6 pin as it would be a straight swap.
I found a 6 pin for £30. KEDU KJD22 4Pin 6Pin 250V 12(10)A Electromagnetic Waterproof Pushbutton Switches | eBay

Colin

 

[ajs]

To clarify this is a three phase machine yes?

 

[niall Y]

I would echo what @eribaMotters has said and just replace like for like. After all there are 6 wires shown connected in the photo. if you go for the 4 pin option this will obviously leave two unconnected.
Although these KJD switches are common on Chinese machines they don't seem to last long. I had the self same fault with the one on my sander, which only lasted three months from new. Thankfully, the replacement has lasted a lot longer.

 

[Daniel.l]

Definitely not 3 phase cheap B&Q table saw this won't be my main use saw as I have a Laguna however it'll get a bit of rough use.
This seems to be the same Amazon.co.uk
I think the spare two are for a motor brake

 

[ajs]

Definitely not 3 phase cheap B&Q table saw this won't be my main use saw as I have a Laguna however it'll get a bit of rough use.
This seems to be the same Amazon.co.uk
I think the spare two are for a motor brake

That may be the case, the diagram seems to indicate the extra contact has the opposite sense to the others, i.e. it is on when the other the others are off and vice versa. I'm happy to admit I'm above my paygrade there. Perhaps @Spectric may be able to advise.

 

[Dabop]

Definitely not a 3 phase setup lol
It is a rather unusual configuration- in the electrical trade, thats a 2xSPST NO and a SPST NC with a (latching???) coil
(thats Single Pole, Single Throw, and Normally Open or Normally Closed for the various initials lol)

The way it is configured seems odd...

IF that is a latching coil (connected to output pins 2 and 4), then it needs a further NC 'upstream' to be able to turn it off (ie on the mains supply side)

(I don't know that particular switch- and the Chinese tend to use electric symbols incorrectly- so without one 'in hand' to test, I am working off the connection diagram- which can often be misleading in these cases lol- if that bottom contact IS an NC contact, then it is drawn incorrectly- you don't just 'draw it upside down, but in the position it is in in a given state (usually 'off')

eg

 

[ajs]

No it does make perfect sense to me. It is awkward to discriminate between NO and NC contacts for a latching switch, but in this case the switch is only latching so long as the coil is energised. If the power goes the switch unlatches back to the "off" position. That I'm happy with. Just never seen a reverse sense contact for what I assume is a braking circuit, but that is speculation, there are better people than me here to comment.

 

[Dabop]

I found the switch concerned- its a awkward beast to draw electrically- but it is technically a MC 3P3T unit... Momentary Contact 3 poles, 3 throw ie with 2 poles NO, one NC with a ''not running' (as shown in the first post and again below), one momentary position for 'on' and another for 'off' when either of the two buttons are pushed...

So this is the circuit when 'not running, no buttons pushed'

With the incoming mains switched on both lines (1 is Active/line, 3 is Neutral), pushing the I (on) button closed the 1,2 pair, and the 3,4 pair- applying power to the motor via 2 and 4, and also to the 'hold in solenoid' internal to the switch... 5 and 6 are held 'wider open' during this push action...
While running the 1,2 pair and the 3,4 pair are held in (closed) by the hold-in coil with the 5,6 pair still open, until the O "off" button is pushed, this physically pushes the solenoid slug back out against the magnetic pull of the coil (it isn't a particularly strong coil, doesn't need to be to hold the solenoid slug and contacts arm in place), breaking the 1,2 and 3,4 pairs open circuit, and killing power to the solenoid (and the motor) and also finally closing the 5,6 pair of contacts (motor brake???)

Its a simple switch in operation (but hard to draw electrically lol) and really 'should' be perfectly reliable for decades unless poorly designed or made (inadequate rating for the currents involved??? unplated contacts???)

ETA this is basically what it really is...

 

[Spectric]

These types of switches are really just really cheap versions of a proper DOL starter and can have really horrible switching, the one on my BS400 has fallen apart again and has always required a hard push to start. The way to picture a DOL is that the on button puts power onto the coil via the normally closed OFF button contact, when the main contacts close an auxilary set of contacts effectively bridge the normally open ON contact to maintain the coil current, this is the latch part. The OFF button simply breaks the power to the coil and it drops out.

 

[Dabop]

These are slightly different in that the actual off position doesn't break a NC contact, but physically pushes the switch armature back out of place, breaking the 'hold in ' power to the solenoid contact

You could wire up a 'normal' on/off/emergency button set (which has two completely separate switches- a NC momentary switch on the off button, and a momentary NO switch on the on button, by adding a contactor/relay for the hold in circuit, but then the brake circuit would be an issue...

This is one I made up to replace a pair of panels- a 'clockwork' factor timer which had died of old age, and an 'engine management board' that controlled a diesel water pump on a farm (used for filling the cattle troughs from a dam) It was awkward to use, you had to turn on the engine ign, wind up the clockwork timer (which had died) and then when it had finished pumping, drive back down to the pumphouse to turn off the ign or the start battery went flat on you...- worse you had to open a water valve when starting to 'unload' the pump- then turn it back on after the diesel motor had started up...
All in all, not a simple 'anyone can use it' contraption

The control box I made up did all of it for you- all you had to do was press the start button, and it 'automagically' did everything for you- no second trip, no opening and closing valves...
The stop button wasn't 'really needed' but it was part of the switch I chose- and meant you didn't have to run the entire cycle (say for testing etc)
The stop/start switch on the left (black is start momentary NO, red is stop momentary NC)

Finished box on the pump (on/off on the right of the new control box)- the lamp in the center of the the stop/start became a flashing 'warning light' for if the engine shut down unexpectedly before the timer ran out...(flashing LED)

The pump (and yes, they were running it with the original engine panel hanging like that lol- the vibration of the motor and pump had literally torn the mounting screws through the metal over time... hence me 'remote mounting' the new control box on a post)

Replaced the hand tap 'unloader' with electric solenoid

All run by this lol (unlike the original, my 'homemade' panel will shut down the engine if it is low on oil, and monitors the battery voltage as well)- the linear actuator top left controls the bowen cable that is the 'engine kill' cable- this is what the original clockwork timer controlled (can be seen in the control box pic running off to the right...) The two timers inside control the unloader valve and the engine kill actuator, the one on the front panel the run time for the pump

Not one of my neater builds, but I was holidays 1800km away from home at the time, and only had limited resources (whatever was at my mums place lol)
No fancy cad/cam programs... lots of paper, crossing out and redrawing involved... (and simply sitting down and 'imagining' its operation - what happens if....
It worked but- first time...

 

[skeetstar]

I have an nvr switch you can have. It came off an Axi rable saw.
Happily post it to you, providing there are no issues with import export etc.

 

[stuart little]

I recently picked up a free performance power table saw. I couldn't say no really as it was free and he told me about the switch.
So I picked it up and the switch was broken you could press the button and it would start but as soon as you released your finger it would stop. So I took the nvr switch apart and there was a spring that kept popping out of place every time I reassembled it anyway the plastic parts eventually crumbled so it's knackered now.
The original nvr switch has 6 pins see image
Can I swap this for a 4 pin or would I be better off buying a 6 pin. I can get one for £25 pounds on Amazon just worried the same thing will happen. I have a 4 pin and gave swapping them a go but it didn't work kept tripping the breaker
Anyone have any ideas?

About 1/2 that on ebay, I bought one last year for my DW table saw. Works well.

 

[okeydokey]

Whilst I appreciate the skill and knowledge of most of the above replies - just buy a like for like and be done!

 

[Daniel.l]

Thanks for all the responses I wish I had half the knowledge of electrics ye have, what i take from that is the 4 pin nvr switch cannot be just swapped with the 6 pin without modification. I think I will just purchase the 6 pin, I don't mind really as the saw was free. Just out of curiosity I have a manual motor starter laying around would that be possible to wire up, (came off a felder dust extractor now hooked up to a remote system) this is only a brief thought as it would be quite bulky on the front of the saw

Thanks skeetstar for the offer is it a 6 pin nvr the same as I have removed?
I would happily pay for postage

 

[Deckerwoodworking]

These types of switches are really just really cheap versions of a proper DOL starter and can have really horrible switching, the one on my BS400 has fallen apart again and has always required a hard push to start. The way to picture a DOL is that the on button puts power onto the coil via the normally closed OFF button contact, when the main contacts close an auxilary set of contacts effectively bridge the normally open ON contact to maintain the coil current, this is the latch part. The OFF button simply breaks the power to the coil and it drops out.

Axminster tools sell switches like this .

 

[skeetstar]

I'll post a photo in an hour ir so...

 

[skeetstar]

This any good?

 

[joncooper27]

Hi if you look on RS components website they will sell the parts you require! The parts on there will be quality switches that will last you can either buy a switch complete or buy a button and the suitable contacts to go on the button. Schneider is a good make and they will not break.
https://uk.rs-online.com/web/