Author Topic: Bandsaw switch/motor  (Read 488 times)

robgul

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Bandsaw switch/motor
« on: 08 September, 2021, 03:42:03 pm »
I have just acquired a little bandsaw - it's the same as this one 

The NVR switch is not working - I knew that . . .  what I plan to do is replace the NVR on the machine with a regular on/off switch but have the machine connected through a "master NVR" that also protects other machines.

In the picture the square-ish box on the very far right of the picture has the switch button on the right and contains what I assume is the magnet bit for the NVR ( a coil and some wires that link the incoming mains and out to the motor)   

What I can't figure out is what's in the black cylinder shaped unit to the left of the switch box - it just has feed wires from the NVR magnet thing and then a cable to the motor.

Any ideas what it might be for?? 

- I have yet to test it as my new switch isn't here but I'm guessing that if I just connect the mains (via the new on/off switch) the motor will work.

The machine is quite old and the only manual I can find just has operating instructions for use.

Feanor

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Re: Bandsaw switch/motor
« Reply #1 on: 08 September, 2021, 05:00:38 pm »
Motor run capacitor would be my guess.

I'd expect there to be 2 wires coming in: Live and Neutral;
and 3 wires going out to the motor: Neutral, Live, and second (phase shifted) Live going via that capacitor.

robgul

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Re: Bandsaw switch/motor
« Reply #2 on: 08 September, 2021, 05:17:59 pm »
Motor run capacitor would be my guess.

I'd expect there to be 2 wires coming in: Live and Neutral;
and 3 wires going out to the motor: Neutral, Live, and second (phase shifted) Live going via that capacitor.

Thanks - yep - I've been digging around in the machine and the wiring is exactly as you say - and I found a YT video that refers to the capacitor and its function.

On the basis of the current wiring I'm just taking out the NVR magnet gadget and will link the wires (neutral, 2 lives and earth) to the incoming mains via my new switch - when it arrives.   I still have the NVR protection back down the line.

The othere thing I've worked out is the varying the speed which works with a simple pulley (that was seized) that opens to just slacken the toothed belt drive while the motor runs at a constant speed - with the effect of slowing the blade.

Feanor

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Re: Bandsaw switch/motor
« Reply #3 on: 08 September, 2021, 05:26:28 pm »
You can't just link the 2 Lives to the motor.
The one that goes through the capacitor needs to continue to go through the capacitor.
The capacitor needs to remain in-circuit.

Is the housing of the switch assembly openable?
If so, then either repair or bypass the NVR contactor in there.

robgul

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Re: Bandsaw switch/motor
« Reply #4 on: 08 September, 2021, 05:31:26 pm »
You can't just link the 2 Lives to the motor.
The one that goes through the capacitor needs to continue to go through the capacitor.
The capacitor needs to remain in-circuit.

Sorry - I didn't make myself clear!   . . .  what I meant was to take the existing wires coming (back towards the power) from the capacitor and connect them through the new switch to the mains.  Thus all I've changed in the wiring is the switch unit.

robgul

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Re: Bandsaw switch/motor
« Reply #5 on: 09 September, 2021, 10:02:23 am »
The pic is the wiring (with the mains feed disconnected form the choc block on the right) on the dud NVR unit



It looks from the wire colour conventions that the Neutral blue has a parallel black cable and not the live.   

Does that make sense? - and I assume I just connect brown live from the mains to the brown and blue from the mains to the blue-black combo - and obviously earth to earth.

Feanor

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Re: Bandsaw switch/motor
« Reply #6 on: 09 September, 2021, 10:43:45 am »
That link is coming up as a 404 not found error.

robgul

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Re: Bandsaw switch/motor
« Reply #7 on: 09 September, 2021, 11:02:58 am »
That link is coming up as a 404 not found error.

Ah, my fault with Google pix - this should work    https://ibb.co/prr2Q1W

Feanor

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Re: Bandsaw switch/motor
« Reply #8 on: 09 September, 2021, 11:19:12 am »
Yes, the run capacitor looks like it's wired in the Neutral side.

I expect it's wired like this:
The brown wire will go directly to the motor.
The blue will go directly to the motor too.
The black will go to one side of the capacitor, and there will be another wire ( not visible in photo ) coming from the other side of the capacitor going to the motor.

So:
Incoming mains L -> Motor Brown wire.
Incoming mains N -> Motor Blue/Black pair.
Incoming mains E -> Yellow/Green.

Make sure any switch you use is chonky enough to withstand the motor inrush current.
With an NVR contactor, the actual start / stop buttons only carry the tiny current to the contactor windings. The main motor current goes through the much chonkier contactor contacts.

robgul

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Re: Bandsaw switch/motor
« Reply #9 on: 09 September, 2021, 11:31:17 am »
Yes, the run capacitor looks like it's wired in the Neutral side.

I expect it's wired like this:
The brown wire will go directly to the motor.
The blue will go directly to the motor too.
The black will go to one side of the capacitor, and there will be another wire ( not visible in photo ) coming from the other side of the capacitor going to the motor.

So:
Incoming mains L -> Motor Brown wire.
Incoming mains N -> Motor Blue/Black pair.
Incoming mains E -> Yellow/Green.

Make sure any switch you use is chonky enough to withstand the motor inrush current.
With an NVR contactor, the actual start / stop buttons only carry the tiny current to the contactor windings. The main motor current goes through the much chonkier contactor contacts.

Great - got that - thanks.  The switch is the same heavy-duty one that my router table has.   Just waiting for the switch to be delivered.