NVR Switch

Good evening, The lathe forward/reverse NVR switch latches when forward is

selected, but not in reverse. What is the likely reason for this, and can it be

fixed' Thanks, Lynne

Hi Lynne

If it has never worked correctly it could be wrong connections in the fwd/rev switch, is the NVR switch fitted in the line from the fwd/rev before it goes to the motor or starter if you have one fitted.?

Emgee

If it any help, My Mill came with the NVR switch wired between the mains input and the Forward / Reverse Switch.

That is the way that i would prefer it anyway, to make things simple. The mains supply then just goes to the Fwd / Rev without any complication.

Howard

Is the NVR and reverse switch an integrated unit or are they two separate switches? I have never come across an integrated unit. Normally the NVR is on the mains input and the forward/reverse switch is on the output from the control board and just swaps over the positive and negative lines. So changing direction should have no impact on the NVR switch.

Peter

What sort of Lathe ? What Sort of motor ? AC or DC brush or brushless ! NVR MUST be before the reverse switch ! Has this just happened ? what sort of Forward and reverse switch do you have ? As always pictures will be a big help ! Noel

The inexpensive units generally found on import tools are, as Oven Man says, almost invariably integrated with the forward - reverse selector after the NVR system. Select direction then turn on with the NVR unit. Usually the direction selector is under a cover.

For example :-

**LINK** https://www.chestermachinetools.com/product/electrical-n-v-r-switch-415v/

I dislike those because the direction selector is hidden and has no clear indication of which way the machine will run when started. The NVR unit often used to only operate on one line too, the live feed. Which is sort of OK if all is wired correctly but is neutral and live are interchanged! Hopefully current versions operate on both but ....

If the NVR isn't latching in one direction either a wire is off or something is broken. Early ones were very confusing to install and it was possible to connect with NVR latching only on one direction. I suspect the one I played with was made that way so you could have a "jog" reverse to back off a jam rather than free running. If yours is like that one sorting without a wiring diagram will be a headache.

The real industrial rated thing has separte mechanically interlocked contactorsto give NVR functions both ways.

You use this

**LINK** https://www.shutterbits.co.uk/3-way-push-button-station-288-p.asp

with this

**LINK** https://uk.rs-online.com/web/p/contactors/0758793

(pretty much what I have in stock to operate my American style bifold garage door when I finally get fed up with the temporary winch.)

Clive

Edited By Clive Foster on 04/11/2021 10:28:09

The symptoms suggest to me that the forward/reverse switch has failed. Either the Reverse contacts have broken, or maybe a wire has vibrated loose and broken the reverse connection.

On my machines the switches have always been mounted on front panels that can be unscrewed and lifted off to see the wiring or change the switch. A dangling connector should be obvious, and is generally an easy fix. Otherwise, the F/R switch can be replaced : they're not difficult to source. A photo would help identify it.

Which machine is it? Someone might have a circuit diagram.

Dave

The big question here is what type of motor is it, AC or DC?

I guess the Chester integrated unit referred to above is for single phase AC motors with switched (centrifugal) start winding and run winding, the modern equivilent of an NVR and Dewhurst switch.

Peter

SOD

The OP implies that the machine still runs in reverse but the NVR doesn't latch so the start button has to be held down for it to run.

This suggests that the forward reverse switch itself is sound but there is no power being supplied to the NVR coil in reverse. So, as I suggested in my previous post, reverse is operating in jog mode.

Connection issue with the NVR unit either internally or, if it is intended to have a jog mode connection, externally.

Assuming its one of the inexpensive import NVR units similar to the one I linked to above, best to simply change the unit if its not an obvious external connection failure.

Personally I'd swop for an industrial rated system like that in my second links. The interlocked contactors can be found more cheaply. Think I paid around £40 for mine and £15 (ish) for the button box. Roughly double what a the common import unit costs so not scary out or reach.

But I dislike the compromises often inherent in affordable equipment and can afford to indulge that affectation. Which many folk can't.

Clive

Hi Lynne,

By 'the lathe' I take it you mean your ML7B in your photo album. So you should have the NVR as your motor on/off contactor, then the forward/reverse switch, then the motor.

It sound like the NVR is in the wrong place.

Thanks for the responses. Let me try to clarify things. The switch is an integrated unit, made by Kraus & Naimer,

and was a factory fit by Myfords, when Myfords was Myfords,so I guess that means its getting on in years, a bit like me. It is operating on mains AC, and has operated fine for years, and it is only recently that it has started not to latch when selecting reverse. This is an intermittent fault, as this morning it held ok. The selector is mounted on the top of the unit, not shrouded. I will take some pictures, but it may be a while before I get them up here,

Regards Lynne

Lynne

Sounds like it could well be a proper industrial type unit with mechanically interlinked forward-reverse contactor pair inside somewhat like that in the final link of my first post.

If so the problem could well be wear, adjustment or simply gunge issues in the mechanical interlock. The interlock basically protects against selecting forward and reverse at the same time. If the travel on one, or both, sides is limited for any reason it will prevent latching by inhibiting the coil "keep alive when running circuit" on that side.

Clive

We know now this is Myford Lathe My thoughts are that some contacs in the NVR control are either worn or require cleaning also is this working on 3 phase or single phase . Lack of info is giving rise to a load of unneded answers.

More Info Please

Bee M

good morning, Thanks for all your responses. I have opened the unit,& as the switch/coil is an intergrated assy, I am not inclined to dismantle further. I will live with it as it is. I did contact Kraus & Naimer uk, & they say they are not aware of a stockist, as it is a power failure release switch which are direct from the factory, & which to me sounds expensive.

BeeM. May be you have'nt picked up on my post @ 12:27:23.

I have put some pictures of the switch into the album. Regards Lynne

The last time I enquired about a price for a similar switch for an Emco Milling machine cost was £94

Is there a part number showing on the switch ? if so a replacement could be sourced.

Emgee

Yes I did note that your post @ 12;27;23 stated that it does work some times ,, This is why a said that the possibilty was that the contacts in your NVR Contact or the forword and reverse switch may be dirty so causing a poor connection sometimes , If you can get access to these contacts with a small brush and some meths a clean may work together with a puff of air if you have a airline, I used to do a maitenance program on a large laundry which envolved cleaning contactors on 3 phase motors of 25 HP plus which proved a good and reduced breakdowns.

Good Luck

Bee>M

That switch stack looks fairly open, you could try a blast of compressed air.

There is a Pt.No. on the switch, but I think it is going to be difficult to source a replacement, since the UK arm of Kraus & Naimer are not aware of a stockist. I would be reluctant to buy 2nd hand, not knowing how much use it had been subjected to. I would certainly give it a blast if I had compressed air. There are no contacts exposed so meth and a brush are out. Thanks again. Regards Lynne

If hyou have a Poundland near you you can buy a aerosol Air Duster for £1.00. This is worth a try I use these very often for quickness.

Regards Bee.m