By continuing to use this site, you agree to our use of cookies. Find out more
Forum sponsored by:
Forum sponsored by Forum House Ad Zone

Wiring an NVR switch

All Topics | Latest Posts

Search for:  in Thread Title in  
Robin Graham15/06/2018 22:56:46
945 forum posts
295 photos

A while back I asked for advice on restoring an old Multico mortiser - mechanical stuff now done (thanks!) , just electrics left.

For some reason the previous owner had bypassed the original NVR switch, just wiring the motor directly to the mains, but I can't see any obvious evidence of failure. A couple of pics:

starterfront.jpg

starterbottom.jpg

 

Sorry they're sideways, but helpfully the manufacturer has marked TOP!

The terminals hidden between L1, L2 and L2, L3 lead directly to the solenoid coil which measures 400 Ohms DC. Obviously there's something wrong as wired because the latter isn't connected to anything.

I think I can see how to wire it up to work (albeit with some redundancy) but I'm uncertain about the 'OFF' switch (the red button towards top left [top right now, I have rotated picture - Neil]). This seems to operate a rather flimsy switch:

Closed:

starterclosed.jpg

starteropen.jpg

Open.

Logic tells me that this switch has to be in series with with the solenoid to unlatch it, but fear tells me it's too flimsy. Have I missed something?

Robin.

 

 

Edited By Neil Wyatt on 16/06/2018 08:32:30

Edited By Neil Wyatt on 16/06/2018 08:33:30

john swift 115/06/2018 23:27:03
avatar
318 forum posts
183 photos

single & 3 phase wiring

dol starter wiring single phase.jpg

dol starter 3 phase wiring.jpg

john

Emgee15/06/2018 23:58:50
2404 forum posts
285 photos

Hi Robin

John's schematic should be followed, depends if you have 3 phase or not as to which one.
The contactor is a sturdy Crabtree BD15 model and the switch you believe is flimsy is only switching coil current, not the motor load.
The coil operating voltage will be shown on the coil, best check it is the voltage you will be using.

Emgee

SillyOldDuffer16/06/2018 09:28:55
Moderator
8469 forum posts
1885 photos

The most likely reason for bypassing an NVR is that it's faulty. Before going to a lot of trouble rewiring what may be a dud, check the coil for continuity with a multimeter. You can also check the 95 to 96 contacts by working the overload reset.

When you open up an equipment and find someone else has been 'at it', bear in mind they might have been an electrical genius or a complete incompetent. Either way, proceed with caution!

Dave

Andrew Johnston16/06/2018 11:41:53
avatar
6574 forum posts
701 photos

Hmmm, the way I read it the small red knob is used to set the overload characteristic. Screwed in the trip is automatic, usually based on a bimetallic strip. Screwed out it's manual, ie, needs pushing. It's nothing to do with normal operation of the contactor. Without going to look I'm pretty sure the on/off switches on all my 3-phase machines are completely separate from the contactors.

Andrew

Edited By Andrew Johnston on 16/06/2018 11:42:36

SillyOldDuffer16/06/2018 12:10:05
Moderator
8469 forum posts
1885 photos
Posted by Andrew Johnston on 16/06/2018 11:41:53:

Hmmm, the way I read it the small red knob is used to set the overload characteristic. Screwed in the trip is automatic, usually based on a bimetallic strip. Screwed out it's manual, ie, needs pushing. It's nothing to do with normal operation of the contactor.

...

Andrew

Edited By Andrew Johnston on 16/06/2018 11:42:36

Agreed the red knob sets the overload characteristic. But looking at John's circuit, it's essential that the overload contacts are closed to energise the coil, thus closing switches T1, T2 and T3 and applying power to the machine.

For the coil to operate:

  • Connection L1 to A1 must be intact
  • Coil between A1 and A2 must be in working order
  • Connection A2 to 95 must be intact
  • Overload Switch between 95 & 96 must be closed (either by the bimetallic strip or manually)
  • Connection 96 to 2 must be intact
  • On/Off n/c Switch between 2 &1 must be closed
  • Connection 1 to 4 and 15 must be intact
  • On/Off n/o Switch between 3 &4 must be closed ( this switch is bypassed by 13/14 when the coil is operated to latch 'on', and does the NVR part)
  • Connections 3 to 13 and 13 to 5 must be intact

If it's not working, follow the circuit with a multimeter to identify the break. In order of likeliness, switches and contacts are always suspect, especially more complicated types like bimetallics, wires & terminals vibrate loose, and - rarely - coils burn out.

Dave

Andrew Johnston16/06/2018 12:22:09
avatar
6574 forum posts
701 photos
Posted by SillyOldDuffer on 16/06/2018 12:10:05:

Agreed the red knob sets the overload characteristic. But looking at John's circuit, it's essential that the overload contacts are closed to energise the coil, thus closing switches T1, T2 and T3 and applying power to the machine.

Yeahbut, the overload contacts are marked N/C so in automatic mode, at least, they're closed all the time, unless there is an overload. So they're "invisible" to the user.

The biggest problem with open frame contactors as shown is chatter due to dirt on the pole pieces. I've lost track of the number of times I've needed to take contactors apart to clean them, especially on the Britan repetition lathe and horizontal mill. On the Bridgeport the only issue I've had, so far, was duff auxiliary contacts, which I bypassed.

The OP seems to think that the red button is part of the normal on/off controls, which is rather worrying.

Andrew

SillyOldDuffer16/06/2018 18:39:22
Moderator
8469 forum posts
1885 photos

Can anyone explain the red arrowed feature on Robin's contactor?

contactorq.jpg

Looks like it's adjusted by thumb. The visible graduations are strange - 4.7 and 5.7

I doubt it's part of the overload protection because that's on the other side of the box. So what is it?

Dave

john swift 116/06/2018 19:05:41
avatar
318 forum posts
183 photos

that's the adjuster to set the trip current for the motor you are using

Dave Martin16/06/2018 19:09:07
101 forum posts
11 photos

Dave (SOD) - its the adjustment for 'Full Load Motor Amps"

Dave

john swift 116/06/2018 19:35:55
avatar
318 forum posts
183 photos

I have found a view of the mechanical latch on another D.O.L. starter

when the over load has been reset it holds a normally open switch closed

the dial (or on some units a lever ) adjusts the value of current the latch is released

when one or more of the bi-metallic stripes are heated by the motor current 

exceeds the maximum current you have set as the trip current

the adjustment of the green knob moves  a hinged  insulated bar that the  bi-metallic strips push on to release the latch

dol starter over load mechanism.jpg

 

   John

 

 

Edited By john swift 1 on 16/06/2018 19:55:12

Emgee16/06/2018 22:22:55
2404 forum posts
285 photos

Andrew

This BD range of starters from Crabtree were available open chassis or enclosed in pressed sheet metal or cast iron enclosures. The Stop/start buttons were positioned on the lid with the operating spindles in line with the small red button which acts as the stop switch, also the start switch is the lower light coloured button.
They are only switching coil current so of adequate size.

The magnet poles on these contactors are of adequate size to provide saturation so giving silent running (no hum)
The main fixed and moving contacts are replaceable, I believe I may still have a set in my w/shop.

Emgee

Robin Graham16/06/2018 23:54:41
945 forum posts
295 photos
Posted by SillyOldDuffer on 16/06/2018 09:28:55:

When you open up an equipment and find someone else has been 'at it', bear in mind they might have been an electrical genius or a complete incompetent.

The latter I suspect - it looks like the previous owner had just disconnected the motor input from the switch and put a plug on the short length of cord without even trimming the wires to fit. So the clampy thing that's meant to grip the outer sheath was doing nothing. That sort of thing makes me nervous!

I did what checks I could with a multimeter and all seemed to be in order so I wired it up with reference to John's schematic (it's single phase). Many thanks John, that was very helpful.

Emgee, you are spot on in your identificaction of the unit - it has the pressed metal case inside which there is sticker giving part numbers for replacement contacts etc. A relic of the days when things were designed to be maintainable perhaps. The red button is indeed the stop switch rather than an adjustment, it is actuated by the Big Red Button on the front casing of the unit, as you know.

I'm still in the dark about the white wheel Dave pointed to. It's calibrated in Amps, and is marked max current or somesuch. I just left where I found it at somewhere around 5A. Could it be somehow connected to the overload trip mechanism? The motor is 3/4 HP 4.5A according to the plate btw.

Anyhow, all is working fine now, and I'll never know why the NVR was taken out of circuit - maybe the previous owner just couldn't figure out how to wire it.

I did have a shaky moment when I first fired it up and it appeared not to stop when I hit the red button - turned out the motor takes about 35 seconds to wind down, so the bearings are in good shape I guess!

Thanks again for the help, Robin.

Edited By Robin Graham on 16/06/2018 23:56:30

Emgee17/06/2018 17:01:41
2404 forum posts
285 photos

Robin

The white wheel to which you refer is as has been stated the setting for the motor full load current, so in your case you could turn it down until the quoted motor FLC is indicated opposite the arrow shape at the top, at present it is set slightly high.

Emgee

Robin Graham17/06/2018 22:37:08
945 forum posts
295 photos

My apologies to John Swift and Dave Martin, I somehow missed your answers to the question of the white wheel's function. All is now clear I think.

Robin.

All Topics | Latest Posts

Please login to post a reply.

Magazine Locator

Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!

Find Model Engineer & Model Engineers' Workshop

Latest Forum Posts
Support Our Partners
Eccentric July 5 2018
Rapid RC
Dreweatts
cowells
Eccentric Engineering
Subscription Offer

Latest "For Sale" Ads
Latest "Wanted" Ads
Get In Touch!

Do you want to contact the Model Engineer and Model Engineers' Workshop team?

You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.

Click THIS LINK for full contact details.

For subscription issues please see THIS LINK.

Digital Back Issues

Social Media online

'Like' us on Facebook
Follow us on Facebook

Follow us on Twitter
 Twitter Logo

Pin us on Pinterest