Motor protection

[MikelkieParticipant @mikelkie]

I automated my band saw about a year ago for cutting short pieces from bar stock, it was necessary to stop when things go wrong so i installed a system to stop the motor if the driven wheel does not complete a revolution in a preset time (blade brake. slip off or jamming) This work great and i can do other work while the saw carries on.

[noel shelleyParticipant @noelshelley55608]

The No volt release offers NO protection to the motor. Cheap ones will be nothing more than a self holding relay that once released will not relatch until the start button is pressed after a break in the supply. Noel.

[petro1headParticipant @petro1head]

TeC seem to get reputable reviews

they do a 350w motor, same as my friends saw with 14mm shaft for £90 or a 500w with 19mm shaft for £120

Which would be easier, adapting a pully with 16mm hole to 14 or 19mm

Edited By petro1head on 03/02/2022 18:07:15

[not done it yetParticipant @notdoneityet]

Very clearly, boring it to 19mm is easier than boring, sleeving then boring again. No real contest on that score – as long as there is sufficient metal for safe boring, but I would try to go with the correctly sized motor. Ringing mm might possibly lead to finding the real truth re that motor (but I would not be holding my breath while trying that🙂 ).

Perhaps time to purchase a new pulley? They are cheap enough and may have a keyway already (if needed).

Looking after motors is usually far better than repairing after burning them out. Forgotten your burned out motor while trying to drill 22mm holes?

Bite the bullet and do it properly, whatever you decide is the best course of action.

[Colin WhittakerParticipant @colinwhittaker20544]

I have recently bought a slow start relay from China for a central vacuum cleaner. (The original slow start failed and a direct replacement from Europe was perhaps 10 times the price.)

The reason I say this is that if you want an electrical safety cut off that doesn't trigger under the start up current surge then you could consider installing a slow start relay such as this.

Cheers, Colin

[HOWARDTParticipant @howardt]

I also burnt my motor out about three years ago, replaced with a o.5 hp 1380rpm motor from Bearing Boys. Also fitted new pulleys and a clogged belt to give me a cutting speed nearer to what Tuff Saws recommend for cutting steel. No real need for the stepped pulls speed change as I rarely cut softer metals and speed is still adequate when I do. Now I don’t leave the cut unattended.

[petro1headParticipant @petro1head]

Posted by Colin Whittaker on 04/02/2022 00:35:10:

I have recently bought a slow start relay from China for a central vacuum cleaner. (The original slow start failed and a direct replacement from Europe was perhaps 10 times the price.)

The reason I say this is that if you want an electrical safety cut off that doesn't trigger under the start up current surge then you could consider installing a slow start relay such as this.

Cheers, Colin

Don't have any understanding of these relays, how would it protect the motor?

[EmgeeParticipant @emgee]

Posted by petro1head on 04/02/2022 09:12:13:

Posted by Colin Whittaker on 04/02/2022 00:35:10:

I have recently bought a slow start relay from China for a central vacuum cleaner. (The original slow start failed and a direct replacement from Europe was perhaps 10 times the price.)

The reason I say this is that if you want an electrical safety cut off that doesn't trigger under the start up current surge then you could consider installing a slow start relay such as this.

Cheers, Colin

Don't have any understanding of these relays, how would it protect the motor?

By reducing the start up current to allow the use of a Fast acting fuse rated close to the motor plate flc.
Still IMO best to have the protection of an overload set to flc.

Emgee

[Mike PooleParticipant @mikepoole82104]

Inverter drive supermarket supply WEG Starters with overload fitted at very reasonable prices. A starter will include the NVR so once you have an NVR it is easy to incorporate remote EStop and cutoff switchs once the job is finished.

Mike

[noel shelleyParticipant @noelshelley55608]

Hi Colin, as I understand things your motor failed under load ? If so then a soft start will be of little help, complicate things and be something else to go wrong ! What you need is an over current cutout ( DOL ) – this device will handle the considerable overcurrent on start up but only for a short while – if the high current lasts more than a few seconds then the heater will warm up and cut out. If this happens then some investigation is needed. It may be as simple as the load was to high or it could be the centrifugal switch has failed, condenser has blown or gone out of spec Etc. The idea is that it protects the motor, this I understood to be part of your original post ! If the machine worked well with the original motor then replace it with a motor of a similar power !

There are people on here who will make – adapt – or cobble together, often with great skill to get where they want to be, or use what they have to achieve a goal. I once came across a diesel driven lathe !!!!!

For those who's expertise lay in other fields but want to build things or use machinery there is this forum !

We do our best, ME 4643 July 2020 may help you understand your problem.

Best wishes Noel.

[petro1headParticipant @petro1head]

Hi Noel

Do you have a link to such a device please

[noel shelleyParticipant @noelshelley55608]

I don't claim to be good with computers so a link is not something I know how to do BUT what you want is a Direct On Line starter with a current range of about 2A to 4A and a coil voltage of 220V . It must have overload protection . They are normally made for 3Ph and you wire up for single Ph. There are numerous makers, IMO, Telemechanique, MEM, Etc. The way they work you also get the No Volt function as a bonus. Noel. PS others may be able to help with a link ? A quick look on the net shows many, DO NOT go for the cheapest, expect to pay £50-£100 and a reliable supplier..

Edited By noel shelley on 04/02/2022 11:40:28

[not done it yetParticipant @notdoneityet]

Posted by Emgee on 04/02/2022 10:04:39:

Posted by petro1head on 04/02/2022 09:12:13:

Don't have any understanding of these relays, how would it protect the motor?

By reducing the start up current to allow the use of a Fast acting fuse rated close to the motor plate flc.
Still IMO best to have the protection of an overload set to flc.

Emgee

I, for one would not rely on a fuse for protection as some can quite easily remain closed circuit at approaching 150% of their load rating, for longer than one might expect – particularly the usual BS1362 spec. type that has some considerable thermal resilience but is not specifically rated as slow-blow.

The way to go is as Noel pointed out (virtually?) at the beginning of this thread. Common sense, simple, effective solution to motor stalls/overloads – provided the overload settings are set up properly, of course.

At one place where I worked, there were several hundred (possibly over a thousand) motors, ranging from 6000 to fractional horse power. None were directly protected by fuses. Nearly all were fitted with thermal overloads within the starter, or other overload protection. I suppose one might say it is is simply the industrial standard for operating electric motors.

Fuses were there to protect the wiring from the supply to the machine, not to protect the motor.

[noel shelleyParticipant @noelshelley55608]

PLAN B, NEVER leave the machine running unattended ! One could adopt a manual form of overload protection by using an overscale ampmeter. This would show the initial starting surge which could be as high as 1200% of the running figure followed by a steady reading for the unloaded condition, rising to full load current. If the full load current is exceeded by much for 5 seconds – reduce the load or HIT THE STOP BUTTON ! or unplug it. Now look for what caused this high current situation ! Any change in running sound eg a drop in revs that has no obvious cause – stop the machine and investigate. Noel.

[Mike PooleParticipant @mikepoole82104]

**LINK** **LINK**

the two components by IMO would make a starter with NVR function and motor protection overload, you are probably nearer to a Toolstation than you are to a rat these days. IMO are a good quality manufacturer.

**LINK**

This item from WEG is very attractively priced and although WEG are relatively new they are a large company based in Brazil and seem to be generating a good reputation. My personal choice would be the WEG as I feel reasonably comfortable that it would perform satisfactorily and the IMO is the thick end of a hundred quid and may or may not be a better device. The links are examples and you will need to select an overload with the range to cover your motors full load current and adjust to your exact requirement or in the case of the WEG select the unit to suit your motor. The IMO basic unit is for a 240v motor up to 4kW in power and will need the overload selected for your motor current. The WEG unit will need to be a single phase model to suit the motor you have. These are examples of what you are looking for so trawl the internet to see if there is a good deal to be found.

https://www.tlc-direct.co.uk/Main_Index/Distribution_and_Switchgear_Index/DOL_Starters/index.html#Crompton_DOL_Starters

if you have a branch of TLC electrical near you this could be another option, again select a base unit and overload to suit your motor.

Mike

 

Edited By Mike Poole on 04/02/2022 13:16:21

[petro1headParticipant @petro1head]

Posted by Mike Poole on 04/02/2022 13:10:06:

**LINK** **LINK**

the two components by IMO would make a starter with NVR function and motor protection overload, you are probably nearer to a Toolstation than you are to a rat these days. IMO are a good quality manufacturer.

**LINK**

This item from WEG is very attractively priced and although WEG are relatively new they are a large company based in Brazil and seem to be generating a good reputation. My personal choice would be the WEG as I feel reasonably comfortable that it would perform satisfactorily and the IMO is the thick end of a hundred quid and may or may not be a better device. The links are examples and you will need to select an overload with the range to cover your motors full load current and adjust to your exact requirement or in the case of the WEG select the unit to suit your motor. The IMO basic unit is for a 240v motor up to 4kW in power and will need the overload selected for your motor current. The WEG unit will need to be a single phase model to suit the motor you have. These are examples of what you are looking for so trawl the internet to see if there is a good deal to be found.

**LINK**

if you have a branch of TLC electrical near you this could be another option, again select a base unit and overload to suit your motor.

Mike

Edited By Mike Poole on 04/02/2022 13:16:21

Thanks Mike, so do I choose the overload protection based on the stated amps on the motor?

[Mike PooleParticipant @mikepoole82104]

Yes, the full load current FLC is usually stated on the motor info. plate. The overload units usually have a current range of a few amps and an adjuster you set to match the FLC of your motor. The basic control is a box with push buttons and a contactor that has an operating coil that is suitable for your supply, for a single phase unit this will be somewhere in the range 220V to 240V typically. When you have your chosen motor then you will know the overload module required for the contactor box. Ideally the contactor and overload unit should be from the same manufacturer as they will fit together neatly.

Mike

[petro1headParticipant @petro1head]

Posted by Mike Poole on 04/02/2022 20:28:02:

Yes, the full load current FLC is usually stated on the motor info. plate. The overload units usually have a current range of a few amps and an adjuster you set to match the FLC of your motor. The basic control is a box with push buttons and a contactor that has an operating coil that is suitable for your supply, for a single phase unit this will be somewhere in the range 220V to 240V typically. When you have your chosen motor then you will know the overload module required for the contactor box. Ideally the contactor and overload unit should be from the same manufacturer as they will fit together neatly.

Mike

Thanks

Probably a stupid question but to use the saw I assumemi will have to push the button on the overload using and the saw at the same time?

[Mike PooleParticipant @mikepoole82104]

The overload module can usually be set to reset automatically or manually, the stop button will often operate the reset button on the overload if manual reset is selected. The overload module has a contact wired into the NVR circuit so when an overload occurs it will trip the NVR. Reset may require a few minutes for the heaters and bimetal actuators to cool before the latches can be set again. There should be no need to open the box to reset the overload.

Mike

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