Thread: Help please! VFD SCM Braked Motor

Originally Posted by DomAU

That was the plan and is what i'd still like to do. The only issue is the motor brake on the motor which I believe to be electromagnetically released. The machine looks to have a rectifier to convert the incoming line voltage into DC voltage (but looking at the rectifier I can't figure out what voltage is needed in and what is coming out) which I assume is to disengage the brake by providing power to it (it is otherwise on with no power supplied) and believe this is also why there is something that looks like a delay circuit/box in the machine - to ensure the motor brake is off before the motor can be turned on. In any event, the sticking point is figuring out how to either provide the right power to the motor brake to disengage it, or physically remove it from the motor if possible. For the former I guess i'd need to run a second 240v supply line through a rectifier and a switch or relay so that I could energise that before switching on the motor with the VFD.

Cheers, Dom

Looking at your first pic of the motor the wiring diagram shows Star or Delta connections and there is a a terminal block in your pic to the left of the motor, so if you disconnected the wiring done by the factory from this terminal block and directly wire L1,L2 & L3 from your VFD to the motor would this not bypass your electric brake issue because the brake would no longer be apart of the circuit?

Originally Posted by DomAU

I think i'll see if another motor is available off the shelf that has the right mounting and more importantly shaft dimensions first - that will be the cheapest option by far.

I just had a look and an RPC will be well north of $5-6k. Three phase is potentially years away as it wasn't in the cards unless I move given that I would need to get under about 10m of concrete to run a new conduit to the power pit - which I assume is going to be very cost prohibitive - but maybe i'll get a quote. Can't see it being less than $5-6k though.

If the choice were between 3phase wired in or an RPC I assume the former would be the better option?

Cheers, Dom

I built my own RPC a few years back for under $1K and apart from having to replace the odd capacity it's never let me down.

Dom, remove the motor terminal box cover and take a pic....then i can advise you further

Originally Posted by ericks2

Dom, remove the motor terminal box cover and take a pic....then i can advise you further

20220330_153924.jpg

Sorry it's hard to get a clear shot, there isn't space to get to min focus distance. Let me know if this is clear enough. Thank you!

So I guess the brake needs 25w at 100VDC

Motek's three phase brake motors Series ETP with gradual brake are particularly suitable for applications that require gradual and silent load stopping without any particular need for precision. They are designed to both ensure user's safety and prevent damage to machine parts. The braking torque – non adjustable – corresponds to the pressure of springs which, when no voltage is applied, keep the brake disc in contact with the internal surface of the cast iron fan. To release the disc, feed the electromagnet via a rectifier. If necessary, the air gap adjustment screw can be reached without removing the fan cover.

Its easy to wire and program the drive to control the brakes on and off function.

Some of this info might help

This photo suggests the brake is embedded in the motor
9 Nm, 25W, using 230VAC and 100VDC
Screen Shot 2022-04-15 at 6.32.33 am.jpg

According to the Motek website

Motek's three phase brake motors Series ETP with gradual brake are particularly suitable for applications that require gradual and silent load stopping without any particular need for precision. They are designed to both ensure user's safety and prevent damage to machine parts. The braking torque – non adjustable – corresponds to the pressure of springs which, when no voltage is applied, keep the brake disc in contact with the internal surface of the cast iron fan. To release the disc, feed the electromagnet via a rectifier. If necessary, the air gap adjustment screw can be reached without removing the fan cover.

This means the brake is always on until power is supplied so a simple solution may be to just remove the brake springs. The brake sounds like it's part of the cooling fan so it sounds like removing the brake springs may not require the motor be completely dismantled as the brake appears to be part of the cooling fan. It may be possible to just that "air gap" they refer so that the brake doesn't make any contact with the fan?

Motek's website show this photo but it doesn't help all that much
Screen Shot 2022-04-15 at 6.50.49 am.jpg

In the picture below the word FRENO means "brake" in Italian, while Alimentatore means power supply
The single sided lump symbol suggests its a half wave rectifier which provides the DC to the brake
Screen Shot 2022-04-15 at 6.31.06 am.jpg

So if I were to supply 240V AC to this rectifier would that release the brake? It only has two thin cables going in / out so.

Cheers, Dom

Maybe I need to pull the motor out, remove the dust shroud and see if the fan and brake are seperate items and if the brake can be removed independently of the fan. That would solve all of my problems presumably.

Cheers, Dom

Originally Posted by DomAU

Maybe I need to pull the motor out, remove the dust shroud and see if the fan and brake are seperate items and if the brake can be removed independently of the fan. That would solve all of my problems presumably.

Surely it would be a heck of a lot easier to "feed the electromagnet via a rectifier" as per the manufacturer's notes?

Originally Posted by jack620

Surely it would be a heck of a lot easier to "feed the electromagnet via a rectifier" as per the manufacturer's notes?

Easier if you are electrically minded haha, i always prefer a mechanical solution I can better understand.

If it's easy enough to just feed another 240V power source to the rectifier in the motor then that should be straighforward enough. I think that would need to be a seperate line to that coming from the VFD though as the brake would need to be disengaged before the VFD starts applying power to the motor? Presumably, running a 240V line and neutral to the rectifier and the earth to the motor earthing point would do it?

Cheers, Dom

Originally Posted by DomAU

Easier if you are electrically minded haha, i always prefer a mechanical solution I can better understand.

If it's easy enough to just feed another 240V power source to the rectifier in the motor then that should be straighforward enough. I think that would need to be a seperate line to that coming from the VFD though as the brake would need to be disengaged before the VFD starts applying power to the motor? Presumably, running a 240V line and neutral to the rectifier and the earth to the motor earthing point would do it?

Cheers, Dom

If you have 2 feeds the one to the rectifier would probably need a normally open momentary switch, this could release the brake while you use the 2nd feed to start the VFD, I am assuming you only need power to the rectifier to energise it, but do not want power to it all the time, just in case there is a power cut

Originally Posted by BobL

It may be possible to adjust that "air gap" they refer so that the brake doesn't make any contact with the fan? This is the simplest solution. And would be the first thing I would try.
The small white box is a diode module that provides the DC to the brake.



Screen Shot 2022-04-15 at 6.31.06 am.jpg

It is a bit more complicated than "to just feed another 240V power source to the rectifier in the motor ". It is not designed to be on 100% of the time. At the moment you have 230V going to a transformer that outputs 110V. That 110V then goes to the red safety relay. When you hit the start button the safety relay pulls in and energises the brake via the diode pack (to give half wave rectification). After a time delay, in the safety relay, the motor contactor energises and supplies power to the motor. I realise you probably haven't run the machine but the safety relay seems to have a fixed time delay of 20 seconds which seems like a long time to me. Other versions of that relay have an adjustable time delay. Anyway, thats my read of the info so far. Unless you can rewire the control circuit so that the brake is only energised while the motor runs you risk burning out the diode or the brake solenoid. Which means the brake is on all the time and you are back to square one

Originally Posted by DomAU

So if I were to supply 240V AC to this rectifier would that release the brake? It only has two thin cables going in / out so.

Cheers, Dom

Unless you can control the brake from the VFD (which ericks says is possible and the more i think about it the more it seems possible but by my way of thinking you will need to set up some sort of intermediate control) and given your limited electrical skills maybe removing the brake is the simplest option. Feeding power to the brake independently runs the risk that if there is a power failure a powering down VFD and the locked brake won't play nicely.