Thread: Help please! VFD SCM Braked Motor

Pulled the motor out. Very light and small for a 5kW motor - 19.8kg only and very compact. Smaller and much lighter than the 3kW 3 phase motor used in my dust collector.

The brake air gap adjustment screw is an allen bolt at the top of the motor/fan. If I back this out the brake appears to disengage completely a couple of turns out. The torque on the bolt doesn't appear to change and still feels like it's acting against springs. I can spin the motor freely at this point.

Not sure if there is any risk leaving it and running it like this, or if I should undo things completely and see if the brake can be removed. I'm a little worried about undoing it and then not being able to get things back together!

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Cheers, Dom

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Have you got the VFD there?

If so, would connect up the VFD direct to the motor (3P and earth) on the bench and try it out - leave any brake electricals disconnected . If it starts and stops under VFD control - I'd say you are good to go.

Can you take and post a picture of the motor connection/terminal block?

Originally Posted by BobL

Have you got the VFD there?

I would connect up the VFD direct to the motor (3P and earth) on the bench and try it out - leave any brake electricals disconnected . If it starts and stops under VFD control - I'd say you are good to go.

Can you take a picture of the motor connection/terminal block?

Do you think it would be safer to remove the electromagnet and friction disc and refit the fan by itself - like this -

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The friction plate and magnet -

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Terminal block -

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I would just need to snip these electromagnet cables and recrimp later if required. Until this point i would not have disturbed any of the electricals other than disconnecting the original cables to the motor - but nothing permanent / cut. Not an issue though right? Easy to recrimp with a terminal later if required.

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VFD photo -

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That goes to the machine terminal -

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I know, I didn't have 4 core so used the earth core - I will be the only person wroking on/with this and will swap out for correct colours asap

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Then I will terminate the same colours to the motor terminals L1 L2 L3 and earth.

If something doesn't look right please let me know - of course I won't take that as meaning something mightn't be wrong - i will just consider your observation and act if I choose to - don't want anyone to feel exposed at all - these are my actions only and I don't treat anyone here as an expert to be trusted.

Cheers, Dom

Originally Posted by DomAU

I would just need to snip these electromagnet cables and recrimp later if required. Until this point i would not have disturbed any of the electricals other than disconnecting the original cables to the motor - but nothing permanent / cut. Not an issue though right? Easy to recrimp with a terminal later if required.

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Should be OK but I would tend to leave the whole thing assembled in one piece and try the motor out using a separate power cable from the motor back to the back to the VFD.

Whatever you snip or disconnects make sure the ends of all cables are well insulated, just in case anyone tries to power to the machines plug.

One thing you will need to be aware of is that a machine like that will have interlocks to stop the motor when certain things are moved - these will then be inoperable and you need to be aware of this.

Thanks Bob,

Yes good point about the interlocks. I will have to consider that carefully before use and then create a system to ensure I cannot inadvertently create a hazardous situation for myself or the machine.

I'll wire up and try - here goes nothing (well hopefully the motor but nothing bad!).

So go with just the fan attached? I think this minimises any risk of things moving or issues between the friction plate, magnet, fan etc and keeps as much thread / bolt holding the fan.

Ok, it all seems to be running fine.

I will just do another check of the VFD settings to ensure things are all good.

I hope this gets me by for at least a while until I either buy a rotary phase convertor or maybe get 3 phase wired to the house.

I'd also like to wire in a start/stop switch to the vfd that can be close at hand on the machine - some reading to do there for me.

Thanks so much to everyone for their help in this and have a great Easter.

Also, looks like the VFD has a function to provide startup current for a braking device with a delay - so if I were to get a transformer to step down the voltage I could presumably use the brake?

Cheers, Dom

Geez, who'd have thought that buying a new machine for the price of a new small car would require so much stress and work haha.

Originally Posted by DomAU

Also, looks like the VFD has a function to provide startup current for a braking device with a delay - so if I were to get a transformer to step down the voltage I could presumably use the brake?

Cheers, Dom

Assuming your VFD has braking circuitry it will be cheaper/easier/safer to get a brake specific to the VFD. Remember, to protect the VFD and motor the VFD needs to be the system master.

Make sure you set that current limit asap.

Originally Posted by DomAU

Ok, it all seems to be running fine.

I will just do another check of the VFD settings to ensure things are all good.

I hope this gets me by for at least a while until I either buy a rotary phase convertor or maybe get 3 phase wired to the house.

I'd also like to wire in a start/stop switch to the vfd that can be close at hand on the machine - some reading to do there for me.

Thanks so much to everyone for their help in this and have a great Easter.

Things to check,
Acceleration time/speed - - a slow start is good for all drive components eg bearings, belts, chains etc. Seeing as the machines usually starts unloaded I'd go for at least 3s
Slow down speed - you will have to experiment with this. Without a brake, too fast will trip the VFD, while it can handle a few of these long term this is not good start off at about 10s and see what happens, then bring the decel time down incrementally until the VFD trips and then add back a couple of seconds.

As well as an easily accessible motor stop/start switch connected to the VFD I'd also seriously consider an emergency switch on the input power to the VFD. Something like a big mushroom switch that you would normally leave on. If things go pear shaped with regards the wood processing the usual start/stop switch should be fine (better of course with a brake) but if things go wrong electrically you want an instant power off to everything from the VFD forwards. you don't want to be going back to the GPO to do this It depends on the VFD and what the motor is doing at the time but repeated sudden power failure/removal is probably not all that good for the VFD but if its a dire electrical emergency you will be glad you have it. It's not like you will use it very often - hopefully never.

Originally Posted by BobL

Make sure you set that current limit asap.

With the current limit, is the current the output current per phase of the 240v three phase output, or the 240 single phase input current? It's currently set by default at 23Amps.

As for Accel / Decel, the units are configured as 0.1s and it's set at 10 for accel and 10 for decel, but it certainly takes longer than a second - more like 10 - so I guess the units are in seconds despite the manual saying that each unit of time is 0.1s (selectable as either 0.1, 1)

Good idea regarding the quick isolator - i'll need to figure out how to achieve that.

Cheers, Dom

Originally Posted by BobL

Make sure you set that current limit asap.

Originally Posted by DomAU

With the current limit, is the current the output current per phase of the 240v three phase output, or the 240 single phase input current? It's currently set by default at 23Amps.

THE 23A will come from the fact that 23A x 230 (or 220V) = ~5KW
At 240V / 5kW, the current is nominally 20-21A so you could drop that a bit more.
If you want to play really safe get hold of a current clamp meter and measure the current drawn when the machine is under its highest load, widest/deepest cut in hardest wood. Then add say 10% and set it at that. More current will be drawn when the blades are blunter so you might have to make an allowance for that.

[QUOTE]As for Accel / Decel, the units are configured as 0.1s and it's set at 10 for accel and 10 for decel, but it certainly takes longer than a second - more like 10 - so I guess the units are in seconds despite the manual saying that each unit of time is 0.1s (selectable as either 0.1, 1)

10s is fine - really gentle but if it gives you teh toim tits you can always change it - same with decel although its really is worth getting it as low as you can.