Rewiring a 3 phase motor to Delta

[Dcal]

I didn't explain it very well. But, as they say, a picture paints a thousand words.

Here is the switch and also the 'cut off' switch witch is supposed to turn the saw off as soon as it has finished cutting. Remember it is called a donkey saw for a reason, you will get old standing there waiting for a cut to finish .




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The coil in the switch is 380-440v, so it will not work with ~240v.

No
However if you PM me I can send you a 240v coil.

 

[Agroshield]

You do not need the auto-memota with the VFD. It is considered undesirable to switch a VFD downstream of its output.

The auto-cut-off is just a microswitch that would break the feed to the coil in the auto-memota switch. You can reuse the microswitch and plumb it into the VFD.

 

[daleyd]

I didn't explain it very well. But, as they say, a picture paints a thousand words.

Here is the switch and also the 'cut off' switch witch is supposed to turn the saw off as soon as it has finished cutting. Remember it is called a donkey saw for a reason, you will get old standing there waiting for a cut to finish .




View attachment 283295

View attachment 283296
View attachment 283297

View attachment 283298

The coil in the switch is 380-440v, so it will not work with ~240v.

Ah ok, that’s a contactor - when you said switch I assumed a simple rotary switch/isolator.

 

[Dcal]

Very good point @Agroshield and it's the reason I've some old switch gear kicking about.

 

[Smouser]

You do not need the auto-memota with the VFD. It is considered undesirable to switch a VFD downstream of its output.

The auto-cut-off is just a microswitch that would break the feed to the coil in the auto-memota switch. You can reuse the microswitch and plumb it into the VFD.

Oh, I didn't know that. Why is it undesireable?
Undesireable or very bad for the inverter?
My machines get relative light/infrequent use, it is not like they are working in a busy workshop.

That means my Meddings pillar drill is also set up incorrectly. I have been using the off/forward/reverse switch on the drill itself.

No
However if you PM me I can send you a 240v coil.

Thank you very much for the offer. However, it seems like the switch/contactor is not a very good idea.

 

[My Old Landy]

Make yourself one of these to feed from the vfd. It gives (wired) remote control and the functionality required.

 

[Seadog]

Undesireable or very bad for the inverter?

Very bad for the VFD.

 

[Agroshield]

It is a difficult subject.

The earliest VFDs used different technology to modern ones and could very easily be terminally damaged by downstream switching. That is how the prohibition originated.

Modern ones use different electronics that suffer less from this, potentially allowing the prohibition to be watered down a bit.

However, the general advice is still not to do it unless specifically noted as acceptable in the manufacturer's literature. If the manual categorically prohibits it, then follow its advice. If it does not mention it at all, and you decide to do it, it might not let the smoke out straight away but it stands a chance of shortening the VFD's life by an indeterminate amount*. The robustness of the device to this kind of ill-treatment also depends on its quality and country of origin. Cheap, no-brand Chinese VFDs are unlikely to suffer it as well as quality, branded units from an established manufacturer.

If retention of authentic switchgear is important, it can almost always be reconfigured to act as a control (at control voltage) to the VFD.

* as you say, you are a hobby user. If an industrial control is lifed at 10,000 normal operations and downstream switching reduces this life by half, that is still 5,000 operations - a lot of holes drilled in a hobby workshop where you probably use it less than once a day.

 

[mtt.tr]

Can't see many reasons to switch down stream of the vfd when the vfd has so much functionality

 

[Smouser]

It is a difficult subject.

The earliest VFDs used different technology to modern ones and could very easily be terminally damaged by downstream switching. That is how the prohibition originated.

Modern ones use different electronics that suffer less from this, potentially allowing the prohibition to be watered down a bit.

However, the general advice is still not to do it unless specifically noted as acceptable in the manufacturer's literature. If the manual categorically prohibits it, then follow its advice. If it does not mention it at all, and you decide to do it, it might not let the smoke out straight away but it stands a chance of shortening the VFD's life by an indeterminate amount*. The robustness of the device to this kind of ill-treatment also depends on its quality and country of origin. Cheap, no-brand Chinese VFDs are unlikely to suffer it as well as quality, branded units from an established manufacturer.

If retention of authentic switchgear is important, it can almost always be reconfigured to act as a control (at control voltage) to the VFD.

* as you say, you are a hobby user. If an industrial control is lifed at 10,000 normal operations and downstream switching reduces this life by half, that is still 5,000 operations - a lot of holes drilled in a hobby workshop where you probably use it less than once a day.

Great reply. Thank you.

 

[6ply]

Nice to see you are trying to make use of that old motor on your Q&S hacksaw. Mine came with the same motor but on the basis of the time involved plus some noise (possibly the bearings) and just too many projects on the go I ditched it and bought a replacement motor. When you do sort it out, make sure you set your VFD on a nice slow start - it's like an old steam train setting off from the station. I rarely adjust the cutting speed any other time but then again I've got an 8-pole motor which runs at about 700 RPM (@ 50 Hz)