Three phase motor capacitor wiring help

[Smouser]

Good evening all.

Background
After I received such good and friendly advice on my previous motor wiring questions here and here which resulted in my Qualters and Smith Hacksaw restoration here I have come for some more help.

Yesterday I acquired an old Metalclad rip saw.

The motor is a BEAST!
I can just about lift it on my own but it makes my piles pop out

What I think I know
1. Three-phase motors do not require capacitors to run
2. Three-phase motors can be run on single-phase power with the help of capacitors
3. Running a three-phase motor on capacitors will never be as good as running it on three-phase power or via a VFD

The previous owner said he ran the saw on three-phase power but this saw probably had many many owners in its life.

I have found three capacitors on the saw (the cable was cut and they were not in use).

Can somebody help me to wire this motor up to run on single phase with the capacitors?

The photo below shows the setup. The top capacitor has got a value of 30uf 440v and the bottom two 60uf 320v.
I assume they are for starting and running (I do not know which is which) with a timer box switching between the starting and running capacitors after a few seconds.

How do I wire this up starting from the supply?

 

[Bornfree]

I've never seen a 3ph 200v motor before.

 

[mtt.tr]

You have a star delta DOL there

I would get rid of all that and go vfd you also benefit having the blade braked

 

[Smouser]

You have a star delta DOL there

I would get rid of all that and go vfd you also benefit having the blade braked

Tell me more!

I probably will go the VFD route eventually if I keep the saw.
But I want to make it work with the capacitors first.

 

[mtt.tr]

Tell me more!

I probably will go the VFD route eventually if I keep the saw.
But I want to make it work with the capacitors first.

It will turn but will have no power.

 

[not done it yet]

This might help, but that 200 Volt might complicate matters. Presumably a 6 pole motor at 930rpm, as well, so connections may be completely different?

 

[mtt.tr]

This might help, but that 200 Volt might complicate matters. Presumably a 6 pole motor at 930rpm, as well, so connections may be completely different?

Poles are internal so make little difference to wiring.

200v indicates is delta would

 

[Richiew]

In my ignorance I would have assumed that 200v is close enough to 220v not to matter.

 

[Smouser]

In my ignorance I would have assumed that 200v is close enough to 220v not to matter.

That is what I read too. 10 - 15% difference in voltage does not matter too much.

 

[Dave-sparks]

200v indicates is delta would

How so?

200V strikes me as a pretty unusual voltage for a TP motor.

 

[m_c]

In my ignorance I would have assumed that 200v is close enough to 220v not to matter.

Officially, UK mains voltage is stated as 230V-6%/+10%, however that is due to EU harmonisation.
UK mains voltage is still mostly 240V, with the limits being 216 to 253V.

Given how old that saw and motor looks, I'd hazard a guess it was a probably specified to be run either from a generator, or some kind of local supply before there was really any consistent mains voltage tolerances.
Although a quick google shows Japan uses 200V, and the US 208V can also be 200V.

 

[m_c]

You have a star delta DOL there

I would get rid of all that and go vfd you also benefit having the blade braked

There's not enough contacts for that to be a star-delta starter, so it has most likely been a basic time delay static phase converter start up.

 

[mtt.tr]

There's not enough contacts for that to be a star-delta starter, so it has most likely been a basic time delay static phase converter start up.

You are spot on, i apologise for not properly looking.

 

[Dave-sparks]

Officially, UK mains voltage is stated as 230V-6%/+10%, however that is due to EU harmonisation.
UK mains voltage is still mostly 240V, with the limits being 216 to 253V.

Even 240/415V is a bit of a myth as the vast majority of substations are still 250/433V output as per the early days of the national grid.

Either way that motor is 200V 3 phase, so it's a long way off the 415V you get from the DNO.

 

[mtt.tr]

How so?

200V strikes me as a pretty unusual voltage for a TP motor.

Look at most name plates it will state

230v delta or 440v star

 

[Dave-sparks]

Look at most name plates it will state

230v delta or 440v star

On a modern motor it may well do, but that old Crompton in the OP is something else.

 

[m_c]

Can somebody help me to wire this motor up to run on single phase with the capacitors?

The photo below shows the setup. The top capacitor has got a value of 30uf 440v and the bottom two 60uf 320v.
I assume they are for starting and running (I do not know which is which) with a timer box switching between the starting and running capacitors after a few seconds.

View attachment 297179

How do I wire this up starting from the supply?

Have a look at the diagram with the yellow background about half way down this page - Static Phase Converter [Pros and Cons] - Electric Problems
Actually, here it is for easy reference-

I'd guess the two identical capacitors will have been permanently connected to the false phase (L1-L3 and L2-L3 in the diagram), then the odd capacitor has been connected via the contactor and time delay relay.
Using a time delay relay is a bit of a crude way to start the motor, but it will work. You ideally want the time delay just long enough that the motor just about gets to speed before it disconnects. If it remains connected for too long, you risk the motor running very rough, and high voltages on the false phase, but if too short a time delay, you risk the motor just stalling.

Using a static phase converter, you're limited to around 2/3 of the motors rated HP, and if you push too hard using the basic time delay relay, you'll just stall the motor. I'd personally swap the time delay to a relay with a suitable voltage coil connected between the false phase, and one of the other phases, so if the motor load become too much, the start capacitor will get reconnected (this is essentially what the 'Boost' mode is on the static phase converters the likes of Machine Mart sell).

 

[mtt.tr]

No pretty common on most induction motors

 

[Smouser]

Have a look at the diagram with the yellow background about half way down this page - Static Phase Converter [Pros and Cons] - Electric Problems
Actually, here it is for easy reference-
View attachment 297219

I'd guess the two identical capacitors will have been permanently connected to the false phase (L1-L3 and L2-L3 in the diagram), then the odd capacitor has been connected via the contactor and time delay relay.
Using a time delay relay is a bit of a crude way to start the motor, but it will work. You ideally want the time delay just long enough that the motor just about gets to speed before it disconnects. If it remains connected for too long, you risk the motor running very rough, and high voltages on the false phase, but if too short a time delay, you risk the motor just stalling.

Using a static phase converter, you're limited to around 2/3 of the motors rated HP, and if you push too hard using the basic time delay relay, you'll just stall the motor. I'd personally swap the time delay to a relay with a suitable voltage coil connected between the false phase, and one of the other phases, so if the motor load become too much, the start capacitor will get reconnected (this is essentially what the 'Boost' mode is on the static phase converters the likes of Machine Mart sell).

Thanks, that looks like what I am after.
I am going to dig into this tmrw and do some reading. A forum member kindly sent me some motor books which will be a great help too.

 

[Turbo]

Running a 3ph motor using capacitors to create a dummy phase is quite hard on a motor, especially if the capacitors are faulty or not correctly sized. Given its age I would not like to run an old motor like that permanently using capacitors, maybe a short test to see if the motor is working.

The price of vfds has come down so much that its the most sensible way to run something simple like that saw, plus you can set it up so the vfd stops the blade nearly instantly.