Rewiring a 3 phase motor to Delta

[Smouser]

I recently got a three phase motor with a machine that is 950RPM (uncommon) but unfortunately it is only wired for 380/440v (background https://www.ukworkshop.co.uk/threads/rewiring-a-3-phase-motor-to-delta.130053/).

I am looking to rewire the motor so that I can use a VFD @ ~240v.

Would anybody be able to offer advice/guidance on where to look for the star point from a photo of the motor?

 

[Maker]

Cut off all the binding around the windings and pick out all the joints, the star point in the one with three wires going into it.

 

[Smouser]

Ok....

I was hoping someone more knowledgeable than me could point me roughly in the right direction (if that is even possible with just a photo).

I am trying to disturb the motor as little as possible.

If I do cut all the bindings around the windings, what do I do to replace the bindings?

 

[Maker]

what do I do to replace the bindings?

I used small tie wraps last time but I doubt they're the best option, they could melt if the motor gets too hot. Nothing's broken yet though so probably no need to worry about it,

The star point is the three twisted wires at the front of this picture, for some reason I stripped every joint and had to go through putting heatshrink back on them all but there's no need for that, just find where three wires meet and desolder that one.

 

[Smouser]

Ok. After staring at the motor for a while, I THINK I have found the Star point.

It is at the 'top' of the motor. Opposite side to where the wires are which goes to the connection plate.

Can somebody please confirm there is only one place in a motor where three wires meet?

What do you think of the photo?

 

[Smouser]

I think I have found it on my first try!

There are no shorts between the wires and contacts. Each wire corresponds with one wire at the existing connection block.

 

[Hopefuldave]

Good job, now to find a 6-way terminal block to bring the existing and new wires out to! (Hint: EvilBay)

Dave H. (the other one)

 

[Smouser]

I was just going to connect the wires to the existing terminals.

I still need to figure out/read up on where the new wires need to connect to.

 

[hooblah]

Hmm just 3 singles? That may be correct, but it seems like an awful lot of wire in there for that.

You need to extend the wires so they go into another set of terminals. Make sure you sleeve them to prevent shorting. Usually you'll have a junction box with terminals labeled U1 V1 W1 and U2 V2 W2. From there you attach links between the terminals depending if you're wiring it for star or delta.

You can use string or ribbon to tie the windings back together. Spray it with lacquer or paint or whatever you want after to make sure it can't move. Ideally you'd dip it in a vat of lacquer and bake it. There's no such thing as too much lacquer

 

[Smouser]

Hmm just 3 singles? That may be correct, but it seems like an awful lot of wire in there for that.

Oh no you are starting to spread doubt. Hopefully it is correct as it is. Will test it today if I get a chance.

You need to extend the wires so they go into another set of terminals. Make sure you sleeve them to prevent shorting. Usually you'll have a junction box with terminals labeled U1 V1 W1 and U2 V2 W2. From there you attach links between the terminals depending if you're wiring it for star or delta.

Sure, that is how it 'normally' is on a dual voltage motor, but not all of them are like that. My Brooke Crompton three phase motor only used 4 terminals.

U1, V1 and W1 and the other three wires all went to a neutral terminal. When changing from Star to Delta you just 'double up the wires' on the correct terminals.

I am going to use the same principle here.

 

[Spark plug]

It looks like your on the right track from here, 3 terminals will do just fine.

A for the connections it’s simple enough:

First label the end of each winding, U1-U2, V1-V2, W1-W2.

Now connect the wires as follows:

Terminal 1, U1 & W2

terminal 2, U2 & V1

terminal 3, V2 & W1

 

[Agroshield]

Your meter readings look good. For final checking, make sure that each wire at the star point has continuity to one and only one of the terminals.

The siliconised fibreglass sleeving is better to use than standard heatshrink. Similarly, the wires that you bring out to the six-way block should also have some heat-resisting ability. If you can find a discarded electric oven, the wires inside that are good to repurpose. The star point wires are likely enamelled and varnished, so a gently scrape with a blade prior to soldering on the new extensions will help. Clean off all flux residue (IPA and toothbrush) before encapsulating them.

 

[Smouser]

Your meter readings look good. For final checking, make sure that each wire at the star point has continuity to one and only one of the terminals.

The siliconised fibreglass sleeving is better to use than standard heatshrink. Similarly, the wires that you bring out to the six-way block should also have some heat-resisting ability. If you can find a discarded electric oven, the wires inside that are good to repurpose. The star point wires are likely enamelled and varnished, so a gently scrape with a blade prior to soldering on the new extensions will help. Clean off all flux residue (IPA and toothbrush) before encapsulating them.

Thanks.

I made sure each wires at the start point only have continuity to only one of the terminals.

I have been trying to get heat resistant sleeving/cable for about an hour locally this morning. NOBODY stocks it. I even rang oven repair places and they don't have any either. Frustrating to say the least.

I will probably have to wait for an ebay/amazon purchase to get delivered.

 

[Agroshield]

I have been trying to get heat resistant sleeving/cable for about an hour locally this morning.

Commercial catering equipment suppliers and repairers (anyone who repairs the fryers in your local fried pigeon shop) carry it if there is one nearby. Possibly look into your local auto-parts store. You often get the sleeving in the box with domestic downlights/spotlights.

 

[Munkul]

Interesting thread. I always assumed that if there was no break-out wiring, then it couldn't be done... but of course once you seperate the windings at the Star junction, it all makes sense!

 

[Smouser]

Success!

The motor is running! Hoover motor first run

I just used my existing inverter to quickly test. Now it is time to get another inverter and get some sort of switch on the machine as the current switch is 400v only.
I need some sort of a switch because the saw turns itself off when the cut is finished and that cut off switch will need to be wired in too.

I am well chuffed.

I also updated the motor plate .

Thank you to all who helped and contributed, I could not have done it on my own.

 

[daleyd]

Well done on getting the motor sorted - not sure I understand why the switch is 400v only though? If you mean the rating of the switch that’s “up to”, unless you mean there’s already 400v into the switch?

 

[Bornfree]

Well done on getting the motor sorted - not sure I understand why the switch is 400v only though? If you mean the rating of the switch that’s “up to”, unless you mean there’s already 400v into the switch?

400v coil in the contactor I would have thought.

 

[mtt.tr]

Name all the star point wires as 1s or 2s dont mix ends as you will be out of phase.



Others than that you look to be on the correct path

 

[Smouser]

Well done on getting the motor sorted - not sure I understand why the switch is 400v only though? If you mean the rating of the switch that’s “up to”, unless you mean there’s already 400v into the switch?

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 .

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