Thread: Clarifying 3ph Motor connections

Glad the books helped.

What I did at this point was cut the ties and pulled the leads away from the coil end so I could trace the links beween the coils. I ended up with a drawing for each of the phase groups showing the coils and the winding direction in each slot. You probably dont have to do it this way but this is how I made sure it was wired correctly.

I guess this is the point where you have to commit and decide if your going to pull it apart more! Looks like you will have to to get access to the junction points anyway.

If you pull the leads apart you will need some materials to re-tie and insulate it. I got high temp silicon wire (for the new leads) and fibreglass insulating tube from ebay and ended up getting a little bit of tie cord (I think its nomex or something) to tie the winds back up from a local rewinder. I resprayed it with a spray pack of crc urethane seal coat after it was all tied. If you can find the supplier that the rewinders uses you should be able to get it all there. The fella here pointed me to engineering supplies in welshpool but I'm not sure where to go over there.

Originally Posted by gallegos

Glad the books helped.

What I did at this point was cut the ties and pulled the leads away from the coil end so I could trace the links beween the coils. I ended up with a drawing for each of the phase groups showing the coils and the winding direction in each slot. You probably dont have to do it this way but this is how I made sure it was wired correctly.

I guess this is the point where you have to commit and decide if your going to pull it apart more! Looks like you will have to to get access to the junction points anyway.

If you pull the leads apart you will need some materials to re-tie and insulate it. I got high temp silicon wire (for the new leads) and fibreglass insulating tube from ebay and ended up getting a little bit of tie cord (I think its nomex or something) to tie the winds back up from a local rewinder. I resprayed it with a spray pack of crc urethane seal coat after it was all tied. If you can find the supplier that the rewinders uses you should be able to get it all there. The fella here pointed me to engineering supplies in welshpool but I'm not sure where to go over there.

Yes, this is that point. I will inquire into getting the bits required before I go any further. The cost could be an issue at the moment. Forget the "could be". It is!

I have found high temp silicon wire in sizes up to 8AWG and 5mm diameter acrylic coated fibreglass sleeving rated up to 155 deg C. I am still looking for the tie cord. The existing wire is 2.4mm². 5m of 12AWG (3.3mm²) is $21.29 ex UK. 5m of the sleeving is $14.90 ex Melbourne. The sealer is less than $20 but I need to find a local supplier. Blackwoods is the most likely place to carry it around here but is still nearly 100km away.

Why did you replace the wire if you only pulled the leads away from the coils? I can see no need for this on my motor unless there is a specific reason. It all looks in excellent condition. I could probably get away with only using new ties and resealing.

Dean

I ran extra leads from the point i split the windings so I ended up with 12 leads from the windings in the junction box. If the existing leads up to the point they join are long enough to reach to the juction box you can use the existing ones. The other option is you can join them together internally and just have 6 leads to the junction box but again this depends on the location of everything and you could still need a bit of extra wire to make them reach. I think I had a few bits of silicon wire left over that might be the right size so ill have a look in the shed when I get a chance.


I had trouble finding the right tie cord too so ended up dropping into a motor rewinding shop and asking... they fella gave me a few pieces and an old terminal block for free. what a top bloke. I think they used to just use twine but depending on the motor temp rating you need to find something with better temperature resistance. The urethane bonds it all together but I like the idea that everything is securely fixed in place with the cord too.

I have the same issue being remote... Ebay is great but there still seems to be lots of stuff that requires a trip to town.

neil

Originally Posted by gallegos

I ran extra leads from the point i split the windings so I ended up with 12 leads from the windings in the junction box. If the existing leads up to the point they join are long enough to reach to the juction box you can use the existing ones. The other option is you can join them together internally and just have 6 leads to the junction box but again this depends on the location of everything and you could still need a bit of extra wire to make them reach. I think I had a few bits of silicon wire left over that might be the right size so ill have a look in the shed when I get a chance.


I had trouble finding the right tie cord too so ended up dropping into a motor rewinding shop and asking... they fella gave me a few pieces and an old terminal block for free. what a top bloke. I think they used to just use twine but depending on the motor temp rating you need to find something with better temperature resistance. The urethane bonds it all together but I like the idea that everything is securely fixed in place with the cord too.

I have the same issue being remote... Ebay is great but there still seems to be lots of stuff that requires a trip to town.

neil

I wondered if you split the wires. I could easily do the same as they are sitting right on top. The reason I asked about this is that the wire I mentioned is bigger than is already on the motor but if the wires are split, then I could go for a smaller size (I hope) wire which is about half the price. I would have some trouble getting double the wires out of the junction box due to the existing wires taking up quite a bit of space. Drill a bigger hole, fit another cable gland, get bigger conduit. It can be done. The conduit is currently hanging down draining out 16 years of accumulated oil. I probably have the cable glands and I am pretty sure I have a connector block from a motor somewhere. Will they both fit tho?

I sent an email to the nearest Motor Rewinders about the ties, last night. Just read his reply. He is asking why I want to move the wires so I explained a bit more adding the comment that I was intending to ask for their advice, providing they had experience with this type of motor connections. I can expect 1 of 2 possible replies. Either bring it in and we will have a look, or a genuine offer to help considering my distance from them. I generally ignore the "bring it in and we will have a look" brigade. Maybe I will get some help. Here's hoping.

A few years ago I rang a local electronics shop for assistance on a kit sold by Jaycar of which he is a stockist. This kit was a charging device to fit to NiCad chargers so you can use it for NiHi batteries. I wanted it for a cordless drill battery upgrade. He told me to bring the drill in and he would have a look. What the? Needless to say went to a Jaycar store in Adelaide next time I was there and he missed out on a nearly $300 sale.

Dean

I received a reply to my email to the motor rewinders today. It was interesting. I will quote the body of the message in full.

Hi Dean,



Most modern motors these days from major manufactures are suitable for
VSD application.



We really don't know if this motor will be suitable or not.

Class B is a thermal rating and has no indication of its resistance to
high peak voltages. ( dV / dt)

The age of the motor is also a concern that it may not be manufactured
with windings that are suitable for VSD.



All 3 phase squirrel cage motors will run from a VSD but the main factor
is how long will they last.????



My advice here would be to find out any information that you can about
the motor to see if it is suitable for VSD PWM output.



If the you are willing to take the risk, considering the above, and go
ahead and try it out ,then it is your choice.



Finally I would recommend if you do go ahead ,keeping the PWM switching
frequency low and the motor cables to the drive short.

A load reactor at the VSD output could also added as additional
insurance if you prefer, or a new motor be installed that you can trust.



In regards to tape to re tie, you can use any twine/string/cotton
webbing, you don't have to use high temp stuff, as the tape/string just
holds the windings together, it has nothing to do with any the actual
windings.

Yes we do quite a lot of 240V VSD's



Hope this helps.



Regards

The bit about the string is interesting.

Dean

Originally Posted by RayG

Hi Dean,

Wire it for double delta, as per my earlier post, but go to a motor rewinder to do it, and he will get the phasing right for the windings that have to be split and reversed.

Ray

Sorry for taking my time replying Ray. I haven't forgotten about what you said. This thread is actually a reminder for me which is one of the reasons I dribble on so much in my posts. I can go back later and remind myself of everything that has been written, including by me.

The other reason that I have dribbled on so much is that I always dribble on a lot anyway.

Dean

Originally Posted by Oldneweng

I wondered if you split the wires. I could easily do the same as they are sitting right on top. The reason I asked about this is that the wire I mentioned is bigger than is already on the motor but if the wires are split, then I could go for a smaller size (I hope) wire which is about half the price. I would have some trouble getting double the wires out of the junction box due to the existing wires taking up quite a bit of space. Drill a bigger hole, fit another cable gland, get bigger conduit. It can be done. The conduit is currently hanging down draining out 16 years of accumulated oil. I probably have the cable glands and I am pretty sure I have a connector block from a motor somewhere. Will they both fit tho?

I'm not sure if i was clear about what i mean by running12 leads from the windings to the junction box, you end up with 2 wires internally from the motor under each of the 6 posts on the terminal block. You only have the 3 cores and earth from the vfd into the motor connected as normal in delta. Because the extra wires are mostly in the motor housing and just stick out a little into the terminal box there shouldnt be an issue fitting them... At least i didnt have a problem.

You are keeping the current through each part of the windings the same as the original design so wire size should be the same assuming you run each lead back to the terminal box (12 leads from the windings to the terminal box). If you join them inside the motor the single cable after the join will need to be bigger because current will be double. By splitting the windings that would normally be connected in series and running them in parrallel then running them from 240v you approximately double the full load current thats on the nameplate so the cable from the vfd will need to suit. I probably should try and explain this better but im on a tabelt so typing is slow and painfull. Let me know if this makes no sense and i will try again on a real pc.

That rewinder sounds like he will be helpful. If in doubt i reckon he would be a good choice. The fellow i talked to over i dont think really understood what i was trying to do.

Hi Dean,

You can forget most of the warnings from the rewinder about voltage breakdown, so long as you keep the cabling from the drive to the motor less than 25 ft you won't have a problem.

What he is talking about is cable capacitance causing high voltage spikes across the motor winding insulation, they used to call motors with high voltage rated insulation VFD compatible. The cure is usually to have dv/dt filtering at the drive, this is not LC filtering or harmonic filtering, it's a type of filter specifically for fast voltage spikes. He called it a reactor in his email, that's not quite correct, but let it slide.

So why is he going to all this palaver about insulation ratings... simple, he wants to make sure there is no come-back on him if the motor fails. That's fair enough.

The only times I've ever seen that type of failure is where there have been cable runs of hundreds of feet without proper dv/dt filtering.

Two things going in you favour, one is 240V is lower than 415V.... second, you don't have hundreds of feet of cable capacitance to cause the problem in the first place.

Ray

Nearly forgot to mention, the "string" you were talking about is called "lacing" normally nylon, if you do a search for braided lacing tape...

500yd Gudebrod MIL T 43435B Synthetic Braided Lacing Tape 18H SZ 3 Type I | eBay

Ray

Originally Posted by gallegos

I'm not sure if i was clear about what i mean by running12 leads from the windings to the junction box, you end up with 2 wires internally from the motor under each of the 6 posts on the terminal block. You only have the 3 cores and earth from the vfd into the motor connected as normal in delta. Because the extra wires are mostly in the motor housing and just stick out a little into the terminal box there shouldnt be an issue fitting them... At least i didnt have a problem.

You are keeping the current through each part of the windings the same as the original design so wire size should be the same assuming you run each lead back to the terminal box (12 leads from the windings to the terminal box). If you join them inside the motor the single cable after the join will need to be bigger because current will be double. By splitting the windings that would normally be connected in series and running them in parrallel then running them from 240v you approximately double the full load current thats on the nameplate so the cable from the vfd will need to suit. I probably should try and explain this better but im on a tabelt so typing is slow and painfull. Let me know if this makes no sense and i will try again on a real pc.

That rewinder sounds like he will be helpful. If in doubt i reckon he would be a good choice. The fellow i talked to over i dont think really understood what i was trying to do.

Sorry about that confusion. My fault. I was thinking too far ahead. I realize the cables only go to the motor junction box, but I had a little moment there. I was however thinking along the lines of 12 terminals and bridging as required. I'll try to behave now.

I understand what you are saying about the cable from the vfd. I have never tried typing on a "tabelt" tho. Sounds difficult. I have been looking into cable to use for this, but I don't think I have any left. Probably get some from work. There is loads of second hand stuf lying around. Up to over an inch in diam (500mm²). That is in ali tho!

I mentioned in my reply to this email " My next issue is to determine in what configuration to connect the motor."

Received a reply today asking whether I was supplying 415v 3ph. I replied 240v, of course.

Last night I watched a Tubalcain video about fitting a VFD to a drill press. His VFD supplied the full 220v from 110v input. Are these readily available for 415v?

The rewinders do have a pretty good name in this area, but then they are probably the only ones this side of Adelaide.

Dean

Originally Posted by RayG

Nearly forgot to mention, the "string" you were talking about is called "lacing" normally nylon, if you do a search for braided lacing tape...

500yd Gudebrod MIL T 43435B Synthetic Braided Lacing Tape 18H SZ 3 Type I | eBay

Ray

Thanks Ray, and thanks for the info about the motor in your first post. Like you say he is covering his bum.

The cable should be pretty short as the lathe will be about 700mm from the wall the vfd will be mounted on. It may be better to mount the vfd on the rear of the lathe so the input cable can drop straight down from the roof. I need to have room to get around the end of the lathe without climbing over cables.

Dean

Originally Posted by Oldneweng

...........Last night I watched a Tubalcain video about fitting a VFD to a drill press. His VFD supplied the full 220v from 110v input. Are these readily available for 415v?.........Dean

Dean, these 110V input 220V output VFD's use "voltage doublers", a combination of diodes and capacitors. See here for the principle explained:
Voltage doubler - Wikipedia, the free encyclopedia

Where a normal VFD uses a full-wave bridge rectifier to convert 240VAC ac into 340VDC (240*1.41=338.5), these VFD's use a half-wave voltage doubler circuit to convert 120VAC into 340VDC. As far as I know, these VFD's are only manufactured for very low horsepower motors. They are paticularly popular in the USA, where many houses are only fed with 110 or 120V. These household powerpoints are limited to 15A. 15A*120V=1800W or 2.4HP, less the losses in a VFD makes for about max 2HP drive power. Due to the larger capacitors needed, such VFD's will be a little larger and more costly than plain 240V input VFD's. Chris

Originally Posted by cba_melbourne

Dean, these 110V input 220V output VFD's use "voltage doublers", a combination of diodes and capacitors. See here for the principle explained:
Voltage doubler - Wikipedia, the free encyclopedia

Where a normal VFD uses a full-wave bridge rectifier to convert 240VAC ac into 340VDC (240*1.41=338.5), these VFD's use a half-wave voltage doubler circuit to convert 120VAC into 340VDC. As far as I know, these VFD's are only manufactured for very low horsepower motors. They are paticularly popular in the USA, where many houses are only fed with 110 or 120V. These household powerpoints are limited to 15A. 15A*120V=1800W or 2.4HP, less the losses in a VFD makes for about max 2HP drive power. Due to the larger capacitors needed, such VFD's will be a little larger and more costly than plain 240V input VFD's. Chris

Thanks for that Chris. Now I understand.

Cheers

Dean

Originally Posted by Oldneweng

Last night I watched a Tubalcain video about fitting a VFD to a drill press. His VFD supplied the full 220v from 110v input. Are these readily available for 415v?

What Chris said + yes they are readily available* up to at least 7 1/2 Hp.............. Got a spare $1900?

I've been meaning to ask a certain forum member just how hard it would be to build a voltage doubler in the 3hpish sort of power range........I can hear him running now

Stuart

*if by "readily available" you mean from one guy on the other side of the planet