Use of induction motors in the home workshop - updated Iss2

[OldWood]

One comment I will post on is that it is not difficult to open up older 3p motors , which are typically wired for 415v in the star formation as Bob says, locate the coil ends, extract them and reconfigure as delta for 240v operation - ie join the pairs of ends together to create the triangle of coils set-up, and bring the junctions out to the junction box.

You do need to cut the lacing but it is easily replaced and painted over with shellac.

I would say in general that this is quicker and easier than fighting with a replacement motor requiring new feet, new wiring setup and a new pulley system. It was an afternoon's work on a Graduate motor and then it went straight back in - and that was a one off.

One thing about electronic inverters is that they are designed for professional business use and the instruction manuals are directed towards professional installers, add to this that the one manual may well cover sophisticated motors up to 100kW and you can see that the amateur with his basic 1kW motor is at a slight disadvantage in understanding what seems like gobble-de-gook to begin with. I would suggest that there is probably several on this site who have now gone up this learning curve and would be able to help if needs be; There is no need to spend time to re-find the wheel, so just ask!

Rob

 

[9fingers]

One comment I will post on is that it is not difficult to open up older 3p motors , which are typically wired for 415v in the star formation as Bob says, locate the coil ends, extract them and reconfigure as delta for 240v operation - ie join the pairs of ends together to create the triangle of coils set-up, and bring the junctions out to the junction box.

You do need to cut the lacing but it is easily replaced and painted over with shellac.

I would say in general that this is quicker and easier than fighting with a replacement motor requiring new feet, new wiring setup and a new pulley system. It was an afternoon's work on a Graduate motor and then it went straight back in - and that was a one off.



Rob

Rob,

Thank you for your input.

I quite agree and have taken this approach many times myself.
I thought quite hard before deciding not to include this option in my write-up on the basis that most people with the ability to perform this properly, access to high temperature insulate wires, suitable lacing cords etc and the confidence to dive into a motor to find the star point, were highly likely to know lots about motors and not need my guide.

I guess I was trying to avoid leading those with confidence but little knowledge down a path where they might ruin a motor or worse still do some damage to themselves. Less and less engineers have an appreciation of high voltages and insulation. Even graduates who I used to employ consider 3.3 volts normal and 5volts as high on the electronics they are used to working with. More and more circuitry is designed to work on 1.8 volts recently

I set out to try and explain the basic options for running 3 phase motors and some background as to why.

I'm still considering the wisdom or otherwise of a further chapter on home brewed converters. Something I build quite regularly at home for a dedicated machine not needing speed control but should I be encouraging others down this path??

I really am finding it hard to decide.

Bob

 

[Steve Maskery]

Well whatever you decide, Bob, I think this thread is very valuable. Thank you.
S

 

[OldWood]

Bob
You did very tactfully fill in one somewhat critical omission in my input - thank you. Yes, a couple of feet of high temperature wire is needed - and the insulation has to be the type that doesn't creep with pressure.

From your knowledge of motors would the silicon coated wire from Maplins with a top temperature of 180C be OK? I got some military grade wire when I did my motor. Lacing I cadged from the local motor rewinding company.

I like your comments about modern electronic engineers - as a now retired engineer of that faith, the lack of breadth of engineering knowledge in today's disciples concerns me, but then it probably did our forebears too.

Coming back to your article, I would leave it in it's excellent form, and let addendums like mine be taken up by the more adventurous if they wish. Don't over egg the more than adequate cake!

Rob

 

[9fingers]

Rob,

The silicon(e) cable from Maplins looks fine to me if horribly expensive!
The silicone rubber will be quite soft so don't lace it in too tight. I use adhesive lined heatshrink sleeves to protect the connections into the windings.

However, there is some high temperature 3 core cable sold for use between an immersion heater and the wall outlet. I'd be tempted to try this and strip out the inner cores. Rather bad practise to use the green and yellow for one of the phases but I won't tell if you don't!!

The cable is 3039Y and in 1.5mm^2 should be about a pound a metre in cut lengths from electrical suppliers.

Thanks for your kind words about my article.

Bob

 

[dickm]

There is a source on the 'bay that sells all sorts of rewinding-type wire, in various quantities. Dunno if that would be better than Maplins (whose staff, to my mind, are one step even further down from PC World's in terms of lack of knowledge)

 

[dannykaye]

someone asked about step up transformers to convert 240v to 415v.

three phase is three sets of live wires out of phase with each other, if you take one phase and measure the rms voltage with respect to earth (neutral is just earth) you will measure 240v there is no need for step up or down. i.e the 415v is the same just measured in a different way

 

[9fingers]

someone asked about step up transformers to convert 240v to 415v.

three phase is three sets of live wires out of phase with each other, if you take one phase and measure the rms voltage with respect to earth (neutral is just earth) you will measure 240v there is no need for step up or down. i.e the 415v is the same just measured in a different way

There are nevertheless applications for a 240/440 transformer and they are made. But it should be understood that stepping up from single phase 240v to 440v only produces single phase power at a higher voltage.
It is but the first stage in a converter used in combination with other components to run 3 phase motors from a single phase 240v supply. See figure 24 and 25 in my paper.
http://homepage.ntlworld.com/bob.minchi ... Issue1.pdf

Bob

 

[Willis]

really good, I shall keep that safe and refer as and when needed

thank you

 

[Jonzjob]

Blimey Bob, that takes me back to my yoof when I was in the Boy Entrants learning to be an aircraft elleky in the R.A.F.

Very informative and more important understandable for a near novice, I think so anyway?

It reminded me of the method of reversing a single phase induction motor too! I am on he lookout for a motor to replace my drill for power sanding on my lathe and I had forgotten the reversal method, so big ta!

 

[9fingers]

Glad you found it useful.

Bob

 

[9fingers]

Following on from a thread that has identified a potential problem with a single phase motor, I have now added Annex F to my motor document.

The updated version can be found here

http://homepage.ntlworld.com/bob.minchi ... Issue2.pdf


Or by using the link in my signature below.

Thanks to Graeme for raising the issue and providing some photos.

Bob

 

[GraemeD]

Nice update Bob.....glad I could help!
Graeme

 

[dickm]

Superb piece of work, Bob. I wish the guys who used to write this sort of stuff for me had been half as clear

 

[9fingers]

Thanks for your kind comments gents.

I guess years of working in research has taught me how to put information in a form that non engineers can appreciate. It was vital to be able to communicate with business people to secure future funding.

Bob

 

[jack]

Hi 9 fingers, interesting reading, and it answered a question that i was looking for an answer to, nvr 3 phase swith on 1 phase supply ,
great stuff

 

[9fingers]

Hi Jack,

Glad to hear you found it helpful.

Thanks for taking the trouble to post about it.

Good Luck

Bob

 

[jack]

Hi Bob a wee query for you.
i have a double nvr switch for saw table,, the main saw is 3p and the scoring motor i assume is 1p as there is the standard wiring 3core from the dual switch to it , colours blue , brown, green yellow, which i assume i lne.
I also have an l1,l2,l3 going to the maim motor which is 3p.
ow i am assuming that the nvr switch for the scoring blade is 240v
, is there a possibility that the nvr switch relay, may aslo be rated at 240 with the 240 v being taken from the 3p feed, from either l1. l2 or l3 and the neutral?
or am i talking pants

 

[9fingers]

Hi Jack,

The main NVR could have either a 240 or 400v coil. The machine manufacturer could have specified either. I'd guess at 400 being more common but I have not worked on a saw with a scoring blade before.

Usually the NVR has a label, maybe inside the box which may help. Also the coil itself, which may be fairly well buried should be marked with its operating voltage.

Finally you could trace the route of the neutral wire inside and see if it is even connected to the main motor NVR.

hth

Bob

 

[antonello]

I did use this inverter 240/415 3P

to feed this machine

I installed it about a year ago, everything seems to go well, for now......

Here

http://legnowood.globalfreeforum.it/vie ... ?f=14&t=58

downloading this pdf document

Alimentazione di una combinata trifase tramite inverter

more detailed information are available....... but in Italian..... sorry.

Cheers

Antonello