O.T. Rewinding electric motors

Specifically a 6hp 4 pole 3 phase induction motor.

Is it stupidly expensive? It's an old motor with an unusually long shaft
on an old machine; a modern motor is going to look silly.
Anyone know a place that would do this; near to North Wales?

 

Putting rewind and Chester into Yell.com got this lot
http://tinyurl.com/ydzmm9h
As for cost, I can't help you. It's about 18 years since I had something
rewound and it wasn't that complicated an item either.

--
Malc

Rusted and ropy.
Dog-eared old copy.
Vintage and classic,
or just plain Jurassic:
all words to describe me.

 

£400 to £800 at a rough guess.

 

Get onto BSL (bearing suppliers) and you might find a replacement is
cheaper. Rewinding is only really a viable option on motors where you
can't find a replacement because you're trusting a load of
semi-skilled winders to do a decent job.

 

Andy Bonwick used his keyboard to write :

Agreed, and/or seek out a second hand one.

 

Hmmm. I've been on the phone to a few guys today and it's mostly cheaper
to rewind than buy a new one. Even the dear guys prices pan out as about
the same.
My preferred firm has rewound some motors for some other people near me
so I can ask them ho wit went.
I need to get a new switch; the old one was an oil filled job that must
be over 50 years old.
The motor is wired up star delta at the moment and the switch fires up
the motor slowly and after 20 seconds it comes up to full speed.
I'm getting conflicting advice on this. I always thought this was in
sympathy for the big spinny round metal work in the machine but some
were saying it was due to the poor power supplies of yore and that I
could just fit a direct switch now.
Any thoughts?

Why would a firm who does rewinding be semi skilled?

 

mark brought next idea :

A little of both reasons. Star connection puts two windings in series
on any pair of phases to both reduce the initial load on the motor and
the load on the supply. Once it is ramped up to speed, then it switches
over to delta connected with just a single winding between each phase.

So whether or not it would work satisfactorily via a direct on line,
depends upon both of the above needs being satisfied.

To replace it - You need an appropriately rated star delta starter with
over loads (they come in ranges) to match the current rating of the
motor on full load. Basically 3x 3 phase contactors, 1x overload, 1x
timer, 1x 3phase O/L, start and stop buttons plus a case or cabinet.
Coils need to be either 240v or 415v depending upon whether you will be
including a neutral into the box or not.

DOL just needs 1x contactor, 1x O/L plus the start and stop buttons.

 

snip>

Not the firm, the guys doing the work.

I used to work for a company who had a rewinds division and all the
winders were semi-skilled monkeys who made even welders look clever.
It's not actually a difficult job and you'd be looking at the same
sort of skill levels as a tyre fitter on smaller motors. Avoid.

 

Ah but how about a small one man band that only does motor repairs and
rewinds?
He had a lot of time to explain what he would be doing and I didn't get
the impression that he was clueless.

I take it you're referring to big shops that actually make motors?

 

I was referring to companies that do rewinds as their core business.

Just remember that you'll not get a guarantee worth a **** on a
rewound motor whereas you'll get at least a year on a new one. Any
quote from a winder will be for a basic rewind assuming no damage is
found where the bearings fit in the casing or on the rotor and if they
suddenly find either the price will either rocket or they'll bodge it
with Belzona.

It's not a coincidence that we've gone from a situation where every
town had a couple of small rewind companies to one where they're a
rarity. Companies like BSL have got agreements with manufacturers such
as Siemens and they'll sell smaller motors at a loss in order to get
huge discounts on the bigger units where there's a lot of money to be
made. Big companies want to be able to get on the phone and have a
serviceable motor sitting in their maintenance shop within a couple of
hours of the original one failing and they're subsidising people like
you who don't need that service.

 

That is a very good point.

I'm going to whizz the bugger apart this weekend to check this out
myself in any event.

You make this sound like a bad thing

My biggest problem is mating a new motor (1) shaft to the current drive
shaft (2). I'll need to cut this out of the old motor to get enough
length for the new motor and coupling.
Its very expensive to have a new shaft put on a new motor.
I also would need one of them fancy 3 part couplings which allow
different diameter shafts to join end to end.

A rewind makes it a lot simpler but thanks for the advice.

1.Which seem to have larger metric shaft diameters to comparable power
old motors
2. Which is actually the existing motors shaft; 13" long.

 

In message <>, Harry

<useful switch info snipped>

Cheers for that. I'm on a bit of a learning curve here

 

It's over 20 years since I did any 3 phase motor stuff but from what I
recall we only used star/delta switching at powers over about 7.5 kW [1] and
maybe not even less than 10kW. 6HP is about 4.5kW so direct on line starting
should be fine unless your power supply cannot take it.

[1] But that was industrial plant and I have no idea what your application
is.

--
Malc

Rusted and ropy.
Dog-eared old copy.
Vintage and classic,
or just plain Jurassic:
all words to describe me.

 

The supply is fine. The motor is driving a 1922 20" planer thicknesser.
Lots of heavy stuff to turn; 5" diameter cutter head, feed rollers and
all the gears and pulleys to drive it all. I wouldn't like to just start
it all up at full speed to be honest

 

I suspect the smoke would come out. It would never have been designed
for DOL starting and even rewound with modern wire I'd be inclined to
leave it as original spec.

 

Don't forget the cheapy Chinee imports - huge effect on the rewinding
market.

 

My ex-employer was shutting down all their small motor rewinds because
of the surplus of new motors available. They'd actually reached the
point where they'd converted a rewind shop into a distribution centre
for moving out new units and offered a guaranteed 24 hour delivery
anywhere in the country. They also scored heavily because they'd got
the capability to manufacture any new couplings or adaptors needed
within a very small timescale so even if the new motor was metric and
the old one imperial it didn't make much difference.

It's not as if ukrm hasn't got enough regulars with the capability to
make a sleeve if required and coupling blanks are dirt cheap to buy
from any bearing supplier.

 

Agreed for the old motor.
This was advice regarding a new motor...

 

I could make a sleeve/coupler myself but they are cheap enough to buy.
The fancy ones allow for a bit of misalignment as well.
It's the time spent messing about to be honest.
New motor means possibly fabricating a new frame (or adapting the old
one) and chopping out the old shaft.
Rewound motor means I have to transport it there and back and bolt it
back up.
Both options mean removing motors, pulleys off shafts and re wiring of
new switch.
I'll be taking the old motor to bits this weekend to see if its anything
other than windings. I'll weigh it all up then.
The 'new motor with guarantee' is the argument that's swaying me.
Thanks for the opinions; sometimes its nice to be knocked out of the one
track, my way, dark work shop obsessive mind set

 

Motor's off and on a bench.
Got one pulley off but the other want's to stay where it's been for the
last half a century odd.
Gave up on stripping when half the slot headed screws decided they
weren't coming out.
Examining the motor through the huge vents I can't see anything wrong.
This led me to examine the ancient star delta switch.
Its a mechanical beast with most of its workings in half a gallon of
oil.
There's two transformer inside it side by side.
Underneath in the oil are two sets of contactors. (So 6 in total)
With the bath off; switching it on shows the left hand side having a
complicated arrangement of levers and switches slowly rising up.
I'm assuming it starts up in 'start' and when the levers get to the top
the left hand contactors open (disconnecting 'star') and feed power to
the right hand transformer and that makes the connection and the 'delta'
takes over.

I think.....

The rate of movement looks too slow. There is a lever that follows a
curved indicator graduated from 7 to 18. I'm assuming this is the time
it spends in 'star'.
That rate at which it rises seems too slow for even the 18 (seconds?).

So I'm suspecting I may just need a switch.
Any thoughts?

P.S, (Is it a bad thing to turn these switches on out of their oil
bath?)