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Home > Archive > Electrical Engineering > May 2006 > rewinding motors
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| Motor 2006-05-04, 11:21 am |
| I want to attempt to re-wind the feild windings in a 2000w angle
grinder, i have removed and counted the old windings, though it got
messy ,and i am only accurate to within + - 5, will this matter ?
How can i estimate how much wire i will need ? I can get the correct
enammeled wire.
Is there any thing else i need to know ?
Before you ask, new spares cost more than a new tool !
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| daestrom 2006-05-04, 7:21 pm |
|
"Motor" <tadworth178@hotmail.com> wrote in message
news:1146749334.983023.239360@g10g2000cwb.googlegroups.com...
>I want to attempt to re-wind the feild windings in a 2000w angle
> grinder, i have removed and counted the old windings, though it got
> messy ,and i am only accurate to within + - 5, will this matter ?
>
Probably not. How many turns did you come up with? If +- 5 is less than
about 3% of the total, I wouldn't worry about it.
> How can i estimate how much wire i will need ? I can get the correct
> enammeled wire.
Form two or five turns of wire and unwind it. Try to make the loops as
large as the largest ones you took out. Divide by the number of test turns
you used and this gives you length per turn. Remember, the first few turns
will likely be shorter than the last in a simple winding because the wire
length grows as the coil builds.
>
> Is there any thing else i need to know ?
>
What you plan to use for slot insulation? Enamel wire doesn't like being
wound directly on the iron, iron scraps the enamel off. Believe it or not,
some ordinary paper (about the thickness of a 3x5 card) can work quite well.
Pre-form it to extend out both ends of the slots.
Some sort of wooden/plastic tool and a small hammer can be used to 'tamp'
the wires down into the slots. You'll find that getting the same number of
turns of wire into the slot as what came out is a challenge. Then you need
something to act as a wedge to put in the top of the slot to keep the turns
in place. A variety of things can work/have been used. Everything from
custom molded plastic pieces to wood strips with a paper 'cap'. Then slice
off the excess paper sticking up through the sealed slot.
After the windings and wedges are in, in larger machines it is customary to
coat with varnish and bake it. Then it would be ready for hi-pot testing,
but you probably wouldn't need to bother with such a small unit.
When you unwound the thing, did you note carefully the connections between
coils and the direction the winding enters each coil?
Is this a universal motor (with commutator) or an induction motor?
You're brave to try it. Have done quite a few in my day, and 'the devel is
in the details'. Connections are a major part of getting it right. And
getting the new connection splices and such to fit back into the same space
as before.
daestrom
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| Rheilly Phoull 2006-05-05, 5:21 am |
| daestrom wrote:
> "Motor" <tadworth178@hotmail.com> wrote in message
> news:1146749334.983023.239360@g10g2000cwb.googlegroups.com...
>
> Probably not. How many turns did you come up with? If +- 5 is less
> than about 3% of the total, I wouldn't worry about it.
>
>
> Form two or five turns of wire and unwind it. Try to make the loops
> as large as the largest ones you took out. Divide by the number of
> test turns you used and this gives you length per turn. Remember,
> the first few turns will likely be shorter than the last in a simple
> winding because the wire length grows as the coil builds.
>
>
> What you plan to use for slot insulation? Enamel wire doesn't like
> being wound directly on the iron, iron scraps the enamel off. Believe it
> or not, some ordinary paper (about the thickness of a 3x5
> card) can work quite well. Pre-form it to extend out both ends of the
> slots.
> Some sort of wooden/plastic tool and a small hammer can be used to
> 'tamp' the wires down into the slots. You'll find that getting the
> same number of turns of wire into the slot as what came out is a
> challenge. Then you need something to act as a wedge to put in the
> top of the slot to keep the turns in place. A variety of things can
> work/have been used. Everything from custom molded plastic pieces to
> wood strips with a paper 'cap'. Then slice off the excess paper
> sticking up through the sealed slot.
> After the windings and wedges are in, in larger machines it is
> customary to coat with varnish and bake it. Then it would be ready
> for hi-pot testing, but you probably wouldn't need to bother with
> such a small unit.
> When you unwound the thing, did you note carefully the connections
> between coils and the direction the winding enters each coil?
>
> Is this a universal motor (with commutator) or an induction motor?
>
> You're brave to try it. Have done quite a few in my day, and 'the
> devel is in the details'. Connections are a major part of getting it
> right. And getting the new connection splices and such to fit back
> into the same space as before.
>
> daestrom
In another time we used to make a wooden plate the internal size of the old
field coil (Flattened out) and the same thickness as the original coil. The
coil was then rewound on that 'former', counting the turns with a mechanical
meter. The completed coil was then taped with cotton tape and formed to fit
the field laminations, prior to tapeing of course the insulated leads were
"fused" or soldered to the ends of the windings. New insulation was put into
the 'slots' were the windings go and the windings installed. Once the new
fields were mounted and secured with whatever method was used the assembly
was dipped in varnish and baked. It is important to know the start and ends
of the windings so that one field does not oppose the other in operation.
Another important thing to check is the integrity of the armature, since
"shorts" will burn out the fields before the armature windings in the usual
case.
In the case of a double insulated machine rewinding is not really practical.
--
Regards ......... Rheilly Phoull
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| daestrom 2006-05-05, 5:21 pm |
|
"Rheilly Phoull" <Rheilly@bigpong.com> wrote in message
news:445b056a$0$3287$5a62ac22@per-qv1-newsreader-01.iinet.net.au...
> daestrom wrote:
>
> In another time we used to make a wooden plate the internal size of the
> old field coil (Flattened out) and the same thickness as the original
> coil. The coil was then rewound on that 'former', counting the turns with
> a mechanical meter. The completed coil was then taped with cotton tape and
> formed to fit the field laminations, prior to tapeing of course the
> insulated leads were "fused" or soldered to the ends of the windings. New
> insulation was put into the 'slots' were the windings go and the windings
> installed. Once the new fields were mounted and secured with whatever
> method was used the assembly was dipped in varnish and baked. It is
> important to know the start and ends of the windings so that one field
> does not oppose the other in operation.
> Another important thing to check is the integrity of the armature, since
> "shorts" will burn out the fields before the armature windings in the
> usual case.
> In the case of a double insulated machine rewinding is not really
> practical.
>
Hey!!! Nice to see someone else with motor rewind experience here. Yes, we
had several different coil forming machines. For AC stators it was a bit
tricky getting the form to have enough 'kinks' in the end turns, but once
you did, worked well. Yep, taped them while on the machine and then took
them off the machine. We didn't varnish/bake them separately in AC
equipment as then you can't get them into the slots without breaking the
varnish.
But for 'bolted' pole type machines, yes, we varnished/baked the taped up
coils (completely taped the coil with fiberglass tape on the large DC
machines and AC salient-pole rotors).
Before dipping the final assembly, it was important to cover the interior
faces of the laminations (or outside surface for rotors) so the varnish
wouldn't build up on them. One poor guy forgot to do this one time and when
it came time to insert the rotor, it wouldn't fit. The clearances between
rotor and stator are *not* very large ;-)
Take care,
daestrom
>
> --
> Regards ......... Rheilly Phoull
>
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| Long Ranger 2006-05-10, 3:21 am |
| I rewound the rotor on a Hilti hammer-drill that was given to me. It still
works great after 12 years. I even had to splice the magnet wire half way
through because the dinky spools of wire I got at Radio Shack weren't long
enough. Go for it.
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| This is a simple commutator motor in a power tool, and i didn't note
down the connections, though i have other similar windings to look at,
i'm guessing it will be the same.
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