Thread: Winding a coil

Sounds like a plan. What are you going to use to turn the bobbin? You going to mount it on your lathe chuck or something?

Why can't you start with the steel centre already in place? That would save having to slide it into a tight fit or worrying about damaging the enamel on the wire but I assume you have a good reason for the proposed sequence!

Simon

Originally Posted by .RC.

I have to wind a coil for a relay in the control box in my 10EE.... The coil is small... 22.5 OD 11mm ID and 14.5 mm wide...

it uses AWG40 wire which is tiny and has off the top of my head 10 000 turns..

I have a devious plan and have now gathered all the ingredients together I think I will need...

Candle wax, masking tape, super glue.... Hell sounds like a weekend out on the town.....

I did price getting one wound, $200....

So the plan is to make a bobbin out of candle wax, then start winding, every few turns, add some super glue, keep winding until the bobbin is full or we get the required number of turns.....

Then place the full bobbin in hot water and watch it melt away leaving your glued together coil, glue the steel centre in and tape up with electrical cloth tape and I hope to end up with a replacement coil....

Anyone foresee any problems?

Picture?

I'm interested in what you are doing Richard, please let us know the details. I volunteer at the Laidley Pioneer Village, and a few of the magnetos on the stationary engines are dud because of coil problems. Rewound coils can be purchased but if the coil rewinding can be DIYed without too much drama that will save them a few dollars.

it uses AWG40 wire which is tiny and has off the top of my head 10 000 turns..

You wont have enough fingers and toes.

Dean

For winding coils you really do need a counter.

Hi .RC.

Do you have a part number for the relay?

Failing that, what is the coil voltage, and can you be a bit clearer on the dimensions, is the inside 11mm id a round or square hole? a picture would be good.

I've got no shortage of relays of all shapes and sizes, chances are I'd have something suitable if I know what to look for.

Regards
Ray

For some ideas, have a look at youtube "DIY coil winding"
lots of options there.

It is normal to wind the coil on an insulating medium, otherwise you will destroy it placing it on the core at the end. It only take a scratch in the varnish of the winding wire on a couple of turns in the base layer while fitting it to the metal core to form a shorted turn and the whole thing is toast.

Modern practice is to wind a plastic bobbin of suitable size, older practice was to make a wooden former in parts, i.e two side plates and a core block held together by a though bolt and pins. The core block is normally made with a slight taper so that it can be removed from the finished winding without difficulty. The former was then lined (core and sides) with Kraft paper for low voltage or Rhino Hide paper for higher voltage (mains and above). Kraft paper was a variety of brown paper while Rhino hide was a varnish coated card about 1mm thick, the material I was used to was blue in colour. Closest common thing I can think of would be the greeny coloured stuff that they make hang files for filing cabinets from, but Rhino was about twice as thick and stiffer because of the varnish.

The coil is normally wound on a winding machine with wire tensioning systems and the lay of cable on the former controlled by hand to get an even build with windings neatly laid side by side. This is the method I used as a student.

My father successfully rewound coils of up to 3000 turns of 40ga on a Southbend lathe hand driven by pulling the feed belt with one hand while laying the wire with the other, but it took about a day and a half. Running under power in lowest speed back gear is viable with thicker wire, but fine wire will not stand the starting torque so hand powering is a better but more tedious option. Either way some form of mechanical counter is very helpfull.

At the start of the winding, terminate the winding wire in a pigtail of flexible wire and feed the pigtail out of the paper and between the end block and side paper. There is normally 1.5-2 turns of paper on the former, and the transition from winding wire to pigtail is taped down to the paper under the last 1/4 turn of paper to ensure a layer of paper between it and the metal core and the rest of the winding.

Similarly, it was common to include a layer of paper insulation every few layers of winding for interlayer insulation, and a couple of layers of the heavy duty paper over the complete winding, again with the transition to a pigtail buried midway in the this layer.

The whole winding and insulation was then removed from the formers and dunked for 24 hrs or more in a varnish, withdrawn and allowed to drip off excess, and then baked to cure the varnish. In engineering school, our windings intended of mains applications where then mounted on the core and isolation tested to 1500VAC (twice rated plus a thousand volts).

Hope this helps.

Originally Posted by RayG

Hi .RC.

Do you have a part number for the relay?

Failing that, what is the coil voltage, and can you be a bit clearer on the dimensions, is the inside 11mm id a round or square hole? a picture would be good.

I've got no shortage of relays of all shapes and sizes, chances are I'd have something suitable if I know what to look for.

Regards
Ray

It is a struthers dunn CX3334A.. Coil is 125V DC

With this contactor I do not know how vital the coil has to be... it operates the dynamic brake relay... When engaged it injects 115V into the DC motor field coils which helps to bring it to a fairly rapid stop..

Originally Posted by malb

It is normal to wind the coil on an insulating medium, otherwise you will destroy it placing it on the core at the end. It only take a scratch in the varnish of the winding wire on a couple of turns in the base layer while fitting it to the metal core to form a shorted turn and the whole thing is toast.

Modern practice is to wind a plastic bobbin of suitable size, older practice was to make a wooden former in parts, i.e two side plates and a core block held together by a though bolt and pins. The core block is normally made with a slight taper so that it can be removed from the finished winding without difficulty. The former was then lined (core and sides) with Kraft paper for low voltage or Rhino Hide paper for higher voltage (mains and above). Kraft paper was a variety of brown paper while Rhino hide was a varnish coated card about 1mm thick, the material I was used to was blue in colour. Closest common thing I can think of would be the greeny coloured stuff that they make hang files for filing cabinets from, but Rhino was about twice as thick and stiffer because of the varnish.

The coil is normally wound on a winding machine with wire tensioning systems and the lay of cable on the former controlled by hand to get an even build with windings neatly laid side by side. This is the method I used as a student.

My father successfully rewound coils of up to 3000 turns of 40ga on a Southbend lathe hand driven by pulling the feed belt with one hand while laying the wire with the other, but it took about a day and a half. Running under power in lowest speed back gear is viable with thicker wire, but fine wire will not stand the starting torque so hand powering is a better but more tedious option. Either way some form of mechanical counter is very helpfull.

At the start of the winding, terminate the winding wire in a pigtail of flexible wire and feed the pigtail out of the paper and between the end block and side paper. There is normally 1.5-2 turns of paper on the former, and the transition from winding wire to pigtail is taped down to the paper under the last 1/4 turn of paper to ensure a layer of paper between it and the metal core and the rest of the winding.

Similarly, it was common to include a layer of paper insulation every few layers of winding for interlayer insulation, and a couple of layers of the heavy duty paper over the complete winding, again with the transition to a pigtail buried midway in the this layer.

The whole winding and insulation was then removed from the formers and dunked for 24 hrs or more in a varnish, withdrawn and allowed to drip off excess, and then baked to cure the varnish. In engineering school, our windings intended of mains applications where then mounted on the core and isolation tested to 1500VAC (twice rated plus a thousand volts).

Hope this helps.

Thanks for that Mal... I was going to start the coil on some insulating material... The steel centre is only 3/8 diameter, while the coil ID is 11mm... The original core former was some hard cloth type material...

I will turn it on my vfd equipped hercus 260, so I can set a ramp up time to speed thus no jerky rapid starts, plus I do have a mechanical counter somewhere in the shed that reads to 9999 or 999...

I have some Kraft paper here somewhere as well, but will not need it since I picked up the fibreglass tape today...

I have enough copper wire for about 8 attempts I think....

When I looked into this, I came across the Universal type coil, which is sort of self-supporting and doesn't need a bobbin. It's intriguing to watch being wound.
Morris Gingery Ham Radio Coil Winder - YouTube

If you need a bobbin but can't find the exact size you need, maybe a good application for 3D printing?

Jordan

Originally Posted by .RC.

It is a struthers dunn CX3334A.. Coil is 125V DC

I had a look on their web site, and can't find that particular part number, but they might be able to offer a modern equivalent? Manufacturer of High Quality Relays & Controls - Struthers-Dunn



Might be worth sending them an email.

Sounds like you are well on the way to start winding already anyway, should be a fun project!..

I have some WW2 era US radio gear that has relays with 125VDC coils, but that stuff is buried pretty deep ( don't ask ) .. I won't start looking unless your coil winding experiments fail to get it going.

Regards
Ray

Is the wire on a proper bobbin? If it is you should be able to take it off the end and not have to worry about turning the bobbin. You might need to have a eye(what are those things on fishing rods called?) above the bobbin, though I doubt at the speed you'll be going its going to be an issue.
Are you limited in the finished OD? the difference between layer wound and scram wound can be a lot more than you might think.(assuming the factory one was lay wound in the first place)

Originally Posted by malb

It only take a scratch in the varnish of the winding wire on a couple of turns in the base layer while fitting it to the metal core to form a shorted turn and the whole thing is toast.

As I understand it, as long as you are only shorting winding 9998 to winding 9999 it will work just fine......... still best not to.

Stuart

Originally Posted by Stustoys

Are you limited in the finished OD? the difference between layer wound and scram wound can be a lot more than you might think.

Definition of scram wound please?

Jordan

Originally Posted by RayG

I had a look on their web site, and can't find that particular part number, but they might be able to offer a modern equivalent? Manufacturer of High Quality Relays & Controls - Struthers-Dunn



Might be worth sending them an email.

It is from the 1940's. is an old long since obsolete relay.. A bit of discussion on the PM forum about them and a chap in the US does wind them, although on a proper computer controlled winder..