DIY Lucas E3L field coil rewind

[KiwiGF]

The field coil on my E3L dynamo is toast. I could buy a new aftermarket one for not too much, even with the freight to nz from the UK, but they look easy enough to make and I've got enough 0.7mm enamelled wire to do it.

There are a few old threads on this, and it has been done,  but I've not found too many details on how its done 'DIY" style. So some advice please.

Should I make a wooden former and wind onto that? Or is it ok to wrap it directly onto the core? (after taping the core up to insulate it).

Anyone got a pic of a suitable former?

Is it important to get the shape of the core right (eg slightly "bent" to match the casing diameter) or will it be bent anyway when the case screws are done up?

I've got some "Kapton" polyimide tape said to be good for 400 deg c, is that ok to use to hold the coil in shape? Its a bit thin but I could use several layers.

Any other tips on wrapping and winding the coil?

[Rex]

I would definitely make a wooden former, and keep dressing the corners in tightly too or you'll end up with a vague oval coil shape and less turns. Cut through the old coil to get an idea of how many turns Lucas used.

[morris]

Is it important to get the shape of the core right (eg slightly "bent" to match the casing diameter) or will it be bent anyway when the case screws are done up?

Can't help with the rest of your questions but the coils that are sold are always flat.
You pull them into shape by pushing the shoe and coil against the outer casing and tightening the screws.
I have made an expanding tool for that because pulling the coil up and insure that the shoe makes good contact with the casing won't work by just tightening the screws.

[trevinoz]

Kiwi, I made a former out of a plastic material that I had.
Made the two sides and drilled 1/4" holes in the four corners of the shape.
I made a 3/8" shaft with a thread on one end to mount the cheeks between two nuts with a suitable spacer between.
Then made up four 1/4" bolts with just enough thread to fit nuts and ensuring that there was only bare shank between the cheeks.
Also cut four slots in the mid of each side of the cheeks wide enough to slip a thin cable tie in.
If you are winding on a lathe you will need a counter.
First pull a length of wire through one of the slots and wrap around the shaft then wind the coil.
After winding, slip two cable ties through opposite sides and tighten enough to stop the coil falling apart.
Pull the former apart and remove the coil.
I wind a piece of polyester tape around the centre of each side to hold it together and cut off the ties.
I then bend the coil around a large diameter bar to give it some shape.
Attach the leads, insulate the connections with sleeving and tape coil.
I use 12mm cotton tape. I also paint the finished article with electrical varnish.
I will post pictures later.
The former I made is drilled to make E3l & E3H coils.

[KiwiGF]

Is it important to get the shape of the core right (eg slightly "bent" to match the casing diameter) or will it be bent anyway when the case screws are done up?

Can't help with the rest of your questions but the coils that are sold are always flat.
You pull them into shape by pushing the shoe and coil against the outer casing and tightening the screws.
I have made an expanding tool for that because pulling the coil up and insure that the shoe makes good contact with the casing won't work by just tightening the screws.

Thanks, “bent” it is then! (Before it’s installed)

[KiwiGF]

I would definitely make a wooden former, and keep dressing the corners in tightly too or you'll end up with a vague oval coil shape and less turns. Cut through the old coil to get an idea of how many turns Lucas used.

Thanks, your comment has made me realise trying to wind directly onto the  core is a non starter, what was I thinking!

[KiwiGF]

Kiwi, I made a former out of a plastic material that I had.
Made the two sides and drilled 1/4" holes in the four corners of the shape.
I made a 3/8" shaft with a thread on one end to mount the cheeks between two nuts with a suitable spacer between.
Then made up four 1/4" bolts with just enough thread to fit nuts and ensuring that there was only bare shank between the cheeks.
Also cut four slots in the mid of each side of the cheeks wide enough to slip a thin cable tie in.
If you are winding on a lathe you will need a counter.
First pull a length of wire through one of the slots and wrap around the shaft then wind the coil.
After winding, slip two cable ties through opposite sides and tighten enough to stop the coil falling apart.
Pull the former apart and remove the coil.
I wind a piece of polyester tape around the centre of each side to hold it together and cut off the ties.
I then bend the coil around a large diameter bar to give it some shape.
Attach the leads, insulate the connections with sleeving and tape coil.
I use 12mm cotton tape. I also paint the finished article with electrical varnish.
I will post pictures later.
The former I made is drilled to make E3l & E3H coils.

That’s great, thanks for the info. It really helps a lot, I can just about fully understand how to make a former (cable tie tip in particular is “gold”) but if you can post up a pic that would make my day!

Out of interest I’ve got a spare E3N? (48w, short body) Dynamo, with a good field, and I was going to fit that temporarily, but then I noticed it has a b31 “gear” drive end, incompatible with the a10 sprocket drive arrangement. I didn’t realise there were different armatures.....other than length.

[trevinoz]

Your E3N is a bit of a bodgie.
It was originally a Matchless/AJS single generator with a tapered shaft.

[trevinoz]

Kiwi,
Pictures attached.
This one is for the field coils.
The shaft is actually 5/16" and this one has large windows in the sides rather than slots.
The nut on the end with the screw in it is the attachment for my counter.
There are 300 turns of 0.028" or 0.7mm wire.
When you are making the lead connections, the start of the coil will be on the inside of the coil. It needs to be taken up and across the end and run on the outside. Sleeve the conductor from the inside right up to the joint.
I use silicon insulated wire for the leads, I've found that PVC will go hard after a time.
The coil pictured is an original one reworked. I don't have any new ones to hand, I usually only wind 12V coils and to order.
Hope this helps, good luck.

[chaterlea25]

Hi All,
Trevor, for information sakes can I ask how many turns and what gauge for a 12v field coil
What resistance should the could read?
I have a dynamo with new field coil but do not know if it's a 6 or 12v

Thanks
John

[KiwiGF]

Kiwi,
Pictures attached.
This one is for the field coils.
The shaft is actually 5/16" and this one has large windows in the sides rather than slots.
The nut on the end with the screw in it is the attachment for my counter.
There are 300 turns of 0.028" or 0.7mm wire.
When you are making the lead connections, the start of the coil will be on the inside of the coil. It needs to be taken up and across the end and run on the outside. Sleeve the conductor from the inside right up to the joint.
I use silicon insulated wire for the leads, I've found that PVC will go hard after a time.
The coil pictured is an original one reworked. I don't have any new ones to hand, I usually only wind 12V coils and to order.
Hope this helps, good luck.

Thanks again Trevor, it helps a lot. I’ve almost finished my own former (pic Below) I’ve made it with 6mm corner bolts, drilled and placed to make a coil of inside dimensions 1 1/16” x 2 1/4”, and 5/8” thick (eg 5/8” spacer between plates).

I’m going to have to hunt around for some silicon insulated wire and sleeving  - its a bit of effort to do all this but it won’t be a “one off use” tool as Ive just measured my b31 field coils resistance, and it’s getting low so I’ll be winding a second coil (assuming the first works ok, but no reason why not eh).

[trevinoz]

Well done, Kiwi.
I use fibreglass sleeving over the wires, 1mm over the single wire and 3 or 4mm over the joints.
You may have to hunt around for polyester tape to hold the coil together and it is not cheap. You could probably get away with common cellulose tape, the original coils seem to have used something similar in many cases. Some use a paper type tape. Doesn't matter which as the outer binding will hold it all together.
When you start winding, make the first layer nice and even with the wires side by side, then it's open slather, just keep the wind as uniform as possible across the former.

John, the 12V field coil resistance could be anything, depending on the thoughts of the winder.
Originally I was making them 450 turns of 0.6mm wire giving a resistance of about 5.6 ohms.
I was not completely happy with this even though the generator would work just fine but I was concerned about the heating of the generator as flat out the field would be consuming 24 Watts against the 6V version consuming 12 Watts.
I was discussing this with Chris Zoch (Zochy's Magnetos) and he did a bit of playing with different gauges of wire and turns. He came up with 620 turns of 0.5mm giving a resistance of around 11.5 ohms.
We have both tried this with good results.
A bit long winded but I hope this helps.
Trevor. 

[chaterlea25]

Hi Trevor,
Thanks for the info,
I have a couple of dynamo's to sort out (one of the days)

John

[KiwiGF]

Some pics of progress, I’ve been a bit slack getting onto this but I now I have to get the bike on the road for a few hundred miles of a rally weekend mid April.

I’ve yet to work out to bend it, but the winding was much easier than I expected, the lathe turned at about a rev per sec, Ideally that would be slower for a novice 

I found some high temp sleeved wire for making the thermals in an old motor, and I bought some “kapton” high temp tape for holding things together whilst I fit the terminal wires and bending.

I’m wondering if that sort of tape could be used to do the final covering? It’s thin but I could put a few layers on...

[chaterlea25]

Hi Kiwi
Ask for some winding tape at a motor rewind shop
It was cotton I think originally, some sort of composite material nowadays
Usually soaked in insulating varnish once formed into place

John