Any practical alternatives to hand winding an obsolete solenoid coil?
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  1. #1
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    Default Any practical alternatives to hand winding an obsolete solenoid coil?

    One of two solenoids which release the brake pack on a large capstan winch has failed. The remaining solenoid is strong enough to retract the brake pack but since the consequence of complete failure is serious, I'd like to repair it and make a backup in case of future problems.

    The machine is from the early 1950s and no parts are available. It's a simple coil, about 2 1/2" square by 1" thick. That's from memory, it's still in the machine and no pictures. When I looked at it, I thought it would be straightforward to rewind. Measure the wire diameter, count the turns and buy some magnet wire to rewind. Maybe varnish for stability. Motor is 7 1/2 hp operating at 480 V, 60 Hz. Coils see 240 V as I recall.

    Is there much more to it than that? Or other methods I should pursue?
    Thanks,
    Jim

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    Much more to it? Can be,. How's your insurance?

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    There are many professional outfits that rewind solenoids. Why not get it done professionally?

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    I'll take the other path. As you said, count the turns, measure the wire, dip the finished product, and you know who's your uncle. It's about as simple as it gets. Don't get the lawyers involved, they don't know shit! Open your wallet and check your man card..its gotta be there.

    Stuart

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    find two average quality volt ohm meters and use a D cell battery to push 1.5 volts across the solenoid, with one meter measuring amps the other volts.

    use your micrometer to measure the wire diameter.

    don't waste your time counting turns. wind a new coil.


    good quality magnet wire can handle 200C temps for something like 1000 hours these days. don't overthink it.


    i have 71 pounds of 26 awg wire on hand if that's what you need.. can send you a pound of it for a few bucks.

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    I have wound lots of them. I have a coil winder but I don't know if I want to commit to it right now. You can do it on a lathe with the fine feed set to slightly more than the thickness of the wire which will give a better stacking factor than scramble winding. Guide the wire by cutting a slot in a half inch square piece of phenolic or delrin, or whatever. Mount it like a tool bit. Set the reel of wire on the floor so the wire comes off it like a spinning fishing reel. Tension the wire as it winds by holding it with a couple layers of folded paper towels between your fingers. Mix up some slow setting epoxy and paint on a coat with each layer so the wires are winding through it and so are completely encapsulated. I vacuum impregnate coils but you likely do not have the equipment and the paint on epoxy is as good. One thing to look out for is the wire pulling down to a lower layer. the insulation on magnet wire works because the voltage from turn to turn is low. You don't want to have two turns at a very different voltage touching. To get the inner end of the winding out of the coil, if the form has a hole in its flange, fine. If not, run it up the inside of a flange and cover it with several layers of mylar tape, or better yet Kapton. Comparing the DC resistance of the old and new coils will serve as a check at the end.

    Bill

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    I had a washing machine coil go out 2 or 3 times over 10-15 years. I machined a coil form from plastic and mounted it on a wood shaft.
    The shaft was connected to a 1hp 3 phase motor. The motor was connected to a VFD with a foot switch. The winding operation was slow but
    the turns came out neat. It was not an exact replica of the original but coils don't have to be perfect.

    The coil was from a Sears washing machine and the parts list called it the Wig-Wag.

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    This is one of those projects where you've got to ask yourself: "what could possibly go wrong?"

    If the engineers thought this application was critical enough to include two fully redundant solenoids in the design, they really didn't want this machine to fail. Replacing a critical component with a home-made alternative increases the odds of exactly that happening. Less of a matter of whether it *can* be done... much more a matter of whether it *should* be done. Especially if failure of this machine could end up injuring third parties/coworkers or damaging property - you could be held liable. Rewinding the coil for a washing machine valve is one thing... but playing engineer with lifting/hauling equipment is a world of hurt waiting to happen.

    If it's 70 years old, being used in a critical application and you can't get parts to service it anymore... it might be time to consider preventative replacement.

    E.g. when was the last time the gearbox was inspected for wear or rebuilt? If it's never been opened up then the load could potentially be riding on tiny little worn-down points waiting for an excuse to shear off instead of actual gear teeth.

    Things to think about.

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    Quote Originally Posted by 9100 View Post
    Mix up some slow setting epoxy and paint on a coat with each layer so the wires are winding through it and so are completely encapsulated. I vacuum impregnate coils but you likely do not have the equipment and the paint on epoxy is as good.
    Bill
    You need to be very careful when you say epoxy. Most of the epoxies I know of are thermal insulators not conductors. That's the last thing you would want. If you are going to wet wind it you need to use the proper resin paste - and it makes a mess.

    You have a thixotropic resin in your VPI tank? Very few outfits have the proper resin to VPI random wound coils. With the proper resin, VPI does do well in random wound applications, but if its not thixotropic its not doing anything. The the resin vendors that claim their product is good for both random and form wound are full of it.

    The question begs - is this coil bare or does it have resin? If it has resin it won't be easy to take apart unless you roast the windings out and then are you maybe damaging something else. If it is bare, then I suppose you can go back bare. If you do need to impregnate it, I would probably choose a trickle method. Heat the coil some after winding then pour the resin slowly over the coil. You can buy it in quarts and if you are careful you can repour it several times.

    Personally I would just send it out........ Last time I had one done it was relatively cheap but it was years ago.

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    Quote Originally Posted by Jim S. View Post
    One of two solenoids which release the brake pack on a large capstan winch has failed. The remaining solenoid is strong enough to retract the brake pack but since the consequence of complete failure is serious, I'd like to repair it and make a backup in case of future problems.

    The machine is from the early 1950s and no parts are available. It's a simple coil, about 2 1/2" square by 1" thick. That's from memory, it's still in the machine and no pictures. When I looked at it, I thought it would be straightforward to rewind. Measure the wire diameter, count the turns and buy some magnet wire to rewind. Maybe varnish for stability. Motor is 7 1/2 hp operating at 480 V, 60 Hz. Coils see 240 V as I recall.

    Is there much more to it than that? Or other methods I should pursue?
    Thanks,
    Jim
    Lots of devices, the designing Engineer selects goods - solenoids on the list - BTDTGTTS - from major-maker standard product lines.

    Some of the solenoids stay in the line for more years that most folks would believe. Because so very MANY things were built to utilize them. Then more. newer things, so the early "host" may vanish, but the solenoids have already found new "hosts", and are still available.

    Same coil specs, air-gap, pull, mounting...changed only on the plastic from old to new, for example.

    You could get lucky, you deep-dive the major makers - of basic solenoids as components, not of brakes or clutches - and find drop-in ready-mades still exist, and at reasonable prices.

    Annnnd all the major makers as well as for-sure the smaller players offer custom winds as well!

    It's a major part of what they do. No need to DIY. It's their "Day Job".

    My old standby:

    Solenoids | Deltrol Controls

    See also Magnetrol and Endicott.

    Lists of others:

    Solenoid Coil Manufacturers | Solenoid Coil Suppliers

    Solenoid Coils

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    I appreciate all the input. Bill, your practical advice was the kind of input that I was hopeful of. And I will consider thermal conductivity of insulation material when/if attempting this project. The unit is only used seasonally and currently in winter storage. Final details available when put into service in May.

    For those who point to liability and injury/damage considerations, this capstan is for line tensioning only. It is very robust, regularly inspected and load tested annually. Failure of the brake to release will not injure or damage, but considerably limit capability of a capital asset.

    Point taken about redundancy of coils. But I certainly want to have a back-up in case the remaining coil fails.

    For Mr. T, yes, I certainly have searched for a drop-in replacement, OEM end item notwithstanding. If you wish to apply your considerable search skills, I'll welcome them.
    Jim

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    Quote Originally Posted by markz528 View Post
    You need to be very careful when you say epoxy. Most of the epoxies I know of are thermal insulators not conductors. That's the last thing you would want. If you are going to wet wind it you need to use the proper resin paste - and it makes a mess.

    You have a thixotropic resin in your VPI tank? Very few outfits have the proper resin to VPI random wound coils. With the proper resin, VPI does do well in random wound applications, but if its not thixotropic its not doing anything. The the resin vendors that claim their product is good for both random and form wound are full of it.
    For VPI I usually use a standard transformer varnish. I bought a 15 gallon drum and am still using it. I was doing custom coils for s GE shop and they recommended it. I never had a complaint. Re unwinding, one time I wound transformer for a Dana DVM. It was made in the transitional period when we had transistors but no LED displays. The transformer was only about 1.5" cubed but it had 7 windings for the different components, one 200 V one for the Nixie display. I called the manufacturer for winding information and a girl was looking for it when her boss asked what she was doing. He said to tell me to unwind it and count the turns. Fortunately it was a schlok job, no impregnation, just some black paint sprayed on the ends of the coil. I told the customer that it probably would cost more than the obsolete meter was worth, but they had it integrated into a computer system and didn't want to reprogram, so I counted the turns on all 7 windings and properly impregnated it.

    When I started VPI I wound some coils similar to the one the OP has with fine wire. After impregnation and bake, I sawed them up and found that the varnish had penetrated all the way through.

    Bill

    P. S. After posting, I think I remember the brand of the varnish. Sterling comes to mind. I'm at home and the varnish in the basement of the shop. If it really matters to anyone, I can look the next time I get there.

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    I second Bill's notes, and STERLING is correct... they've got all sorts of other product-type names, ELANTAS PDG, etc.,

    This brake, like most any other hoist brake, is spring applied, and power released. Failure of the solenoid means the brake APPLIES, not releases. That being the case, a failure of the solenoid doesn't pose a frightful risk. The elevator brakes I worked on included a set of contacts on each actuator to signal when the actuator was in a released AND applied position, so that the hoisting motor would NOT attempt to overrun the brake for more than a few seconds (elevators have to BLEND... they actually apply force to the hoisting drum THEN release the brake, and vise versa, to prevent jostling the passengers).

    Winding a new solenoid is simple... it can be determined 'forensically' (meaning, after it's been totally smoked) by just taking a measurement of some surviving wire, and then figuring out the AREA cross-section of the wraps, then calculate the layers and rows, then circumference. As Bill noted, perfection is not high. I get a good solid estimate of the wire length, simply so I've got more'n enough on hand.

    I've done hundreds just by making a coil form, or core-holder, and chucking it in the lathe. I've got a spool, with a simple friction drag, and a mechanical turns counter in the side. I use the turns-counter to double-check my work against my calculated wraps and layers. A nice, tidy wrap will make a fine replacement. Men made them originally, men can still make them.

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    To add to this thread, I too have wound solenoids and magnets because it was simple and a fun exercise, and being friends with the local motor shop, I took the wound item in and had them dip and cook it just like they would do with a motor rewind.

    Maybe that would be something available to the original poster.

    Stuart

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    Quote Originally Posted by DaveKamp View Post
    I've done hundreds just by making a coil form, or core-holder, and chucking it in the lathe. I've got a spool, with a simple friction drag, and a mechanical turns counter in the side. I use the turns-counter to double-check my work against my calculated wraps and layers. A nice, tidy wrap will make a fine replacement. Men made them originally, men can still make them.
    I mounted a mechanical counter on my South Bend lathe. My coil winders use electronic counters, which may seem more modern but are not as easy to use. The big advantage of a Veeder-Root counter is that if you make a mistake and get a few turns out of place, you can unwind them and the count will back down. The electronics count each time a tab passes a photocell so the unwinding runs the count up more and you have to compensate.

    When I worked for a company that made gyros, most of the coils were wound by women. The HIG 3 gyros were about the size of a roll of quarters, so You can imagine how small the microsyn coils were. Many used wire under .001" and the insulation was proportionally thin. At a time of the month, women's perspiration would attack the insulation and cause shorted turns. The foreman had to keep a list of the women's periods and move them to other work at the bad times. The reader can imagine the ribbing he got.

    Bill

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    Quote Originally Posted by 9100 View Post
    ...
    P. S. After posting, I think I remember the brand of the varnish. Sterling comes to mind. I'm at home and the varnish in the basement of the shop. If it really matters to anyone, I can look the next time I get there.
    We used to use GE 7031 varnish. Nasty stuff, stinks pretty badly. For winding a multi-layer coil like that, the first few layers go nicely, after that it's
    not quiet scramble wound, but almost. Helps to put a layer of fine paper in between winding layers.


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