Rewinding a coil for a meter

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Harold_V
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Rewinding a coil for a meter

Post by Harold_V »

Guys,
Some of you may know that I have been pursuing a rather energetic project of putting an old motor generator induction furnace back in service. It's been a dreadfully expensive and time consuming project---one that is intended to satisfy my almost lifelong desire to be able to pour castings. An induction furnace opens the door to melting pretty much any metal desired, plus offers the ability to create such alloys as ductile iron. Should I be successful, I'll be able to pour castings that most folks only dream of, and the project has given me a good excuse to get up each day.

The power supply for the furnace employs four meters, each of which performs a critical function which allows the operator to maximize power, including correction of power factor (for the output of the power supply). These meters monitor the output of the motor/generator of the power supply and have nothing to do with the input power. This won't be about how the furnace operates, but it will be about the repair of the replacement kilovar meter, which is no longer made nor supported. If you talk to meter people about such a meter, their eyes glaze over.

The kilovar meter displays lead or lag of the amperage as it relates to the voltage. It must NEVER lag, as that offers the opportunity to damage the generator. Proper operation dictates that the power supply be operated with current slightly leading, as the expected changes as the charge heats moves the balance towards lagging. When amperage and voltage are in lock-step, the unit is referenced as being in unity. At that point the entire output us being put to use in melting, not wasted by heating the generator.

So then, about three months ago I had intended to attempt to pour some wheel guard castings for my cutter grinder. I had made some upgrades to the furnace (I converted the furnace from manual tilting to hydraulic tilting) and had improved the preheat for the pouring ladle. This would be a great way to determine if the changes were successful. I fired up the power supply only to discover that the KVAR meter didn't function. I had no clue why, as it worked perfectly well when I shut down previously.

I removed the meter and did my best to discover the problem, but I was not successful. I was already painfully aware that analog meters of this nature were no longer supported by the maker (Hickok), so I had no recourse but to try to find a replacement. Good luck with that, as the meter is specifically made for use @ 3,000 Hz, and was restricted to a given maximum of voltage and amperage.

About a year previously I had seen a similar meter listed on ebay. It was made by Westinghouse, but shared the same values. I visited ebay without success, but I had saved the information because the original meter had been somewhat troublesome, which I had discussed previously in a different thread.

I contacted the seller to discover that the meter was actually still listed for sale. I made an offer slightly below his asking price, which he accepted, and the deal was closed. I had a new meter, new old stock, which had been sitting on a shelf somewhere and the box really looked like it. Inside, however, was a nice unused meter. I was elated. On the negative side, the meter didn't look like the original, nor would it mount in the same hole, as the body diameter of the new meter was much larger and the mounting holes were not the same. I addressed that issue by buying a 4" hole saw and opening the old hole, then drilling new mounting holes. With the meter installed, I was in business, although not without concern. On the face of the meter was the notation USE EXT. COMP. SER 116. What does that mean? Information from Westinghouse was not at my disposal. I had no clue. I did not want to dismantle the new meter, for obvious reasons. That would prove to be a mistake, however.

I fired up the power supply and applied power to the furnace. The meter appeared to work just fine, albeit rather sensitive. It worked well for the first few minutes, then Susan, my wife, happened to comment that she observed smoke coming from the meter. Then it stopped working. My fears were confirmed. I had fried the meter. I needed the missing unknown component, what ever it may be. Had I dismantled the new meter I'd have known, as it was perfectly obvious once I did.

I sat on the foundry bench, totally dejected. There was no other alternative as I saw it; I had to abandon the project after having spent tens of thousands of dollars and years of my life. I found that option rather unappealing, however, so I removed the damaged meter to investigate. That's when I had an epiphany. The meter lacked the capacitor and resistor that was included in the original meter, both of which were required to lower voltage to the volt coil, which I had soundly fried.

Burnt coil.JPG
Burnt coil.JPG (395.53 KiB) Viewed 3460 times


All I needed was a new coil and the addition of the necessary missing components and I'd be golden. I'll rewind the coil, says I. After all, what do I have to lose? I'm already dead in the water.

I neglected to put something in the image to give you an idea of size. The shaft on which the coil (and needle) mount is .055" diameter.

I'm out of time for today, but I'll add more to this as time allows.

H
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liveaboard
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Re: Rewinding a coil for a meter

Post by liveaboard »

There are (or used to be) specialists who rewind and repair old speedometers for classic cars and motorbikes.
If they can do it, you can do it!

But I always wondered; with the old coil melted together, how do you determine the correct number of turns?
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Atkinson_Railroad
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Re: Rewinding a coil for a meter

Post by Atkinson_Railroad »

Two painful observations:
The availability of the original wire size used in making the coil.
And, the ability to make the required solder connections to the wire without having to invent too many
fixtures to keep everything in place while doing the delicate work.

Soldering very small magnet wire is not for the faint-of-heart and one is perfectly normal if they feel intimidated by the act of doing such a thing.
The smallest wire I’ve soldered is number 38… and it was not easy to do without a lot of practice and accepting a learning curve along the way.
Adequately removing the insulation and cleaning the wire for making the electrical connections is painful enough for me to think about.
You’ll discover you may be making more than one coil and picking the best from the pile of your efforts.

Restoring vintage electrical equipment to working order does have a following.
(It is a mostly a hidebound activity that receives little or no press which is fine with me.)
There are a few other forums that come to mind that would likely be a better place to share this problem,
but even then… replies would likely be similar as here.
Blank stares, useless solutions, and why don’t cha do this… which you’ve likely read a zillion times.

I think it’s pretty neat you’ve brought such a problem forward to the street for folks to marvel and ponder over.

John
jcfx
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Re: Rewinding a coil for a meter

Post by jcfx »

Atkinson_Railroad wrote: Tue May 09, 2023 4:46 am The availability of the original wire size used in making the coil.
Finding the correct size wire shouldn't be a problem I think, I did a quick search and found this place -

https://www.remingtonindustries.com/

They seem to have all sizes from 14 AWG to 44 AWG, I got a chuckle when selecting a 44 AWG,
2 oz is 9975 feet ! A few lifetimes supply !
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Harold_V
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Re: Rewinding a coil for a meter

Post by Harold_V »

To be clear, before I undertook any effort to repair the now destroyed meter, I did ample research. I went so far as to contact Ram Meter Inc., where a very helpful Ms. Cowell provided some encouragement. She had informed me that when Westinghouse stopped production of their meters that one of their associated companies, Weschler Instruments, had assumed rights to the products and had in their employ a gentleman named Joseph May, who worked for Westinghouse when such meters were built. After considerable delay, I finally heard from him, but the results were not encouraging. They could possibly provide a solid-state device that might be able to substitute for the original meter, but when the frequency was discussed, that option went off the table. I was left with my original thoughts---that I may have to abandon the induction furnace.

At this point it was obvious that I was out of options, aside from just sitting back and waiting to see if something might appear on the used market (ebay). That wasn't a solution, not at my age (83). I have to rewind the burned coil.

I was able to measure the existing wire, which I determined to be #43 AWG. Small. Very, very small. I knew I didn't want to deal with that, but I also knew that I couldn't vary far from the small size, otherwise the coil would not have the proper value. I chose to buy #40 (.0035" diameter), which is readily available, and while the cost per pound is outrageous, two ounces yielded over 4,000', enough to wind about 20 coils. Cheap at twice the price, says I. It was just $14 delivered.

With the wire ordered from ebay, I started thinking about how I'd go about doing the actual winding. I didn't want to start on a bobbin until I had the wire, as the number of turns involved would play a role on the width, which I knew would have to be slightly different from the original, that due to my switch in wire size. That would also necessitate that I knew the number of turns and the number of layers.

I am much like a crow. I don't discard anything, and I have a large cabinet with cubbyholes in which I store all manner of material, plastics as well as metals. Where I live there are no options to buy aside from one steel supply, and they deal in structural shapes, not bar stock. I turned to my storage to find pieces that might be suited to build a small winding fixture. You'll notice that the base plate has many holes that do not pertain to the winding jig (it's a plate used for various shop aid fixtures that I had not discarded) and that one member is black, which is an anodized piece that I used from an old tape deck mount I had built for my stereo system when I lived in my first home. I had stored that piece of material since 1983, when we moved to the castle.

I won't go in to any details in the construction of the winding jig---just suffice it to say that it evolved and was adequate for the task at hand. I wouldn't have changed any of the features. Here's an image of what it looks like.

Winding jig.JPG
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You may have noticed that there's a center piece to the coil, which I'll call the armature. It's made of Bakelite, and was injection molded. That was beyond my ability, so I chose to make mine from some paper based micarta, a material commonly found in electrical devices. The use of other plastics was pretty much eliminated because the coil has to be attached to the armature by an adhesive, which, in my case, I knew would be epoxy. I also chose to make mine slightly larger, so they would be easier to wire and provide a greater mounting surface for the coil. The differences were minor, but useful.

I knew I could have problems with the project, so I made four of the armatures. Even then I had to go back and rework them due to breakage, a problem to do with the aids I used in winding the coil. No big deal, just time consuming.

With the wire and armatures in hand and the winding jig finished, I turned my attention to the bobbin. I knew it would have to be made from Teflon (I have that on hand, too), as the coil, while wound on a form, is not supported once removed from the bobbin. That's the reason for the two flat and parallel ends when the sides of the coil are viewed. That flat surface binds the two sides of the coil together. The coil would be epoxied as it was wound and removed from the bobbin only after the epoxy had cured. First, however, I had to determine the number of turns. In order to do that I had to unwind the burned coil, which had been enameled after winding so it would be self-supporting. The enamel had been burned, but it was still robust enough to keep the wire together. But how does one unwind a long thin wire and end up with a method to measure its length?

I chose to unwind it in lengths that were reasonable, measure them, then record their lengths. That turned out to be a wise decision, as the wire didn't unwind uniformly so long sections were not possible. No matter, however. Just record each and every piece that is removed, which I did. It took several hours, but I finally measured the last short piece, some of which were only an inch or two. Hard to believe how such a small coil can be so long!

I now had a total length, then by doing the math I could determine the number of turns and layers. I had pre-measured the coil in all dimensions, so it could only be a certain number, so as long as my conclusion was reasonable, it should work.

I'll pick up on this soon. There's more.

H
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Bill Shields
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Re: Rewinding a coil for a meter

Post by Bill Shields »

My father used to wind toroid transformers with #44 wire and solder the ends.

IIRC he used to remove the insulation, then dip the end of the wire in molten solder to 'tin' it.

The connecting end was similarly prepared.

From that point on, it was just a case of getting the wire into place and warming the joint with a very small heating tip.

There are companies that make specialty irons for just such situations ..

Darn if I can remember their name, but one of them is located in the Baltimore area and used to be a customer of mine.

It all sounds so simple until you actually have to do it.
Too many things going on to bother listing them.
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Harold_V
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Re: Rewinding a coil for a meter

Post by Harold_V »

Thanks to those who have commented. I'll continue with my posts without responding, aside from this mention. That way I won't repeat information that is a part of the overall report.

With the length per turn determined, I divided that into the overall length, and concluded that the coil had 476 turns. If I wound it in 7 layers consisting of 68 turns, with the turns split equally between the two sides of center, it would work out quite nicely with the width only marginally wider than the original coil (due to the larger wire size I chose) with the wire ends located near the attachment points on the armature. The die was cast! I now knew the required width of the coil at the ends, so the bobbin could be machined. I didn't have much guidance in that regard, so I just started whittling on the Teflon, working to the desired dimensions of the coil. Again, this isn't about how the items were built, but about the end result. Suffice it to say that after some trial and error, I ended up with a bobbin that held the armature in the correct orientation and permitted winding the necessary coil. This is an image of the finished bobbin. The long pin that one sees at the top right in the image is the anchor point for the starting end of the wire. I sealed any minor gaps in the bobbin with bee's wax, including the hole in which the wire was threaded to the anchor point. I didn't want epoxy where it was not needed. That proved to be quite effective.

Bobbin.JPG
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I had previously rewound one of the electromagnetic clutches for my Graziano lathe for which purpose I had purchased a counter. I put it to use for counting turns by creating a small steel washer that allowed for mounting a small magnet piece on the washer face. All that was left to do now was to actually wind the coil. I started out with the idea that I'd likely make several mistakes, which proved to be true. One thing I learned quickly was that it was difficult to orient the wire as it was wrapped, especially in keeping it on the proper side of center. To solve that riddle I made some winding guides, the white ones made from Teflon, the others from some urethane I had on hand. They were intended to be a slip fit on the ends of the armature, but once installed they were difficult to remove and they had to be changed regularly as winding progressed. Due to the difficulty of their removal, I broke the ends off the armatures. I solved that riddle by splitting the ends of the winding guides. The broken armatures were repaired by epoxying a new member internally. The wall thickness of the broken ends is quite thin-----only .016".

These are the aids I used to assist in winding the coils (I made a total of four).

Winding aids.JPG
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Here's an image of one of the coils being wound, showing the first layer.

Coil rwind.JPG
Coil rwind.JPG (208.61 KiB) Viewed 3330 times

Keeping tension on the wire was critical. It had to be sufficient to provide a snug wrap, but not too much to attempt to straighten the wire, which was offset as the coil was wound. I knew that friction would not be a good choice, so I decided on a weight. I made a small donut from plastic, which was then hung on the wire. With a long loop towards the floor, the weight of the donut would keep a constant tension on the wire and it could be fine tuned by adding a little weight if needed, which proved to be the case. I addressed that issue by simply adding a short length of copper wire to the donut.

Wire tension weight.JPG
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Using a shortened bristle camel hair brush, I applied epoxy to each layer after it was wound. That proved to be an acceptable method for bonding the armature to the resulting coil, as well as bonding the windings to themselves. Once cured, the coils were easily removed from the (dismantled) bobbin and the armature was firmly attached to each coil.

two coils.JPG
two coils.JPG (422.39 KiB) Viewed 3330 times

I'll get back to this soon.

H
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Bill Shields
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Re: Rewinding a coil for a meter

Post by Bill Shields »

:mrgreen:
Too many things going on to bother listing them.
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Harold_V
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Re: Rewinding a coil for a meter

Post by Harold_V »

With the required coil wound and connections wired to the armature, I had to install the coil on the needle shaft. I used a wooden fixture for that purpose so it would be properly oriented, parallel with the needle and buffer. The armature was epoxied to the shaft and allowed to cure.

new coil on shaft.JPG
new coil on shaft.JPG (221.72 KiB) Viewed 3290 times

In the image one can see what appears to be wire ends. Those are the attachment points that hook the coil to the meter base. They were made from .001" copper shim stock, and while I made no attempt at a given width (which I just eyeballed), they are about .020" wide. They solder to the pin you see on the armature, then make a 360° wrap around the armature, loosely, and are then soldered to the two leads in the meter body. What they do is allow the meter needle to swing side to side without restricting motion. That's the reason for the ultra-thin but wide physical size. There's a hair spring on the needle shaft that returns the pointer to the vertical position when the meter is not receiving power. Here's an image of a pair of the flat hookup wires.

Hookup flat wires.JPG
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While I had no clue of the impedance of the original coil in the meter I was attempting to restore (it no longer conducted because it was fried), I measured the impedance of the coil from the original meter. Because of my choice of larger wire size, there was a difference of about 60 ohms between the two. In case that was of importance, I chose to install in the power supply chassis a box in which I installed a 5,000 ohm potentiometer, one that had been a part of the original watt meter of the power supply. When I had the meters rebuilt (in the mid 90's) they had provided a new one, so it was properly matched to the watt meter. It was set at about 60 ohms so I would more closely match the overall impedance of the original meter. I had to start somewhere, afterall.

I had already concluded that the lack of the internal resistor and series of capacitors was the reason I had fried the Westinghouse meter, so I duplicated, as near as I could, the values, and rewired the Westinghouse meter internally. I was fortunate that there was an unused chamber in the meter housing that permitted the installation. Here's an image of the installed resistor and caps.

added resistor and cap stack.JPG
added resistor and cap stack.JPG (347.4 KiB) Viewed 3290 times

I won't go in to much more detail, suffice it to say that I had to remove the meter and reinstall one of those thin connecting wires, one of which had broken while I was messing with the balancing of the coil/shaft assembly and it went unnoticed.

The day came when I was ready to fire the induction furnace. I was eager to attempt to pour those wheel guards, as the molds had been sitting idly for a long time, but, more importantly, I wanted to know if I had been successful in rebuilding the meter.

To my delight, the moment I excited the generator, the KVAR meter responded. Turns out it is slightly less sensitive than the original, which I could easily rectify by either an adjustment of the potentiometer, or by the addition of another capacitor. However, that isn't really necessary. While I make no attempt to suggest that the meter is accurate, it need not be. If it displays lead and lag, it has done its job. It does that. The run was successful, and, for the first time, I poured, successfully, some wheel guards for my cutter grinder, although that matter is beyond the scope of this thread.

What I have learned from this experience.

I understand electricity and electronics to some degree. At least well enough to be dangerous! As an example, I wired my house and shop, including installing the panels and CT can (three phase, for the shop). I built the low voltage switches for our lighting system and installed the entire system without outside help. However, I lack a great deal of theory and am easily confused. Still, this rank amateur managed to bring back to life a meter that now allows me to operate a piece of equipment that, otherwise, would have been relegated to the junk yard. That, in and of itself, was a major accomplishment. Just goes to show, one has no idea of their ability to perform any given task until called upon to do so.

I consider this project a complete success!

Thanks for looking.

H
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rmac
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Re: Rewinding a coil for a meter

Post by rmac »

I hereby award you one attaboy! You deserve it.

-- Russ
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Re: Rewinding a coil for a meter

Post by NP317 »

Harold:
A Major Accomplishment, indeed!
Sharing your journey is most appreciated.
Thank you.
RussN
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Steggy
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Re: Rewinding a coil for a meter

Post by Steggy »

Yee-haw! Brought back from the dead.

Good work, Harold, and a compliment to your tenaciousness.
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