Funky ohm numbers -tension questions.

[David King]

I just had my apprentice wind a few coils for practice and very strange things were happening. He's consistently been ending up with very loose, sloppy looking coils when all the winder settings are the same. I figured that inconsistent tension was the problem so I went out and got a little 0-30 gram tension meter. My two felt disc tensioners combined were giving me 5 grams total. I'd never had a problem winding at this tension but I figured I'd bump it up a bit since the recommended tension for 42 AWG is somewhere between 22 and 30 gram. My felt discs are spring loaded and I screwed down the adjustment screws about 10 turns each and could only get the tension to register 12g but that gave me a tight and orderly looking coil. Apprentice again winds a very loose looking coil which I strip off. The next three coils I oversee and slow down the wind speed a little and they all come out looking great. I solder off the ends and measure resistance and get 4 different ohms readings with the longer coils reading lower and identical pairs off by more than 10%.
I do ohms per foot calculations and I should be getting close to 9.9K but instead am getting readings on 7.8-8.5k . WTF? No magnet shorts.

Is there a cheap, easy way to check for internal shorts between layers?

Does 12g tension seem ridiculously high?

Is my wire defective?

I've never had this problem with this spool or winder setup before. My coils are usually within 1-2%.

How can two operators get such totally different results when the only variable is a modest difference in winding speed?
TIA

[Stevenson]

I just had my apprentice wind a few coils for practice and very strange things were happening. He's consistently been ending up with very loose, sloppy looking coils when all the winder settings are the same. I figured that inconsistent tension was the problem so I went out and got a little 0-30 gram tension meter. My two felt disc tensioners combined were giving me 5 grams total. I'd never had a problem winding at this tension but I figured I'd bump it up a bit since the recommended tension for 42 AWG is somewhere between 22 and 30 gram. My felt discs are spring loaded and I screwed down the adjustment screws about 10 turns each and could only get the tension to register 12g but that gave me a tight and orderly looking coil. Apprentice again winds a very loose looking coil which I strip off. The next three coils I oversee and slow down the wind speed a little and they all come out looking great. I solder off the ends and measure resistance and get 4 different ohms readings with the longer coils reading lower and identical pairs off by more than 10%.
I do ohms per foot calculations and I should be getting close to 9.9K but instead am getting readings on 7.8-8.5k . WTF? No magnet shorts.

Is there a cheap, easy way to check for internal shorts between layers?

Does 12g tension seem ridiculously high?

Is my wire defective?

I've never had this problem with this spool or winder setup before. My coils are usually within 1-2%.

How can two operators get such totally different results when the only variable is a modest difference in winding speed?
TIA

Maybe try winding a couple of coils yourself using the same wire to rule that out at least.

[Joe Gwinn]

One can detect shorted turns by measuring AC resistance using a Extech 380193 LCR meter. There are many threads on this.

[David King]

What about this bad boy? HP 4262A LCR Meter REDUCED | eBay

There seem to be lots of them around for cheap and the test frequency is 100Hz. Of course the shipping about doubles the price. Circa 1978.

Stevenson, That's exactly what I'll have to do. Oh and I'll test my gram scale for accuracy too.

[jason lollar]

You can get a bad spool once in a while- also if the tension gets loose look for a little ball of wax and dusts on the wire where it is pinched between the felt- the wire has a lubricant applied during spooling, sometimes they get too much on. The slightest build up of smutz will make the wire loose tension. Another thing weve had happen a few times is the counter can get off - if its mechanical it will eventually wear after 50 years of use or actually with selenuim diodes in these things probably 60 years or if you have a digital counter the trigger can get off from various things depending on what type of switch you have. The counter problem is hard to diagnose
also its amazing how many ways someone new can screw up- ways you never thought of

[Jim Shine]

What is the winding machine setup?

[David King]

Thanks for those suggestions Jason, I'll replace the felt. The counter sensor is optical but it feeds an old Durrant digital preset model that seems rock solid. The coils look identical but i'll check them by weight too and see for sure.

Jim it's an antique sewing machine with a tailstock tacked on for good luck.

[Jim Shine]

I am not saying this is it, but it very well may be. I discovered that the way my hand allowed the wire to approach the coil made a huge difference in just this way. I am going to have a hard time verbalizing it I am sure. But I will try. Keep in mind, the setup is unchanged.

I found that sometimes my hand let the wire catch on the bottom corners of the bobbins. So the bobbin would revolve and the wire would seat on the bottom corner. I could see the wire jumping around as it laid on the bobbin. The final product is a lose, sloppy looking coil. If I made a minute adjustment in how I held the wire in relation to the guide, the wire would grab at the top corner, and the tension created between the coil and my hand would smooth out the travel of the wire between us. You can actually watch the winds lay down in a neat orderly fashion. The final result is a nice, even looking coil that isn't loose.

Sometimes I still have this problem if I am tired or haven't wound anything in a while. I see it pretty quick and adjust to it. EDIT- I also sometimes have this problem if I get into a rhythm of winding a bunch of pickups in the same direction and I have to do one in the opposite direction by reversing the winder motor. When that happens I have to switch which corner I let the wire "bite" and seat into.

Again, not saying this is it, but this issue is what gave me similar results.

[jason lollar]

when i teach classes we check for smutz ever other coil- you just pull the little smutzig ball off and you are off and running again. Jim has a possibility there. I have taught so many people- hundreds- dont be suprised, anything unexpected could happen

[Joe Gwinn]

What about this bad boy? HP 4262A LCR Meter REDUCED | eBay

There seem to be lots of them around for cheap and the test frequency is 100Hz. Of course the shipping about doubles the price. Circa 1978.

This will work just fine. The section on theory of operation is worth reading. Here is the manual: http://cp.literature.agilent.com/lit...4262-90007.pdf

In some cases, may require recalibration, at least in theory. Anyway, test any new (to you) instrument against a known item.

[David King]

So I just wound an identical coil with the tension backed off. It looks good and has a little squeezeability on the sides. The DCR jumped up to 9.4kOhm which is a definite improvement but not the 9.8k I would expect. I'll see if the other coil's resistances coalesce around this new number.

[rhgwynn]

I have found that if I wind too fast, they can get a bit loose and sloppy; so it makes sense that backing off the speed would help. I'm not entirely sure why this happens. Maybe higher speeds need more tension. If I could see it in slo-mo it might be more clear just what is happening.

[rhgwynn]

Just back to mention another thought. If you don't wind close enough to the edges and do so with high enough tension, what happens is that the pressure of the winds coming down on the rest of the coil pushes the windings down and out to the side. So what you end up seeing is a bunch of windings that were basically shoved away from where they were originally laid so they get all loose and whatnot. Does it seem like that's what's happening?