Coil Winding Mystery?

[ken]

Has this ever happened to you?

I was winding a series of 12 Strat pickups to all the same spec for a customer, with all the same bobbins, all the same magnets, all the same winding to 8250 turns of PE. The third one in the series measured 4.9k DCR and 1.5 Henries. All the other pickups measured somewhere around 5.7 to 6K DCR and 2.? Henries. I rewound this specific pickup and got 5.1 K DCR, 1.2 Henries, 5.0 ACR @120Hz/9.1K@1 Khz. Rewound it yet again, and got a 'normal' 5.85K DCR.

WTF? I didn't do anything different to this pickup at all. I tried to make every one of these the same, same wind pattern and all.

Thank you,
Ken

[black_labb]

the net is much more reliable at reproducing results

i dont have enough experience with pickup winding, but got pretty pissed off this pm when i snapped the inside wire to a hb just where it entered the coil. was just soldering the wires on to put it into an instrument i've nearly finished.

[ken]

I checked my coil wire, and I had a bad patch of wire on my spool. I wound the third coil, tested it, scrapped the wire, wound it again, tested it again, etc. and third time was the charm. All the other coils were wound after this one with no issues. I took samples of the bad wire, and checked it with my microscope. The bad wire was actually thicker in diameter, somewhere around 41 gauge wire. The spool said 42gauge single PE.

Actually, hand winding 12 pickups in one day with only one off pickup IMHO is pretty good. You can change the DCR of a coil just by pulling on the wire a bit harder and stretching it, and not even notice it until you do your electrical measurements.

In fact, I read in a book that S.D. once hand wound a series of pickup coils exactly the same and his winds varied by hundreds of ohms from coil to coil.

Ken

[Spence]

Has this ever happened to you?

I was winding a series of 12 Strat pickups to all the same spec for a customer, with all the same bobbins, all the same magnets, all the same winding to 8250 turns of PE. The third one in the series measured 4.9k DCR and 1.5 Henries. All the other pickups measured somewhere around 5.7 to 6K DCR and 2.? Henries. I rewound this specific pickup and got 5.1 K DCR, 1.2 Henries, 5.0 ACR @120Hz/9.1K@1 Khz. Rewound it yet again, and got a 'normal' 5.85K DCR.

WTF? I didn't do anything different to this pickup at all. I tried to make every one of these the same, same wind pattern and all.

Thank you,
Ken

Not all magnet wire is consistent in diameter and things change if you stretch it too. However, it may be that it's shorting on the outer magnets. You can test for this by connecting the meter to the hot and the other terminal to the magnet at each end of the bobbin. ie. the top or bottom E magnets.

[ken]

Thank you, Spence.

I had a patch of wire on my spool that was slightly larger in diameter (lower DC resistance) than the rest of my spool. I was using a 10 pound spool of single PE I bought on Ebay awhile back at the time.

I wonder how the wire companies test for this when they make the wire?

Ken

[David Schwab]

I also think you have a short. test it like Spence said.

[Spence]

Thank you, Spence.

I had a patch of wire on my spool that was slightly larger in diameter (lower DC resistance) than the rest of my spool. I was using a 10 pound spool of single PE I bought on Ebay awhile back at the time.

I wonder how the wire companies test for this when they make the wire?

Ken

The tolerances on the wire are huge. sometimes there can be hardly any difference between a spool of 42 and 43. It's not unusual for old stock wire to wander within the tolerances all on the same spool.

[kevinT]

I've noticed too that the outer wraps of magnet wire on some larger spools are stretched, which can increase the DCR. The further you work your way down into the inner wire of the spool, it tends to even out to normal.

[jason lollar]

if the same bobbin keeps coming out low look carefully at the magnets- usually the ones on the end -and youll probably find a tiny metal chip thats shorting out the wire.

I can no longer imagine not making pickups in batches or working with specific ranges of DC resistance and henries so you can catch this sort of thing other wise its very common to get a short and if you only wind one at a time to some custom turn count its really hard to tell what you have. thats my experience from winding 10's of thousands of coils.

some variation is normal but resistance varies more than henries if you have consistant parts, tension and method. Having one particular bobbin that continually reads low having been rewound several times is usually a sign of a defect in the bobbin- could be the flatwork is flairing and pinching the wire between it and the magnet too.

[Possum]

....

I recently got a spool of wire from MWS that suddenly at the end of the spool went from .00265" to .00255" diameter. I think they maybe respool this stuff at really fast speeds and stretched the wire at the beginning, totally screwed up some pickups I was winding, they are suddenly got alot darker readings on the extech.

As Jason said, if you wind a strat bobbin and get the same short out problem twice it means there is either a small bit of metal or something that is cutting or abrading the wire as it winds on, this happens fairly frequently around here, I usually do a quick sanding of the bobbin flanges before I wind to avoid it....

[ken]

My bobbin was OK, not flared, and the insulating varnish I used was OK. I also brush off the magnets with a brass wire brush and a tweezers to remove any metal pieces before and after varnishing the bobbin assemblies.

Now I'm all paranoid, I have half a 10 pound spool of wire I don't want to use because I don't want it to happen again. Maybe I'll use it to teach people how to wind.

Thank you,
Ken

[Possum]

...

You might wind with it using alot less tension than you're using, I get 43 PE that often shorts out real easy if it has much tension on it at all, I have one pickup that a real loose wind is actually part of the formula so its gets used there....