DC Resistance after potting

[Chadheckler1]

Does it make sense that the DC resistance would increase after potting a single coil pickup? I know that I need to wait for it to cool down, but even after it cools I am seeing about a 1.5k jump in DC resistance. Am I doing something wrong?

I know that DC resistance is only a leading indicator and that the inductance is more important...but I must know.

I'm using 43AWG - PE...from MWS if that makes a difference.

BTW: I am new to the pickup winding world but I am eager to learn...so go easy on me.

[chevalij]

A 1.5k jump? You don't mean .15k? Even when I measure pickups hot out the wax, the temp is only about .2k higher. When totally cool it comes back down to pre-wax levels.

[Chadheckler1]

A 1.5k jump? You don't mean .15k? Even when I measure pickups hot out the wax, the temp is only about .2k higher. When totally cool it comes back down to pre-wax levels.

Nope. I meant 1.5k. I was asked to try to wind something a touch hotter than a "texas special" tele bridge pickup so I was shooting for around 11k. After winding 11,600 turns and terminating the leads I got around 9.4k...after potting and after it cooled down to room temp it measured 11.05k (I thought the 11.05k sounded about right for 11,600 turns of 43AWG). Didn't really make sense to me...thats why I thought I did something wrong...is there anything that could cause this?

...maybe I was wrong about the first measurement...I'll have to try winding another and see what happens.

[J S Moore]

It might have been shorting against the magnets and the wax provided some extra insulation to stop it.

[Chadheckler1]

It might have been shorting against the magnets and the wax provided some extra insulation to stop it.

I was thinking something along those lines...but wouldn't the initial reading of the coil show a very low resistance if it was shorting on the magnet since there would only be a few hundred turns max? I guess the short could be anywhere in the coil...

If this is the root cause do you think it will cause problems in the future or should I give it a try?

Thanks so far...

[J S Moore]

I've had 200 or 300 ohm differences which I don't really worry about. 1500 ohms is a lot though. It does sound like it shorted in the windings with that much of a change.

Shorting against the magnets will still show a relatively high resistance as there are only so many winds against the magnets.

[John_H]

...maybe I was wrong about the first measurement...I'll have to try winding another and see what happens.

How does it sound? You might not need to wind another. To me it seems peculiar that the resistance would increase that much other then if the potting fixed a short, and that's unlikely. It could be that you got a bad reading the first time. I'd try it out.

[Zhangliqun]

Another vote for shorting against magnets. That kind of crap drove me crazy, would get fluctuating readings even while I was winding, as in I added turns and the next reading was BELOW the last. D'0H!!!

So I started taping over the magnets before winding and haven't had a problem with that since.

[Chadheckler1]

Another vote for shorting against magnets. That kind of crap drove me crazy, would get fluctuating readings even while I was winding, as in I added turns and the next reading was BELOW the last. D'0H!!!

So I started taping over the magnets before winding and haven't had a problem with that since.

I dip each assembled magnet/flatwork set in lacquer for two reasons...one to kind of lock things in place...and two to try and prevent this exact scenario (Is this a good idea? I thought I read it somewhere...) I could have made matters worse by doing this if I got some foreign fiber "Lacquered" to the magnet and created a stress concentration or sharp spot for the wire to "Kink" itself on...I think the tape is probably the safest method. I just want to get the coil as close to the magnets as possible...What kind of tape do you use...masking?

[David Schwab]

Dipping in lacquer is a standard procedure.

I always tape off my poles/magnets before winding. You will not get a short that way, and in the future you also don't have to worry about corrosion making the lacquer fail.

The small amount of space created by the tape won't effect the pickup. I use white paper tape (it's like smooth masking tape, used in the graphic arts field) but I've also used electrical tape and Scotch "magic" tape, which is nice and thin.

[Scott S.]

I use the 3M #56 mylar tape, works great, and only 1 mil thick, certainly not enough to be audible, might even be thinner than the dry film thickness of a laquer dip.

[Chadheckler1]

Thanks to all that posted...Lesson learned...I will use some sort of thin tape in the future...even if that was not the root cause it seems like a good preventive measure.

The pickup actually sounds really good for now...I guess I will keep an ear on it and see how it holds up.

[Steve A.]

I believe it was Mark Hammer who suggested using plumber's teflon tape. This was on the outside of a coil although I think it would also work on the inside. The idea was something that could be removed later without tearing the fine coil wires...

I do like the idea of lacquer around the pole pieces- would that help with guitarists who insist on adjusting the stagger "just a little bit"? I try to tell them that they are taking a chance since it can tear the coil wires...

Steve Ahola

[chevalij]

I do like the idea of lacquer around the pole pieces- would that help with guitarists who insist on adjusting the stagger "just a little bit"? I try to tell them that they are taking a chance since it can tear the coil wires...

Steve Ahola

I think that would actually make it worse. The magnets are smooth and slippery, I think the lacquer would actually drag the windings and have more chance of breakage.

[MistaT]

Hello,

I too am just getting started on winding pickups, and I am also having my pickups change after potting. The last pickup I wound, I was shooting for 6.5k. When I was finished winding, that was what I measured. However after potting it, and letting it cool for several hours, it read 7.1k.

People in the past have suggested shorted turns, but it seems to me if turns were shorted, then resistance would go down instead of up.

Also on my potting I accidently let the wax temperature get a little too hot (like 170 deg.).

I would greatly appreciate suggestion, thank you!

-- Mike