How to Measure TPL

[TheGrateOz]

I have read a number of threads regarding TPL (Turns Per Layer). It sounds as though there is a way to measure this, but I struggle with the technique being used.

Can anyone shed some light on this?

-Rock on

[Rick Turner]

Count 'em!

Are you machine guiding or hand guiding?

If by controlled traverse machine, just wind a layer and count.

If you are "true scatter hand winding, each layer will have as many turns as you want. Once again, count.

[Magnut]

Measure the height of the inside of the bobbin. Then divide that by the diameter of the wire being used. That will tell you how many turns can fit on one layer across the bobbin.

.5" bobbin / .0025 wire = 200 tpl

[belwar]

It depends, are you talking about while winding a new pickup? Or examining an old pickup?

When examining an old pickup, start unwinding the pickup turn by turn. Count the total number of rotations from the top side of the bobbin to the bottom side of the bobbin - that is the number of turns in 1 layer of wire. ususally I will measure 20-30 layers and average them. Make sure you are counting TOTAL rotations, and not half a rotation. Being dumb as a cork I made that mistake once.


The first layer or two are usually un-reliable. I recently unwound a hand wound 52 fender pickup and it was all over the place.. layers than had 10 turns, and others that had 150 turns. Counting TPL is really only useful for machine wound pickups. Even then in most cases winders use the formula that magnut put up above.. The average humbucker is .25" tall, which dived by .0025 leads to 100tpl.

[TheGrateOz]

Thanks guys - you rock.

I was thinking of true scatterwound pickups as a I analyzed the possibilities... You have all covered my question well.

@ Belwar - I too have made that mistake recently while rewinding. I guess I fall into the cork club too =)

[Bruce Johnson]

If you're running a machine-guided winder, you can also figure the TPL by counting the number of traverse cycles (across and back) and dividing it into the total turns. You can even test the setup of the machine by running it without wire. For example, if it does 50 traverses while running up 5000 turns on the spindle, you have 100TPL.

You can use the same general technique when hand winding. If you're aiming for a specific TPL, first divide that into the total turns that you're planning to wind. That'll tell you how many traverse cycles you should be making by the time you reach the total turns. Figure how many that is per 1000 turns, and then as you wind, count as you traverse and try to match the numbers as you pass each 1000 on the counter.

[eehanj]

I just did this the other night. I was attempting to find a broken connection on a dead 80s Gibson humbucker coil, and doh!!! broke the start wire off and could not retreive it. So.. I started stripping the wire of the bobbin by cutting it on one side. A thought came out of the blue that this would be a good opportunity to do some "research" so I peeled the cut wire away untill I reached solid windings. Then, once I was able to consistantly unwind without breaking the wire, I waited until I got to the end of one layer and started counting once for each complete revolution until i reached the other side of the layer. It took a few tries to be consistant, and a four different places in the inner third of the coil I obtained some consistant counts.

You know, it may sound kind of dumb, but the whole process was kind of fascinating, especially that big "hairy" mess of wire at my feet once I was done.

I also measured the wire with a micrometer.

After reading about this process more than a few times, and now actually doing it, it all makes sense.

No on to building a winder....

Ianj

[David Schwab]

I used to think it was impossible to count TPL while hand winding... because I couldn't. But that's because I was scattering. Now I wind as neatly as possible and notice that if I start when the counter is on an even number, I can count how many turns when I get to the other end of the bobbin. I just have to keep an eye on both at the same time! I was doing that so I would know how to program my CNC winder when I eventually finish it.