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Old 6th March 2005, 05:11 PM   #1
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Default Multi-tapped inductors

Has anyone tried winding multi tapped inductors?

I've just tried winding 2, 0.02mH to 0.18mH in 0.02mH steps and 0.2mH to 1.4mH in 0.2mH steps.

The first one worked fine, within about 10% of the desired values.

The bigger one has gone deeply wrong somehow, the values are all over the place. The wire IS intact, I checked that with a meter. The values range from 0.013 to 0.7mH, the disparity between calculated and actual value is not constant which REALLY confuses me.

I'm winding them on my lathe with a turn counter. I've wound a few single value inductors and they come out almost spot on.
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Old 7th March 2005, 06:46 PM   #2
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Default Re: Multi-tapped inductors

Quote:
Originally posted by BlackCatSound
Has anyone tried winding multi tapped inductors?

I've just tried winding 2, 0.02mH to 0.18mH in 0.02mH steps and 0.2mH to 1.4mH in 0.2mH steps.

The first one worked fine, within about 10% of the desired values.

The bigger one has gone deeply wrong somehow, the values are all over the place. The wire IS intact, I checked that with a meter. The values range from 0.013 to 0.7mH, the disparity between calculated and actual value is not constant which REALLY confuses me.

I'm winding them on my lathe with a turn counter. I've wound a few single value inductors and they come out almost spot on.
What's the equation you are using?

John
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Old 8th March 2005, 07:01 PM   #3
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http://lalena.com/audio/calculator/inductor/
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Old 8th March 2005, 07:52 PM   #4
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The equation seems well behaved. I ran a #16, 1 inch dia, .5 inch long coil, and got:

.2 72 turns
.4 96
.6 112
.8 126
1 137
1.2 147
1.4 155
1.6 163



Are you expecting .2 mH between sucessive taps? the equation only works from the start lead..all taps have to reference it.

Cheers, John
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Old 8th March 2005, 08:46 PM   #5
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0.2mH incremental steps from the start point.

But its not behaving like that.

I'm starting to think I've damaged the insulation somewhere and there is a shorted turn.
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Old 8th March 2005, 09:04 PM   #6
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Quote:
Originally posted by BlackCatSound
0.2mH incremental steps from the start point.

But its not behaving like that.

I'm starting to think I've damaged the insulation somewhere and there is a shorted turn.

Ah, that'll certainly do it..

That's difficult to find without a Q meter, or a micro-ohmmeter..

Can you push an amp into it, and use the taps as voltage measuring points?

Ah, forget it...for the cost, it's better to just re-do..

Maybe you're winding with too much tension..

Good luck.

Cheers, John
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Old 9th March 2005, 02:20 PM   #7
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Default insulation

We have trouble with winds at the climb to the next layer. The first layer wire tends to pinch the climber against the wall, and we worry about stresses there. The worst is when the wire is a square cross section, it really crushes the corners where the climb occurs..

If you prefer not to drop the tension, then perhaps you can stop the process, and put a wrap of paper, or nomex, over the layer.

We use something called green putty as the filler at the end of a layer. It's a two part hand kneaded modelling clay consistency stuff, that we use to complete the layer cylindrically. It takes a coupla hours to harden, then we spiral the other way..

Cheers, John
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Old 10th March 2005, 11:09 AM   #8
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I've not checked the Q figure, not been in the workshop all week!

Using round section wire, tension is not too high as I'm holding the wire.

I'm going to try again at the weekend.
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Old 10th March 2005, 08:08 PM   #9
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Hmm.. the Q of the faulty one is very low, 0.89 at the first tap. A single inductor of the supposed same value has a Q of 5.
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Old 12th March 2005, 07:03 PM   #10
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Just wound another one, works this time! Must have shorted a turn.

Within 1% on the first 2 coils, 3% for the next 2 and 4% for the last 3 Not bad for a first try!
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