60cm coil for Hammerhead

[1843]

Hi all,

I want to build a 60cm coil for hammerhead without changing damping resistor and wire gauge.

Please tell me information for it.

Does anyone know the coils equation?


Regards

[bbsailor]

1843

Making a 60cm coil for the Hammerhead PI, assuming that you want to make a 500uH coil, requires 15 turns of wire. Matching the inductance of both coils will not match the coil's capacitance and will require changing the damping resistor value.

The best way to match the capacitance of your new 60cm coil to your old 25 cm coil is to measure the old coil's self resonance frequency. Then make the new coil with one or two extra turns, then measure the new coil's self resonance, then remove one turn at a time to match self resonance frequencies of both your old and new coil. This will make a coil with about the same capacitance and the damping resistor should be about the same for both coils.

If your 25cm coil has 26 turns, then it has 20.42 meters of wire on the coil. I guess that your new coil will have 13 turns and will have an inductance closer to 350 uH if you are making a coil with about the same length of wire as your 25 cm coil, which would have close to the same coil capacitance.

The self resonance of your new coil is best measured as suggested above if you want to keep the damping resistor the same.

If your new coil is slightly underdamped (meaning the damping resistor is too high), you should add a small resistor (in the 1K to 5K ohm range) in the new coil plug to fine tune your new 13-turn coil. For example, a 5K ohm in parallel with the 680 ohm damping resistor will drop the effective damping value to about 600 ohms.

It is very difficult to calculate your requirements accurately. This is best done using an oscilloscope to view the output of IC6 while adjusting the damping value.

Let us know how your new coil works?

bbsailor

[1843]

bbsailor

Thank you very much,
I will tell you the performance of my new coil.

[diminute]

Formula

What formula (equation) you use for aproximate inductance value ???

Having diameter, wire gauge, turns... obtein inductance.

Sorry for my bad english

Thank

diminute

[bbsailor]

diminute

Go to the following web site: http://my.athenet.net/~multiplx/cgi-bin/airind.cgi

Multiply the wire outside diameter by 4 for a coil length with 13 to 15 turns and by 5 for a coil with 18 to 20 turns. Enter this number into the coil length input of the coil calculator in the above web site. This should get you close.

bbsailor

[Reg]

Hi,

BBsailor provided a lot of good information but the coil winding link takes you to a finished result. The link you need is the one below, which takes you to the main page where you plug in what you know or desire. You can select either cm or inches for the diameter or the length.

Now, for those of you who have not used this formula, the length of the coil will refer to the "thickness of the windings in this multi layer winding case. The forumula is basically designed to be used to build a single layer coil, but will work well for winding coils where the windings are bunched on each other. When wound this way, the bunch size or diameter becomes the "length" part of the equation. So, once the windings are laced and are tight, a simple measurement of the diameter of the bunch will work for the length measurement. Sometimes this "length" has to be adjusted so the calculations match the actual inductance as measured.

Personally, I usually start out with a guessed length of about .22 to .25 inch and will be reasonably close. However, I will adjust this number a little to compensate for any differences.

This is the link to the coil winding calculation:

http://my.athenet.net/~multiplx/cgi-bin/airind.main.cgi

Once you have selected all the values, and they are submitted, you will be given two possible answers. I normally use the 1% accuracy and it is always very close providing you are using the same wire as on previous coils that were calculated.

Unfortunately, even changing the type of insulation can throw the results of quite a bit and may require adjustments in the "length". As an extreme I have found it is possible to be off as much as 20% from calculated if you change things such as the wire size, insulation thickness or insulation type.

Now, normally if you keep the inductance the same or greater than your working coil, the new coil should work fine. If the new coil is much larger the the inductance becomes more critical and may need to be either more inductance or have an additional damping resistor in the coil housing. If you are critically damped with your smaller coil right now, there is a good possibility more damping may be needed for a larger coil of the same inductance. If your smaller coil is over damped, then the larger one will probably work fine. If you increase the inductance of the larger coil, then it is more likely to work because the greater the inductance the higher the damping resistance value is generally needed for damping.

The problem with building a larger coil is the capacitance goes up signficantly, or can go up. This has or can have a serious affect on the damping.

Most likely you will have to extend the delay out to make the larger coil work. It is quite difficult to make a large coil work at the delays a smaller coil can work.

The nice thing about the HH is it is very forgiving and can work with a wide range of coil inductances and wire sizes just fine. Personally, I have used wire size ranging from 30 awg to 22 awg and all coils have worked well. I have tried magnet wire, plain hookup wire, litz wire, and teflon coated wire and had good results with all. Some are a little better when trying to build the fastest coil possible, but all will work.

Reg