Re: Help! Coil design?
- From: "miso@xxxxxxxxx" <miso@xxxxxxxxx>
- Date: Fri, 5 Jun 2009 18:43:31 -0700 (PDT)
On Jun 5, 4:44 pm, Scott Newell <new...@xxxxxxx> wrote:
I'm having a terrible time getting an air core coil wound
for my RFID project. The big problem is that I simply don't
know how to specify a coil, and the engineers at the magnetics
company can't seem to help me fill in the blanks. Can anyone
shed some light on how I should procede?
I've told them I'd like a 750uH coil with a max OD of
40mm to fit our physical constaints. Exact DC resistance
doesn't matter too much, but I suggested 10-12 ohms or so
based on some coils I wound by hand. Exact wire gauge doesn't
matter either, so I suggested 34 gauge or so, again, based
on my hand wound samples. I told them the coil thickness
didn't matter much either, but a max of 5 mm or so seemed
reasonable. The coil is to be operated at about 125 kHz.
I'd like to maximize the OD without exceeding the 40 mm spec,
as it is acting as an antenna.
(Sketchy specs, I know, but I had to start somewhere.)
So, what did I forget and what do I do wrong? For the last
week I've had to take calls daily with question after
question..."can the ID be 10mm?" Probably not, if you expect
to make the OD ~40mm, but how would I know? "What is the series
resonant frequency?" I don't know that I care? "What is the Q?"
Isn't that set by the inducatance, operating frequency, and
the DCR? Why are you asking me?
I haven't felt this ignorant in at least a month.
Should I have iterated through with the approximate
coil formulas and just told them ID, thickness, gauge,
and number of turns? Am I asking the impossible? Will
I end up winding 500 coils my hand on a toilet paper tube
form next week?
ARGH!
--
newell
I'd ask for their standard coil form sizes as a starting point. I
can't say I've seen a 40mm form. That's nearly two inches. The again,
125KHz is more like audio frequency than RF. Maybe you need to find a
company that makes components for speaker crossovers. Ah, but those
use overlapping wires. This is quite the pickle you got yourself into.
[RFID project?]
I suspect their are all sorts of pitfalls if you don't use one of
their standard core sizes. Can their machine handle the size, blah
blah blah.
.
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