EMRFD Message Archive 13711
Message Date From Subject 13711 2017-03-16 20:20:24 nothdurftm Toroid inductors - Al values vs inductance charts I have a question regarding what appears to me to be a discrepancy between published Al values and the inductance charts published by the same manufacturer. For example. Published Al for an FT37-43 core is 350. Ten turns on this core would calculate to be 35 µH but the inductance charts show that 10 turns would give you 42 µH, a 20% difference. Another example for a T37-6 core. Al = 30 so ten turns should give .3 µH per calculation but the inductance chart says 10 turns give an inductance of .4 µH. a 30% difference. Can anyone explain the difference and which gives you the more accurate result?
13712 2017-03-16 20:27:06 Dana Myers Re: Toroid inductors - Al values vs inductance charts 13713 2017-03-17 00:05:31 Mvs Sarma Re: Toroid inductors - Al values vs inductance charts VE2azx indicated the AL value for FT37-43 of AMIDON as 420 and not 350.Perhaps, the manufacturer datasheets may have to be referred , instead of venders and users. 13714 2017-03-17 01:28:47 kerrypwr Re: Toroid inductors - Al values vs inductance charts I consulted my files on the Amidon data for the FT37-43; it says Al = 420;
Note also that inductance, related to u' in the following graph, is frequency-dependent;
Initial permeability of about 800 is only maintained up to about 1 MHz; it "rolls-off" quickly thereafter.
Measurement of inductance at the required frequency is useful for things like transformer design; most L-meters, including the wonderful AADE meter, measure at low frequencies.
13715 2017-03-17 03:50:11 Andy Re: Toroid inductors - Al values vs inductance charts "Published Al for an FT37-43 core is 350. Ten turns on this core would calculate to be 35 µH but the inductance charts show that 10 turns would give you 42 µH, a 20% difference."Can you point us to an example of that?http://toroids.info/FT37-43.php shows 35.00 uH for 10 turns. But that's a simple on-the-spot algebraic calculation. Maybe the manufacturer knows something we don't about how the inductance of their toroid varies with the number of turns.It's interesting to note that the Al for the FT37-43 has a tolerance of +-20%. I wonder if someone misread that and used Al=350+20%.Andy 13716 2017-03-17 08:04:28 K5ESS Re: Toroid inductors - Al values vs inductance charts
The Amidon site I access lists an Al of 350 for the FT37-43 and 440 for the FT50-43.
13717 2017-03-17 09:31:52 K5ESS Re: Toroid inductors - Al values vs inductance charts
Well I just went to the Amidon site and got these pages which both list the Al for FT37-43 as 350.
However, this page lists the Al as 420
The second reference shows the same inductance values as the chart Kerry references but the Al is listed as 350 instead of 420.
Maybe I’ll see if I can get an answer from Amidon.
I also measured an FT37-43 core with 10 turns and got the following results:
Measured at 1, 2, and 7 MHz. Inductances of 38.5, 35.8, and 20.2 µH. Which would indicate Al’s of 385, 358, and 202. Measurements made using series resonance method described in EMRFD. This material shows a very low Q and the resonance dip at 7 MHz was barely discernable. The Al number of 202 at 7 MHz of course shows the fall-off of the permeability above around 4 MHz based on the chart on page 2-48 of the Amidon Tech Data Book. This chart is much different than Kerry’s second link which shows the roll-off starting at 1 MHz. I suppose his is probably the most recent as it calls it a “New Version”. It would be nice to have a consistent set of data.
13718 2017-03-17 10:03:23 Nick Kennedy Re: Toroid inductors - Al values vs inductance charts When I need an FT37-43 toroid, I'm usually grabbing one out of the box that Dan's Small Parts described as "type 43, like FT37-43 but fatter", so I know the AL value doesn't apply. But I'm not generally concerned with the exact inductance value.With powdered iron, I usually *do* need to know the exact value so I measure it. As I said in an earlier and similar thread, the measured inductance is usually higher than predicted so I wind up taking turns off and/or spreading the windings.I consider AL to be something to put me in the ballpark. For ferrite, being in the ballpark is generally good enough.73,Nick, WA5BDU
If the final inductance is important, measure it.
13719 2017-03-17 11:43:13 Andy Re: Toroid inductors - Al values vs inductance charts "Perhaps, the manufacturer datasheets may have to be referred , instead of venders and users."Is it true in this case that the manufacturer would be Fair-Rite, and Amidon would be the vendor?It's hard for lowly users to tell. But it's been said that Fair-Rite is the actual manufacturer of most ferrites out there, and even companies such as Amidon buy their stock from them.Andy 13720 2017-03-17 11:59:13 Dana Myers Re: Toroid inductors - Al values vs inductance charts 13721 2017-03-17 12:27:47 K5ESS Re: Toroid inductors - Al values vs inductance charts
Can’t say whether Fair-Rite provides the material for Amidon or not but Fair-Rite gives an Al of 350 ± 20% for a core equivalent to an Amidon FT37-43.
Part number 5943000201.
So I guess the two values posted in Amidon’s data represents the mid and max values to be expected. And I’m probably making too much out of this anyway .
13722 2017-03-17 21:08:51 Lasse Moell Re: Toroid inductors - Al values vs inductance charts Looked in my Amidon catalogue dated august 1984 :)Ferrit material #43FT-37-43 AL 420FT-50-43 AL 523So it seems the material it self has changed over time or their way of measuring AL has changed.../Lasse SM5GLC 13723 2017-03-18 03:22:48 Lasse Moell Re: Toroid inductors - Al values vs inductance charts Looked in my Amid 13724 2017-03-18 06:47:20 wb8yyy_curt Re: Toroid inductors - Al values vs inductance charts I sense there are enough variables here to keep us speculating for a long time. Need I say someone invented a trimmer capacitor for this very matter.
The nature of RF items -- wire radiators and coils - is such that we live with some empiricism, in spite of understanding the theory - in part because our precision in modeling everything can be less than ideal at times.
Coupled with this - there isn't a huge motivation for exactness in making the core materials (unless we want to spend a lot more for them) - as there are other variables in the winding anyway. I use the wire antenna analogy as we all have had our experience with 468/F in regard to a dipole (see Ward Silver's nice research published on this). our toroids are similar in concept, perhaps one could relate our experience with different soil conditions with the variation in ferrite.
With capacitance of windings involved - this can explain non-linear nature of AL.
Practically, use the tools we have. Maybe W8DIZ still has a toroid inductance calculator at his 'shop' for everyone's free use? We have been blessed as builders by his less than Amidon prices as well as his enthusiasm to encourage us all to build.
Sorry if I repeated earlier remarks, I did skim them. We can let little nuances disturb us in RF, lest we only build things with digital circuitry and software. A good LC instrument is desirable to have. Here I use the humble Elsie that was kitted and graciously handed out for Atlanticon - a simple PIC based frequency counter that computes L or C -- sufficiently accurate for HF building. one can hope that a useful instrument for so few dollars were still sold somewhere, but CW readout works just fine for me.
13725 2017-03-18 16:03:07 kerrypwr Re: Toroid inductors - Al values vs inductance charts As Mike said, the #43 permeability chart that I posted is marked "Newer Version"; I marked it that way as there are two flavours of #43, old & new. My chart for the earlier mix is, naturally, marked "Older Version".
I was alerted to this by Jack, K8ZOA;
The later mix maintains its initial permeability (ui) as u' of about 800 up to almost 1 MHz; the earlier version's ui of about 850 drops quite quickly to a u' of about 600 at 1 MHz.
I understand that manufacturers' Al figures are for 10 kHz (according to Ron Sanders VK2WB who was Amidon's VK agent for many years); since Al is related to ui, that implies that Al is not a good basis for designing at RF as "true" Al is frequency-dependent.
I use the excellent DL5SWB calculator;
which is probably based on manufacturers' Al figures.
It doesn't always agree with my AADE meter or my N2PK and DG8SAQ VNAs.
I think that the AADE meter operates at around 1 MHz, plus or minus.
It would differ from the calculator with, say, "old" #43; with, say, #61, which maintains its ui of 125 as u' up to about 10 MHz, it probably wouldn't differ much. This is theory; I've never actually done comparisons.
A VNA, of course, "tells it like it is".
When using ferrite for RF transformers, one aim is to provide a certain minimum reactance, ie L, at the lowest frequency; use of #43's ui-based Al for calculation at perhaps 3 MHz will not result in a huge design error.
The effect will be that the minimum reactance will be a little less than we wanted but, for many amateur purposes, this may not matter very much.
The effect of u'/Al dropping with frequency may be compensated-for by just adding a turn or two; if a better method than this rather crude one is wanted, measurement is the key to knowledge.
With other materials the Al might be safely used without compensation, eg #61 which maintains its ui, and therefore its Al, to about 10 MHz.
13726 2017-03-19 11:08:47 kb1gmx Re: Toroid inductors - Al values vs inductance charts First toroids are +- 15% for AL. Actual inductance is wider than that due to actual windingand distribution on the core.FYI: every time I buy toroids I test a few with a ten turn winding too see if I get near the bogyinductance or a wild number. Its usually close. I also do that for odd cores as I can thenclassify them and write the worked out AL on them.The other is for any given material especially ferrites the AL does vary with frequency due tochanging mu vs effective mu. A crappy but useful explanation is a AL (mu) is like skin effectfor copper wire. With increasing frequency the depth of penetration for the magnetic fielddecreases. For the moment I'll leave loss factors out, but a weak generalization is they go up.For wideband RF transformers in typical amature use this is not a big problem as you onlyneed to have enough inductance at low frequencies.In the end its a matter of choosing the right ferrite and Type 43 is widely used but not alwaysoptimal and I've used J and type 61 in many cases for lower losses. For many uses whereloss is really important type 2 or 6 (powdered iron) are much better but may require manymore turns for enough inductance at low frequencies.Like someone else said and EMRFD said as well, knowledge is through measurement.Just using what someone else did is what was referred to as lore and without measurementat best a guess. Making the measurements is not rocket science as it only requires basicgear and the willingness to setup an experiment to make basic measurements. Then youknow.Allison/KB1GMX 13732 2017-03-23 02:04:14 John Re: Toroid inductors - Al values vs inductance charts For powered iron cores, which is what one would usually use if looking
for a specific inductance value, Micrometals would be the usual
13733 2017-03-23 08:38:58 email@example.com... Re: Toroid inductors - Al values vs inductance charts I think, the ,material batch changes the properties.
Thus, the best way appears, to evaluate the AL value by 10 turns evenly wound and then use that value for computing the needed inductor turns.
Finally better to cross check across LC meter like AADEs. ( we lost neil)
13734 2017-03-23 14:49:01 Alberto I2PHD Re: Toroid inductors - Al values vs inductance charts