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Old 14th April 2004, 07:13 PM   #1
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Default Inductance Meter

I would like to wind my own inductors. Can someone reccomend an inductance meter?

In the spirit of DIY, I have found the following kit:

http://www.rainbowkits.com/kits/ia-1p.html

Will this provide me with resonable measurement of inductance. I figure 2-5% would be good enough.

Cheers.
GM.
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Old 14th April 2004, 09:18 PM   #2
Ron E is offline Ron E  United States
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The standard formula is accurate to 2-5%


from:
http://geoffreyegel.tripod.com/wheeler.htm

-----------------------------------------------------------------
L (uH) = 0.8 * a^2 * n^2 / (6*a + 9*b + 10*c )

where
a = average radius of windings
b = length of the coil
c = difference between the outer and inner radii of the coil.
all dimensions in inches.

It states that it is accurate to 1% when the terms in the denominator are
about equal. This is also an equation by Wheeler. It applies as long as the
coil has a rectangular cross section.
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Old 14th April 2004, 10:15 PM   #3
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Jameco sells a kit which attaches to a DVM -- it's OK. There are still Heathkit RLC bridges which are acurate to a few percent and these go for less than $20 on the Bay.

I use a GenRad which I bought for $50. There's always one on sale on EBay:
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Old 15th April 2004, 12:32 AM   #4
Ron E is offline Ron E  United States
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I have wound several coils with the formula above, and they are quite accurate. There is no need to buy an LCR meter.

If you HAVE to measure because you don't know math or you don't trust me or whatever other reason you might have, inductance can be measured by other methods. The best is probably to build a wallin jig and use speaker workshop to measure your coils. Then you can measure speaker parameters and frequency response and all that as well as simulate your crossover before you buy or make the components.

I find inductors are a waste to wind as they end up costing only a few percent less than store bought unless you have a cheap source for wire. It is tedious work even with a winding jig.....

LCR meters are for sorting large quantities of unmarked components, I don't feel they are useful for anything else, and they are a stupid purchase for a DIYer unless you already have ALL the tools needed for making and measuring speakers, or if you have money to waste....
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Old 15th April 2004, 01:42 AM   #5
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Quote:
Originally posted by Ron E

I find inductors are a waste to wind as they end up costing only a few percent less than store bought unless you have a cheap source for wire. It is tedious work even with a winding jig.....

LCR meters are for sorting large quantities of unmarked components, I don't feel they are useful for anything else, and they are a stupid purchase for a DIYer unless you already have ALL the tools needed for making and measuring speakers, or if you have money to waste....
tell me, how can you tell if an inductor is within a 2% tolerance when you don't have a high quality LCR meter/bridge?

how can you tell the inductance if you use a ferrite or iron powder core? how do you characterize a core without a meter?

how can you tell the primary impedance of an SMPS transformer without measuring it?

i guess it depends upon how serious you are about your avocation.
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Old 15th April 2004, 03:16 AM   #6
Ron E is offline Ron E  United States
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Quote:
Originally posted by jackinnj


tell me, how can you tell if an inductor is within a 2% tolerance when you don't have a high quality LCR meter/bridge?

how can you tell the inductance if you use a ferrite or iron powder core? how do you characterize a core without a meter?

how can you tell the primary impedance of an SMPS transformer without measuring it?

i guess it depends upon how serious you are about your avocation.
First question, you measure it with a series resistor at several frequencies and do a little math to figure out DCR and L. How many frequencies does the typical cheap LCR meter measure at - usually 1 - like either 400 or 1K?

How do you know your uncalibrated 35 year old piece of electronics bought off of Ebay from someone you don't know is accurate to 2%?

Tell me where you can buy silicon iron laminations or audio ferrite at small quantities. If you want to characterize a core for audio use, you need to be able to vary frequency. Some have a nonlinear mu...

You can measure a SMPS transformer windings with a signal generator as well. What makes you think the original poster wants to build Switch mode power supplies

Remember the question. THe guy wants to measure an inductor. There is no need. The wallin jig, built for $20-30, will get one a lot farther in this hobby as a beginner than an LCR meter. You can measure LCR and S, for speaker

I guess it all depends on how practical you are with other people's money when making recommendations.
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Old 15th April 2004, 04:35 AM   #7
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Quote:
Originally posted by Ron E

First question, you measure it with a series resistor at several frequencies and do a little math to figure out DCR and L. How many frequencies does the typical cheap LCR meter measure at - usually 1 - like either 400 or 1K?

Tell me where you can buy silicon iron laminations or audio ferrite at small quantities. If you want to characterize a core for audio use, you need to be able to vary frequency. Some have a nonlinear mu...

Remember the question. THe guy wants to measure an inductor. There is no need. The wallin jig, built for $20-30, will get one a lot farther in this hobby as a beginner than an LCR meter. You can measure LCR and S, for speaker

The series resistor way of measuring inductors for me, with 1% resistors, were within 5% of what some digital LRC meter had told me.

Place in NH (forgot the name) has type M5 EI silicon iron laminations (and others I'm sure) for about $3 a pound.

Why didn't you tell me about the wallin jig when I needed it
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Old 15th April 2004, 04:39 AM   #8
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Quote:
Originally posted by Ron E
How do you know your uncalibrated 35 year old piece of electronics bought off of Ebay from someone you don't know is accurate to 2%?

uuuhhhhh, could be becuz I got a Physics Lab with standardized (NIS) Leeds n Northrup equipment.

secondly, if you can measure time acurately, you can dependably measure inductance.
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Old 15th April 2004, 06:44 AM   #9
sam9 is offline sam9  United States
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Look at this :

http://my.integritynet.com.au/purdic...er-project.htm
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Old 2nd October 2004, 09:14 PM   #10
extremy is offline extremy  United States
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Default LCR meter,

If I have ranges on my LC meter that are labeled, 2mH, 20mH, 200mH, and 2H. How do I use the ranges? Do I multiply by 2?

I wound up a small 24 gauge inductor. By measuring with the meter I got .44mH on the 20mH range. I took off some wire and remeasured and lost a few mH, it read .41. So I took off a few more turns and its reading .33mH

I need an inductor for sending the subwoofer signal to the sub, so it sounds like I need between 3.5 and nearly 5mH. I'll need a lot more windings than I tried for the test.

Someone had mentioned one of the spreadsheets that have an equation,
L = 0.8 * a * N / (6a + 9l + 10c) uH
Where
N is the number of turns.
a is the average radius.
c is the height of the windings
l is the length of the coil.

But, as I figure this formula from measuring what I have on my coil, this equation isn't even close. { Just my observation on this test. }

Any ideas welcome!
Greg
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