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Trying to measure crossover coil inductance... inaccurate results?

N

nonsub

pfm Member
I am trying to find the values of some coils that the labels have fallen off for. When I test two known pieces (one is a .28mH, the other 3.5mH) the results are consistent each time but the first is about 12% low/off and the second maybe 16% low/off.

I've tried with 2 different meters. They are both cheap devices one is a dedicated LCR and the other has transistor/diode, ESR features as well. Both report values lower than expected and are within maybe 5% of each-other. Yes I zero the devices. Capacitance measure perfectly.

So is it possible that you don't measure coils just by attaching LCR directly to stripped wire ends?

On same subject... is there a proper way to measure inductance and capacitance of a wire pair? My thought is that for inductance I would connect the meter to wire A on one end and wire B on the other. For capacitance just to A and B on the same end (open on other end.)

Thanks for any help!
 
One thing I found on one meter that is now giving me better readings (but still low) is to use the "BIG inductance" setting from the manual ("Test frequency: L/C about 500KHZ Big inductance about 500HZ")
 
They do generally have poor tolerance. I use Jantzen coils which are quite tightly toleranced and each one is measure individually. I measure mine with my DATS which I have found to be very accurate.
 
nonsub said:
One thing I found on one meter that is now giving me better readings (but still low) is to use the "BIG inductance" setting from the manual ("Test frequency: L/C about 500KHZ Big inductance about 500HZ")
Click to expand...

You have discovered what I was about to say. Most meters autochange the frequency to keep the readings at a range where the meter is sensitive. If it is measuring beyond audio range then the reading will have a lot of error. With my old 'Peak electronics' LCR I keep an aircored 1.6mH around, and if necessary connect it in series with the unknown. I subtract the DCR and inductance of the 1.6mH from the total. This gives a better low frequency reading with a meter using a feeble battery. Inductors will vary from spec with frequency much more than capacitors. There are different types of ferrite or metal core, and no reason why they should choose the best for audio. Power rating is very important. Personally, I would just buy from Falcon and keep a UK supplier who does an excellent job going.
 
Thanks for the replies guys. The coils are Solens which claim to be highly accurate. I'm actually moving to active xo but am trying to understand the 4-way xo I've pulled out.
 
Hey orangeart. I'm using a MiniDSP 4X8 running into 3 X NAP250.

First I want to just seperate off the bass driver ... biamp because I will probably be satisified with that BUT I would also like to see how to tri-amp but with that I will need to keep the tweeter - super tweeter crossover.

So really what I'm trying to do is figure out where to chop, what the current xover frequencies and filter types are.

Will post pics when I wake up. Thanks for looking!
 
Actually here's a pic. Looks like an abomination.

I am making a diagram with part values (which was why I was trying to get accurate measured values.)

11rt3dz.jpg
 
Are you trying to measure them in circuit? If so, you'll need to lift one end to get a good measurement.
 
You need to measure them with both ends disconnected and ideally away from any other component or metal.

What frequency are you measuring them at? they will be wound to be a certain inductance at a particular frequency.
 
London Lad said:
Can you set it to measure at 1k ?
Click to expand...


No. I don't know what rhyme or reason there is to these 2 cheap meters. One of them has a high and low LC button.

Anyway the good news is that I found some of the missing labels. Sods law though the one I'm most interested to know the correct value for is missing. The lowest frequency setting on the meter was around 6.5kHZ and this gave a value for that coil of 5.87mH... so I'm guessing it's 6mH.

I spent the whole day trying to trace the connections and make diagram. I've never made a schematic before. I'm hoping someone would be kind enough to look at this and help me validate/plan. Might be some beers in it even :) I'm hoping to avoid frying amps and drivers as this is what led me to this project in the first place!

OK so here's what I want to do:

First note that I've split into two circuits. The original configuration was bi-wired to a single amp.

Part A:

Verify diagrams are correct
Determine filter type and frequency being used for the bass driver
Determine which parts to "snip" in this current crossover to leave me with passive for mid-tweeter-supertweeter
With that info I will be able to separate the bass driver out and use the dsp to filter/xover


Part B:
Determine filter type and frequency being used for the mid to tweeter+supertweeter section.
Determine filter type and frequency being used for tweeter to supertweeter (just for knowledge)
Determine which parts to snip to separate out the mid.
With that info I will be able to use 3 amps. I don't think I will bother going this far but would like to know.

Not sure if I ought to make a separate thread for this.

Thanks!


Diag: http://i67.tinypic.com/2kh6zb.png
Photo:
11rt3dz.jpg
 
Surely you have two of them? Are they both faulty?
Measurements can be made quite accurately with a laptop and a little software.
 
http://s842.photobucket.com/user/stephenclifford/media/buildthismonitorspeaker-hi-fians-aug75-xover.jpg.html
david ellwood said:
Surely you have two of them? Are they both faulty?
Measurements can be made quite accurately with a laptop and a little software.
Click to expand...

Yes but this is my only music source and I "cannot" get by without music for the amount of time it will take.

Also nothing is faulty, I just cut connections and glue is undone.

I'll be happy if I can at least separate out the bass driver... obviously I can just snip those wires and run them directly to the amp but hopefully wouldn't it be beneficial to take out the uneeded coil (or is it 2?) and cap(s) ?

Also this is probably very similar in fact I am using B110 + B139 drivers:




thx
 
... so for starters if someone could confirm that cutting out L1, C1+C2 is the correct way to remove the bass crossover that would be great. thx
 
Sort of..it would be nice to confirm what the mesh at the top [c3,l2,c4,c5,l3,r1] is doing. As you have drawn it, it isn't crossing anything. Can you check it doesn't join anywhere?

It is true that they sometimes have seperate blocks just to flatten the impedance curve - KEF loved that sort of thing. It seems a lot of expensive parts doing not much.
 
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