Winding specs for 3H, 5H, 7H inductor on E20 lams and bobbin

[volker]

So are you saying that if I use for instance 0.25mm gauge which can take 860ma of current that i should be using a gauge of wire that can take much less?
Would like to know a bit more about what you have said, as allowing for lower current, your saying that the current will only be 150ma.
I'm confused on this!!

A certain wire diameter does not have one fixed maximum current. The maximum current is chosen/calculated based on the core size and a temperature target. On a bigger core the wires will heat up more at a particular current than on a smaller core since convection is worse for inner layers and they are stacked higher. There are tables for differenct core sizes where you can find recommended current densities based on the temperature the transformer should be run at. So the bigger the core, the lower the recommeded current will be. It doesn't matter for your choke, but for a tube power transformer for example you would have the heater windings on the outside since they carry the biggest current. That way they cool better and can be run at a bit higher current density than the inner layers.

 

[vari-mu]

HI Spencerleehorton!
I think you need to wind 1800-2000 turns of 0.25 - 0.27mm wire and make the gap of 0.12 - 0.15mm.
  Good luck!

 

[Spencerleehorton]

Thank you vari-mu, that was one of my next moves to wind something around the 2000 turns area, thanks for the gap info, will try that and post the results.

I have a micrometer so can measure the 0.15mm

 

[trobbins]

You can make inductance measurements with DC using a relatively simple test rig that I find very convenient for chokes:
https://www.dalmura.com.au/static/Choke%20measurement.pdf

 

[Spencerleehorton]

I have an inductance meter which is fairly accurate but will look into what you have shared.

 

[abbey road d enfer]

I have an inductance meter which is fairly accurate but will look into what you have shared.

Does your inductance meter operates at 100-120Hz? Does it have DC bias?
If not, it gives only a very approximate measurement.

 

[Spencerleehorton]

It's a fairly accurate inductance meter as I've tested it against a 5k inductance test equipment at the local transformer company and it delivers the same result.
Also tested bought inductors and transformers and they measure to what they are specified at, so I'm pretty confident the meter is good.

 

[Spencerleehorton]

Well with 2000 turns I get 4H at 88ohms, with a 0.15mm gap.
Will wind one more at 1850 turns and see what I get.

 

[Tubetec]

I have one of the budget LCR meters , anything in terms of psu choke Ive ever measured came within a reasonable ball park of its on paper spec ,at any frequency upto 10khz . With a smoothing choke were primarily concerned with whats going on at 100 or 120 hz not dc. Yeah ok +/-20% inductance tollerance ,it makes no odds one way or another in a smoothing circuit

 

[abbey road d enfer]

It's a fairly accurate inductance meter as I've tested it against a 5k inductance test equipment at the local transformer company and it delivers the same result.
Also tested bought inductors and transformers and they measure to what they are specified at, so I'm pretty confident the meter is good.

That means the meter is good for measuring transformers, not chokes that have DC in them.

 

[abbey road d enfer]

I have one of the budget LCR meters , anything in terms of psu choke Ive ever measured came within a reasonable ball park of its on paper spec ,at any frequency upto 10khz . With a smoothing choke were primarily concerned with whats going on at 100 or 120 hz not dc. Yeah ok +/-20% inductance tollerance ,it makes no odds one way or another in a smoothing circuit

You seem to forget that DC in a choke considerably reduces its inductance.

 

[Spencerleehorton]

Well I'm not aware of how dc reduces inductors, it's all news to me!!
I'm just going by, I've measured a 3H inductor commercially made and it reads as 3H on my inductor meter, the inductor I've just wound reads 4H, so I must be in the ballpark with it!!?

 

[abbey road d enfer]

Well I'm not aware of how dc reduces inductors, it's all news to me!!
I'm just going by, I've measured a 3H inductor commercially made and it reads as 3H on my inductor meter, the inductor I've just wound reads 4H, so I must be in the ballpark with it!!?

Many chokes' nominal value is taken without DC in them, but they are by definition used with DC in them! But good specs indicate the inductance value with a certain value of DC in them, some even indicate two values corresponding to different conditions.

 

[Spencerleehorton]

Ah ok well I think I understand what your getting at.
So I should put some DC through the choke and then measure to be sure?
It would benefit me if you know of a simple test procedure to share and i will test.

 

[trobbins]

I suggest it won't be easy to make a measurement with DC and using your existing inductance meter.  The DC connection would have to exhibit a relatively high impedance to the AC signal used by the inductance meter, and not harm the inductance meter.  Can you manage to ensure that?

Otherwise I suggest post #23.

 

[Spencerleehorton]

Ok trobbins,  I'll see if I can set that up!!