Inductor Values.

[Joe]

I want a 470µH inductor - I'm a cheap date!

I can't buy one for a sensible price but do have some second-hand ones from my TV PCB. However I can't make sense of the colour-coding.

   

The top one is Yellow Violet Brown Silver Silver and the bottom one Yellow Violet Red Silver Gold. For all that they were labelled Lxxx on the PCB they have an immeasurably high (>2MΩ) DC resistance so I very much doubt that they are suitable. I am still curious as to just what they are though.

I can buy two 1000µH ones but can't remember if these would need to be connected in series or parallel to get 500µH.

Thanks in advance

Joe

[Tedzed1]

Hi Joe, Download Electronics Assistant from this site

http://www.electronics2000.co.uk/download.php


May be of some help.

[Mark R]

Tis the sum of individual inductances, you add them in series.

cheers Mark

[Joe]

Thanks, chaps.

That Electronics Assistant thing is certainly worth having.

Cheers

Joe

[pwdrive]

Two 1,000 uh in series would be 2,000 uh ? The series/parallel for inductors is the same as resistors I think providing there is no mutual inductance, not sure what the crack is if there is.

If you are not stuck for space you can unwind an old valve IFT winding down to 470 uh no problem, not to sure about transistor IFT's as I hate transistors.

Lawrence.

[Robert Darwent]

Hi Joe,

I'm not sure what sort of current rating you need, but these look similar to those in your image;

http://www.ebay.co.uk/itm/10x-Axial-Magn...upplies_ET&var=&hash=item3cc3787919#ht_761wt_1037

And these are rated up to 350 mA;

http://www.ebay.co.uk/itm/WUERTH-ELEKTRO...upplies_ET&hash=item3a70f0966e#ht_500wt_1288

Any good?

Regards

[Yorkie]

If you look at the colour code calculator for inductors Joe you'll see that Yellow/Violet/Brown = 470uH - the value that you need. Yellow/Violet/Red is 4.7 mH. Silver = +/- 10% tolerance, gold = +/- 5%. Not sure what the extra silver band signifies. They're far too small to have very high inductance values, and to put the resistance (rather than inductance) of chokes into perspective, I've just measured a 15mH choke and its resistance is 300Ω. A 2uH choke was 1Ω. Although in your pic your little objects do look like small chokes, I wonder if in fact they're very high value resistors, because unless they're open circuit, they'd only have a resistance of a few Ohms - no way would they be in excess of 2MΩ, or anything approaching that, so that's a bit of a puzzler!

(Two 1,000 uH in parallel = 500uH, so if you can get a couple, that will solve the problem).

Hope that helps a bit Joe.

[Joe]

Thanks, Robert. I don't think current will be an factor. I can get all the others I need from Spiratonics but they don't do 470µH ones for some odd reason.

I'll try my luck in Bardwell's some time next week and if they don't have them I'll get those off e-Bay - I've put them on my Watch List.

David - I was confused by the extra band too. According to t'interweb an initial silver band signifies Military Specification but these are at the back end.

I too doubt that they are any good for what I want given that DC resistance; I've checked several with the same result. I've looked at the PCB again and the ones that remain are all marked L-something.

- Joe

[Robert Darwent]

I'll try my luck in Bardwell's some time next week and if they don't have them I'll get those off e-Bay - I've put them on my Watch List.

I'd be surprised if Bardwell's stocks them, but you can always check their website for nothing.

As far as colour coding, they should be just about the same as resistors with minor exceptions. I believe the two silver bands refer to tolerance, as with resistors, and the other may be current rating but I'm not sure.

Regards

[Joe]

You never know with Bardwell's. I'll be passing anyway and it's always worth calling in. Sadly their website only shows a fraction of what they do have, and a few things they don't.

I've just tried putting one of the ones I've got on my megger and on that it reads zero resistance. I know that doesn't test with straight-line DC so I'll have fiddle with a signal generator and oscilloscope tomorrow. I know they're no good for what I want but am getting very curious as to just what they are.

- Joe