I did not say parallel, I said series, which would be identical. Black box electronics, if you have an ideal coil with a 100Ω resistor, or a coil with 100Ω in the windings, you could not tell the difference.

Tesla23's quote of yours is from post #43, where you didn't say series and you didn't say parallel; you said "add an external resistance".

In post #50, you said "The wire resistance is in series, not parallel though. An equivalent circuit is the 100Ω is series with an ideal inductance.". This is the only post where you used the word "series" in this connection, but you weren't talking about where to place an additional resistance, you were just pointing that the resistance of the wire making up the inductor is in series.

In post #54, again you didn't say series or parallel; you said "compensate".

You're not the first to make the assumption though, I wonder why? It seems obvious to me.

In post #57, you said "I was thinking of a lower ohmage part, I saw several during my search.", but you never posted a link to a 6H inductor with less than 100 ohms, nor did anyone else. The only lower ohmage parts from your link http://4sale.sbszoo.com/inductors.htm are less than 6H, and are mechanically too large.

It's because all the inductors that people had found on the web, and had mentioned in this thread, that were 6H, had substantially more than 100 ohms, so everybody could see that adding resistance in series wouldn't reduce the effective resistance. Therefore, they figured you must be thinking that adding resistance in parallel would do the job, since that was the only other possibility other than adding in series.

All this is why people made the assumption:

You're not the first to make the assumption though, I wonder why?

 

@Bill_Marsden
I have Noticed that some of your answers in this thread is a bit to much patronizing. I could be that you just have a direct style of writing and do not mean any harm at all. But as long as most of the people in this forum do not know you in person, they can be offended by your direct style. Also remember that the skill and education level in this forum cover a broad specter. A thing obvious to you may not be so obvious to other. An example is how the add on resistor should be connected in series or parallel. After all, the posters in this thread was only trying to help.

 

@Bill_Marsden
I have Noticed that some of your answers in this thread is a bit to much patronizing. I could be that you just have a direct style of writing and do not mean any harm at all. But as long as most of the people in this forum do not know you in person, they can be offended by your direct style.

I've been here a over a year and have never had a problem with Bill's style. He certainly has never meant any harm. I just reread all his comments in this thread and they don't seem patronizing or offensive to me. You really have to judge someone over the long term here. Everyone makes mistakes and has off days, or rushes a post without thinking about how it can be misinterpreted. Anyway, Bill is one of the good guys.

I was able to follow Bill's point about the inductor and resistor in series. My first thought was also that most of the inductors had higher resistance, so maybe he meant parallel resistor which wouldn't work. But, I knew Bill would know the equivalent circuit for an inductor and gave him the benefit of the doubt. He commented after there was a suggestion to use an opamp circuit (a very good suggestion by the way). I"m sure he was thinking "If you're going to go to that extent, just find a bigger 6H coils with less than 100 ohm resistance and compensate".

The assumption that Bill did not know such a basic thing continued even after he clearly stated "series resistance", so it's no wonder he was assertive in his defense.

 

Funny thing is, I toned it down a bit after the first entry. There have been posts I've deleted (you can do that here, unusual as that is) after the heat of the moment. I most definitely don't try to offend, quite the contrary. I generally try to give beginners thoughtful answers that will answer their questions to a level they will understand, and scale up to the professional level, such as the OP. If you read back you will find a small tiff between a Mr. Millwood and myself, I deleted my comments so as to not distract from this thread, and frankly I expect him to return under another name. He managed to stir up enough people by deliberately misunderstanding posts (which was done in this case), making insulting and snide remarks, and otherwise being deliberately obnoxious his welcome was plum wore out. In the year and a half I've been here that is a first, this site is among the most open I've ever met. Nowhere can you indefinitely edit your posts (though it keeps copies of the previous posts forever), delete entries without a time limit, upload large files, and are basically trusted to be a responsible adult without any fuss or proof who you are.

If I make a brain fart (it happens) I acknowledge it and apologize if necessary, since that is the other side of integrity. In this case I didn't say anything out of line, so I didn't and don't feel the need to correct anything.

In post #13, I pointed to several vendors. Some of them have quite small 6H inductors, though not as small as the OP's, but not the monsters I though 6H would have to be before this thread. Frankly I've never run into such large inductances before, most of the stuff I deal with is the other end, RF, power supplies, and such. Mounting them is going to be a pain, but you can still buy reasonably small units that would replace the problem unit, and adjust as I indicated.

I'm currently working 7 days a week, so I'm not spending as much time on the site as usual. Being a confirmed addict, it will take more than that to keep me off though, although I may not have as much time to review my replies as I would like. I am not anonymous, you can find out all about me here...

Bill's Index

 

Bill, did you actually find a 6H inductor with less than 100Ω DC resistance somewhere on the web? Can you post a link?

I think a big part of the reason your post confused me was that even though we all know that if you could find an ideal 6H inductor, you could certainly make it have 100Ω series resistance, the OP wanted a real inductor. Since all the real 6H inductors that people had found (as far as I could see by following the links posted) had series resistance greater than 100Ω, it seemed that any suggestion made to help the OP with the available real inductors would have to offer a way to get the resistance back down to 100Ω. (I actually thought about suggesting that he build an opamp based negative resistor, and put it in series with one of the available inductors, but the gyrator seemed a better option.)

Clearly, putting a resistor in series wasn't going to do it with the available real 6H inductors, and the only other option was to parallel a resistor. I assumed that you were having a brain fart, which is why I asked "What is to be done if the 6H inductor already has 500 ohms resistance?"; maybe some had a little less than 500Ω but certainly more than 100Ω, which was the case for all the 6H inductors that had been found on the web as far as I could see.

I sometimes find your contributions a little terse; adding an extra word or so can avoid ambiguity. For example, in post #43, you could have said "...then add an external resistance in series...", and there would have been no mistaking your intent.

Anyway, I expect your contributions to the forum to continue to be a net benefit as they have been so far.

 

Tired computing has put my foot in it again. This vendor (the one I mentioned earlier) jumps all around it, such as 3.5H at 39Ω and 2.5 at 17Ω, or 7H at 170Ω, but their small inductors (the ones most likely to be direct replacements and fit in the same foot print) are 6H at 500Ω. It took me around 20 minutes to find that guy, I'll browse around and see who else is out there.

**************************

Guess I got lucky with that vendor, electronics surplus seems to be the best search words. I'll keep my eyes open, but I just spent almost 2 hours on it (guess I can sympathize with the OP a bit more).

The gyrator idea is looking better all the time.

I'm wondering how they wind a toroid? I can't imagine it is by hand for a lot of windings. As I understand it the shape boost the apparant inductance (but not too sure about that). Does a transformer shape (two loops of laminated iron around a coil) do something similar?

 

Bill:

"I love you man" (quote taken from old beer commercial as you may recall).

I appreciate the effort all have made; sorry for any caused fussing. I took no offense from anybody as of this point, and found all comments constructive.

Yes I too was amazed in the value of the "inductor from hell"

Search you tube on how to wind a toroid transformer, and you will be amazed. It is quite a magic trick:

http://www.youtube.com/watch?v=6lvm3FGTHSI&feature=related

I kind of gave up on looking....unless someone has any other ideas...

Aram

 

I remember from Star Trek, that they used something called a warp coil. Perhaps you should get your hand on one of those . Well kidding aside. you may perhaps try the OP amp gyrator. At least as a temporary solution. If you use a AD817 (8 pin DIL). You may the 32 volt power supply. As it can work with voltages up to 36 volt (single supply). Very few components are needed so you should be able to make something small, that fit in on a prototyping boards.

 

Hello,

During a search on the internet I stumbled upon this little program:

http://www.dl5swb.de/html/mini_ring_core_calculator.htm

It can calculate inductors on ringcores,

Greetings,
Bertus

 

Hello,

During a search on the internet I stumbled upon this little program:

http://www.dl5swb.de/html/mini_ring_core_calculator.htm

It can calculate inductors on ringcores,

Greetings,
Bertus

I ran this program for the ferrite core FT50-H which has a relative permeability of 15000 and appears to work in the audio range. The core has OD=0.5 inches, ID=0.281 inches and h=0.188 inches. A 6H coil requires 859 turns which works out to 43 ft. This can yield less than 100 ohms with a small wire gauge. For example, 40 ga wire would have 45 ohms. It seems that 40 ga or smaller wire at 859 turns would fit on that core without a problem.

The videos give you a hint how you can wind such a coil yourself. It will be very time consuming and tedious. You'd have to make a special spool that breaks open and allows the core to go over it. Then, you have to wind 43 feet of wire on that spool. Then, you have to slowly wind the wire onto the core.

Use the thickest wire practical which can fit on the core. This makes winding easier, but results in too low a resistance. Then use Bill's idea to put a resistor in series to get 100 ohms.

It can be done, if you are motivated enough.