Inexpensive open frame Relays

It might help to complete the magnetic-field path around the ends of your coils. You can use iron bars, be sure cross-section area is much-larger than your coil cores.

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 Thanks, 
    - Win

The pair of coils from an alarm bell?

I tried that and it got worse, A few minutes ago I removed all external magnetic path and It all got better, in that I could go further into saturation and get to 0.68uh. However, that is using my DE5000 LCR meter. I just found, using me DE-5000 at 100kHz I can adjust the 100uH inductor to 34Uh with Magnetic bias, but when I check it on my Boonton

260A Q meter the inductance at 850kHz is 89uh. Back to the drawing board. If you have any suggestion about a material that will work from 500kHz to 4MHz and saturate fairly easy, pass it along. Or even a physical layout that would saturate easier. Here's what I'm doing now.

Mikek

The coils should be polarized the same way.

--
 Thanks, 
    - Win

I'm thinking about looking at some automotive relays. They may have a coil with a higher Magnetic field. Mikek

Yep, that makes a difference, I can tell when I have the clip leads wrong. Mikek

Most relay coils don't need all that much field. Solenoids need lots of field, especially strong ones. Many types work at quite high currents, with frame-mounting provisions for heat removal.

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 Thanks, 
    - Win

This large solenoid with an iron rod in the core works. I got at it to go from 127uH to 8uh with 12V @ 380 ma. At 8uH the Q is 60 at 2.5MHz. This is a larger core than I have been using, because it fits the solenoid geometry. I like this, I can get litz wire on it.

Mikek

Mikek

Whoa, where'd you get that, what's its story?

--
 Thanks, 
    - Win

I've had 8 of them so long, I don't even know where I got them, I think it's been more than 25 years. I had dreams of making a V8 solenoid engine with them. :-) I woke up! Hart-Advance 402511560-AX, No hits on Google. I may work on the magnetic circuit a little to see if I can increase the saturation of my core. What is the plunger made of that it doesn't have residual magnetism? I cut an iron rod to make the core, but could cut the original plunger if it would work better. It's made for 115V AC with a 25 ohm coil, 12V is where I have tested it. Doubling that doesn't get much reduction in my inductor and then the solenoid starts to warm up. 12V may be as high as It should go. I should find out if it is made for continuous operation. But it does seem to warm at 12V.

Mikek

Just wind a DC wire onto your toroid and forget using an external field. Toroids are designed to enclose their field, which means they reject external fields too (unless they're massive).

Clifford Heath

Ya, that has problems too. the windings couple, so the DC winding is trying to drive the impedance of the power supply and this loads the original inductor. This whole project may have too many problems for me to overcome, but I have to solve the first problem before I can work on the second one. I'll continue until, I get to frustrated.

Mikek

So decouple the DC drive with a large (RF) inductive impedance. It'll still work fine at DC. They make fluxgates that way, and those seem to work.

What size inductor do I need at 500kHz? Where do I get one that will also work at 4MHz? Mikek

maybe take a small split bobbin E-I mains transformer remove the "I"s and one of the windings and wedge the ring core into one of the gaps

eeeeeeeeeeeeee eeeeeeeeeeeeee _________eeeeeeeeeeeeee RRR RRR eeee RRRRR RRRRR eeee RRR_________RRR eeee eeeeeeeeeeeeee eeeeeeeeeeeeee eeeeeeeeeeeeee eeeeeeeeeeeeee eeeeeeeeeeeeee eeeeeeeeeeeeee eeee eeee eeee eeeeeeeeeeeeee eeeeeeeeeeeeee eeeeeeeeeeeeee

eeee silicon steel "E" core from a transformer RRRR ferrite ring core (major axis pointing up the page) if it works you may be able to find some U cores of the right size.

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  When I tried casting out nines I made a hash of it.

An order if magnitude (500KHz-4MHz) is easy enough, but you're asking the question the wrong way.

What is the required turns ratio between your variable coil and your DC coil? What is the transformed impedance that's acceptable? Then choose your series inductor to have 10x (or more) that impedance at 500KHz.

Clifford Heath.

My first iteration was using E core laminations from a transformer. It's been a few months and I think the problem was I couldn't get enough turns on it to make it saturate the core. I did have two ferrite E core pieces with a large gap. I put about 600 turns on each leg. This worked, but it was from my junque box, I have no idea what the material was and I don't want to pay for the ferrite Ecore and have it gapped. Here's a picture of that.

or

Mikek