Hi,

I was wondering if you have suggestions for inductors for Meyer cell test.

When looking at Valentin Petkov work, he suggests 1.7mH (x2) in some schematics and in some cases, 4.3mH (x2). I am not clear if these are bifilar wound (it seems in some videos they are not) but these appear to be air core.

Lawton suggests 100 turns of 0.7mm wire on a 3/8 ferrite; bifilar wound.

So, what would your suggestions be (to start). Bifilar, or individual. Air core or ferrite?

It seems all parties agree a wire size somewhere between 0,6mm and 1mm.

Appreciate any input. Thanks,

So, I had a go at this earlier today. Digging into Valentin Petkov videos a little more, he recommends a 1.7mH inductor bifilar wound. He states a winding of 380 turns of 0.6mm wire to achieve this. Using some very accurate LCR meters, I hand wound a 1.7mH air core bifilar coil, in my case that took 423 turns to get very closely to 1.7mH. I will update bobbin details later for measurement purposes.

any pictures ?

Sure, I'll try to grab some for you tomorrow. Not a lot to show at the moment, Dan. The inductor took exactly 423 winds of bifilar to bet to 1.7mH on both winds. I'm working on some other stuff today but can send some shots tomorrow if useful.

 yes open source is the way always nice to see more people share some things

Sorry Dan, I wanted to upload here but it is asking for a url. I will find a host but I don't like using them, things dissappear over time. I might use my own site when further along.

 yes I know it is hard to click attach and post on a sharing  forum?

After typing some text if you hit the Preview button you get button that allow you attach an item it's how I upload pictures and documents you just point to file on your system.

Earl

seams easy ,

Sorry, just checking back on this thread i have been out of the country for some time. Thanks for the reminder, Earl. Not trying to hold anything back I was having an issue with the process on the mobile, Dan. My fault, im sure its easy when you are used to it but I don't interact with the forum much so tend to forget the interface.

Here's a picture of the air-core bifilar inductor and the LCR.

The bobbin has an ID of 20mm with a length of 54mm. As noted previously, 423 turns of 0.6mm wire, carefully bifilar wound. I am waiting on capacitors to continue my work. More later.

Continuing on my journey, I find that ferrite core is indeed important for the inductors, so I am exploring the work of folks that have been successful and have published details on their windings. I am sure there are more but I start with lawton. He states using 100T of 0.71mm (21AWG) on a 9mm diameter ferrite rod single wind. Reproducing this on my rod results in 538uH @ 1kHz measured. Of course my ferrite could have different specs. He does not specify this. He also states it is 1" long. But doing the math this is obviously impossible in a single layer (0.71mmx100T would be 71mm minimum). So, the question then is: how accurate is anything else he says. I don't know at this point but we will explore it anyway.

Heres a picture

I do this just for interest, to see if commonalities in inductance occur between references i find. Next, I will attempt reproduction this bifilar choke https://youtu.be/pAdyXI-83uU which is bifilar and stated as 1mH.

I also picked up a new ferrite U core, U126x91x20-CF13 with the intention of following some of valentin petkovs latest work with the scr variant.

Specifically, I refer to this video. https://youtu.be/qOSV-oSneOA

Other hints from Stephen as highlighted

nice

Thanks, Dan. So, moving ahead slightly to the U Core (8XA) I need a bobbin, I also need some idea of the wire length necessary to produce the bifilar wind counts (detailed below Valentins video). I did some basic calculations on this, and two 500gram spools should be enough to achieve the winds necessary. I should have those to hand. Each spool caries approx 70M of wire, with a spec of
0.012ohm/Meter for 1mm wire. My estimation has me at around 53M of wire to achieve the turns ratio. Again, to be tested.


Here is the basic bobbin design I made a moment ago that will be 3D printed, I will print this in three parts; one Centre and (2x) End pieces which will be glued on afterwards. Dimensions are 120mm height (internal) and I kept flanges the same (120x120). The ID of the Middle tube is 30 x 21 and wall is 1.5mm thick. I hope this should be enough. We will see. I am going to try printing this today, and will glue it all together afterwards. More soon.

First part prints out fine and is a pretty good fit. We will see how it goes with other parts

Here's the result of the final print. The square hole in the end pieces were designed such that when printed they have a 0.1mm gap, this resulted in a good/tight push fit with the centre tube straight off the printer. I might not need to glue it but may "weld" the meeting joints with heat (soldering iron, plastic welding) to prevent them coming apart easily. Winding will be next but I may need to order some parts. More soon

looking good

Thanks, yes taking shape. I have to sidestep to variable psu today and order things. I got my varaic and rectification done. I need a bleed resistor for safety, though. These caps store a lot of power.

Variac > kbpc5006 (rectifier) >  2x 1000uf/400v vishay caps (parallel) > DC (ish) out

All a bit messy at the moment, but we will tidy this up later

notes

https://youtu.be/PdbOrnHJKWg

Input: 220 Volts / 50 Hz
Half-wave unipolar frequency next the Graetz - 100 Hz
Gate frequency to the Optocoupler`s input - 51Hz (or 49 Hz) / 50% Duty-cycle
Anode Inductor C1 - 400 turns
Cathode Inductor C2 - 404 turns*

How to "fine tune" the Cathode inductor "L2":

If "L2" have exactly 400 turns /like L1/ - the Waveform is "most Positive":
 
If "L2" have 410 turns /10 turns more/ - the Waveform is
"non symmetrical" - the Negative voltage outweighs the Positive voltage:
 

Thanks Dan. Im going to remove the caps for any scr versions when I get to that point. I see that we need the half-wave recified output there. I thought it would be good to have the caps here and tested for gated versions later though (plus I'm using the psu for other tesla coil/bulb developments) I need to put together a test cell soon then steer back to the circuitry. Thats next on my list after testing the bifilar winding of the ferrite rod. The one from this video: https://youtu.be/pAdyXI-83uU

Related. Has anyone tried an SSR in place of the SCR plus opto combination with the 8xa? I'm not the best expert on all variations but it seems to me it might work, no?