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Old 20th Jan 2020, 12:44 am   #1
Uncle Bulgaria
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Default 'Ferrite Pot Core Pairs'?

Ahoy,

I'm considering making the capacitor leakage tester and reformer featured in 'Everyday Practical Electronics' of September 2012. One of the parts it requires is a small, PCB-mount transformer ("ferrite pot core pair, 26mm OD, with bobbin to suit"), with instructions on how to wind it. The parts needed are available from Jaycar in Australia (LF1060 and LF1062 for the accompanying bobbin) where the design is from, but similar search terms come up blank around here.

In general, threads I've found on transformers on this forum suggest that the days of buying parts for one's own winding are gone for whatever reason. The Variable Voltage Technology company mentioned in another thread has broken links for their 'kits' page (I was interested in making some for a Mullard 5-10 possibility with a friend).

Are parts for this little PCB transformer around, and in 2020 are there any options for buying new laminations and parts for larger projects?
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Old 20th Jan 2020, 1:12 am   #2
G0HZU_JMR
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Default Re: 'Ferrite Pot Core Pairs'?

It might be worth posting up any info about the winding and the inductance and if it is designed as a gapped core.

The equivalent pot core might be something like this '25mm' 3H1 core below but I think more information is needed.

I think the pot core pair below is specified as ungapped.

https://uk.farnell.com/ferroxcube/p1...ngdom%2Fsearch
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Old 20th Jan 2020, 9:21 am   #3
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Default Re: 'Ferrite Pot Core Pairs'?

Jaycar parts look like the standard mullard jobs. Iíve got a whole box of mullard/philips/ferrox pot cores and bobbins floating around somewhere. Iíll dig it out this evening and see what I can find. May be a match!

If I donít reply please PM me so I donít forget. Got busy day with work unfortunately first

Edit: part is philips FX 2240

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Old 20th Jan 2020, 6:37 pm   #4
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Default Re: 'Ferrite Pot Core Pairs'?

FX2243 was the pair that everybody wanted in the early seventies, for the PE Scorpio electronic ignition project 😄
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Old 24th Jan 2020, 6:32 pm   #5
Uncle Bulgaria
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Default Re: 'Ferrite Pot Core Pairs'?

Thanks all. I haven't yet decided to do the project or not (though a reformer/tester would be a good wheeze).

G0HZU_JMR - the quoted text is all the magazine gives as a specification - the diameter. Not having gone through the circuit I'm not sure what the transformer does. Thanks for the Farnell link. I did have a look but as I've never wound one before I wasn't sure what components are required, what they look like or how they fit together. Most of what I've read concerns the larger E I type.

Is winding transformers just something not done these days? Is there anywhere to buy the relevant parts (particularly for high-voltage valve stuff)?

Aub - My MGBGT came with electronic ignition, so no need for that project just now! However, the battery has just gone so some electrical work is required.

MrBungle - Thanks. Did you find something? I'm away this weekend but I'll be back on next week and will decide whether I'm going to make this. At the moment I'm awaiting a meter for the ESR meter there was a long thread on in about 2011. I've done the perfboard and am now considering a case...
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Old 24th Jan 2020, 8:24 pm   #6
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Default Re: 'Ferrite Pot Core Pairs'?

Still haven’t had a minute to attack the cupboard yet. Will let you know when I do. Hopefully tomorrow if nothing goes wrong
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Old 24th Jan 2020, 8:32 pm   #7
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Default Re: 'Ferrite Pot Core Pairs'?

I'm pretty sure Farnell and RS stock ferrite cores, bobbins, clips, wire, tape. Yes, winding is done, though not so often by hobbyists so the hobby suppliers don't stock much stuff, and the industrial suppliers aren't so geared up for the odd £10 order.
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Old 24th Jan 2020, 10:19 pm   #8
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Default Re: 'Ferrite Pot Core Pairs'?

RS tend to throw out a situation where you can buy two ferrite cores for £1 and then you have to buy a bag of 100 bobbins for £45 or something ridiculous.

I decided to take the cupboard to bits entirely and reorganise it this evening but the box of ferrites is completely missing. Not sure what happened there. I will ask Mrs Bungle if she’s moved of filed any of my stuff when she gets back from getting trashed
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Old 24th Jan 2020, 10:30 pm   #9
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Default Re: 'Ferrite Pot Core Pairs'?

Ok it appears, as they say in America, that I am a dumbass. The box has been sitting in front of me on my desk shelf for the last month and I though it was something else. After writing this I will go sit in the corner and don the dunce hat.

I dug around and typically I only have FX2242 and FX2241 parts. Both have significantly different AL value according to databook

Also have a bunch of LA4130, FX3438 and FX3440 cores if they are any use.

Photo included...
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Old 25th Jan 2020, 2:39 am   #10
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Default Re: 'Ferrite Pot Core Pairs'?

Hi!

I might be able to offer a tip:–

I don't know how many he has – I bought one – but enter:–

"Core fi26 AL5000 M4" in an eBay search –

. . .this is a 26–27 mm pot core pair, gapped, with a base and pins – you can dismantle this to remove the pins and then place the assembly in hot water to separate the halves (suggested by seller) – only snag is the postage, £5.50 – is about five times the cost of the part, as it's from Poland!

Compared with paying £30 in p & p for Jaycar to import the thing from Oz or the daft multiple quantities RS, Farnell & Mouser etc., expect you to buy, it's about the cheapest you'll get as a one–off!

You do have to strip the old winding off it's bobbin tho!

Unfortunately EPE have deleted PCBs before Jan 2013 from their online store list, so I don't know if you can still buy EE 861 from them to make this! (I bought mine direct from Silicon Chip – it costs about £17.60 including postage – at the time I ordered mine the SC website showed a stock of 8!)

S.C. supply the F.P. artwork and the hex. free with each PCB order!

Chris Williams

PS!

The original plastic storage box used for building the prototype is still fairly readily available on eBay!
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Old 31st Jan 2020, 1:23 am   #11
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Default Re: 'Ferrite Pot Core Pairs'?

Chris55000 - on the EPE online shop all the PCBs appear to be available: https://www.electronpublishing.com/p...former-tester/

I was toying with just making it on perfboard, or perhaps some good old tagstrip, but it would certainly be easier to use their PCB!

I thought a nice wooden box with a hinged transparent lid for the capacitor in question (some brass plates, too?) would be more appealing than the plastic box they built it in, so I'd be investigating that once I've sharpened my dovetail saw...

MrBungle - I don't know enough about the subject to see if those parts are suitable, but many thanks for looking through your box. Or perhaps Mrs Bungle should be thanking me for providing the cupboard-sorting impetus!

I've attached the diagram so you can see how the circuit functions. The transformer is part of the step-up from the DC supply, and the winding instructions are included.
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Old 31st Jan 2020, 9:12 am   #12
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Default Re: 'Ferrite Pot Core Pairs'?

Ooh that’s a nice simple little circuit. There’s not much to go wrong. You can probably use anything such as a reasonable sized material 43 toroid for that. I’d just stack a couple of FT82-43’s and use that. Be aware though the switchers built like this are quite explodey. Use a current limited supply if you can on power up and wear safety glasses. IRF5x0 devices go with quite a bang. This usually happens when the Vds max voltage is exceeded or the Ic max is exceeded. Both of these can happen depending on the loading of the secondary and when the oscillator stalls while switched on. I’ve been abusing them as switching supplies and RF power amplifiers for about three years now

If try and keep the layout around the gate drive circuit fairly tight otherwise it can turn into an unexpected and violent suicidal oscillator.

Here’s one I built about 3 years ago to do the same task (leakage check). This was only 200V. I used 555 and LM311 to control it instead of the 34063. Not very accurate or efficient (45%) but it worked with what was on hand.

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And yes it did indeed help with the cupboard sort out and that did indeed help with Mrs Bungle

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Old 1st Feb 2020, 9:51 pm   #13
Uncle Bulgaria
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Default Re: 'Ferrite Pot Core Pairs'?

Thanks for the thoughts - and for that Manhattan delight!

I'm afraid about 3/4 of what you wrote went over my head with a great whooshing sound. I can follow the circuit as I read the accompanying text, but I haven't yet reached the stage where I can explain it to someone else.

I hope they've considered the exploding aspect, as they do make some effort to drive home the safety aspect of the design!

Are any of your box parts suitable for this? I can't see that it's too critical as it's just a step up transformer as far as I can see...not exactly a phono coupling stage!

I'm impressed at the level of ingenuity here. For those of us not trained in electronics, the ability to fashion a useful circuit from scratch is quite awesome.

I've had a look for "FT82-43" and end up with some ferrite rings. Are you proposing I just wrap the wire around that and let it be, without the associated surrounds, pins and cores?
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Old 2nd Feb 2020, 3:25 pm   #14
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Default Re: 'Ferrite Pot Core Pairs'?

I've had a dig around and found some data on the cores.

The FX2240 is ungapped, AL value circa 4000 to 8000 nH/t
The Neosid 26 -16 transformer core is a similar spec.

The reformer article has just the centre-limb gapped to 0.06mm (i.e. 3 thou,) which doesn't sound very hygenic, so i'd be inclined to shim the outer rim as well. It looks like the gapping reduces the AL to about 1000nH/t.

Please find a scan of the relevant data from me little archive!

John
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Old 2nd Feb 2020, 6:23 pm   #15
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Default Re: 'Ferrite Pot Core Pairs'?

Ferrite is rather brittle. The core in that article is not gapped, which some manufacturers code as oL in their markings (EG Siemens/Epcos)

Shimming the centre post does indeed gap the centre, but it also gaps the outer as the stuff is so stiff. So you get two gaps in the magnetic circuit. With the gap, the AL value of the core will be much lower than the ungapped use would give, but also the saturation current is improved.

They make ready-gapped cores where just the centre post is ground (below the level of the outer) and this makes the core self-shielding. Helpfully, they printed the AL values on them too. Watch out though, some cores were ground equally on both halves, others got the whole gap on one half only. Usually these had a nut for an adjuster glued in on the non-ground half. You could bodge an ungapped core from two bottom halves!

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Old 2nd Feb 2020, 7:18 pm   #16
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Default Re: 'Ferrite Pot Core Pairs'?

Quote:
Originally Posted by Uncle Bulgaria View Post
Thanks for the thoughts - and for that Manhattan delight!

I'm afraid about 3/4 of what you wrote went over my head with a great whooshing sound. I can follow the circuit as I read the accompanying text, but I haven't yet reached the stage where I can explain it to someone else.

I hope they've considered the exploding aspect, as they do make some effort to drive home the safety aspect of the design!

Are any of your box parts suitable for this? I can't see that it's too critical as it's just a step up transformer as far as I can see...not exactly a phono coupling stage!

I'm impressed at the level of ingenuity here. For those of us not trained in electronics, the ability to fashion a useful circuit from scratch is quite awesome.

I've had a look for "FT82-43" and end up with some ferrite rings. Are you proposing I just wrap the wire around that and let it be, without the associated surrounds, pins and cores?
Mostly me ranting about the exploding fragility of MOSFETs

Anything will probably do the job here. I'm not sure if any of the parts I listed were good. I don't have data for them off the job of my head. I can probably find out but am unfortunately stuck in a hotel on my laptop at the moment

On the FT82-43, yes you pretty much just wrap the wire around it. The toroidal cores confine the majority of the magnetic field inside the core which means a lot of shielding isn't required. On low power ones i usually just use a glue gun to stick them to the board. I've made a few like that as they are cheap and easy to reproduce. After digging around in the bowels of this laptop i found a picture of a simple bipolar supply which was made using a Royer oscillator and an FT82-43. This was specified as 5v in (from USB charger) to +/-15V for an opamp circuit.

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These things are repeatable and available in vast numbers for not a lot of money and are quite useful (you can run coax through them a couple of times to make RFI filters too)
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