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Old 18th Jun 2020, 12:31 pm   #1
Uncle Bulgaria
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Default EPE Electrolytic Capacitor Tester/Reformer Construction

Good morning all,

Some of you may have seen my lengthy thread trying to get to grips with magnetic theory as a precursor to making this Everyday Practical Electronics (pace Silicon Chip) project. It contains a self-wound ferrite pot core pair which I was keen to avoid buying from Australia and which is not available from the usual sources in the UK. Much calculation and explanation by more knowledgeable Members ensued in the endeavour to deduce the original's characteristics, and a donation of various ferrites gave me something to go on.

The board has now arrived from the EPE online shop after being out of stock, so I thought I'd record the construction here as and when it occurs. There are a few threads about this project from about ten years ago, so perhaps there'll be some interest in a current build.

The board feels of good construction so now it's in my hands I just need to consider the case...
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Old 18th Jun 2020, 9:45 pm   #2
SiriusHardware
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Default Re: EPE Electrolytic Capacitor Tester/Reformer Construction

Hi UB,
Is this the item for which you were going to need a PIC programmed and did you ever get that sorted?
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Old 19th Jun 2020, 5:52 am   #3
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Default Re: EPE Electrolytic Capacitor Tester/Reformer Construction

"Is this the item for which you were going to need a PIC programmed" Would think so, it's got PIC6F88 or 99 (or 98/89)printed on the PCB.

Looks good, green too, like green PCB's. There's nowt like a proper PCB to make construction easy and make the job a good un. I still love mounting and soldering them after all these years. Mind you I don't have to do 600 a day, that might take the shine off.

Andy.
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Old 19th Jun 2020, 7:34 pm   #4
Uncle Bulgaria
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Default Re: EPE Electrolytic Capacitor Tester/Reformer Construction

Yes - that PICKit 2 MerlinMaxwell was offering that you put me on to is here on my desk. I've not done the programming yet, but I think I have all the tools to do so now.

I'll admit I've been putting off winding the ferrite because of uncertainties about inductance and how much it matters, and my own ability to evaluate when it's working properly or not. Radio Wrangler has assured me it's not critical, but it's nice to engineer rather than bodge! My skills are such that I feel better doing the right thing as I don't know enough to bend the rules.

I haven't the specified thicknesses of transformer wire, so I'm first going to try winding with hookup stuff I have and see what happens. I do have some approx. 0.25mm wire on a wooden spool from my grandfather labelled 'The London Wire Company', which is what's specified for the secondary. Perhaps it's cotton insulated. It's got something on.

I understand the wire CSA is mainly for current handling and cost efficiency in mass production, so using something other than the 0.8mm specified in the original EPE instructions won't make too much difference, especially in a configuration like this, when the spacing is more important.

No doubt I'll be needing help with measuring inductances or otherwise monitoring the high-frequency performance without frying a DMM (I've already done that this month - silly ass, at least it was a cheap Chinese one, but now my IDM67 is on the fritz too!)
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Old 19th Jun 2020, 9:17 pm   #5
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Default Re: EPE Electrolytic Capacitor Tester/Reformer Construction

Hello,

I built one of these capacitor reformers back in 2014. It was a very enjoyable project. Here is a photo of my completed unit in use.

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I had programmed PICs previously, but like you hadn't previously constructed a transformer.

I bought the specified bobbin and ferrite pot core, along with the LCD display from Jaycar Electronics. [I used a QP-5518 display because the QP-5516 was not available at the time.]

I bought small reels of the 0.25mm dia and 0.8mm enamelled copper wire required for the transformer. Re-reading the EPE articles it says that 1m of 0.8mm wire and 10m of 0.25mm wire is needed. The chances are that there is enough left on my reels to wind another transformer. Let me know if you are interested.

It is a really nice unit, albeit somewhat costly for a capacitor reformer.


Regards,

Richard
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Old 14th Jul 2020, 1:27 am   #6
Uncle Bulgaria
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Default Re: EPE Electrolytic Capacitor Tester/Reformer Construction

Thank you Ricardo, that's a very kind offer - and a nicely made reformer too! I'm making things more difficult for myself by intending to make a wooden box for it as a first test for some of my dovetail saws, so who knows when it will be in a finished state!

Tonight I have attempted to wind the transformer on an FX2241 core. I'm using the wire the core originally came with as the primary, and some ancient, possibly silk-covered wire I found among my grandfather's things as the secondary. I might need that wire of yours, if this shorts out...

How do I go about testing this to see whether it's in the right area for the circuit in question? I suppose when powered, whether or not it breaks down will show whether the wires are sufficiently sized, but how about checking the impedance?
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Old 15th Jul 2020, 7:19 am   #7
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Default Re: EPE Electrolytic Capacitor Tester/Reformer Construction

To check IP Z put a signal into your tfmr about 1v ish, then get a pot, put it across the tfmr or in parallel, adjust till your reading is halved. Remove pot and measure, that's you IP Z. Remember to use a frequency your tfmr will see in use, so 50hz for your bog standard mains tfmr, whatever khz for SMPSU types.

Andy.
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Old 15th Jul 2020, 8:48 pm   #8
Uncle Bulgaria
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Default Re: EPE Electrolytic Capacitor Tester/Reformer Construction

Thank you, Andy.

So the pot. is across the output of the transformer (which in this case has half shared with the input as the primary and secondary are tied together)? The frequency will be 33kHz so I think I'll be better off with my oscilloscope. I've already blow up one multimeter with high frequency...
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Old 15th Jul 2020, 9:15 pm   #9
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Default Re: EPE Electrolytic Capacitor Tester/Reformer Construction

The way I read it I think DA means you to put the pot in parallel with the INPUT winding of the transformer. Should the transformer also have a realistic output load, though, during this process?
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Old 15th Jul 2020, 9:35 pm   #10
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Default Re: EPE Electrolytic Capacitor Tester/Reformer Construction

I came to the same conclusion as you, having run a search using keywords from Diabolical Artificer's post - a few sites have circuits showing the pot on the input, but they do have a load resistor on the secondary.

In the Reformer circuit, the output voltage is varied by changing the resistance divider values in the autotransformer's feedback loop, and the switching transistor is between ground and the primary/secondary join. Suppose I put a load resistor equal to that required for 10V output on the secondary? Am I then simply reproducing the generation part of the reformer circuit with the signal generator and resistor?
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Old 16th Jul 2020, 10:09 am   #11
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Default Re: EPE Electrolytic Capacitor Tester/Reformer Construction

Do not load the output.

Drive with 33kHz sine from a signal generator of some sort. Feed the primary VIA a variable resistor or a resistor substitution box

Use 2 channel scope.

Probe grounds to sig gen ground and its end of the primary

One probe to sig gen output, other probe to monitor voltage on primary.

Play with variable resistance until primaty voltage is 70.7% of sig gen voltage

Now the resistance = the inductor's reactance

Only now get out your multimeter and measure the resistance out of circuit.

R = 2*Pi*f*L

So L = R/(2*Pi*f)

Job's a good un.

David
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Old 17th Jul 2020, 1:52 am   #12
Uncle Bulgaria
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Default Re: EPE Electrolytic Capacitor Tester/Reformer Construction

Thank you, David.

Something's wrong somewhere - I end up with ~20 Ohms, so 8.44x10-5 H! Tomorrow is another day...
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Old 17th Jul 2020, 9:18 am   #13
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Default Re: EPE Electrolytic Capacitor Tester/Reformer Construction

84.4 microhenries.

How many turns in that winding?

Square the number of turns and then divide 84.4uH by it.

You now have the inductance of a single turn winding, in uH

Multiply by 1000 to get in in nH. THIS is the value usually quoted as Al value. The inductance in nH of a 1-turn winding.

David
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Old 19th Jul 2020, 5:26 pm   #14
Uncle Bulgaria
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Default Re: EPE Electrolytic Capacitor Tester/Reformer Construction

That's a simple copy of the article's instructions, as the FX2241 appears closely matched to the suggested core. That's 10 primary and 80 secondary turns. As they're connected, I used 90 squared, which ends up with 10.4nH. The quoted Al value is 5815, which suggests I've done it wrong!
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Old 1st Aug 2020, 1:14 am   #15
Uncle Bulgaria
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Default Re: EPE Electrolytic Capacitor Tester/Reformer Construction

I'm going to need some more help, please. I thought the ratio of primary to secondary turns was the crucial thing here. Is it actually the inductance per turn that matters? Since the 2240 (which we think was the same specification as the Jaycar part specified in the EPE instructions) has a nominal inductance factor of 3432 - 8227 nH/turn, there's quite a lot of leeway (as you mentioned in the other thread, David).

I got the 10.4nH value with the FX2241 core (inductance factor 5815) using the same number of turns as the instructions demand. I used a gapping of 0.1mm as that was the spacing of the two mica shimming washers that were already in the FX2241.

Most likely is that the old, thin wire I used was shorting. That seems to me to be a likely cause of an unexpectedly low inductance, though I could be entirely up the wrong tree.
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Old 1st Aug 2020, 5:19 am   #16
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Default Re: EPE Electrolytic Capacitor Tester/Reformer Construction

Both matter.

n a normal transformer, the turns ratio sets the voltage ratio, and it's easy to just leave it at that, but the inductance of the primary can be thought of as shunting the primary of a perfect transformer.

Get enough inductance and the magnetising current is trivial, you just see whatever current the load on the secondary transformed by the turns ratio.

Get too little inductance and it starts to look like a short across the input. So you need to design to get enough inductance for the lowest frequency in something like an audio output transformer or a microphone transformer.

Go for too much inductance and you run into increased problems with internal capacitance in the windings and self-resonance.

So, for an ordinary transformer, there is a sweet spot, but it's wide enough to leave you some wiggle room.

HOWEVER, this application is not an ordinary transformer. It is the inductor of a boost converter, and then on top of that, it has an overwind to increase the output voltage further.

Primarily (oops, pun!) you have to get the primary inductance right for the boost converter to be able to run the current up to the right value in the time set by the choice of operating frequency. If you have the right cores and get any gapping called for, the inductance should come out OK. If you're uncertain about the cores you have and not sure about gap spacer thickness, then you need to measure inductance. This sort of inductor often foxes those little LCR meters. They're OK on C and R, but L is a bit harder to measure. So the sig gen, resistor and scope approach is less likely to be confusing.

The turns ratio to the secondary will have a bit of leeway.

If the core chosen has an inductance factor of 5815 nH/turn, multiply this value by the number of turns squared, and that's the inductance you should have had without the gapping spacer. That spacer will bring down the inductance rather dramatically, but not as far as 10nH. That has to be a mixture of shorted turns, which bring inductance crashing down, plus the errors in measuring such low inductance.

There is a root cause of all this difficulty. Designers of magazine construction articles really ought to describe the design choices and figures for any custom transformers involved and take people through the numbers of turns and the calculations of the magnetic effects of adding gapping shim. It's all well and good having kits available, but their article loses its value when the kits go out of production and people may still be interested in the thing. Besides, doing such work out in the open might just allow people to LEARN something from the article. I don't suppose it's trying to profit from a captive audience for kits, I think it's publishers wanting to fit things in a given page count, even if it ruins the article for many people... besides, all that magnetics stuff is boring... just calculations and explanations and it takes up the space they could put that DIY tamagochi article in!

Pet rant!

David
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Old 1st Aug 2020, 2:50 pm   #17
Uncle Bulgaria
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Default Re: EPE Electrolytic Capacitor Tester/Reformer Construction

Once again you demonstrate the gift of being able to explain in terms that the tyro can grasp. I think I understand what's going on here now. Another of your posts I've printed to put in my 'references' folder!

I'm populating the board, and was for most of last night with the company of Miss Marple. I haven't 'done' PCBs before and putting all the resistors in the right holes was strangely meditative.

I decided the turns must have been shorted, and rewound the secondary (very roughly). This time, I used one spacer (0.05mm) and got a result of 4167nH per turn. This sounds much more reasonable.

I agree, the fact that a page of instructions on how to wind the thing doesn't include the basic specifications of the core or the rationale behind the winding is pretty annoying. It's taken the previous thread and the contribution of people who knew ferrites well enough to propose datasheets for the core the Jaycar part was based on to enable me to get to this point. I'm very grateful!
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Old 1st Aug 2020, 8:03 pm   #18
Uncle Bulgaria
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Default Re: EPE Electrolytic Capacitor Tester/Reformer Construction

I had some difficulty getting a 6V coil SPDT relay when I was getting the pieces together for this project, and now find that the one I got is too small. If anyone else wants to make this using the EPE board, it's as well to bear in mind that the Omron G5V-1 is a bit small. I've bent out the legs and managed to make contact, but the hole spacing on the board between the NC/NO pair and the coil is 3mm, and 10mm between coil and the common pair.
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