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Old 28th Sep 2023, 1:55 pm   #21
Chrispy57
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Default Re: 2023 Options for Capacitor Reformer/Tester

Hi John,
thanks for that, I do like the idea of re-purposing an old piece of equipment for a new role, and it has ignited a spark here, I must go off in search of my EF80!

I didn't want to make too many assumptions without some circuit details, but your original description of the EF80 as a series regulator AND current limiter was intriguing. Can you elaborate on its current limiting function - is it just the valve "topping out" around 14mA or can it be adjusted at will to limit current within the useful range of a reforming capacitor?

Cheers
Chris
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Old 28th Sep 2023, 4:36 pm   #22
ian_rodger
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Default Re: 2023 Options for Capacitor Reformer/Tester

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Originally Posted by buggies View Post
Ian - apologies for not returning to your original thread.
I built it with only minor mods - works well and has had a lot use.
Just taken the pic attached.
Hi George,

Thanks for the update. Looks good - tidier than mine! Don't know what your mods were, but looking at your display it looks like you may have tweaked the firmware to address one issue I was aware of - when the switch is set to discharge the display shows the inverter output voltage rather than the reforming capacitor voltage.

My proposed solution was to add a diode as shown in the attached diagram; this should make the display show the greater of the inverter voltage or reforming cap voltage. Sometime I may get round to adding it to mine!

Ian
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Old 28th Sep 2023, 4:56 pm   #23
ian_rodger
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Default Re: 2023 Options for Capacitor Reformer/Tester

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Originally Posted by Dazz100 View Post
Hi
I am going to make any further posts on this topic to the thread here:
Capacitor reformer and leakage current indicator
Dazz - I think that thread is closed and locked. You could maybe ask a mod to reopen it.

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Quote:
Originally Posted by ian_rodger View Post

A logic gate base multivibrator with complementary outputs could work just as well. It would need to have an inhibit input that sets both outputs low to avoid unnecessary power dissipation in the drive transistors and transformer, also some frequency adjustment to optimise voltage out from the transformer.
I am thinking direct drive from controller outputs to a pair of self-protecting drive transistors. Implement no-driver-short in software, or alternatively, use a half bridge driver device. The aim to keep the circuit as simple as possible.
If I understand correctly, you are considering a single Arduino to drive the inverter and handle the control logic? If so, the challenge will be to optimise the code to have the inverter frequency high enough and stable whilst it is monitoring and averaging voltage/current measurements. From memory, my transformer was standard mains 3VA 6-0-6v. Optimum output was when driving it at around 400Hz.
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Old 29th Sep 2023, 2:10 am   #24
Dazz100
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Default Re: 2023 Options for Capacitor Reformer/Tester

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Hi
I am going to make any further posts on this topic to the thread here:
Capacitor reformer and leakage current indicator
OK I can't do that because the thread is closed.
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Old 29th Sep 2023, 10:19 am   #25
Dazz100
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Default Re: 2023 Options for Capacitor Reformer/Tester

Hi
The other thread is closed so I can't post there.

Some questions for Ian just to understand some design decisions.

What is the peak output voltage, zero leakage current?
What is the peak output voltage at max design leakage current?
What transformer is used?
Why was the voltage multiplier used on the transformer output?

I am thinking that a max output of 5W or 500V at 10mA would be sufficient. Allowing for say 50% efficiency, this would require a 12V/1A power supply. Too much power risks exploding capacitors.

I am thinking of using an off-pcb ferrite pot core transformer to produce up to 500V directly from the driver transistors. Rather than using discrete driver transistors and related components, I think I would use a full H bridge IC. A full H bridge would equivalent to driving the transformer with 24VAC ( with 12V supply). Getting to 500VDC would then require a winding ratio of about 15:1. Not onerous and would reduce parts count.

Rather than using switches for input controls/menu select/ range etc, I would use a rotary encoder switch. These are cheap, versatile and wire directly to an Arduino without additional components.

A rated switch would still be required for selecting reform/isolate/discharge.

I think I would replace the op-amp with a transimpedance amp to reduce parts count.

The Arduino Nano works with 6-20VDC unregulated supply so the LM7805 would not be required. Most of Ian's code could be reused.

I think I would use PWM and missing pulses to control the output voltage. The issue with the Nano is that the PWM output is limited to about 1kHz. A higher freq would require a physically smaller transformer.

So I think I could refine Ian's design and reduce the parts count by about half while reusing a lot of the code.
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Old 29th Sep 2023, 2:25 pm   #26
ian_rodger
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Default Re: 2023 Options for Capacitor Reformer/Tester

Dazz,

I’ll do my best to recall and take a few measurements – it’s been a good few years since I worked on this!

The voltage multiplier was included so I could get to 450V – that seemed a sensible limit for my needs. I can get to just over 450V with an output current of 4 mA, input voltage above 10V to hit this with input current around 150 mA.

Transformer is 230V primary, 3VA 6V+6V secondary reverse connected. Here’s a link to the one I used;

https://www.jprelec.co.uk/categories...35-401~835-401
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Old 30th Sep 2023, 6:27 pm   #27
60136 Alcazar
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Default Re: 2023 Options for Capacitor Reformer/Tester

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Originally Posted by Chrispy57 View Post
Can you elaborate on its current limiting function - is it just the valve "topping out" around 14mA or can it be adjusted at will to limit current within the useful range of a reforming capacitor?
Chris
Hi Chris
You're right - the current limit is just the saturation current, this ensures there is no runaway, but allows currents applicable to 450 volt caps from up to 80 years ago to be reformed as best they can. Attached image of the front of the unit. The output is fed via an inline DC milli/micro-Ammeter to the cap under test. It is just a simple basic unit to do a particular job, made from what was on hand at the time. The original transformer was around 200-0-200 feeding a FW valve rectifier - I kept the transformer and put a bridge circuit across the whole of the 400V secondary instead to achieve the required 500v maximum.
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Last edited by 60136 Alcazar; 30th Sep 2023 at 6:30 pm. Reason: Additional info.
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Old 30th Sep 2023, 8:42 pm   #28
Chrispy57
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Default Re: 2023 Options for Capacitor Reformer/Tester

Hi John,
thanks for your comments and the photos - classic good-looks stand the test of time. "It is just a simple basic unit to do a particular job, made from what was on hand at the time" - that's my kind of project!

Cheers
Chris
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Old 2nd Oct 2023, 2:41 pm   #29
Gabe001
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Default Re: 2023 Options for Capacitor Reformer/Tester

For my capacitor reformer I used paul stenning's circuit from this site, just added a transformer for safety as I had one in the junk box, and the voltmeter is a 0-3v analogue meter permanently mounted.

It does the job. Seen in action in the pic attached. Still need to make 2 proper leads.

Gabriel
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Old 12th Oct 2023, 9:16 am   #30
Dazz100
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Default Re: 2023 Options for Capacitor Reformer/Tester

Hi
I have continued the info exchange here:
https://www.eevblog.com/forum/projec...26/#msg5095626

for those that might be interested.
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