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Old 26th Mar 2023, 8:50 pm   #1
sparkymike
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Default Vintage power supply/battery charger?

I have an old power supply unit which gives out 12 or 5 volts DC via a decent sized mains transformer possibly Parmeco or Gilson ?
I would like to vary the DC volts with the aid of a wire wound potentiometer.
What range/value should I buy ?
Camera out of action at the moment but will post pictures later.
I am updating this with Euro socket for mains lead and new output terminals etc.
Mike.
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Old 26th Mar 2023, 10:10 pm   #2
G.Castle
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Default Re: vintage power supply/battery charger ?

You would be better off with a variable voltage regulator as in the LM317 LM350 LM358 family. Check out the manufacturer data sheets for application circuits.
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Old 27th Mar 2023, 9:21 am   #3
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Default Re: vintage power supply/battery charger ?

I am using it for an elecrolytic rust removal tank. It has been working fine , just want to vary the voltage a little to experiment a bit. I don't need to buy a new fangled gadget full of integrated circuits, just happy to carry on with my old school bit of kit. I suppose for starters I could vary the input to the transformer with my variac.?
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Old 27th Mar 2023, 10:43 am   #4
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Default Re: vintage power supply/battery charger ?

Photos of part completed unit.
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Old 27th Mar 2023, 11:02 am   #5
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Default Re: vintage power supply/battery charger ?

Quote:
Originally Posted by sparkymike View Post
I am using it for an elecrolytic rust removal tank. It has been working fine , just want to vary the voltage a little to experiment a bit. I don't need to buy a new fangled gadget full of integrated circuits, just happy to carry on with my old school bit of kit. I suppose for starters I could vary the input to the transformer with my variac.?
Ah! Context that wasn't in the OP. Devil is in the detail you know.

So, what youre really asking is to vary the current through the solution? Measure the current through the liquid in a typical situation and apply ohms law.

Variac would work. Seems like you've answered your own question at no cost.

Good luck.

Regards,
Greg
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Old 27th Mar 2023, 11:31 am   #6
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Default Re: Vintage power supply/battery charger?

A heavy duty multi-way switch and some power resistors would probably be good enough for this application.

Fuses and/or thermal overload devices would be useful.

The meter might shake itself to bits if it is continually measuring non smoothed voltage or current.
A capacitor and protection diode across the meter movement would help.

A momentary push button to activate the meter is worth considering.
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Old 27th Mar 2023, 5:10 pm   #7
sparkymike
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Default Re: Vintage power supply/battery charger?

What sort of value would the resistors have to be if I fit a multi way switch ?
Mike.
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Old 27th Mar 2023, 6:22 pm   #8
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Default Re: Vintage power supply/battery charger?

I've done a bit of electrolytic cleaning. The current depends on the strength of the solution,the area of the object to be cleaned and its surface finish. All of these are very variable. I found that altering the current (with a variac) didn't make much difference except possibly with the time required to fully clean. I used 12v and around 2A as a rule for quite large objects. Steel & iron parts need to be dried as soon as cleaning finished otherwise,rust forms quickly.
That looks like a Ferranti ZR30 rectifier in your supply? An ancient relic these days!
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Old 27th Mar 2023, 6:35 pm   #9
Roger Ramjet
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Default Re: Vintage power supply/battery charger?

Quote:
Originally Posted by Bill View Post
I've done a bit of electrolytic cleaning. The current depends on the strength of the solution,the area of the object to be cleaned and its surface finish. All of these are very variable. I found that altering the current (with a variac) didn't make much difference except possibly with the time required to fully clean. I used 12v and around 2A as a rule for quite large objects. Steel & iron parts need to be dried as soon as cleaning finished otherwise,rust forms quickly.
That looks like a Ferranti ZR30 rectifier in your supply? An ancient relic these days!
Hi Bill,

Not seeking to stray OT but what "solution"' do you use & does this process require a anode / cathode for the rust to migrate to ?

Rog
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Old 27th Mar 2023, 6:52 pm   #10
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Default Re: Vintage power supply/battery charger?

Rog,
The solution(electrolyte) is washing soda dissolved in water ( I use "Elco" soda,because it's made locally). The other electrode is a thin stainless steel plate which does not attract any deposit and does not erode away in use. The solution becomes disgusting in appearance but still works, the only requirement of the solution is that it conducts electricity. I can imagine you could use sea water but that might corrode something in no time.
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Old 27th Mar 2023, 7:05 pm   #11
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Default Re: Vintage power supply/battery charger?

My brother used an old car battery charger, a bucket with washing soda solution, and on old brake disc as the anode.

12V car bulbs such as a 50W headlight and 21W indicator bulb will limit the current and give an indication that current is flowing.

Ohms law will give you a rough idea of the current output.

4 Ohms will give 3Amps, 6 Ohms will give 2 Amps and 12 Ohms will give 1 Amp into a short citcuit.
That single diode will give you 'half wave' rectification. It may overheat the transformer.

The 4 Ohm resistor will dissipate 36Watts approximately. A 50Watt resistor bolted to a heatsink should be OK.

If you can get the current you require from the 5V winding, it would be more efficient and the resistors would be less expensive.

Last edited by Silicon; 27th Mar 2023 at 7:08 pm. Reason: correction
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Old 27th Mar 2023, 9:27 pm   #12
sparkymike
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Default Re: Vintage power supply/battery charger?

In practice I found that stainless steel did not work as well as bright mild steel.
That was with 12 volts at 2 amps.
I am using a 3'' X 3'' folded angle approx. a foot long for my anode.
Is full wave better than half wave rectification ?
Mike.
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Old 28th Mar 2023, 12:53 pm   #13
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Default Re: Vintage power supply/battery charger?

I vaguely recall reading something in a US vintage-machinery/automobile magazine that using half-wave-rectified AC rather than smoothed-DC (or a car battery) gave a supposedly better de-rusting effect.

Electrolytic processes can sometimes be wierdly behaved, since they combine electricity, chemistry, and when bubbles of gas are evolved in the process, physics too.
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Old 28th Mar 2023, 1:38 pm   #14
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Default Re: Vintage power supply/battery charger?

I've used electrolytic cleaning system and adjusted the cleaning rate by simply put a car bulb in series with the power supply. I have read about the dirty DC idea but had a bridge and transformer already wired up, so never given it a try. The fumes are unpleasant, a friend said they are hydrogen gas which could be dangerous, so I leave it all bubbling away outside, just in case. We have an external socket outlet. Ted
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Old 31st Mar 2023, 7:30 am   #15
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Default Re: Vintage power supply/battery charger?

A suggestion is to use a variac on the incoming mains side, if the output is rectified without capacitors then it should work.
A good example of this is Griffin power supplies, it has been in use for a few years and plated many bits of metal without problems.
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