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PSU for anodising.

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Robin Graham14/01/2020 20:19:08
754 forum posts
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I'd like to have a go at anodising aluminium and have the chemicals and other stuff, except for a power supply. I have got a 12V car battery charger which claims to be capable of 6A - that should be enough for the part I want to anodise (about 30 square inches), but there is contradictory advice out there on the internet. Some say 12V is fine, others say results are 'likely to be variable', but don't go into more detail.

I'm wondering if anyone on here has experience of trying this with a battery charger?

Robin.

SillyOldDuffer14/01/2020 21:01:09
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Posted by Robin Graham on 14/01/2020 20:19:08:

I'd like to have a go at anodising aluminium and have the chemicals and other stuff, except for a power supply. I have got a 12V car battery charger which claims to be capable of 6A - that should be enough for the part I want to anodise (about 30 square inches), but there is contradictory advice out there on the internet. Some say 12V is fine, others say results are 'likely to be variable', but don't go into more detail.

I'm wondering if anyone on here has experience of trying this with a battery charger?

Robin.

Not tried anodising but it's amps that do the work in electrochemical processes. You only need enough volts to get current flowing, about two. The extra 10 to 12V volts will cause nothing but unwanted snap crackle and pop, tending to disturb the finish.

A resistive dropper will waste a lot of power, but easier than finding a 3V 10A psu. Try wiring a 12v car headlamp bulb in series with one of the DC connections, it will drop about 12V, probably OK because chargers run at about 14V. The DC from a car battery charger is pretty dirty - about 14vdc unsmoothed, I'm not sure if that matters. I'm assuming car battery chargers are as crude as in my youth; a modern one might be beautifully smoothed and too clever for anodising.

Worth a try, why not?

Dave

noel shelley14/01/2020 21:07:02
111 forum posts

the resistive load a bath will leave you with the voltage to high and the amps will be to low I fear, It may work but not very well. No harm in trying though. Noel

Oldiron14/01/2020 21:34:45
481 forum posts
22 photos

Never got round to trying it myself but do intend to do so eventually. I watched an awful lot of videos on the subject of homeshop anodising on Youtube and many of them use a 12vdc battery charger at both 6 and 10 amps or a very similar supply. Best try it on a test piece and see how it goes. Try what you have before lashing out money on something you do not need. Nothing ventured nothing gained.

regards

Oldiron14/01/2020 22:16:40
481 forum posts
22 photos

OOPS Forgot to add a link to a YouTube video. Anodising

regards

Frances IoM14/01/2020 22:54:02
804 forum posts
26 photos
multi-amp 3.3V or 5V are available from many computer PSU's - they generally cost less that ?5 at my local auction house - 12V high current (80A+) tend to be somewhat more expensive especially if they come with many 4 or 6pin graphics card interfaces as these are popular with bit-coin miners
Robin Graham14/01/2020 23:14:47
754 forum posts
185 photos

OK, thanks. I guess I just need to suck it and see.

Dave's suggestion that 2V might be enough is surprising and seems to go against the tide of opinion and experience. I thought about trying to make calculations based on the conductivity of dilute sulphuric acid solutions, but it seems that the surface resistivity of the electrodes is dominant. Maybe that's why it's all a bit up in the air.

Making the cathode will be fun, melting old lead pipes in a saucepan on the sitting room fire might raise a wifely eyebrow.

Robin.

 

 

 

Edited By Robin Graham on 14/01/2020 23:16:58

Gerard O'Toole15/01/2020 09:14:27
78 forum posts
7 photos

You could try with a battery first. My book suggests 2 A and 10 V so it might be worth a try with a car or motorcycle battery, or even with a 9V battery

 

Edited By Gerard O'Toole on 15/01/2020 09:22:32

Martin Kyte15/01/2020 09:22:28
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2009 forum posts
36 photos

Stick a car light bulb or two in the cct for crude current regulation.

Martin

Edited By Martin Kyte on 15/01/2020 09:23:02

Neil Wyatt15/01/2020 09:42:49
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I had great results with a 12V 4A charger. I use a moving ammeter to keep an eye on current. It swings off the scale at first, but drops in less than a second.

The current self-regulates with the area of the piece, and if a bit low just keep it in longer. I always turn the part once.

For smaller parts keep the cathode further away.

I anodised most of this scope, the main tube is about 10" long, about 3" diameter so that's approaching 200 square inches inside and out.

Neil

66ed (4).jpg

Don't obsess about the voltage the things that matter are thorough stripping, cleanliness, good electrical contact between cathode (I use TI wire, cleaned with abrasive paper), professional dies and if you want to add another - more cleanliness.

Also, be careful, these are nasty chemicals.

Neil

Edited By Neil Wyatt on 15/01/2020 09:46:57

Martin Kyte15/01/2020 09:49:09
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36 photos

trouble with these 'moving ammeters' is you can never find the darn things one you take your eyes off 'em.

;0)

Martin

Vic15/01/2020 10:14:14
2556 forum posts
14 photos

Nice job on the scope Neil. yes

SillyOldDuffer15/01/2020 10:17:58
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Posted by Robin Graham on 14/01/2020 23:14:47:

OK, thanks. I guess I just need to suck it and see.

Dave's suggestion that 2V might be enough is surprising and seems to go against the tide of opinion and experience. I thought about trying to make calculations based on the conductivity of dilute sulphuric acid solutions, but it seems that the surface resistivity of the electrodes is dominant. Maybe that's why it's all a bit up in the air.

...

Yes, here's what Wikipedia says, my bold:

'The voltage required by various solutions may range from 1 to 300 V DC, although most fall in the range of 15 to 21 V. Higher voltages are typically required for thicker coatings formed in sulfuric and organic acid. The anodizing current varies with the area of aluminium being anodized and typically ranges from 30 to 300 A/m2.'

15 to 21V is higher than I expected, and more in line with the volts produced by a car battery charger.

Wikipedia also says: 'Alternating current and pulsed current is also possible but rarely used.' Watch out, a battery charger is likely to be unsmoothed DC pulses, easily fixed by adding an electrolytic capacitor across the output, big rather than small, I'd guess 1000uF.

Can you report back? A range of 1 to 300V suggests strongly that the electrolyte is the main decider, so experimentation is in order. The ideal power supply would allow the operator to increase voltage until the necessary current was flowing proportional to the object's surface area. (30 to 300 A/m2, another wide operating range)

Sorry to mislead!

Dave

Robert Atkinson 215/01/2020 15:52:31
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751 forum posts
17 photos

I'm going to reveal a hidden gem here:

Get one of the Low voltage AC/DC power supples intended for use in schools like this one

https://www.ebay.co.uk/itm/POWER-SUPPLY-EJ0032-IRWIN-L-V-Variable-AC-8A-DC-5A/254479418781

or 8A one

https://www.ebay.co.uk/itm/POWER-SUPPLY-EJ32-IRWIN-L-V-Variable-8-Amp-AC-DC-volts/124032526494?

Search Irwin power supply. The also made one with stitched positions fron 2 to 12V

Griffin & George also made them.

Some are over-priced eg https://www.ebay.co.uk/itm/Variable-Power-Supply-Griffin-and-George-ltd-London/202874378189?

Some are absolute bargains like this https://www.ebay.co.uk/itm/GRIFFIN-AND-GEORGE-GRIFFIN-LT-VARIABLE-POWER-SUPPLY-/113986088771?

(No I didn't get that one but have an identical one).
These are unregulated and are much more suited to to plating, and running small motors than modern solid state digital units.

Don't forget that if you want to have sulfuric acid stronger than 15% you need an Explosives and Poisons Precursors licence in the UK

https://www.gov.uk/government/publications/licensing-for-home-users-of-explosives-precursors/licensing-for-home-users-of-poisons-and-explosive-precursors

Robert G8RPI.

Edited By Robert Atkinson 2 on 15/01/2020 15:58:10

Neil Wyatt15/01/2020 15:58:28
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Posted by SillyOldDuffer on 15/01/2020 10:17:58:
Posted by Robin Graham on 14/01/2020 23:14:47:

OK, thanks. I guess I just need to suck it and see.

Dave's suggestion that 2V might be enough is surprising and seems to go against the tide of opinion and experience. I thought about trying to make calculations based on the conductivity of dilute sulphuric acid solutions, but it seems that the surface resistivity of the electrodes is dominant. Maybe that's why it's all a bit up in the air.

...

Yes, here's what Wikipedia says, my bold:

'The voltage required by various solutions may range from 1 to 300 V DC, although most fall in the range of 15 to 21 V. Higher voltages are typically required for thicker coatings formed in sulfuric and organic acid. The anodizing current varies with the area of aluminium being anodized and typically ranges from 30 to 300 A/m2.'

15 to 21V is higher than I expected, and more in line with the volts produced by a car battery charger.

Wikipedia also says: 'Alternating current and pulsed current is also possible but rarely used.' Watch out, a battery charger is likely to be unsmoothed DC pulses, easily fixed by adding an electrolytic capacitor across the output, big rather than small, I'd guess 1000uF.

Can you report back? A range of 1 to 300V suggests strongly that the electrolyte is the main decider, so experimentation is in order. The ideal power supply would allow the operator to increase voltage until the necessary current was flowing proportional to the object's surface area. (30 to 300 A/m2, another wide operating range)

Sorry to mislead!

Dave

You're over-thinking it Dave,

A car battery charger, as is, is perfectly suitable. My PSU is just the transformer out of a car battery charger that blewup its rectifier, fitted ina new box with a heavy duty rectifier.

If I can get results with that, anyone can.

Neil

Neil Wyatt15/01/2020 15:59:39
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Posted by Robert Atkinson 2 on 15/01/2020 15:52:31:

Don't forget that if you want to have sulfuric acid stronger than 15% you need an Explosives and Poisons Precursors licence in the UK

Easily avoided by using sulphuric at just less than 15%, which works fine.

Oldiron15/01/2020 16:05:42
481 forum posts
22 photos
Posted by Robin Graham on 14/01/2020 23:14:47:

OK, thanks. I guess I just need to suck it and see.

Dave's suggestion that 2V might be enough is surprising and seems to go against the tide of opinion and experience. I thought about trying to make calculations based on the conductivity of dilute sulphuric acid solutions, but it seems that the surface resistivity of the electrodes is dominant. Maybe that's why it's all a bit up in the air.

Making the cathode will be fun, melting old lead pipes in a saucepan on the sitting room fire might raise a wifely eyebrow.

Don't bother melting the lead down. A big hammer and a decent backing block/anvil you can beat out an anode in very short time.

An old battery charger is much better to use until you want to go upmarket IMHO The trouble with modern type PSU's is that they have to much electronicy bits in them to be suitable. Do not waste your money go old style.

regards

Neil Wyatt15/01/2020 16:25:09
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I don't want to overstate it, but my advice is based on practical experience, and before I started I took advice from Gateros Plating who make their living supporting hobbyist platers and anodisers.

I know the approach I use works from experience and gives good results,even if it isn't theoretically optimal.

You waste a lot of time worrying about exact voltages, but if you do that you should also be fretting about exact bath temperatures, electrolyte concentration, anode area, anodising time etc.

Transformers are good PSUs because they cope well with sudden, brief surges.

Bear in mind this is bucket chemistry, not precision engineering, plus the nature of anodising is that the area of the work helps determine the current. It's got more in common with cooking.

If you want perfectly identical loaves every time you need to control EVERY aspect of the process.

If you want a lovely artisanal loaf out of your wood-fired oven, just get it hot, shove it in and take it out when its cooked properly.

Robin Graham16/01/2020 22:41:28
754 forum posts
185 photos

Thanks. Encouraged by Neil's excellent results with his telescope I made some preliminary experiments with the battery charger using brine as an electrolyte - I just wanted to see how it coped with differences in electrolyte concentration, electrode areas, separation &c and didn't want to splash acid about at this point. It claims to be 'intelligent' but obviously that's for its intended purpose - I don't suppose an anodising tank looks like a car battery from the charger's point of view. But it seems I can fool the thing, and that this is going to work.

As an aside, the ammeter on the charger has two scales - 'effective' RMS amps and 'Arithm' amps:

psu_ammeter.jpg

I suppose this means that the output is unsmoothed, but I don't understand the ratio A_rms/A_arith =1.5 . Any elucidation would be welcome!

Robin.

SillyOldDuffer17/01/2020 12:43:16
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6175 forum posts
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Posted by Robin Graham on 16/01/2020 22:41:28:

...

As an aside, the ammeter on the charger has two scales - 'effective' RMS amps and 'Arithm' amps:

...

I suppose this means that the output is unsmoothed, but I don't understand the ratio A_rms/A_arith =1.5 . Any elucidation would be welcome!

...

Yes, the ammeter confirms the output is un-smoothed. If the anodising results are iffy, I'd try sticking a capacitor across the output to see if it helps.

I think the actual ratio is A_rms/A_arith = 1.414 (approx 1.5 on the ammeter's scale)

1.414 is the square root of 2, and it defines the relationship between AC peak Volts and AC rms Volts in a sinusoidal waveform. Vrms = Vpeak / sqrt(2)

Following a waveform peaking and troughing 50 time a second stretches the imagination. It's often more meaningful to ignore reality and work with the average value instead. Various ways of calculating averages, but Root Mean Square is the most useful way of calculating the average value of a sine wave. It's like flattening out the wave by filling the troughs with the peaks.

Not sure having two scales on the ammeter is worth much beyond a general indication the charger is working. The meter used in chargers is only about ±25% accurate. On a Charger they indicate 'not working or finished', 'about right' and 'lots, maybe too much'. Useful, but not precise!

Dave

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