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M250cnc
21-11-2010, 01:49 PM
Can anyone help me. I want to build a power supply with an output of 20v but with variable amp output.

I am looking in the range of .5 to 15amps (At least 10amps) this doesnt have to have a high precision.

I do a bit of anodising and this is what it would be used for. I would need a complete circuit diagram as i am at the back of the queue when it comes to electronics knowledge.

Any indication of likely cost to build would be useful also.

Thanks

blackburn mark
21-11-2010, 03:49 PM
sorry cant help you with your power supply.... iv looked into doing a touch of anodising myself, are you managing to get hold of sulfuric acid, iv heard it can be a pain to get your hands on in the uk

ptjw7uk
21-11-2010, 04:00 PM
If you want sulphuric acid go to a battery repairers or car breakers plenty in old lead acid batteries, I think its about 25%.
Just dont get it on your clothes it rots them for sure!

Peter

M250cnc
21-11-2010, 04:36 PM
are you managing to get hold of sulphuric acid, iv heard it can be a pain to get your hands on in the uk

I get it from a commercial anodiser along with lots of help

Phil

BillTodd
21-11-2010, 05:26 PM
Frankly, by the time you've screwed one together, it would be as cheap to buy one:

If you're happy with 10A then something like this for 119 + vat would do : It'll do 0-30v with 0-10A I-limit

http://www.rapidonline.com/Electrical-Power/Power-Supplies/Bench-PSUs/10A-0-30V-Triple-output-digital-DC-regulated-PSU/77152

http://www.rapidonline.com/netalogue/zoomed/Large/M077152W01.jpg (http://www.rapidonline.com/netalogue/zoomed/Large/M077152W01.jpg)

Jonathan
21-11-2010, 05:55 PM
That power supply looks good. Similar to what I use for the same purpose just a bit bigger.

I get the sulfuric acid from B&Q...in the form of 'one shot drain cleaner'. It's about 7 for a litre of 91% concentration...so do be careful! One finds all sorts of uses for it...

blackburn mark
21-11-2010, 06:15 PM
haha!! nice one jonathan,,, somthing else to pick your brain on when i get to it :)

Swarfing
21-11-2010, 11:33 PM
Careful the drain cleaner stuff is quite diluted. Go to a motor factor and ask for motorcycle top up acid. You can get it 1 litre bottles for a couple of quid. If you want more take a friend as they sometimes limit you to 1 per customer. i have 6 litres sat on my kitchen floor waiting for me to finish something worth anodising? caustic soda you can ask the local shop to get you some on their next trip to the cash and carry (do that part outside for god sake,,,fumes, fumes, fumes). Dylon dyes work better than the others (not the one you put in the washing machine). Hope this helps

Jonathan
22-11-2010, 01:11 PM
Careful the drain cleaner stuff is quite diluted. Go to a motor factor and ask for motorcycle top up acid. You can get it 1 litre bottles for a couple of quid. If you want more take a friend as they sometimes limit you to 1 per customer. i have 6 litres sat on my kitchen floor waiting for me to finish something worth anodising? caustic soda you can ask the local shop to get you some on their next trip to the cash and carry (do that part outside for god sake,,,fumes, fumes, fumes). Dylon dyes work better than the others (not the one you put in the washing machine). Hope this helps

I'm afraid I have to disagree. The one shot drain cleaner I mentioned is concentrated, 91% sulphuric acid. I don't call that dilute! I also got caustic soda cheap from B&Q. Those are about the only things I'll buy from that shop :lol:

As for the dye I've only used the anodising dye sold on eBay. I found that the red dye I got faded with direct sunlight on my wind turbine - other than that they're fine.

Swarfing
22-11-2010, 02:26 PM
Jonathan

I can only vouch for what i have seen and used, most of the drain cleaners claim to be concentrated but do come in different strengths. What you get from the motor factors is acid and not cleaner which contains other ingredients. The caustic soda i use is commercial grade and stripped all the paint off my 72 year old lathe no trouble at all. Preparation as with all jobs is the critical part and there is very little difference between anodising dye and clothing dye. The stuff you get from Ebay will not be from ICI? others report poor colouring from red in general. If it was a true commercial quality dye it would have the correct fixers for aluminium and the fading would be minimal. Give the dylon stuff a go you may be surprised? and make sure you have thoroughly neatralised the effects of the acid beforeadding the dye.

M250cnc
22-11-2010, 04:09 PM
Thanks Bill they just look so overkill for what i want. Cheaper than ebay as well.

As regards One Shot that is a brand name for Sulphuric acid & yes its 91% concentrated. Drain cleaner can be anything that cleans drains.

The only water you should use in your processes is de ionised to avoid contamination.

The anodising acid should be gently agitated by air bubbles as you can get heat build up around the part with them amps.

Phil

BillTodd
22-11-2010, 09:48 PM
Thanks Bill they just look so overkill for what i want

if you only need constant voltage there are cheaper options (look at Rapids switch mode 30A supplies), but if you want constant current (or current limit) there's no easy/cheap way to do it.

Actually, it is possible to get some current control by carefully selecting incandescent bulbs to run at their warm (low resistance)/very hot (high resistance) transition power, but it's probably not worth it these days.