Agitation in what way? A pump or aerator ?Agitation of the bath solved my burning issues at higher currents
Agitation in what way? A pump or aerator ?
PTFE stir bars are the normal way of agitating acids. You'd have rotating opposed pair of magnets under or on the side of your container - thats whats inside an expensive lab hotplate.
Overhead stirrers are reasonably common too, usually only on really big vessels or really thick liquids which would stall a magnetic bar, they're seriously expensive for what they are.PTFE stir bars are the normal way of agitating acids. You'd have rotating opposed pair of magnets under or on the side of your container - thats whats inside an expensive lab hotplate.
That so cool, I've already got a little peristaltic pump and a stir plate...I wasted quite a bit of time messing around with magnetic stirring and perilastic pumps for drinks dispense, drop a stirring bar into the glass then you could use the pumps to pour a cocktail in slowly enough that the ingredients would stay floating in separate layers. Then carefully put the glass on a ring of led lights on the bar top and it would magically stir itself before the customers eyes.
It was a good gimmick but I never came up with a decent way of stopping people choking on the stirring bars.
I have been using one of the CC/CV boards that has been mentioned in this thread but results have been mixed. I find I have to constantly keep an eye on things as the current can be set but after a while I see it increasing so I have to turn the pot down again, then again and again and if I get distracted I can sometimes find I have cooked the aluminium.
So I decided to go for one of the many bench supplies you can get and it arrived today. It seems good so far messing about with it but the real test will be tomorrow when I use it for actually anodising a part.
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Ideally, a good psu would behave well, in terms of keeping a constant current, from the instant you switch it on. In reality, as the unit warms up, you may get some drift for a few minutes. For the same reason, it's always a good idea to have the psu sitting in a well-ventilated spot, especially if you are using it at a significant fraction of its maximum current rating.
The one I had was just a board that I connected to a 28v DC PSU, it was supposed to be a CC/CV board . I would turn it so it was, say, 24v then usually have to wait a while to set the current as it usually started low but then would increase. So as I go back after a while and see the current is increasing I would adjust the pot to where it just started to drop and you would think great that is it set but no, I would go back again and the current is increasing again so I would turn down the pot again and this would go on. I am not just talking fractions of amps, I can set it at 2 Amps then 20 mins later it is at 4 Amps so I turn down then another 10 or 20 mins later it is again creeping up to 4 Amps. If I do not check again for 30 mins I can go back and it is now doing 7 or 8 amps. I thought at first it was a dodgy board but I have tried 3 and all did the same.I had the same issues when I started doing it.
It's because the anodized coating is an insulator so as the coating grows thicker it insulates the part more so the power supply up's the current to mantain the voltage.
You want a constant current power supply rather than a constant voltage.
You can use the insulation properties of the coating to test for uniformity of coating and coating thickness.
This one has some specs, whether they are Chinese specs or real ones I am not sure but it does seem reasonably good so far but today will tell for sureIdeally, a good psu would behave well, in terms of keeping a constant current, from the instant you switch it on. In reality, as the unit warms up, you may get some drift for a few minutes. For the same reason, it's always a good idea to have the psu sitting in a well-ventilated spot, especially if you are using it at a significant fraction of its maximum current rating.
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@hoods if you are close enough to cook the parts after minutes (rather than hours) of distraction you might be overdoing them anyway. Have you measured any of your coating thickness so far?
Thats odd, Im using the same boards I think, and they work, It will hold the current limit steady, but yes its a pain to initially adjust as I always turn the wrong pot!The one I had was just a board that I connected to a 28v DC PSU, it was supposed to be a CC/CV board . I would turn it so it was, say, 24v then usually have to wait a while to set the current as it usually started low but then would increase. So as I go back after a while and see the current is increasing I would adjust the pot to where it just started to drop and you would think great that is it set but no, I would go back again and the current is increasing again so I would turn down the pot again and this would go on. I am not just talking fractions of amps, I can set it at 2 Amps then 20 mins later it is at 4 Amps so I turn down then another 10 or 20 mins later it is again creeping up to 4 Amps. If I do not check again for 30 mins I can go back and it is now doing 7 or 8 amps. I thought at first it was a dodgy board but I have tried 3 and all did the same.
The one I had was just a board that I connected to a 28v DC PSU, it was supposed to be a CC/CV board . I would turn it so it was, say, 24v then usually have to wait a while to set the current as it usually started low but then would increase. So as I go back after a while and see the current is increasing I would adjust the pot to where it just started to drop and you would think great that is it set but no, I would go back again and the current is increasing again so I would turn down the pot again and this would go on. I am not just talking fractions of amps, I can set it at 2 Amps then 20 mins later it is at 4 Amps so I turn down then another 10 or 20 mins later it is again creeping up to 4 Amps. If I do not check again for 30 mins I can go back and it is now doing 7 or 8 amps. I thought at first it was a dodgy board but I have tried 3 and all
I wired in multiturn pots and put the lot in a housing of sorts so fairly easy to adjust but even before that I still had the issue.Thats odd, Im using the same boards I think, and they work, It will hold the current limit steady, but yes its a pain to initially adjust as I always turn the wrong pot!
I dont have space to store a bench supply, so will have to continue with the boards.
Want to do more anodising but first, I need to make some parts!
Voltage drops.What was the voltage doing when the amps were climbing?
Oh and the bench supply I got is pretty small, it is no bigger than the current PSU and boards I have and much better as it is all in one rather than 3 separates. I measures 200mm front to back, 100mm wide and 150mm high and is 30v/10A....
I dont have space to store a bench supply, so will have to continue with the boards.
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That's not right - sounds like they're NFG. The new PSU sounds ideal.I can set it at 2 Amps then 20 mins later it is at 4 Amps so I turn down then another 10 or 20 mins later it is again creeping up to 4 Amps. If I do not check again for 30 mins I can go back and it is now doing 7 or 8 amps. I thought at first it was a dodgy board but I have tried 3 and all did the same.
if you are close enough to cook the parts after minutes (rather than hours) of distraction you might be overdoing them anyway.
That's not right - sounds like they're NFG. The new PSU sounds ideal.
I use a bench power supply and the current stays completely constant. (The voltage is initially very low - about 6V - but rises rapidly to ~20V then slowly drops for a bit before rising again.)
No, it's the current density that does the damage - you get pitting and the corners get chewed off. It's more of a risk early in the process, before a decent film develops.