Extra resitance Cont.

[potsked]

Back from the holidays im ready to start cracking on this crippling problem of mine. since fibergeek's last correspondance went unanswered ill repost it and answer it


fibergeeks words:


I believe you electrical connections are fine; something else is causing this 13.8V business, Im sure you tested your connections thoroughly.

So what's next? A possibility:

What if your power supply will not go below 13.8 volts (or so) in CC mode, only CV mode. Power supplies made these days operate by series regulation; the variable element (transistor or MOSFET) is in series with the load. In shunt regulation (like my VCCS) the variable element is in parallel with the load. Shunt regulation will go all the way to zero volts and amps but it dissipates more power than series regulation; which means it costs more, hence is less popular. This doesn't apply to premium power supplies; Agilent (HP), Tektronix, Lambda, and many others. These have the electronics to force tight regulation in both modes, which also costs money. I know the data sheet for your Chinese PS says it does CC mode down to zero, but does it really?

This can be tested by putting a power resistor across the power supply (disconnected from the anodizing setup) put the PS in CC mode and see if it will go down to zero volts. The resistor should be about 10 ohms 10W or more watts. Increase the current, don't go over 1 Amp unless the resistor is higher wattage. If CC mode is working correctly, you should be able to vary the current between zero and 1 amp, and the voltage goes from zero to 10 volts. You can get power resistors from your local Radio Shack.

If your PS won't go to zero volts in CC mode, you can fix it by putting an appropriate power resistor in series with you anodizing setup, ideally dropping the voltage to zero or close to it at startup. This should not degrade CC operation if you have enough voltage available (and you do).

There could also be an isolation issue which if fooling the circuitry in your PS, but try the above first.

__________________________________________________ _________

Well i know my power uspply will go below that voltage because when doing very small parts it will go down quite low, but still, not low enough. if you still think it might be a problem, ill go get a resistor from circuit city.

i recently posted about a bunch of fine black dust in my tank, what is this exactly? could it affect results?

some more input that might prove helpful, i adjusted my electrolyte to the old standards of high current anodizing since i was having much more success back then. i have found there to be a dramatic improvement, but im still having flaws like i was back then, maybe a little bit more often though.

i mention this because i think the fact that my results improve when raising the electrolyte acidity and increasing current density might indicate a specific problem. what might this indicate? why would a highger current (12 amps a sq. foot) and more acidic electrolyte improve results?

thanks for the help
Happy New Year

Bill May

[Fibergeek]

Get a resistor and try the test I described. Be sure to do it in CC (constant current ) mode. If it will go to zero in CV (constant voltage) mode it doesn't prove a thing.

You said that with small parts it will go quite low. How low is that in volts?

I don't have a clue what the black dust is. If it were white it could be a buildup of aluminum sulfate, which is a by product of anodization. How much anodizing have you done with your present batch of electrolyte? Aluminum will also buildup in the tank, if it gets to be too much bad things happen. It takes about 100 sq.ft. of anodizing in a 3 gal. tank for this to become a problem.

What is your electrolyte temperature?

Are you using a mist suppressant? If so, what kind?

[neilfj]

I don't know what the black is, but it is a contaminant of some sort and is not normal. Could it be affecting your results? Definately a possibility. It is possible that whatever the contaminate is, is it was in solution during your last attemps and it may have been the reason for the poor results. It is also possible that this same stuff eventually precipitated out of solution, which is the the black power on the bottom of the tank.

The only time I've come across a black substance is when I put the aluminum in stripper and keep it in there for 5+ minutes. A black powder forms on the surface of the aluminum, but it washes off. It is possible that if you have used something to strip the aluminum, some of this residue may have gotten into your electrolyte.

Any contamination of the electrolyte will cause a change in resistance and a change in the conductivity of the electrolyte. This will in turn require a change in the voltage or current in an attempt to compensate for the change.

[potsked]

the black residue seems to be eminating from the cathodes because the Cathodes are covered in a fine dark greyish residue that wipes off. i routinely leave the cathodes in the electrolyte solution because ive been told it has no real negative effect.

ive had them in the electrolyte for around 5 or 6 months, i have recently started taking them out, de-smutting them (which turns them a light light grey) and using them again, but doing this has yielded little effect.

all i ruled out through that is that the condition of the cathodes dont affect the process, its precipitate still might be causing a problem. the only way i could filter that stuff out would be to use an inline pump with some sort of filter, im getting something along those lines prob sometime next week, so ill have to wait until then to find out if this is indeed the problem.

On an end note, neomoses, who is having similar problems to mine, never mentioned any sort of black precipitate. i recently asked him through email if he has had any of this, but ive yet to get a reply.

[neilfj]

The graying of the cathodes is normal and as you stated removal of it is easy, and it really doesn't bother the anodization unless the buildup is so great it increases the resistance of the electrolyte, but the thin layer is normal. I've left my cathodes in the electrolyte for a few months but I haven't had any BLACK material deposited on the bottom of the tank. But, then again, I always clean the cathode prior to using it if it has sat around unused for a long period of time. Not because of the gray buildup, but due to the growth of white salts that build up on the aluminum connectors over time.

Filtering the contaminate out may not fix the problem, especially if it is in solution. You may filter out the precipitate, but it won't remove the item that is still in solution, so it may not fix your problem, (if the 'contaminant' is really the problem). You may find that if it is determined that this is your problem, the only fix may be to replace the electrolyte completely.

Besides the acid and water, has anything else been added to your electrolyte such as mist suppressant? Is it possible that some steel, copper or brass metal has gotten into it?

[neilfj]

Potsked;

I just checked my anodiztion bath and it has dark gray specks at the bottom of the tank. Are your specks dark gray or black? If its dark gray, it is the oxidization of the cathodes that is slothing off into the electrolyte and settling on the bottom of the tank and isn't of any concern. If they are black, then we are back to where we were in the above post.

My acid bath was mixed about 2 weeks ago and has been used twice, so I don't know what happens if it sits for 4-5 months. Perhaps it turns from dark gray to black and the amount increases. I don't know if large amounts of this stuff will affect the process or not.

[potsked]

yes, they are a dark grey, ive had my current electrolyte for 2 months now and ive used it extensively. i believe you are right about it being the oxidation of the cathodes.

[neilfj]

Are you using a mist suppressant?
What temperature are you dyeing the piece at? 110 Deg?

[potsked]

i am not using a mist suppresant and i am dying at probably around 50 degrees, maybe less. i have this whole thing in my garage, and while i heat my ano tank, i dont bother to heat everything else. i know you'll probably point to this as the problem (and now that you mention it i will definitely test it as the problem), but the parts come out dyed inconsistantly, i would think that all cold would do to dyes would be to make them less intense, lighter.

ill test that theory tonight and get back results tomorow, has anyone else had dye temp affect the results in the way i've described?

[neilfj]

Without a doubt, dye temperature will affect the quality of the color, including inconsistent dyeing and washed or faded out colors. Caswell's recommends dyeing at 110 deg F, but I've found that 130-140 deg F works better for me. What ever you do, don't go about 140 deg F. You want to leave a buffer of 30-40 degress between the dye temp and the sealing threshold. Too high a dye temp and you will begin to approach the temperature at which the anodization will seal, in which case you'll seal the coating before the dye can be fully absorbed.

Also, if you are using Caswell products, not using the degreaser, de-ox/de-smut at the correct temperature will also cause problems as these things only work properly when within certain temperature ranges.