DC power supply question

insanity · Mar 29, 2003

I am looking to get a DC power supply in order to do the following, elecroplating, anodizing and etching. From what I've been able to figure out I am looking for a 0-150VDC 0-8 amp power supply, or thereabouts. I was hoping that some of you who have far more knowledge in the electrical arts than I do could tell me if this seems reasonable or if I'm way off base. Thank you

WS

Tom Militano · Mar 30, 2003

I think most of the anodizers that are being used are ac variacs that are run through a bridge rectifier and changed to dc voltage. At least that's how mine is set up. I bought a brand new variac off of E-Bay a couple of years ago for $27.00. There was a used one the same as mine that everybody was bidding on. I was the only bidder on mine for some reason. My variac is 0 to 240 volts and 10 amps. I think it cost me about $35.00 for the entire setup. They sell them ready to go for about $500.00, which is why mine is homemade.

SkaerE · Mar 30, 2003

how many volts and amps do you need to anodize? i have read that almost all of the colors you can reach are w/in the first 50 volts or so then they repeat. so you really wouldnt need more than about 130 max for any reason anodizing right?

rlinger · Mar 31, 2003

You want a lot of current at a lot of DC voltage. As stated in an above post, the most economically effective solution I know of is to use a Variac (Variac is a trade name and the correct technical term is 'auto transformer') and a power rectifying bridge to convert to DC.

I know nothing about electroplating by way of experience but wonder if you need such high voltages for that.

Roger

pso · Apr 1, 2003

What one needs here is a "variable transformer". The term "variac" may have started out as a trade name but it is used as commonly in the electrical and electronics industries as "kleenex" and "aspirin".

An "auto-transformer" is a transformer where there is only one winding so there is NO electrical isolation possible between the input and the output. The adjustable ones are often refered to as "variacs". Please note that not all auto-transformers are adjustable, so be careful when buying one. You may get a non-ajustable auto-transformer.

When choosing your rectifier, get a bridge type. It will save you a lot of wiring, compared to getting individual diodes. They can be mounted with one screw or bolt and the mounting area is electrically isolated from the terminals. This is MUCH easier to do than mounting individual diodes. Get one where the current rating is at least 2 - 3 times the maximum output current rating desired. Get one with a voltage rating that is at least 2 times your maximum voltage. These components are not expensive and it is not much more to get the higher current/voltage models. It is probably not worth it to scrounge one out of an old piece of equipment since it may be quite difficult to determine what the ratings are.

If you don't know much about electricity, then find someone who does to help you. You could get seriously hurt or killed with the voltages and current capacities involved here.

Insanity:

For electroplating, you may need to add a bank of filter capacitors. I recall one of my former co-workers talking about the circiuts that he used to design for electro-plating plants. I do not know if the capacitors are required for etching and anodizing. I could e-mail him and ask though the state of the art may have moved some over the last 20 years.

Phil

Sweany · Apr 1, 2003

caswell

insanity · Apr 1, 2003

This is great I was going to ask about the differences between a bridge rectifier and the diodes. Did I mention that all you folks are great and I've gotten more information from reading this site than anywhere else? If not it's true.

WS

rlinger · Apr 2, 2003

As stated above, a bridge rectifier is an integrated device in a single package which contains (basically) four diodes in the bridge configuration. Also, again as explained above, descrete rectifying diodes can be used instead to make the bridge. Electrolytic capactor(s) (a polorized capacitor - having a positive and negative lead) are used to filter ripple caused by rectifying sinusoidal AC and are attached between the bridge positive and negative output. Depending on the purity required an inducter is sometimes introduced between two electrolytic capacitors to further level the current. These filtering capacitors may not be needed for your purposes and are not incorporated into the integrated rectifying bridge but are attached external to it by you. I do not know enough about electroplating and anodizing to say how clean the direct current should be.

For your usage, mount the bridge rectifier on a heat sink (whether it be one designed specifically for it or an aluminum plate that you come up with).

While it is true most of the industry loosely uses the term Variac as a generic term for the device they make, the device is actually an auto transformer and it is correct that it does not have to be variable to be an auto transformer but that all those seen by me that were refered to as 'Variac' have been variable. I always write the name with a capital 'V' because it is a proper name of a manufacture and not generic or a technical term. When I look for them at places such as Ebay or ask about them in casual talk, I too refer to variable auto transformers as 'variac' (without the capital 'V').

Again as stated above, the auto transformer, by design, is not isolated from source voltage (your wall outlet). Unless you know what you are doing keep its output, including the ground - or negative if it is rectified by the bridge -, away from other electrical and electronic equipement that is also powered by house hold or shop AC.

Here is plans for an anodizer, compliments of Bob Warner: http://www.customknifedirectory.com/CKD_TutorialFrameset.htm
Scroll to the bottom part of table of contents where sub catagory 'General and Shop Tutorials' is.

Roger