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topic 14061

Anodising rectifier and power requirements


Q. 1. I am required to sulphuric anodise a component with a surface area of approx. 7 sq mts. What is the best way of calculating how much power is required and if the existing rectifier will cope. Also is there an anode to cathode surface area ratio which must be taken into account.

2. Given the details above if the rectifier is 24V 1000A would this be capable of anodising the component at 7 sq. mts. surface area.

Ian Beckwith
- United Kingdom


probert book
Aluminum How-To

"The Chromating - Anodizing - Hardcoating Handbook"
by Robert Probert

A. The 24 volts would be plenty; 15 volts would probably be adequate. But I figure 7 square meters is 75+ square feet. That means your maximum possible current density would be 13.3 ASF. That's low. An anodizing rectifier should probably be sized for about 20 ASF.

I wish the rest of the world would enter the 21st century and start using the foot-pound-second system :-)

Ted Mooney, Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey
We need "Aloha" now more than ever


A. Ian,

Your rectifier should be plenty if you are doing type II will not have enough volts to do type III. I don't have my conversion chart here at home (I don't think we Americans will ever totally convert to the metric system).. but you want to anodize around 12-15 amps per square foot of surface area (for type II), so.. 1000 amps will be plenty. I'm not sure if you were asking what the work to cathode ratio should be.. but you want to keep it around 3-1 (work to cathode).

Marc Green
Marc Green
anodizer - Idaho


A. I somewhat stand corrected..thanks, Ted..I mis-calculated the meter-to foot number...however I believe his 1000 amps will BARELY be enough to anodize at 13 asf. Ya'll remember..back in grade school..when they said "10 years from now, EVERY country will be using the metric system"...sheeesh..its been almost 20 yrs.. and we STILL aren't there.

Marc Green
Marc Green
anodizer - Idaho


A. I've designed many anodizing lines, but I don't actually run them, Marc, so I yield to your actual experience; but I would not design for 13.3 ASF--I think it's too iffy. I'd design for 18-20 ASF.

Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey
We need "Aloha" now more than ever


A. You're correct, Ted, he would be pushing the limits -- butI guess I tend to look at things from a different point of view sometimes. I got the impression he had a job he needed to get done, and assuming it wasn't going to be an ongoing production job where the purchase of another rectifier could be an option, that he could "get by" using his current set-up. Sometimes ya just gotta wing it a little bit in our business as long as quality isn't affected. And while running at 13 asf may take a wee bit longer to get his desired thickness, I still believe he could achieve a quality product in the end. (Go St. Louis Blues!)

Marc Green
Marc Green
anodizer - Idaho

January 21, 2014

"Surface Treatment & Finishing of Aluminium and Its Alloys"
by Wernick, Pinner & Sheasby
from Abe Books
info on Amazon

Q. I have an anodizing plant with rectifier size of 24 V, 2000 Amps, using sulfuric acid of 165-170 gm/litre. Size of anodizing tank is 21' x 3' x 3'. We are applying current density of 13 Amps/Sq. ft. for a period of 30 minutes with the batch load being 100-120 Sq. ft.

The problem is with electricity consumption. Actually I am confused with electricity consumption. Right now the electricity consumption is 27-28 units (KW-hr) per batch. Please let me know what should be the actual electricity consumption per batch. Also for information my chiller is of 10TR, cooling tower pump, condenser pump, chilled water pump each of 2 HP. Please guide.


Rahul Mogal
- Nashik, Maharashtra, India

January 28, 2014

A. Hi,
To calculate the energy that you use we need voltage, current and time of processing. We have the time. You give the current density at 13 ASF. Taking a batch load of 110 sq ft (the mid-value), the current is
110 * 13 = 1430 amps.
I guess that the voltage is greater than 16 and less than 20, so let's take 18 volts.
Power used is
18 * 1430 = 25740 watts = 25.740 kw
Time is 0.5 hours so energy in kwh is
25.740 * 0.5 = 12.87 kwh
If the efficiency of your power supply is 80% then load on supply is 12.87 * 100 / 80 = 16.0875 kwh. There is a big difference between the the calculated kwh and actual.
There are 3 possible explanations:
1) I have made a mistake in the calculations
2) The figures I have used are incorrect, especially the assumed efficiency
3) The kwh (27-28) that you quote includes the cooling demand.


Harry Parkes
- Birmingham, UK

March 26, 2014

Q. Hi
I am looking to add to my current factory a type III anodizing facility.
I have 2500 x 200 x 1300 mm Anodizing tank. With a 10-20A; 500-2000V Transformer (can I use this or do I have to upsize?) and will a 240V-250Amp electricity supply be enough?

The Type III plant needs to be a min L x W x H of 2000 x 800 x 1200 mm.
How can I calculate the specifications, including power requirements for Chiller and Rectifier.
Finally what method of chilling is best, direct or indirect. I see some pipes in lead whilst I have been informed that titanium pipes would be better.

Is there anyone who has set up a Type III plant who can start us off in the right direction.
Any help from those who have had a hand in setting up a similar setup would be appreciated.

James Morford
Photofabricators - Durban, Natal, South Africa

March 2014

A. Hi James. Setting up a hard anodizing plant is a large undertaking which, in my opinion, ought to involve retaining an anodizing consultant. You might look at our Directory of Consultants.

But to your specific questions, there appears to be a typo in your question since you say your available tank is 200 mm wide and you need a minimum of 800 mm wide. If it's actually 2000 mm wide, it could hold two loads at a time, which might be useful -- but hopefully you realize that an anodizing line requires a lot more tanks than one :-)

You need to start with the area of the load, and an estimate of the required Amperage and voltage -- perhaps 30 ASF at 75 volts. From this you calculate the rectifier size and the transformer size.

This would give you the maximum instantaneous cooling load, but recognizing the anodizing solution in the tanks and the cooling water reservoirs, etc., the system will have some thermal inertia/momentum, so you probably don't have to size the cooling system for quite the maximum instantaneous load, maybe 75%-80% of it.

I think titanium is a better bet than lead, and that an external heat exchanger is a better idea than cooling coils in the tank. Don't forget a really powerful air agitation system (or eductor system) for hard anodizing. Good luck.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey
We need "Aloha" now more than ever

Can plating rectifiers be used for anodizing?

December 30, 2015

Q. Hello everyone!
I recently ran some initial testing parts for anodizing type II with my nickel line rectifier, but few days later I was told that this electroplating rectifier might get damaged running anodizing, does anodizing require a different type of rectifier?

Alberto Nunez
electroplating - Brownsville Texas, USA

December 2015

A. Hi Alberto. Anodizing tends to require more volts and fewer amps than most electroplating. (Most plating operates at about 4.5 to 9 volts, whereas anodizing will take 12 to 18 volts; many metals are electroplated at about 30 to 40 ASF, whereas anodizing will be about 12 to 18 ASF.

But the biggest difference is that you have to start anodizing at low voltage and slowly ramp up. That's because (per Ohm's Law), current is inversely proportional to resistance, and there is very little resistance in raw aluminum, but a lot of resistance in anodized aluminum. If you don't start at low voltage you'll burn the parts; if you stay at low voltage, you won't build anodizing thickness.

But damaging the rectifier? I don't think so as long as you turn it down at the start.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey
We need "Aloha" now more than ever

December 12, 2016 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Hi,

I wanted to know if a EMS 7.5-300 power supply would work for decorative aluminum anodizing. I am have made several failed attempts on 6061 and I think the size of the power supply is the reason? Any suggestions on what to buy?

david wasserman
- hockley,texas us

December 2016

A. Hi David. We appended your inquiry to an existing thread on the subject. You'll need at least 12 volts absolute minimum even for selected alloys, preferably 18 volts, whereas your unit generates only 7.5 volts. Sorry, it's not enough.You'll need an amperage capacity of, say, 18 amps per square foot of surface area you will be processing.


pic of Ted Mooney
Ted Mooney, P.E. RET
Pine Beach, New Jersey
We need "Aloha" now more than ever

December 2, 2018 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. I need to know what size Rectifier to get to Anodize (class III ) on parts about 1/8" thick by 12" long. Also on a very small piece of aluminum I saw somebody use a 6 Volt battery so is that even possible?
Thanks in advance.

Michael Blount
Student - APOPKA

December 2018


Readers can see our Intro to Anodizing if they are slightly lost :-)

A. Hi Michael. Type 3 anodizing requires more voltage and more amperage than conventional (Type 2) anodizing. You are going to need 24 amps/ft2 and at least 24 volts even for "quasi" type 3 (48V, 75V, and 90V rectifiers are not unusual for Type 3 anodizing, depending on the alloy).

You can put aluminum into a sulfuric acid anodizing bath and only apply 6 volts, and some amount of aluminum will be converted to aluminum oxides, but the result will not be even a realistic type 2 anodized layer, let alone type 3.


pic of Ted Mooney
Ted Mooney, P.E. RET
Pine Beach, New Jersey
We need "Aloha" now more than ever

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