Power Supplies

[Newton]

I was ready to buy the 6 volt, 100 Amp rectifier yesterday, but my Caswell sales person said that the 9 or 12 volt rectifier would be better. He couldn't give me a compelling reason to spend more money. He said he called the rectifier manufacturer, and they told him that the 6V, 100A was regulated with a circuit board, and was suited more to gold plate and wouldn't be good for nickel or chrome. I plan to plate (chrome and copy chrome) motorcycle and auto parts up to 800 square inches. Can anyone tell me the pro's and con's of the power supplies Caswell offers? Is the 6V suitable, or do I need the 9V or 12V?

[fxstcguy98]

First off you must understand that if you plan to plate chrome(triple chrome is copper,nickle,chrome) it requires 1A per sq. in. meaning you would need a supply that is 900A or more to plate up to 800 sq. in.
Assuming that you only plan to plate copy chrome, that only requires 1A per 16 sq. in. and a 100A supply should handle 800 sp. in. As far as what Caswells is saying, I can't say I know a reason, 4 to 6V will plate fine in most situations. They might be telling you that the 9V and 12V supplies are more controlable than the 6V for your application. Caswells people usually know what they are talking about, and are ethical in their treatment of customers, they won't milk you.
If your not in a big hurry to get a supply, I would look on e-bay. You can find a bunch on there for a reasonable price, sometimes as little as $1 to $2 per amp. Make sure you get one that has adjustable current and voltage and that it can operate in constant current and constant voltage mode. I bought two off ebay one is a Kepco 0-36V 5A for $35 I got for smaller projects (more adjustable). The other is a Lambda 7.5V 100A for $150 I have for the larger ones. Both work fine. Hope this helps
Darrin

[Fibergeek]

A 9V or 12V rectifier will be more tolerant of less than ideal wiring. You would have more voltage available to drop in the wiring, allowing smaller AWG wire to be used and sloppier connections. This gets important when you are dealing with high currents.

I agree with lurking ebay for used power supplies, you can find some great deals. Neilfj (on the anodizing forum) scored a dandy and quite large CC/CV power supply, the shipping cost more than the unit did. To do this successfully you must be patient, and do some internet research on what is being offered to be sure it will be suitable for your purposes. Be wary of power supplies that are more than 25 years old. The large electrolytic capacitors (the big cans you see inside of the PS) have a limited lifetime and will eventually degrade, causing erratic operation. These are not difficult to replace (even if you aren't the "electronic type").

[Newton]

I did just that. I found a Lambda 0-13V/90A power supply at a reasonable price. If it works, it's a great deal. I plan to load test it as soon as it arrives.

Thanks for your advice.

[jmerson]

Load test

That's an interesting remark. How do you load test?
Jim

[dadkar2]

Load testing commonly refers to a process by which you test to see if the power supply maintains its output voltage up to the rated current. But it can also be a test to determine if the power supply regulates current properly up to the rated voltage.

You'll need some kind of load. Perhaps the most convenient is a bank of automotive light bulbs. You'll also need some way of measuring the current. That's not easy to do at currents above 10 amps. But, it can be done with even a piece of #16 solid wire in the right length acting as a "shunt" resistor across which you can measure the millivoltage, and then compute the current. If you want to know more about measuring large currents, email me and we can discuss further.

Measuring the output voltage is convenient and easy with any decent $39 digital multimeter.


Kind regards,
Ken

[dadkar2]

Good luck with Ebay. People have mixed luck. I bought a 5 amp power supply about a year ago which was advertised as 100% functional, great deal. It came after 3 months. Then when it arrived, it was an overpriced but otherwise great door stop. Totally non functional. I'm an electrical engineer, but I do not have the time to tear apart a power supply and troubleshoot it. With some of these "deals," replacement parts like transformers can cost almost as much as a new supply--assuming you can find replacement parts. I ended up buying brand new supplies and have been as pleased as could be since.

My lesson is that when tempted to buy used power supplies, just wait a little longer and save up for one of Caswell's.

Kind regards,
Ken