Rectifier Ripple and Electroplating

A. You can check ripple with a ripple meter which measures AC and compares it to DC. Most people usually think 5% ripple is close enough for nickel and chrome plating.

Although a properly functioning 3-phase rectifier will automatically produce only 5 percent ripple--that is at full rating, when the input current is coming in as an AC sine wave. If you are operating at reduced output, so your SCRs are outputting shark fins instead of sine waves, your ripple may be much higher and you probably will need a filter choke.

A. My understanding, from looking at the voltage profile of hexa phase-rectification, is that the ripple at full output will be under 5 percent. Please see letter 1424 for more detail. With an autotransformer rectifier, there is no chopping of the incoming voltage as there is in an SCR rectifier, and I believe the ripple will therefore remain at 5 percent at lower output.

You're the rectifier specialist, not me, Mr. Banerjee, so you'll have to tell us what efficiency you predict based on the windings, the size of the core, whether you use copper or aluminum, and a bunch of other factors. My understanding as a user, not a rectifier designer, is that rectifiers range from about 70 percent to about 90 percent efficiency.

A. You can use a large number of tools to actually see the ripple content. I cannot answer what is good or bad. But you can see the ripple. You can use an oscilloscope, AC power analyser or a data logger. There are many suppliers for oscilloscopes including Tektronics, HP, Fluke etc. For AC power analyser you can go for Fluke. For data-logger you can use true RMS meter and the wave form can be seen on a computer. A good quality true RMS multimeter used to check AC voltage on DC will give you very good idea of the ripple content. This is the fastest and cheapest method to check for ripple.

The ripple is the AC component of DC so you need AC measuring equipment, so do not get confused on the recommendation of AC power analyser!

A. Hi, Kunal. We've already answered 5 percent and explained why, and explained the procedures for checking it. So, unfortunately, I'm not quite understanding the question. Could you please review letter 1424 and phrase your inquiry in terms of what has already been said? Thanks!

Regards,