Q) How well would it work to use a small programmable pulse rectifier to modify the output of a larger (75volt, 500amp) rectifier to generate a pulse output for anodizing?
I intend to connect them in parallel. - Harold Botwright
A) To start with, NEVER connect rectifiers in parallel unless the rectifiers are specially designed to be connected that way, and always check first with the manufacturer. In your case, do not connect them in parallel, or it will be a very short, smoky event.
I assume that you are trying to have the large rectifier ‘follow’ the pulse pattern generated by the pulse rectifier. This is possible by using the output signal of the pulse generator as a reference signal for the large rectifier. First, you need to know what maximum reference voltage or current level the rectifier accepts on the voltage and current inputs (typically 0-5V, 4-20mA or 0-10V) and then make this value the maximum output value of the pulse generator/rectifier. A limiting factor, however, will be the rate of change that the rectifier can output. A standard rectifier will always need a certain time to get to a certain output level, so if your pulse generator outputs relatively short pulse times, the output of the rectifier will not be able to exactly follow the reference signal, resulting in a distorted output waveform.
Q) We plate out copper in a reclaim system for our plate pickling tanks. We are considering the purchase of a new rectifier and I wanted to know how to spec a rectifier for the ripple percentage and how ripple effects plating. Our reclaim tank is comprised of a series of lead and copper plates. The pickling solution is 10/12% sulfuric at 110 degrees. The material we pickle is copper or copper/nickel alloy. - Ray Walkowiak
A) For pickling, the output ripple of the rectifier does not really matter. If you know the maximum voltage and current your process needs, you can select a rectifier with a maximum output of around those values. Using a standard thyristor-controlled rectifier or a tap switch rectifier will give you the lowest ripple (5%) and the highest efficiency.
Q) We have a cathodic electrocoating paint bath in which 2 different lines are passing. The conveyor speeds are same.We are putting 3 sets of electrodes.One at each side & third one at the middle of the tank. The component loading on both the lines may or may not be similar. For this configuration, whether we should go with one rectifier or 2 different rectifiers of same capacity & why ? What is the best alternative? - V.R.Paithankar
A) The best alternative here would be 2 rectifiers. With 2 rectifiers you can individually control the process voltage/current for each line, enabling you to individually control the coating thickness depending on the total surface area per line.
Q) Several years ago we installed variable speed frequency drives to control the rpm rates of the motors on our 2 plating lines. Since that time there has existed an apparent energy field which radiates throughout the building.(11,000sq') For example, when I pull up in front of the bldg to park my am radio station is overtaken with static, second the eddymag measuring units on the shop floor continually loose their set points and accuracy during the day and need to be recalibrated every 2 hrs.
We were advised and did install filters that were supposed to work but have not. I have asked many but seldom gotten a straight answer? -Budd Wines
A) From my experience with VFD’s I can only think of the ‘Carrier Frequency’ setting of your drives as a possible source. I’ve seen situations in the past where the Carrier Frequency setting was set relatively low, resulting in a high level of noise on the motor lines.
Q) Reverse pulse plating in a sulfamate Ni electroforming bath. We are not using such. What are the advantages in time savings, etc? – Bob Adams
A) Reverse pulse plating in a sulfamate Ni bath does bring some advantages.
- Slight improved throwing power: a standard DC process gives about 10% throwing power, reverse pulse can improve this to 25%. I even heard some customers claiming 50%, but that seems high. Some users benefit from this in their electroforming process: they can skip some steps of mechanical machining during their 900 hour process, due to less whisker forming and improved material distribution.
- The crystal structure can be influenced, and therefore the hardness. Hardness between 150V and 500V can be obtained.
Plating time saving is minor, but with thick layer electroforming there are savings possible due to less machining steps.
Q) What are the advantages and disadvantages of using a tap switch rectifier for type II anodizing? – Glenn Triplett
A) There are no advantages only disadvantages
The main disadvantages are:
- No control
You can only set the output voltage. The current will first shoot up and will than drop which results in longer process times in comparison to a controlled system.
So your manufacturing cost are higher because you pay more for energy due to the longer process time. If your coat is 0.6 mil instead of 0.5 mil your energy cost are 20 % higher than you have calculated.For a small 3000 A rectifier these are 0.7 US $ per load. Which totals up to 1.4 US $ an hour for just one tank. So for just one tank per day it is about 17 US $. It sums to about 4500 US $ a year for just one tank.
Of course it gets worse if your deviation between the requested and achieved oxide thickness is even higher.
- More manpower
To set the rectifier correctly somebody needs to stay next to the rectifier to ramp it up and to re-adjust the taps. Of course this also results in additional costs.
- Quality
Manual operation results in pour repeatability.
Rework needed due to burning; over anodizing etc. can not be calculated.
- Maintenance-Tap switches need to be maintained and spare parts are very expensive
Advantage of a controlled system
Money savings from the first load - No or less over anodizing, less manpower, less maintenance.
Q) What does output Ripple of a rectifier mean and how can I measure it?
A) The output Ripple of a rectifier is a fluctuation of the output DC Voltage of that rectifier. Technically spoken it is an AC (Alternating Current) component superposed on a DC (Direct Current) voltage. Different types of rectifiers will behave different as far as the output Ripple is concerned depending on the application and settings. When we talk about Ripple in percentages we are talking about the amount of fluctuation of the output voltage.This Ripple can be calculated by dividing the RMS voltage of the AC component by the average value of the DC output voltage, then multiplying the result times 100%.
There are a number of Ripple meters available from various suppliers.The capability of these meters vary from just a read out of the output Ripple, to added functionality such as warning/fault outputs with adjustable levels.An other common method of measuring output Ripple is to measure the output voltage with a True RMS multimeter in the AC mode to measure the AC component. Then measuring the average output voltage by switching the meter to DC mode. Divide the first measurement by the second and multiply by 100 and you have the output Ripple value.
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