The Many Hats of Rectifier Repair

Do you ever look around your shop floor and wonder where all the downtime comes from? What about feeling the stress of multiple breakdowns? When it rains, it pours. It is easy to feel overwhelmed in the maintenance and upkeep game while dealing with chemicals, pumps, rectifiers, cranes and controls of the vital production lines in your facility. With temperatures warming up and the humidity skyrocketing, electrical repairs in a metal finishing shop are going to happen more and more frequently. How can we take the time to assess our systems, trace the damage and make meaningful repair decisions that work for us, not just band-aiding the line to have another part go down and find ourselves back at square one? In order to make the best repairs, we need to wear a few different hats.

Hat One: Electrical Safety

Safety first, and safety always. You need to focus on the rectifier’s current state, and whether or not it is going to continue to cause damage to itself and other equipment, or present a danger to workers. You should assess the area after a breakdown to see if there are lingering hazards: chemical spill, standing water, arc flash residue, leaning debris, fuses not cleared, stored potential energy in water or capacitors, etc. Once you have determined the coast is clear, you need to lock out the power supply while alerting all nearby parties that you will be performing work on the machine. As an added safety precaution, you should then measure if there is power present on the output buss bars — some processes and machines may have coexisting powers in the tank. With no power present, you can then assess the repair.

Hat Two: Electrical Troubleshooting

Ok, what blew up? What parts are damaged? How do we prove they are damaged or not working correctly? This last question may present a challenge to those less tenured maintenance professionals. How does one check to see if a relay is good or bad? Is the coil damaged? Are the relay contacts within designed limits? Is the mechanical actuation of the relay arm smooth? There are many great sources of maintenance training, from suppliers to books on Amazon, to online videos. If your team needs some dedicated efforts in training, be sure to fill that gap sooner than later — the payback is immediate and significant.

Whatever list of parts are determined to be not functioning, replacements should be sourced or readily available on the shelf. If they are on the shelf ready for install, congratulations! You saved you and your company days to weeks of supply chain uncertainty. If the parts need to be sourced, have someone with the engineering or sourcing experience verify that any alternative parts match the key core engineering specifications required of that part.

• Thyristors and Diodes: voltage and amperage ratings, clamping force, and heat characteristics
• Relays: coil voltages, number of circuits, and options on those circuits
• Fuses: element curves, voltages, currents, and time ratings/cycle counts
• Cooling Blocks: water flow rate, temperature exchange, pressure thresholds
• Fans: RPM (revolutions per minute, current draw, voltage requirement, form factor, pitch of blade for CFM (cubic feet per minute)
• Transformers: Voltage ratio, total available wattage, current capacity, frequency, winding arrangement

Hat Three: Risk Manager

Alright, we assessed the electrical safety, and now we found the parts in the rectifier that failed. Do we just replace them and hope for the best? I am absolutely certain your production team has been screaming at you to restore the line to producing product. What parts or systems were attached to your failed parts? Are these damaged, or compromised now in the life cycle due to the initial failure?

This small bit of analysis can dramatically increase the time between failure on your machine. The responsible approach to proactive replacement of parts will pay dividends in time saved long term. But how do we distinguish between shotgunning parts into a machine and being deliberate and precise with which layers of parts we install? How do we maximize the efficiency of the money we spend before hitting a wall of diminishing returns? I have a method I would like to share with you.

When we analyze the rectifier component that failed, we can trace the power that feeds that part (upstream) and we can trace the power that the failed component itself supplies or feeds (downstream). We used our technical knowledge on the component to know how it functions to qualify it as working or not working. This stream of power gives us a sub-system snapshot of how that “assembly line” is supposed to work.

            A -> B -> C -> D -> E
Let’s say the damaged part is labeled “C” in the flow above.

We can see that in the pictured flow, where C failed. C feeds the downstream D, which in turn feeds downstream E. C is fed by upstream B, which in turn is fed by upstream A. We can almost look at the components in the system like layer rings on a target or growth rings on a tree. If C is the center ring, then B and D are the next outermost layer, and A and E are the farthest most layer.

We can see the B/D layer as the most likely to be compromised in the event of failure. These are the parts that give the largest return on investment for replacement. Of course, there are exceptions, and of course, it depends on the severity of the failure… but as a rule of thumb, this is the greatest payback for your efforts in repair. This limits the spider web effect of damage from shortening the life expectancy of the supporting parts in the system — the parts directly preceding and directly after the damaged component — and having breakdowns happen again in a short amount of time. Bulletproof your repair to lengthen the time between failures of your machine.

Stepping out of your role as a repairman and into the multiple roles that drive value into your repair is difficult but rewarding. The knowledge you employ pays dividends in saved time and maintaining functionality for longer. You can achieve stronger, more durable repairs, improve the life expectancy of your rectifier, save on the cost of ownership, and improve the safety of your facility for your employees.