Choosing a plating rectifier
Most rectifier specifications we are sent are sized from the tank. The tank is not what draws the current — the work in it is.
A plating rectifier is a current source that happens to have a voltage rating. Almost every specification problem comes from treating it the other way round.
Size from current density and work area, not tank volume
The number that matters is amps, and amps come from the area you are plating multiplied by the current density your process calls for. A large tank running small jigs needs far less rectifier than its volume suggests; a small tank running dense racks can need more.
Voltage then follows from the bath: its conductivity, the anode-to-cathode spacing, and the losses in busbars and contacts. Those losses are not negligible and are the usual reason a rectifier that looked adequate on paper cannot reach the required current in practice — the voltage headroom went into the connections rather than the bath.
Add headroom for the largest jig you actually intend to run, not the average one. Then stop. Buying a 3000 A unit for a line that will never exceed 1200 A means running permanently at the bottom of the range, where regulation and efficiency are both at their worst.
Why ripple is a finish problem, not an electrical one
The deposit follows the current. If the current is not steady, the deposition is not uniform, and that shows up as variation in thickness, brightness and adhesion across a batch — usually discovered at inspection, after the work is done and the time is spent.
Acceptable ripple is a process figure, not a general one. Decorative chrome, functional hard chrome, bright nickel, anodising and CED all have different tolerances, and the number to design to is the one on your process sheet. Where a specification is silent, ask the chemistry supplier rather than assuming the rectifier default is fine.
Constant current or constant voltage?
Most plating is current-driven, because deposit thickness follows amp-hours through the bath. Constant current holds the deposition rate as the bath changes with temperature, concentration and loaded area, which is what makes the result repeatable across a shift.
Constant voltage has genuine uses and CED is the main one. Cathodic electrodeposition is normally run to a voltage profile — a ramp then a hold — because film build and throwing power depend on the applied voltage rather than on total charge. If your process sheet gives a voltage curve, the rectifier has to be able to follow it, and that needs to be stated at enquiry rather than discovered at commissioning.
Say which one at enquiry
A unit built for constant-current plating and a unit built to follow a CED voltage ramp are not the same specification. This is the single most common thing missing from the enquiries we receive, and it is the one that cannot be corrected afterwards with a setting.
One rectifier per tank, usually
Sharing a rectifier across tanks only works where they run the same process and always run together. Each bath draws its own current and reaches its endpoint at its own time; a shared unit means they finish together whether the work is ready or not. On a line running mixed work, separate units cost more at order and less in scrap.
What to send with an enquiry
- Process and bath chemistry, and the process sheet if you have one.
- Current density and the maximum work area per load — this is what sizes the unit.
- Required output: amps, volts, and whether you need constant current, constant voltage or a programmed ramp.
- Ripple limit specified by the process.
- Duty cycle: continuous, or batch with rest between loads.
- Cooling available — air or water — and the ambient in the plating shop, which is rarely comfortable.
- Supply available at the tank, and the busbar run length, because that length is part of the voltage budget.
Questions we get asked
Anything not covered here, call us — most of it is faster to answer on the phone.
01How do I size a plating rectifier?
From current density multiplied by the maximum work area you intend to plate at once, which gives amps. Voltage comes from the bath resistance, anode-cathode spacing and the losses in busbars and contacts. Sizing from tank volume is the common mistake and it usually produces a unit that is too large.
02What ripple percentage do I need?
It is set by your process, not by the rectifier. Decorative and functional finishes have different tolerances, and bath chemistry matters. Take the figure from the process sheet or the chemistry supplier and specify it at enquiry — designing to a generic number is how finish defects arrive later.
03What does ripple actually do to the finish?
It makes the plating current unsteady, so deposition is not uniform. In practice that appears as variation in thickness, brightness or adhesion across a batch, found at inspection rather than during the run.
04Constant current or constant voltage for CED?
CED is normally voltage-driven — a ramp and hold — because film build and throwing power follow applied voltage rather than total charge. Conventional electroplating is usually constant current. If your process sheet specifies a voltage profile, the rectifier must be able to follow it and that has to be in the specification.
05Can one rectifier feed two tanks?
Only where both tanks run the same process and always run together. Otherwise each bath reaches its endpoint at a different time and a shared unit forces them to finish together, which costs more in rework than the second rectifier would have cost.
06Does the busbar length matter?
More than people expect. Losses in busbars and contacts consume voltage headroom, and a long run or a poor joint is the usual reason a correctly sized rectifier cannot reach the required current at the work. Give the run length at enquiry so it can be included.
07Air cooled or water cooled?
Rating and ambient decide it. Plating shops are hot and humid, which is hard on air-cooled equipment, so at higher ratings water cooling is often the practical choice. Tell us the shop ambient rather than the outdoor temperature.
08Can you match an existing unit on a line?
Usually, and it is worth doing where operators are used to one control arrangement. Send the make, model and output ratings of the existing unit along with the process details.