Power supply for the MELSEC L backplane
The Mitsubishi L61P is a power supply module for the MELSEC L series PLC rack, delivering a rated 5 A at 5 V DC to the backplane. It accepts a universal input of 100…240 V AC (-15%…+10%) at 50/60 Hz (-5%…+5%), making it usable on 120 V or 230 V line feeds without a tap change. Efficiency is rated at ≥ 70%, and maximum input apparent power is 130 VA — so at full 5 A output the module pulls roughly 25 W from the line, with the rest dissipated as heat inside the enclosure. That heat matters for panel thermal budgeting if the rack is densely populated. Inrush current hits 20 A for ≤ 8 ms on power-up. That's a short pulse, but if you're coordinating a shared branch circuit with multiple supplies, factor it into the upstream MCB or fuse selection to avoid nuisance trips.
Protection and ride-through
Overvoltage protection clamps the 5 V rail at 5.5…6.5 V, and overcurrent protection kicks in at ≥ 5.5 A. That means a sustained overload or a short on the backplane will trip the supply before the 5 V rail sags enough to brown out the CPU or I/O modules. Allowable momentary power failure is ≤ 10 ms — the supply holds up the 5 V rail through a brief line dip or a contactor bounce. For longer interruptions the PLC will see a power-loss flag and the program state depends on the CPU's retentive memory settings. Hi-pot withstand is 2300 V AC for one minute between the combined line/LG terminals and the FG terminal plus output, tested at altitudes up to 2000 m. That's the production-line dielectric strength test; field meggering should stay well below that threshold.
Installation notes
Input voltage distortion should be ≤ 5% to stay within the supply's design margin. Dirtier line power (common on sites with VFDs or welding loads sharing a transformer) may reduce the hold-up time or stress the input rectifier — a line reactor or isolation transformer is cheap insurance.