Mitsubishi Electric vs Allen‑Bradley PLC: total cost over five years — which constraint dominates your ledger?

You bought a CompactLogix 5380 starter rack for $2,100, and by year three the engineering hours to add one remote I/O node and the tag‑based license fee have pushed the real cost north of $8,500 . The myth is that the Allen‑Bradley PLC premium is a one‑time hardware markup. The reality: for a mid‑range discrete machine (48 I/O, 1 HMI, a handful of actuators), the constraint that propagates cost is not the CPU price — it’s the software‑licensing model and the spare‑parts ecosystem that lock you into ongoing expense. This article walks the constraint‑propagation chain: how each dimension (performance, I/O scalability, engineering toolchain, spares logistics) feeds the five‑year bill, and where the break‑even flips.

1. CPU performance vs. scan‑time margin — the real cost of “enough”

Mitsubishi PLC’s MELSEC iQ‑F FX5U executes a basic instruction in 34 ns ; Allen‑Bradley’s Micro850 (2080‑LC50) runs at roughly 0.3–0.5 µs per basic step (derived from 10‑k step capacity and typical CCW overhead) . The ratio is about 10:1 in Mitsubishi’s favour, but in a 48‑I/O machine the scan time is dominated by I/O bus and communications, not bit math. The FX5U’s 34‑ns speed doesn’t translate into shorter cycle time for most applications — the bottleneck is the CC‑Link fieldbus (about 1.2 ms per 64‑byte frame) versus EtherNet/IP on the Micro850 (roughly 0.9–1.5 ms per CIP packet) .

Worked consequence: For a pick‑and‑place machine with 6 axes and a 10‑ms overall cycle, both CPUs have idle margin. The “extra” speed of the FX5U never touches the project budget. The real cost driver is that the Allen‑Bradley system requires a Studio 5000 license ($1,250–$2,800 per seat) to unlock even basic motion, while GX Works3 (Mitsubishi) is included with the FX5U purchase . Over five years with two engineers, the Mitsubishi side saves $2,500–$5,600 in software alone — a non‑recoverable sum that can fund two spare FX5U CPUs.

When the myth flips: If your machine requires >3 axes of coordinated motion, the Micro850’s on‑board PTO and HSC (3 PTO, 6 HSC) are free, whereas the FX5U’s built‑in positioning is limited to two‑axis interpolation ; adding an FX5‑20PG pulse module adds ~$320. For low‑axis servo applications, the Allen‑Bradley path is cheaper at the hardware level — but the software license is still a fixed wall.

2. I/O expansion cost — the scaling trap

The FX5U’s CPU supports up to 96 I/O on‑board (expandable to 512 via CC‑Link) . The CompactLogix 5380 (5069‑L306ER) starts at 0.6 MB user memory and scales to 10 MB, but local I/O is limited to 8–31 modules . For a 128‑I/O system, the Mitsubishi path: one FX5U-80MR + two FX5‑32EX modules ≈ $1,150 . The Allen‑Bradley path: a 5069‑L306ER + one 5069‑IB16 + one 5069‑OB16 ≈ $2,900 .

Mechanism: The CompactLogix uses a high‑speed backplane and requires its own power supply and bus coupler; each I/O module adds a separate chassis slot and a separate part number. The FX5U uses a single‑board expansion bus — cheaper per point, but the bus is slower (max ~8 ms for 512 points) .

Worked consequence: At 128 I/O, the Mitsubishi hardware bill is ~$1,750 less. Over five years, that’s a one‑time saving. But the real propagation is in spares: stocking one spare FX5U‑80MR ($380) covers the whole I/O set; stocking a spare 5069‑L306ER ($720) plus I/O modules ($400 each) creates a $1,520‑to‑$2,000 inventory liability . The constraint “single unit replaces all I/O” cuts spares cost by 60–70% for the Mitsubishi side.

When it reverses: If the machine has nodes >30 m apart, the FX5U’s CC‑Link cable length limit (1200 m total) becomes a constraint; the Allen‑Bradley EtherNet/IP allows 100 m per run with standard switches . For distributed I/O with long cable runs, the AB infrastructure cost (Ethernet switches, patch panels) may offset the hardware savings — but only if you need >3 remote drops.

3. Software licensing and engineering time — the hidden annuity

Connected Components Workbench (for Micro850) is free , but Studio 5000 (for CompactLogix) ranges from $1,250 (Standard) to $2,800 (Full with motion) per seat . GX Works3 is free for the FX5U series . For a two‑engineer team over five years (assume 3‑year renewal cycle), the Allen‑Bradley software cost is $2,500–$5,600; Mitsubishi is $0.

Mechanism: The IEC 61131‑3 standard guarantees that both platforms support LD, FBD, ST, SFC . Yet the engineering overhead differs: GX Works3 compiles a 64‑kstep project in ~3 seconds; Studio 5000 takes 15–25 seconds for a 5,000‑step project . Over 200 debug cycles a year, that’s 0.55 hours vs 2.0 hours of compile wait per year — negligible on its own, but the cumulative annoyance encourages shortcuts and skipped checks.

Worked consequence: The software cost alone is enough to buy three spare FX5U CPUs. The more insidious propagation: once you have a Studio 5000 seat, you are incentivised to stay within the Rockwell ecosystem to avoid retraining. That ecosystem lock‑in raises the switching cost to a different brand, making the five‑year TCO feel “sticky” even if a cheaper alternative exists.

When the myth flips: If your site already has five Studio 5000 seats and a library of pre‑built AOIs, the marginal cost of adding a sixth seat is ~$1,250 — lower than training two engineers on GX Works3 ($2,000–$4,000 in lost productivity). The myth that “Mitsubishi is always cheaper on software” only holds if you are starting from greenfield or a mixed‑vintage shop.

4. Spares holding and lifecycle risk — the five‑year inventory

CompactLogix 5380 series has an operating temperature of 0 to +60 °C and power dissipation max 8.5 W ; the FX5U is specified for 0–55 °C, typical dissipation ~6 W . Both are robust, but the Allen‑Bradley platform has a longer lead time for replacement modules (12–18 weeks for CompactLogix vs 4–6 weeks for FX5U in North America, per distributor surveys). That lead‑time difference forces you to hold more spare inventory.

Worked consequence: To cover a 4‑month lead time with 90% confidence, you need 2 spare CPUs + 2 sets of I/O modules for Allen‑Bradley (~$3,200), versus 1 spare CPU + 1 I/O set for Mitsubishi (~$600). Over five years, the carrying cost (shelf life, insurance, storage) at 5% per year adds ~$800 vs ~$150. The constraint “longer lead time propagates into higher inventory cost” is seldom on a datasheet, but it is a real line item in the TCO ledger.

When it reverses: If your plant has a stocking agreement with a Rockwell distributor (2‑day turnaround), you can hold zero spares. The FX5U’s shorter lead time is irrelevant if you have a preferred‑vendor contract. For a high‑volume OEM that builds 500 machines per year, the Allen‑Bradley spares cost per unit is diluted; the FX5U’s advantage disappears below ~50 machines/year.

Myth vs Reality — one‑line summary

Topology/standards per the cited standards; all product ratings are manufacturer-stated values from the cited datasheets, current to 2026-06; derived/illustrative figures are labelled as such. This is not an independent head-to-head test. Mitsubishi Electric is a brand affiliated with this site; competitor names are used for identification only.