Allen-Bradley PLC: 7 Questions Every Purchasing Manager Should Ask (Before Spending a Dime)

Why I’m Writing This (and Who I Am)

I’m the office administrator for a mid-size automation integrator—about 80 people across two locations. I manage all the vendor purchases, roughly $450k annually across 12 suppliers. When engineers come to me with requests, they don’t care about my job title; they just want the right gear, fast, without blowing the budget.

When I took over purchasing in 2020, I thought buying a PLC was like buying a laptop—pick a model, compare prices, done. Turns out, that’s about as wrong as using an Allen‑Bradley PLC to charge your airsoft gun battery. (Yes, someone actually asked me that. No, it doesn’t work.)

So here’s a quick FAQ based on the questions I get most often—from engineers, from finance, and from my own painful mistakes.

Q1: What exactly is an Allen‑Bradley PLC, and why is it so expensive?

An Allen‑Bradley PLC (Programmable Logic Controller) is the brain of industrial machinery—it reads sensors, runs logic, and controls actuators like motors, valves, and pumps. Rockwell Automation’s Allen‑Bradley line includes CompactLogix, ControlLogix, Micro800, and the classic PLC‑5 series.

The cost isn’t just the hardware. You’re paying for 30+ years of field-proven reliability, a massive ecosystem of I/O modules, and the programming software (Studio 5000, formerly RSLogix 5000) that ties it all together. Cheap knock‑offs exist, but when a line stops, the hourly downtime cost is usually 10x the PLC price.

One thing I wish I’d known earlier: The total cost includes training. An engineer who knows Siemens won’t magically know Allen‑Bradley. Budget for a allen bradley plc programing course—or your shiny new PLC will sit on a shelf for two weeks.

Q2: How do I choose the right model for a pump control panel?

Pump control panels are a classic application. You need a PLC that can handle analog inputs (pressure transducers), handle start/stop logic, and maybe do PID for constant pressure. Our go‑to is the CompactLogix 5380—good balance of cost, speed, and I/O density.

But here’s the trap: engineers often spec a ControlLogix because it’s what they used in a bigger plant. For a single pump panel, that’s overkill. I learned this the hard way—in 2022 we bought a ControlLogix L33ER for a sewage lift station. Worked fine, but we paid 40% more than needed. Now I always ask: “Is there a Micro820 that can do the same job?” (Often, yes.)

If you’re sourcing a pump control panel that includes an Allen‑Bradley PLC, get the panel builder to quote two options—one with a CompactLogix, one with a Micro800. The difference in BOM cost can be $1,200–$1,800.

Q3: How do I test for power with a multimeter on a PLC system?

This question comes up when troubleshooting. Engineers ask me to order spare power supplies, but first they need to confirm if the supply is dead. Here’s the quick version:

1. Set your multimeter to DC voltage (50V or higher).
2. Measure across the +24V and 0V terminals on the power supply. You should see 24V DC ±10%.
3. Check the breaker or fuse. If the voltage is 0, the breaker might be tripped or the fuse blown.
4. Test the AC input first. Most PLC power supplies expect 120/240VAC. If that’s missing, the DC side won’t have power.

I’ve seen engineers skip step 4 and blame the PLC, only to find a tripped upstream breaker. When I consolidated our spare parts inventory in 2023, I realized that 30% of our “dead” power supplies were actually fine—the issue was external. Knowing how to test for power with a multimeter correctly can save you a $200 replacement order and a week of downtime.

Q4: Can an Allen‑Bradley PLC be used to control an airsoft gun battery charger?

No—and I’ll tell you why I have to include this question. Last year, a young engineer asked me to buy a Micro850 to “regulate the charging current for his hobby battery.” He thought a PLC could replace a dedicated charger IC. The idea isn’t crazy in theory—a PLC can output PWM—but in practice, PLCs aren’t rated for the switching frequencies, precision, or safety certifications needed for battery charging.

The point of this story: A vendor who says “we can do anything” is dangerous. A good vendor—or a good internal specialist—knows where the boundary is. For a airsoft gun battery charger, you want a dedicated charger circuit, not an industrial controller. I’m glad I pushed back on that request; otherwise we’d have wasted $1,200 and possibly damaged someone’s batteries.

This aligns with my philosophy: professionalism means knowing what you don’t do well. Rockwell Automation doesn’t make battery chargers, and they shouldn’t. If a supplier claims their PLC is a universal solution for everything, run the other way.

Q5: Do I need to buy programming software separately?

Yes, and this is where first-time buyers get caught. The Rockwell Automation Allen‑Bradley PLC hardware doesn’t include Studio 5000 or RSLogix 500. You’ll need one of these:

• Studio 5000 Mini Edition (for CompactLogix 5380, $~1,500) – limited to small systems.
• Studio 5000 Professional (full feature, $~7,000) – includes everything.
• Connected Components Workbench (CCW) (free) – for Micro800 and some older models.

Pro tip: If you’re a small shop, look at the Micro800 line. The CCW software is free, and the programming is ladder logic. Your engineers may already know it. In our 2024 vendor consolidation, we switched one line from Siemens S7-1200 to Micro820, and the total software cost dropped from €3,000 to zero.

But wait—if you need advanced motion or safety, Micro800 won’t cut it. Know your application before you buy.

Q6: What’s the best way to get allen bradley plc training for our team?

I’ve tried three approaches: in‑person at a Rockwell distributor, online self‑paced courses (Rockwell’s own), and on‑site from a freelance instructor. The most cost‑effective was the online course for basic PLC programming ($200/person for 8 hours of video). But for advanced topics like motion control, the in‑person class (2 days, $1,200/person) was worth it—our engineer came back and immediately fixed a bug that had been costing $800/hour in scrap.

One caution: don’t buy training without checking that the instructor uses the exact PLC model you own. We once booked a generic “Rockwell Allen‑Bradley PLC programming” class, and they spent half the time on ControlLogix when we only had CompactLogix. Waste of $2,400.

Q7: Should I buy from a distributor or direct from Rockwell?

Direct from Rockwell is usually only viable for huge accounts (volume discounts). For the rest of us, authorized distributors like Graybar, Motion Industries, or Radwell offer better pricing, quicker delivery, and local support.

What matters more than the channel: verify stock. In Q3 2023, a supplier promised a 1769‑L33ER in 2 weeks—delivered in 6 weeks. We lost a customer because of that. Now I ask for a stock confirmation in writing, and I keep a backup vendor for every critical model.

Final thought from my desk:

Every purchasing decision for an Allen‑Bradley PLC comes down to three things: fit for the application, total cost (including software, training, and spares), and supplier reliability. Ignore the hype about “one‑stop shops.” Specialists who know PLCs are better than generalists who sell everything. And please, don’t use a PLC to charge your toy batteries.

Prices as of May 2024; verify current rates with your distributor.