Most expensive purchasing mistakes in a controls environment are not caused by the price on the quote. They’re caused by the verification step I skipped before the PO went out.
I’m the office administrator for a 30-person controls company. I manage roughly $400,000 in MRO and spare-part orders per year, and I report to both operations and finance. When I started in this chair in 2020, I thought my value was simple: find the cheapest Allen-Bradley PLC that matched the words in a request. I was wrong.
What my 1756 order taught me about ‘cheapest Allen-Bradley PLC’
Not long after I took over purchasing, an engineer asked me to find a spare Allen-Bradley PLC 1756 input module. In his head, the installed base was obvious. In mine, a 1756 module was just a bulky black rectangle with pins on the back. I searched the supplier site for the lowest price, picked an in-stock Series, and told everyone it was handled. It was not handled.
The module arrived, but the Series did not match what was already installed. The project lead didn’t want to compromise, so we paid a restocking fee, reordered the correct revision, and waited another two weeks. I still kick myself when I remember that purchase order.
‘Cheapest Allen-Bradley PLC’ still shows up in my inbox. Budgets are real, and I understand why people ask it. But I no longer answer it as if it is a complete sentence. First I ask what the plant already runs. Then I ask which communications module and power supply sit next to it. Then I ask whether the request is meant as a replacement or an upgrade. Those questions take far less time than a return label does.
Rockwell Automation publishes series information and compatibility details for the 1756 family so people like me can verify before spending money. The hard part is not access. The hard part is remembering that a spare part is only cheap if it is the right spare part.
Battery chargers taught me the same lesson in 12 volts
The same pattern shows up in our battery orders. A control cabinet may have a 12V backup battery for a wireless signal conditioner, an alarm panel, or a small remote radio. When a maintenance lead asked me to replace a charger, I typed ‘trickle battery charger 12V’ into the same supplier site and assumed I was finished.
I was not finished. The old charger was designed for a lead-acid battery. The new backup battery was a lithium battery. A lead-acid trickle charger keeps a battery at a steady float voltage. A battery charger for lithium battery usually has to control the charge profile differently. They are both 12V in a loose way, but they are not interchangeable.
What made it click was placing the old charger and the new battery side by side. Both labels said 12V. One said float, the other said charge limit. If I had compared labels before ordering, I would have seen the difference in 60 seconds. I didn’t compare because the voltage looked familiar. That was the mistake.
Now I look at the battery chemistry before I look at anything else. If the label says lithium, the purchase line should say ‘battery charger for lithium battery.’ If the label says lead acid, a 12V trickle battery charger can be the right answer. The point is not the category on a supplier website. The point is the match between charger and battery.
How to test AA battery with multimeter, and why I bother
I came to the AA battery question later, through a less technical door. We go through AA cells in meter kits, radios and panel accessories. For a long time, I treated every returned battery as a dead battery. Then I asked our field tech to show me how to test AA battery with multimeter so I could stop ordering duplicates.
The process is simple. Set the multimeter to DC volts and, if it has a manual range, choose the lowest range above 1.5V. Touch the red probe to the positive terminal and the black probe to the negative terminal. A fresh alkaline AA usually reads around 1.5V or a little higher. A no-load reading below about 1.2V tells me not to put that battery back into a kit. If the no-load voltage looks fine but the battery still seems weak, test it under load. Put the battery in a simple flashlight and measure across the battery while the light is on. The loaded voltage tells the truth better than the resting voltage does.
I’m not pretending this is high-level engineering. It just reinforces the same habit: test first, replace second, verify third.
What I say when someone argues there is no time
I know the objection. When a panel is down, nobody wants to hear that an admin buyer needs three more checks before ordering. If the production line is already stopped, every minute feels urgent. But a wrong order does not solve urgency. It converts one downtime event into two. The first downtime is the original problem; the second is the new part arriving in the wrong Series, with the wrong charging profile, or without the spec checked.
Prevention is not the slow path. Prevention is the shortest path to the first working run. Five minutes of verification can save five days of correction. I have seen it too many times to go back to the old habit.
So here is my position: the cheapest Allen-Bradley PLC is not a number in a supplier database. It is the one that matches the system before it is ordered. The cheapest battery is the one tested before it is replaced. And the cheapest charger is the one that matches the chemistry on the label.
