PHILIPS PE-1957/26 | 24VDC Output for Process Control | Direct Replacement Unit

Description

Key Technical Specifications

Product Introduction

I’ve lost count of how many plant shutdowns started with a “mysterious” 24V drop that traced back to a failing power supply humming like an angry bee. The PHILIPS PE-1957/26 was built before “planned obsolescence” became the industry standard. It’s a heavy, metal-cased beast designed for European manufacturing lines that ran 24/7 for decades without a hiccup. Unlike the flimsy plastic units you see today, this thing weighs a ton because it uses real copper and oversized heatsinks.Engineers hunt for these because they handle transient spikes that would fry a modern budget supply instantly. In my experience, the PE-1957/26 maintains its 24V output within 1% even when the input voltage sags to 90VAC during motor startups. That stability keeps your PLCs from rebooting mid-cycle. Just be warned: these are old. If you buy a unit that sat in a humid warehouse for 15 years, the electrolytic capacitors might be dry. Always demand a load test report before installing it in a critical loop.

Quality SOP & Tech Pitfalls (The Reality Check)

The Lab Report (SOP)
We don’t trust 20-year-old electronics until we’ve abused them a bit. Here is our protocol for the PE-1957/26:

1. Visual Inspection: We check for bulging capacitors, burnt PCB traces, or corroded terminal blocks. If the varnish on the transformer looks cracked, we scrap it.
2. Capacitor Reforming: Before applying full power, we slowly ramp up the voltage using a variac to reform the oxide layer on old capacitors. Skipping this causes immediate shorts.
3. Full Load Burn-in: We hook it up to an electronic load and draw 20A for 4 hours at 40°C ambient. If the voltage droops more than 0.5V, it fails.
4. Ripple Measurement: Using an oscilloscope, we verify ripple is under 100mVpp. High ripple kills PLC input cards over time.
5. Safety Test: Hi-Pot test at 2500VAC to ensure isolation hasn’t degraded. Then it goes into an anti-static bag with silica gel.

The Engineer’s Warning (Pitfalls)
The biggest mistake I see? Assuming “24V is 24V.”

• Trap 1: Parallel Operation. Do not simply wire two PE-1957/26 units in parallel to get 40A. They lack current sharing circuitry. One unit will take the entire load, overheat, and shut down, dumping the whole load onto the second unit, which will then trip. You need diode OR-ing modules if you want redundancy.
• Trap 2: Inrush Current. These old supplies have massive inrush currents. If you daisy-chain ten of them on a single 16A breaker, they will trip the breaker instantly on startup. Sequence them or use soft-start breakers. I once saw a whole rack fail to boot because someone didn’t account for the simultaneous inrush of six of these bricks.

Installation & Configuration Guide

Swap this out safely. Electricity doesn’t forgive sloppy work.

1. Pre-Installation (⚠️ CRITICAL):
   • Lockout/Tagout (LOTO): Cut the main AC feed. Verify zero energy with a multimeter.
   • Discharge Wait: Wait 2 minutes after power off. The internal capacitors hold a nasty charge that can bite you.
   • Photo Documentation: Snap a picture of the wiring. Note the L/N/Ground and +/- DC connections.
2. Removal:
   • Disconnect DC load first, then AC input.
   • Release the DIN rail latch (usually a clip at the bottom). Slide the unit down and off.
   • Inspect the DIN rail for corrosion. Clean it if necessary.
3. Installation:
   • Check the Trim Pot: Before mounting, measure the output voltage. Adjust the small potentiometer on the front to exactly 24.0VDC. Don’t rely on factory settings.
   • Clip the unit onto the DIN rail firmly. Ensure it clicks into place.
   • Reconnect wires. Torque the terminals to spec (usually 0.5-0.6 Nm). Loose terminals = arcing = fire.
4. Power-On & Testing:
   • Remove tools and close the cabinet.
   • Restore AC power. Listen for the fan (if equipped) or any high-pitched whining.
   • Measure the DC output under no-load, then gradually apply load. Verify voltage stays stable.
   • Check the status LED. Solid green means you’re good. Blinking red means fault—shut down immediately.

Compatible Replacement Models

Frequently Asked Questions (FAQ)

Q: Can I use this to replace my modern 24V power supply?
A: Physically, yes, if it fits on your DIN rail. Electrically, absolutely. The PE-1957/26 is often tougher than modern equivalents. Just check the dimensions; it’s a bit bulkier than today’s slimline models.Q: My unit is making a loud buzzing noise. Is it dying?
A: Maybe. A slight hum is normal for older linear-style switching supplies under load. But a loud, erratic buzz usually means a loose transformer core or a failing capacitor. If the voltage is steady, it might run for years. If the voltage is jittery, replace it now.Q: How do I know if the capacitors are bad?
A: Look at the top of the cylindrical components inside (if you can see them). If the tops are domed or bulging instead of flat, they are dead. Also, if the unit trips instantly on startup, that’s a classic sign of shorted caps.Q: Is it safe to run this at full 20A load continuously?
A: Only if the ambient temperature is below 40°C. If your cabinet is hot (over 50°C), you must derate it. Run it at 15A max. Heat is the enemy of old power supplies.Q: Can I adjust the output voltage higher, say to 28V?
A: The trim pot usually allows ±10%. Pushing it to 28V is possible but not recommended for long-term operation as it stresses the internal components. Stick to 24V unless your specific load demands otherwise.Q: What is the warranty on these obsolete units?
A: We offer a 1-year warranty. Since these are discontinued, we can’t get new parts from Philips. If it fails, we swap it with another tested surplus unit. We stand behind our testing process.Q: Do I need a special tool to adjust the voltage?
A: No, just a small flathead screwdriver. But do it carefully. Small turns make big differences. Measure while you turn. Don’t guess.