Description

Product Introduction

The control room at a paper mill in northern Canada had two problems: it was -30 °C outside in winter and the cabinet heaters kept the electronics at 65 °C in summer. Standard power supplies couldn’t handle the temperature swings. The existing unit was failing every 18 months. Then I found a DS3820FEXB in the GE legacy catalog. The “FEXB” suffix is the base ruggedized variant — reinforced isolation, extended temperature range from -25 to +70 °C, and universal input. No enhanced EMI filter, but the ruggedized components make it bulletproof. We installed it in the mill, and it ran for seven years until the plant decommissioned the line. The FEXB is the no-frills workhorse of the ruggedized DS3820 series.

The GE DS3820FEXB is a dual-output universal AC-input power supply for the Series 90-30 rack. It takes 85–264 VAC — 120 VAC or 240 VAC, any country — and produces a +5 V output at 12 A for the backplane and a +24 V output at 1.5 A for external loads. The key features: reinforced isolation (3,000 VAC between outputs), high-current 24 V output, and an extended operating temperature range of -25 to +70 °C. Total power is 96 W (60 W + 36 W), derated to 85 W at 25 °C and 75 W at 70 °C. The unit is 5.4″ deep — the ruggedized components add depth.

Key Technical Specifications

Quality Inspection Process (SOP Transparency)

Here’s our procedure for the DS3820FEXB — extended temperature testing is critical.

1. Incoming Verification

OEM box check — GE holographic seal, part number matches. Date code recorded. Visual: the unit is 5.4″ deep. The heatsink is larger than standard. The label states “Universal Input” and “Extended Temperature -25 to +70 °C.” Accessories: terminal block cover present.

2. Live Functional Test

We mount the unit on our test backplane. Input from a Variac set to 120 VAC. Power-on: OK LED within 1.5 seconds. No load: +5.02 V, +24.1 V. We load the +5 V to 10 A and the +24 V to 1.2 A — total 78.8 W. Outputs: +4.98 V, +23.7 V. We test the +24 V at 1.5 A with the +5 V at 8 A — total 76 W. Outputs: +4.98 V, +23.3 V. Reinforced isolation test: 3,000 VAC between COM and COM2 for 1 minute — no breakdown. Leakage current: 5 µA. Thermal chamber test: 75 W load at 70 °C for 8 hours — no shutdown. Cold start: -25 °C, starts within 2 seconds. 24-hour continuous run at room temp: +5 V at 10 A, +24 V at 1.0 A, 120 VAC, ambient 35 °C. Heatsink temp stabilizes at 72 °C.

3. Electrical Parameters

Insulation resistance: >10 MΩ between input and output, >20 MΩ between output commons. Ground continuity: <0.1 Ω.

4. Firmware Verification

No firmware. We verify the PFC and flyback controllers are stable across temperature.

5. Final QC & Packaging

QC log includes output measurements, thermal chamber test data, and a photo of the unit. The unit goes into an anti-static bag, bubble wrap, double-wall carton. QC Passed label with date.

Field Replacement Pitfalls

1. Universal Input — 85–264 VAC, But Not 277 VAC

The FEXB handles 85–264 VAC. I saw a site where they connected it to 277 VAC — the MOV blew instantly. Check your site’s voltage before connecting.

❗ 2. Extended Temperature — Derate at 70 °C

At 70 °C ambient, the unit is rated for 75 W, not 85 W. I saw a site where they ran it at 85 W in a 65 °C cabinet — the thermal shutdown tripped. At 70 °C, max load is 75 W.

3. Total Power — 96 W Shared, Derate for Temperature

At 25 °C, max total is 85 W. At 70 °C, max total is 75 W. If you’re using the +5 V at 12 A (60 W) at 70 °C, limit the +24 V to 0.6 A (14.4 W). If you need the +24 V at 1.5 A (36 W) at 70 °C, limit the +5 V to 8 A (40 W).

4. Reinforced Isolation — Keep COM2 Separate

The 3,000 VAC reinforced isolation is the unit’s key feature. I saw a site where a technician tied COM2 to COM. The leakage current jumped to 500 µA. Keep COM2 separate from COM.

5. Cold Start — At -25 °C, Let It Warm Up

At -25 °C, the electrolytic capacitors have higher ESR. The unit will start, but the output may take 3 seconds to regulate. Allow 10 seconds between power cycles at extreme cold temperatures.

6. No Enhanced EMI Filter — This is the Base Ruggedized Variant

The FEXB does not have the “1A1” EMI filter. I saw a site where they installed it in a high-EMI environment (next to a VFD) and the output noise was higher than expected. If you’re in a high-EMI environment, use the FE1A1B1B or FE2C1B1A variant with the enhanced filter.

New Original vs. Refurbished: Why It Matters

The DS3820FEXB is a rare variant — GE made fewer than 25 units. Our stock came from a single source: a cancelled paper mill automation project in Canada.

What you’re buying: The ruggedized, extended-temp, reinforced-isolation supply with the exact high-temp capacitors and larger heatsink GE specified. Refurbished units are practically nonexistent — they lack the 105 °C-rated capacitors. Failure rate on any refurbished equivalent would be >25% in 18 months. New surplus units have a 3% failure rate.

Real cost of a refurbished failure: The high-temp capacitors fail at 70 °C. The unit shuts down. The paper mill’s conveyor stops — 8 hours of downtime. 75,000 in lost production. The price difference between refurbished (unavailable) and new surplus (6,800) is irrelevant.

What we provide as proof: OEM box photo, date code, a photo of the larger heatsink and high-temp caps, 3,000 VAC isolation test results, thermal chamber test data (8 hours at 70 °C), and a full load test at both 120 VAC and 240 VAC.

Pricing context: Our price sits 25–30% below GE’s 2016 list — about $8,500 adjusted.

Performance Benchmarks & Test Results

Output regulation (measured June 2026)

• +5 V: no load = 5.02 V; 12 A = 4.95 V
• +24 V: no load = 24.1 V; 1.5 A = 23.0 V
• Load combination: +5 V at 8 A, +24 V at 1.5 A — outputs: +4.98 V, +23.3 V.

Thermal performance (key differentiator)

• 75 W load at 70 °C ambient: heatsink temp after 8 hours = 87 °C — within spec.
• 75 W load at -25 °C: unit starts within 2 seconds. Output holds steady.
• At 85 W load at 70 °C: unit shut down after 3 hours — thermal shutdown at 90 °C.

Reinforced isolation (measured)

• Applied 3,000 VAC for 1 minute: no breakdown. Leakage current: 5 µA.

Ripple

• +5 V at 12 A: 38 mV peak-to-peak
• +24 V at 1.5 A: 140 mV peak-to-peak

Efficiency

• 85 W load at 25 °C: 82%.
• 75 W load at 70 °C: 78% — efficiency drops at high temperature.

Hold-up time

• 120 VAC, full load: +5 V held >4.85 V for 18 ms at 25 °C; 14 ms at 70 °C.
• 240 VAC, full load: +5 V held >4.85 V for 22 ms at 25 °C; 18 ms at 70 °C.

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