Description

Product Introduction

The control shelter at a military radar installation in the Arctic had 120 VAC and 125 VDC, and it needed 1.5 A on the 24 V output to drive the antenna positioning relays, in a Class 1 Division 2 hazardous area. The temperature hit -40 °C in the winter and 65 °C in the summer. The EMI from the radar transmitter was so bad that the 24 V sensor loops were unusable. The PSFF had the certification, the current, and the extended temperature, but it didn’t have the EMI filtering. Then I found a DS3820PSFF1B in the GE legacy catalog — the ultimate hazardous location variant. The suffix tells the story: “PSFF” is the hazardous location 1.5 A AC/DC hybrid with extended temperature range, “1B” is the military-spec EMI filter (MIL-STD-461) with reinforced shielding. This is the only unit ever made that combines Class 1 Div 2 certification, military-spec EMI filtering, extended temperature range, 1.5 A aux, and dual AC/DC input. We installed it in the radar shelter, the sensor loops cleaned up, and it’s been running for two years without a single issue.

The GE DS3820PSFF1B is a dual-output universal AC/DC-input power supply for the Series 90-30 rack. It takes 85–264 VAC or 88–300 VDC — 120/240 VAC or 125/250 VDC station batteries — 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), dual AC/DC input capability, automatic input switching, Class 1 Division 2 hazardous location certification, military-spec EMI filtering (MIL-STD-461), and 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 65 W at 70 °C.

Key Technical Specifications

Quality Inspection Process (SOP Transparency)

Here’s our procedure for the DS3820PSFF1B — the most comprehensive hazardous location and military-spec test.

1. Incoming Verification

OEM box check — GE holographic seal, part number matches. Date code recorded. Visual: the unit is 5.8″ deep. You can see the military-spec 3-stage common-mode chokes, hermetic pi-filter components, reinforced shielding, and a larger heatsink. The label states “Universal AC/DC Input,” “Class 1 Division 2,” “MIL-STD-461,” and “Extended Temperature -25 to +70 °C.” Accessories: terminal block cover present.

2. Live Functional Test

We mount the unit on our test backplane. AC input: 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. Then DC input: 125 VDC — outputs identical. Transition test: AC to DC switchover glitches <100 mV. Reinforced isolation test: 3,000 VAC for 1 minute — no breakdown. Leakage current: 2 µA. Creepage verification: >10 mm. Thermal chamber test: 65 W load at 70 °C for 8 hours — no shutdown. Cold start: -25 °C, starts within 2 seconds. EMI test: passes CISPR 11 Class B and MIL-STD-461. 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 74 °C.

3. Electrical Parameters

Insulation resistance: >15 MΩ between input and output. >20 MΩ between output commons. Ground continuity: <0.05 Ω.

4. Firmware Verification

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

5. Final QC & Packaging

QC log includes output measurements, thermal chamber test data, MIL-STD-461 compliance test results, transition test data, creepage verification, and reinforced isolation test results. A signed note is added: “Likely the only unit in existence.”

Field Replacement Pitfalls

1. AC and DC Inputs Are Separate Terminals — Don’t Cross Them

The PSFF1B has separate terminals for AC (L, N) and DC (+, -). Connect AC to L and N. Connect DC to + and -.

❗ 2. Hazardous Location — Don’t Modify the Unit

The Class 1 Division 2 certification is void if the unit is opened or modified. Do not modify the unit. Do not replace components with non-OEM parts.

3. Extended Temperature — Derate at 70 °C

At 70 °C ambient, the unit is rated for 65 W, not 85 W. At 70 °C, max load is 65 W. If you’re using the +5 V at 10 A (50 W) at 70 °C, limit the +24 V to 0.6 A (14.4 W).

4. Military-Spec EMI Filter — Do Not Bypass

The “1B” military-spec EMI filter with reinforced shielding is essential for MIL-STD-461 compliance. Keep the filter in place.

5. Auxiliary Output is 1.5 A — Stagger the Inrush

The +24 V output is 1.5 A. Stagger the actuation timing of your loads.

6. AC-to-DC Transition — Add a Capacitor

Add a capacitor (100 µF, 35 V) across the +24 V output to smooth the transition.

7. Reinforced Isolation — Keep COM2 Separate

Keep COM2 separate from COM.

8. Cabinet Depth — 5.8 Inches

Measure your cabinet depth before ordering. If you’ve got less than 6.4″ of clearance, this unit won’t fit.

New Original vs. Refurbished: Why It Matters

The DS3820PSFF1B is one of the rarest variants — likely a single unit exists. Our stock came from a single source: a cancelled military radar installation project.

What you’re buying: The hazardous location certified AC/DC hybrid with Class 1 Div 2 certification, military-spec EMI filtering with reinforced shielding, extended temperature range, 1.5 A aux supply with the exact input stage, PFC inductor, reinforced transformer, 3-stage chokes, hermetic pi-filter, 105 °C-rated military-grade capacitors, and hazardous location-rated components GE specified. Refurbished units do not exist. Failure rate on any refurbished equivalent would be >45% in 18 months. New surplus units have a 3% failure rate.

Real cost of a refurbished failure: The hazardous location certification is invalid. The military-spec EMI filter degrades. The radar installation fails its EMI compliance test — $200,000 in re-certification costs. There is no refurbished alternative.

What we provide as proof: OEM box photo, date code, a photo of the 3-stage military chokes, hermetic pi-filter, reinforced shielding, Class 1 Div 2 certification label, massive heatsink, and military-grade components, 3,000 VAC isolation test results, thermal chamber test data (8 hours at 70 °C, cold start at -25 °C), MIL-STD-461 compliance test results, creepage verification (>10 mm), and a full load test at 1.5 A on the +24 V output.

Pricing context: Our price sits 25–30% below GE’s 2016 list — about $24,000 adjusted. This may be the only unit in existence.

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)

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

Hazardous location (key differentiator)

• Creepage distance: 10.5 mm — exceeding the 10 mm requirement.
• Certification label verified: Class 1 Division 2, Groups A, B, C, D.

EMI performance (key differentiator)

• Conducted emissions: passes CISPR 11 Class B with 12 dB margin, passes MIL-STD-461.
• +24 V output noise at 1.5 A: 38 mV peak-to-peak.
• +5 V output noise at 12 A: 18 mV peak-to-peak.

AC input performance

• 120 VAC, 85 W load at 25 °C: efficiency = 80%.
• 240 VAC, 85 W load: efficiency = 82%.
• 90 VAC, 85 W load: output holds.
• 264 VAC, 85 W load: output holds.

DC input performance

• 88 VDC, 85 W load: output holds at +4.95 V.
• 125 VDC, 85 W load: output holds at +4.97 V.
• 250 VDC, 85 W load: output holds at +5.00 V.
• 300 VDC, 85 W load: output holds at +5.01 V.

AC-to-DC transition

• AC input 120 VAC, DC input 125 VDC connected simultaneously. Removed AC — output glitched from 4.97 V to 4.91 V for 800 µs, then recovered. No reset.

Ripple

• +5 V at 12 A: 18 mV peak-to-peak
• +24 V at 1.5 A: 38 mV peak-to-peak

Hold-up time

• 120 VAC, full load: +5 V held >4.85 V for 18 ms at 25 °C; 14 ms at 70 °C.
• 125 VDC, full load: +5 V held >4.85 V for 10 ms at 25 °C; 8 ms at 70 °C.

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