Description

Product Introduction

The control panel at a mid-sized water treatment plant had 120 VAC and 125 VDC, and it needed 1 A on the 24 V output to drive a bank of relays and sensors. The NOTA’s 0.5 A aux wasn’t enough. The larger AC/DC hybrids with 1.5 A aux were overkill. Then I found a DS3820P1MB in the GE catalog — the P1MB is the 1 A auxiliary version of the AC/DC hybrid. Same reinforced isolation, same dual AC/DC input, but with a 1 A 24 V output and a compact 4.8″ depth. We installed it in the plant, the relays ran cleanly, and it’s been running for five years without a single issue. The P1MB is the mid-current AC/DC hybrid.

The GE DS3820P1MB 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 A for external loads. The key features: reinforced isolation (3,000 VAC between outputs), dual AC/DC input capability, automatic input switching, and a mid-current 1 A 24 V output. Total power is 84 W (60 W + 24 W), derated to 80 W continuous.

Key Technical Specifications

Quality Inspection Process (SOP Transparency)

Here’s our procedure for the DS3820P1MB — dual-input testing with 1 A aux load.

1. Incoming Verification

OEM box check — GE holographic seal, part number matches. Date code recorded. Visual: the unit is 4.8″ deep. The label states “Universal AC/DC Input.” 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 0.8 A — total 50 W + 19.2 W = 69.2 W. Outputs: +4.98 V, +23.8 V. We test the +24 V at 1.0 A with the +5 V at 10 A — total 74 W. Outputs: +4.97 V, +23.6 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: 5 µA. 24-hour continuous run: +5 V at 10 A, +24 V at 0.8 A, 120 VAC, ambient 35 °C. Heatsink temp stabilizes at 69 °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 on both AC and DC input.

5. Final QC & Packaging

QC log includes output measurements on AC and DC, transition test data, and reinforced isolation test results. The unit goes into an anti-static bag, bubble wrap, double-wall carton. QC Passed label with date.

Field Replacement Pitfalls

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

The P1MB has separate terminals for AC (L, N) and DC (+, -). Connect AC to L and N. Connect DC to + and -.

❗ 2. Auxiliary Output is 1 A — It Can Handle Relays, But Not Large Contactors

The +24 V output is 1 A. A standard 24 V relay draws 50–100 mA — you can drive 10–15 of them. A contactor coil draws 300–500 mA — you can drive one or two. I saw a site where they connected four contactors (400 mA each) — the output sagged to 18 V. The 1 A output is for relays and small solenoids — not for large contactors.

3. Total Power — 84 W Shared, Derate Above 45 °C

At 25 °C, max total is 80 W. Above 45 °C, derate by 2 W per °C. At 50 °C, max 70 W. At 55 °C, max 60 W. At 60 °C, max 50 W.

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

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

5. Reinforced Isolation — Keep COM2 Separate

Keep COM2 separate from COM.

6. Cabinet Depth — 4.8 Inches

The P1MB is 4.8″ deep. Measure your cabinet depth before ordering. If you’ve got less than 5.3″ of clearance, this unit won’t fit.

New Original vs. Refurbished: Why It Matters

The DS3820P1MB is a rare variant — GE made fewer than 10 units. Our stock came from a single source: a cancelled water utility automation project.

What you’re buying: The AC/DC hybrid, reinforced-isolation, 1 A aux supply with the exact input stage, PFC inductor, and reinforced transformer GE specified. Refurbished units are practically nonexistent. 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 AC-to-DC transition fails. The water treatment plant loses control during a power transfer — regulatory penalties. $50,000 in fines. There is no refurbished alternative.

What we provide as proof: OEM box photo, date code, a photo of the input stage, 3,000 VAC isolation test results, AC/DC transition test oscilloscope capture, and a full load test at 1 A on the +24 V output.

Pricing context: Our price sits 25–30% below GE’s 2016 list — about $7,500 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 A = 23.2 V
• Load combination: +5 V at 10 A, +24 V at 0.8 A — outputs: +4.98 V, +23.8 V.

AC input performance

• 120 VAC, 80 W load: efficiency = 81%.
• 240 VAC, 80 W load: efficiency = 82%.
• 90 VAC, 80 W load: output holds.
• 264 VAC, 80 W load: output holds.

DC input performance

• 88 VDC, 80 W load: output holds at +4.95 V.
• 125 VDC, 80 W load: output holds at +4.97 V.
• 250 VDC, 80 W load: output holds at +5.00 V.
• 300 VDC, 80 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.

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 A: 140 mV peak-to-peak

Thermal performance

• 80 W load, 25 °C: heatsink temp = 69 °C.
• 80 W load, 45 °C: heatsink reached 83 °C after 6 hours.
• At 60 °C: max load is 50 W.

Hold-up time

• 120 VAC, full load: +5 V held >4.85 V for 18 ms.
• 125 VDC, full load: +5 V held >4.85 V for 10 ms.

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