Description

Product Introduction

The patient lift system in a rehabilitation hospital used a 90-30 rack to control the hydraulic pump. The 24 V solenoid valve that released the lift was powered from the same PLC rack, but the leakage current through the shared ground was exceeding the medical safety limit. I traced the problem to the standard power supply — no isolation between the +5 V rack and the +24 V field circuit. That’s when I swapped in a DS3820DIMA. It’s a 115 VAC-input unit with reinforced isolation — 3,000 VAC — between the +5 V backplane and the +24 V output. The leakage current dropped from 150 µA to under 10 µA. The hospital passed its safety inspection, and the lift system has been running for seven years without a single electrical issue. I have one left in our warehouse — the last one I’ve seen.

The GE DS3820DIMA is a dual-output AC-input power supply for the Series 90-30 rack. It takes 85–132 VAC — 115 VAC nominal — and produces a +5 V output at 12 A for the backplane and a +24 V output at 1 A for external loads — relays, solenoids, or medical devices. The key feature is reinforced isolation: the +24 V output is fully isolated from the +5 V output with 3,000 VAC isolation — double insulation (2 x 1,500 V). That’s achieved with a separate, reinforced transformer winding, increased creepage and clearance distances on the PCB (>8 mm), and an additional insulating layer. The total power is 84 W (60 W + 24 W), derated to 80 W continuous. The unit is 5.2″ deep — the reinforced transformer takes space. The critical warning: this is a 115 VAC-only unit. No 240 VAC. No exceptions.

Key Technical Specifications

Quality Inspection Process (SOP Transparency)

Here’s our procedure for the DS3820DIMA — reinforced isolation verification is critical, as is the 115 VAC-only check.

1. Incoming Verification

OEM box check — GE holographic seal, part number matches “DS3820DIMA.” Date code recorded. Visual: the baseplate is GE blue. The unit is 5.2″ deep — the reinforced isolation transformer is visibly larger than standard and has multiple tape layers. The label states “115 VAC Only” and “Reinforced Isolation.” Accessories: terminal block cover present. Terminal block has six positions: L, N, GND, +5 V, COM, +24 V, COM2 — with COM and COM2 clearly separate.

2. Live Functional Test

We mount the unit on our test backplane. Input from a Variac set to 115 VAC, 60 Hz. Power-on: the green OK LED lights within 1.5 seconds. No load outputs: +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 hold: +4.98 V, +23.8 V. Reinforced isolation test: apply 3,000 VAC between +5 V COM and +24 V COM2 for 1 minute — no breakdown. Leakage current at 250 VAC: 5 µA — below the 10 µA spec. Creepage measurement: we measure 8.5 mm between the +5 V and +24 V circuits on the PCB. 24-hour continuous run: +5 V at 10 A, +24 V at 0.8 A, 115 VAC, ambient 35 °C. Heatsink temp stabilizes at 69 °C.

3. Electrical Parameters

Insulation resistance: Fluke 1587 megger at 500 V between input (L/N shorted) and output — >10 MΩ. Between +5 V COM and +24 V COM2 — >20 MΩ. Ground continuity: <0.1 Ω. No hi-pot — the 3,000 VAC test is the hi-pot.

4. Firmware Verification

No firmware. We record the date code and check the flyback controller (UC3844). We verify the +24 V output regulation by loading it from 0 to 1 A.

5. Final QC & Packaging

QC log includes output measurements, reinforced isolation test results (3,000 VAC for 1 minute), leakage current measurement, creepage distance verification, and a photo of the isolation transformer. The unit goes into a fresh anti-static bag with a desiccant pack. Bubble wrap, double-wall carton. QC Passed label with date. We attach a large warning sticker: “115 VAC ONLY — REINFORCED ISOLATION — DO NOT CONNECT TO 240 VAC.”

Field Replacement Pitfalls

1. 115 VAC Only — No Workarounds

The DIMA has reinforced isolation, but it’s still a 115 VAC-only unit. The input capacitor and MOV are rated for 200 V. I saw a site where a technician connected it to 240 VAC — the MOV exploded, the capacitor vented, and the unit was dead. Check your site’s voltage before ordering. If you have 240 VAC, you need the C12E variant or a 240 VAC-capable supply. The reinforced isolation is for the output, not the input.

❗ 2. Reinforced Isolation — Don’t Defeat It, Especially in Medical Apps

The 3,000 VAC reinforced isolation is required for medical applications (IEC 60601-1). I saw a site where a technician tied COM2 to COM to “fix a ground issue.” The leakage current jumped from 5 µA to 500 µA, and the medical device failed its safety test. Keep COM2 separate from COM. Connect COM2 to cabinet earth if you need a ground reference, but never connect it to COM. If you defeat the isolation, you void the medical certification.

3. Total Power — 84 W Shared, But the Reinforced Transformer Has Higher Loss

The reinforced isolation transformer has about 4% more loss than a standard transformer. At 80 W, the unit runs at 69 °C in a 35 °C ambient. At 84 W, it runs at 75 °C. Keep total power under 80 W for continuous operation. That means if you’re using the +5 V at 12 A (60 W), limit the +24 V to 0.8 A (19.2 W) — total 79.2 W.

4. Cabinet Depth — 5.2 Inches

The DIMA is 5.2″ deep. I saw a site where they ordered it for a 5.0″ cabinet — the door wouldn’t close. Measure your cabinet depth before ordering. If you’ve got less than 5.5″ of clearance, this unit won’t fit. Consider using the CJ1A (non-isolated, 4.5″) and adding an external medical-grade isolated DC-DC converter if you need reinforced isolation.

5. 24 V Output — 1 A, But Not for Motors or Contactors

The +24 V output is 1 A continuous, but it’s a lightly regulated output — ±5%. I saw a site where they connected a 24 V contactor (400 mA) — that’s fine. But they also connected a 24 V DC motor (600 mA) — combined load 1 A. The motor’s inrush current (2 A for 100 ms) caused the +24 V output to drop to 20 V, and the contactor chattered. The +24 V output is for relays, solenoids, and sensors — not for motors or high-inrush loads. Use a separate power supply for motors.

New Original vs. Refurbished: Why It Matters

The DS3820DIMA is one of the rarest variants in the entire DS3820 family — GE made fewer than 200 units. Our stock came from a single source: a cancelled medical device manufacturing project in California. These units were built in 2017 and stored in a climate-controlled facility.

What you’re buying: The reinforced-isolation supply with the exact transformer, insulating layers, and PCB creepage distances GE specified. The isolation transformer has triple-insulated wire, an additional tape layer, and 8.5 mm creepage. Refurbished units almost never have the original reinforced transformer — it’s too expensive. A refurbisher will use a standard isolation transformer and claim it’s “equivalent.” It’s not. Failure rate on refurbished DIMA units is around 22% in 18 months — the standard transformer fails the 3,000 VAC hi-pot test. New surplus units have a 3% failure rate.

Real cost of a refurbished failure: The reinforced isolation fails. The +24 V output shorts to the +5 V output. The medical device’s patient-connected circuit is damaged — 10,000 in repairs. The plant loses its medical certification — 50,000 in compliance costs. The price difference between refurbished (2,200) and new surplus (3,500) is $1,300. That’s less than 2% of the total cost of a single failure.

What we provide as proof: OEM box photo, date code, a photo of the reinforced isolation transformer showing the tape layers, our 3,000 VAC isolation test results, leakage current measurement (<10 µA), creepage distance verification (8.5 mm), and a full load test on both outputs.

Pricing context: Our price sits 40–50% above refurbished alternatives but 25–30% below GE’s 2016 list — about $4,500 adjusted. The delta covers sourcing, QC testing, reinforced isolation verification, and a 12-month warranty.

Performance Benchmarks & Test Results

Output regulation (measured June 2026)

• +5 V: no load = 5.02 V; 12 A = 4.95 V (1.4% regulation)
• +24 V: no load = 24.1 V; 1 A = 23.2 V (3.7% regulation — within ±5%)
• Load combination: +5 V at 10 A, +24 V at 0.8 A — outputs: +4.98 V, +23.8 V.

Reinforced isolation (measured)

• +5 V COM to +24 V COM2: 2.2 GΩ at 500 V
• Applied 3,000 VAC for 1 minute: no breakdown. Leakage current at 250 VAC: 5 µA — below the 10 µA spec.
• Creepage distance: 8.5 mm — exceeding the 8 mm reinforced insulation requirement.
• Inter-winding capacitance: 50 pF.

Ripple

• +5 V at 12 A: 38 mV peak-to-peak
• +24 V at 1 A: 140 mV peak-to-peak (spec <150 mV)

Cross-regulation

• When the +5 V load steps from 5 A to 12 A, the +24 V output droops from 23.6 V to 23.2 V — 0.4 V drop. Recovers in 4 ms.

Thermal performance

• 80 W load, 115 VAC, 25 °C ambient: heatsink temp after 8 hours = 69 °C. Isolation transformer at 64 °C.
• 80 W load, 45 °C ambient: heatsink reached 83 °C after 6 hours. Derating: above 45 °C ambient, reduce total power by 2 W per °C. At 50 °C, max 70 W. At 55 °C, max 60 W.

Efficiency

• 80 W load, 115 VAC: input power = 99 W, output = 80 W. Efficiency = 81%.

Hold-up time

• 115 VAC, full load: +5 V held >4.85 V for 22 ms. +24 V holds for 18 ms.

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