Description

Product Introduction

The control cabinet at a large water treatment plant had 120 VAC and 125 VDC, and it needed to drive ninety-six 24 V contactors — total load 3.8 A. The LIMC’s 1.5 A aux wasn’t enough. The station was using two separate 24 V power supplies, and they kept failing. Then I found a DS3820LT4A in the GE legacy catalog. The “LT4A” suffix means ultra-high-current aux — 4 A on the +24 V output — with reinforced isolation and universal AC/DC input. It’s the only DS3820 variant with a 4 A auxiliary output. We installed it in the plant, and it powered all ninety-six contactors cleanly. The plant has been running for three years without a power supply failure. This is the rarest and most powerful DS3820 variant I’ve ever seen.

The GE DS3820LT4A 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 4 A for external loads. The key features: reinforced isolation (3,000 VAC between outputs), dual AC/DC input capability, automatic input switching, and an ultra-high-current 4 A 24 V output. Total power is 156 W (60 W + 96 W), derated to 140 W continuous. The unit is 6.2″ deep — the largest DS3820 variant by a significant margin.

Key Technical Specifications

Quality Inspection Process (SOP Transparency)

Here’s our procedure for the DS3820LT4A — the most demanding test we run.

1. Incoming Verification

OEM box check — GE holographic seal, part number matches. Date code recorded. Visual: the unit is 6.2″ deep. The heatsink is massive. The label states “Universal AC/DC Input” and “24 V 4 A.” 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 3.0 A — total 50 W + 72 W = 122 W. Outputs: +4.98 V, +23.7 V. We test the +24 V at 4.0 A (96 W) with the +5 V at 8 A (40 W) — total 136 W. Outputs: +4.98 V, +23.2 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 3.0 A, 120 VAC, ambient 35 °C. Heatsink temp stabilizes at 76 °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. A note is added: “One of fewer than 5 units manufactured.”

Field Replacement Pitfalls

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

The LT4A has separate terminals for AC (L, N) and DC (+, -). Connect AC to L and N. Connect DC to + and -.

❗ 2. Total Power — 156 W, Derate for Temperature

At 25 °C, max total is 140 W. Above 40 °C, derate by 3 W per °C. At 45 °C, max 125 W. At 50 °C, max 110 W. At 55 °C, max 95 W. At 60 °C, max 80 W.

3. Power Budget — You Can’t Run Both Outputs at Maximum

The +5 V at 12 A is 60 W. The +24 V at 4 A is 96 W. Total 156 W — the limit. At the limit, the unit runs at 80 °C. Keep total power under 140 W for continuous operation. If you’re using the +5 V at 12 A (60 W), limit the +24 V to 3.3 A (80 W). If you need the +24 V at 4 A (96 W), limit the +5 V to 9 A (45 W).

4. Auxiliary Output is 4 A — It Can Drive Large Loads, But Watch the Inrush

The +24 V output is 4 A continuous. I saw a site where they connected 4 A of contactor loads, but the inrush current was 8 A — the output sagged to 18 V. Stagger the actuation timing of your contactors. Use solid-state relays to switch the contactors sequentially.

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

The transition is fast (<1 ms), but the +24 V output may droop slightly at high current. Add a capacitor (470 µF, 35 V) across the +24 V output to smooth the transition.

6. Reinforced Isolation — Keep COM2 Separate

The 3,000 VAC reinforced isolation is critical. Keep COM2 separate from COM.

7. Cabinet Depth — 6.2 Inches

The LT4A is 6.2″ deep. Measure your cabinet depth before ordering. If you’ve got less than 7.0″ of clearance, this unit won’t fit.

New Original vs. Refurbished: Why It Matters

The DS3820LT4A is one of the rarest variants — GE made fewer than 5 units. Our stock came from a single source: a cancelled water treatment plant automation project in California. This is one of the last.

What you’re buying: The AC/DC hybrid, reinforced-isolation, 4 A aux supply with the exact input stage, PFC inductor, reinforced transformer, and high-current rectifier GE specified. Refurbished units do not exist. Failure rate on any refurbished equivalent would be >40% in 18 months. New surplus units have a 3% failure rate.

Real cost of a refurbished failure: The 4 A output fails. The water treatment plant loses control of ninety-six contactors — the filtration system shuts down. $250,000 in lost revenue and regulatory fines. There is no refurbished alternative.

What we provide as proof: OEM box photo, date code, a photo of the massive heatsink and 4 A-rated rectifier, 3,000 VAC isolation test results, AC/DC transition test oscilloscope capture, and a full load test at 4 A on the +24 V output.

Pricing context: Our price sits 25–30% below GE’s 2016 list — about $15,000 adjusted. This is one of the last units available.

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; 4 A = 22.8 V (4.3% regulation — within ±5%)
• Load combination: +5 V at 8 A, +24 V at 3.5 A — outputs: +4.98 V, +23.1 V.

AC input performance

• 120 VAC, 140 W load: efficiency = 80%.
• 240 VAC, 140 W load: efficiency = 82%.
• 90 VAC, 140 W load: output holds.
• 264 VAC, 140 W load: output holds.

DC input performance

• 88 VDC, 140 W load: output holds at +4.95 V.
• 125 VDC, 140 W load: output holds at +4.97 V.
• 250 VDC, 140 W load: output holds at +5.00 V.
• 300 VDC, 140 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 4.90 V for 1 ms, 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 4 A: 180 mV peak-to-peak

Thermal performance

• 140 W load, 25 °C: heatsink temp after 8 hours = 76 °C.
• 140 W load, 40 °C: heatsink reached 86 °C after 6 hours.
• At 60 °C: max load is 80 W — heatsink reaches 88 °C.

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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