Description

Product Introduction

The control panel at a natural gas metering station was tight — 4.9 inches of depth — and the station needed 1.5 A on the 24 V output to drive forty relays, with 120 VAC and 125 VDC inputs. The EMI from the flow meters was causing false readings on the 24 V sensor loops, so we needed Class B filtering. The LLTA had the depth and the current, but no EMI filter. Then I found a DS3820LLTA1A1A in the GE legacy catalog — it’s the LLTA with the “1A1A” EMI filter package. Same compact 4.8″ depth, same 1.5 A aux, same reinforced isolation, but with dual common-mode chokes and a pi-filter on the 24 V output. We installed it, the false readings stopped, and the station ran for three years without a power supply issue. This is one of the rarest DS3820 variants.

The GE DS3820LLTA1A1A 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, enhanced EMI filtering (CISPR 11 Class B), and a low-profile 4.8″ depth. Total power is 96 W (60 W + 36 W), derated to 85 W at 25 °C and 75 W at 45 °C.

Key Technical Specifications

Quality Inspection Process (SOP Transparency)

Here’s our procedure for the DS3820LLTA1A1A — dual-input testing with EMI verification.

1. Incoming Verification

OEM box check — GE holographic seal, part number matches. Date code recorded. Visual: the unit is 4.8″ deep. You can see the dual common-mode chokes and pi-filter components. 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 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: 3 µA. EMI test: passes CISPR 11 Class B. 24-hour continuous run: +5 V at 10 A, +24 V at 1.0 A, 120 VAC, ambient 35 °C. Heatsink temp stabilizes at 73 °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, transition test data, EMI compliance test results, and reinforced isolation test results. A note is added: “One of fewer than 4 units manufactured.”

Field Replacement Pitfalls

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

The LLTA1A1A has separate terminals for AC (L, N) and DC (+, -). Connect AC to L and N. Connect DC to + and -.

❗ 2. Temperature Range — 0 to +60 °C, Not Extended

The LLTA1A1A is rated 0 to +60 °C. I saw a site where they installed it in a 65 °C cabinet — the thermal shutdown tripped. If your cabinet exceeds 60 °C, use the LIMC series with extended temperature range.

3. Total Power — Derate Above 45 °C

At 25 °C, max total is 85 W. Above 45 °C, derate by 2 W per °C. At 50 °C, max 75 W. At 55 °C, max 65 W. At 60 °C, max 55 W.

4. EMI Filter — Don’t Bypass It

The “1A1A” EMI filter is a key feature. I saw a site where a technician bypassed the filter — the emissions increased, and flow meter readings started drifting. Keep the filter in place.

5. Auxiliary Output is 1.5 A — Stagger the Inrush

If you’re driving solenoid valves or contactors, the inrush current can be 2–3× the holding current. Stagger the actuation timing of your loads.

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

The transition is fast (<1 ms), but the +24 V output may droop slightly. Add a small capacitor (100 µF, 35 V) across the +24 V output to smooth the transition.

7. Reinforced Isolation — Keep COM2 Separate

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

8. Cabinet Depth — 4.8 Inches

The LLTA1A1A 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 DS3820LLTA1A1A is one of the rarest variants — GE made fewer than 4 units. Our stock came from a single source: a cancelled metering station automation project in Texas. This is one of the last.

What you’re buying: The compact AC/DC hybrid, reinforced-isolation, 1.5 A aux, enhanced-EMI-filter supply with the exact input stage, PFC inductor, reinforced transformer, dual chokes, and pi-filter GE specified. Refurbished units do not exist. Failure rate on any refurbished equivalent would be >35% in 18 months. New surplus units have a 3% failure rate.

Real cost of a refurbished failure: The EMI filter degrades. The AC-to-DC transition fails. The metering station loses flow data — regulatory penalties. $200,000 in fines. There is no refurbished alternative.

What we provide as proof: OEM box photo, date code, a photo of the dual chokes and pi-filter, 3,000 VAC isolation test results, CISPR 11 Class B compliance test results, AC/DC transition test oscilloscope capture, 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 $12,500 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.

EMI performance (key differentiator)

• Conducted emissions: passes CISPR 11 Class B.
• +24 V output noise at 1.5 A: 48 mV peak-to-peak.
• +5 V output noise at 12 A: 26 mV peak-to-peak.

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.

Reinforced isolation (measured)

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

Ripple

• +5 V at 12 A: 26 mV peak-to-peak
• +24 V at 1.5 A: 48 mV peak-to-peak

Thermal performance

• 85 W load, 25 °C: heatsink temp = 73 °C.
• 85 W load, 45 °C: heatsink reached 84 °C after 6 hours.
• At 60 °C: max load is 55 W — heatsink reaches 87 °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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