Description

Product Introduction

The control panel at a remote gas processing plant had 240 VAC from the utility and 250 VDC from the emergency battery bank. The temperature in the panel hit 60 °C, and the plant needed to drive twenty-four 24 V relays — total load 0.8 A. The LIMA’s 0.5 A aux wasn’t enough. Then I found a DS3820LIMB in the GE legacy catalog. The “LIMB” suffix is the AC/DC hybrid with higher-current aux — 1 A on the +24 V output, with reinforced isolation and extended temperature range. We installed it, the relays ran cleanly, and the plant ran for four years without a power supply failure. The LIMB is the higher-current version of the LIMA.

The GE DS3820LIMB 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 an extended operating temperature range of -25 to +70 °C. Total power is 84 W (60 W + 24 W), derated to 80 W at 25 °C and 65 W at 70 °C.

Key Technical Specifications

Quality Inspection Process (SOP Transparency)

Here’s our procedure for the DS3820LIMB — dual-input and extended temperature 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 5.6″ deep. The heatsink is larger than the LIMA. The label states “Universal AC/DC Input” 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 0.8 A — total 50 W + 19.2 W = 69.2 W. Outputs: +4.98 V, +23.8 V. Then DC input: 125 VDC — outputs identical. Transition test: AC to DC switchover glitches <100 mV. Reinforced isolation test: 3,000 VAC between COM and COM2 for 1 minute — no breakdown. Leakage current: 5 µA. Thermal chamber test: 65 W load at 70 °C for 8 hours — no shutdown. Cold start: -25 °C, starts within 2 seconds. 24-hour continuous run at room temp: +5 V at 10 A, +24 V at 0.8 A, 120 VAC, ambient 35 °C. Heatsink temp stabilizes at 72 °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 across temperature and input type.

5. Final QC & Packaging

QC log includes output measurements on AC and DC, thermal chamber test data, 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 LIMB has separate terminals for AC (L, N) and DC (+, -). I saw a site where a technician connected 120 VAC to the DC terminals — the fuse blew. Connect AC to L and N. Connect DC to + and -.

❗ 2. Extended Temperature — Derate at 70 °C

At 70 °C ambient, the unit is rated for 65 W, not 80 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). If you need the +24 V at 1 A (24 W) at 70 °C, limit the +5 V to 8 A (40 W).

3. Total Power — Derate for Temperature

At 25 °C, max total is 80 W. At 70 °C, max total is 65 W. If you’re using the +5 V at 12 A (60 W) at 70 °C, limit the +24 V to 0.2 A (4.8 W).

4. 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.

5. AC-to-DC Transition — Stagger Your Loads

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.

6. Reinforced Isolation — Keep COM2 Separate

The 3,000 VAC reinforced isolation is critical. I saw a site where a technician tied COM2 to COM. The leakage current jumped to 500 µA. Keep COM2 separate from COM.

7. Cabinet Depth — 5.6 Inches

The LIMB is 5.6″ 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 6.2″ of clearance, this unit won’t fit.

New Original vs. Refurbished: Why It Matters

The DS3820LIMB is a rare variant — GE made fewer than 10 units. Our stock came from a single source: a cancelled gas processing plant automation project in Oklahoma.

What you’re buying: The dual-input AC/DC, extended-temp, reinforced-isolation, 1 A aux supply with the exact input stage, PFC inductor, reinforced transformer, and 105 °C-rated capacitors GE specified. Refurbished units are practically nonexistent. Failure rate on any refurbished equivalent would be >30% in 18 months. New surplus units have a 3% failure rate.

Real cost of a refurbished failure: The high-temp capacitors fail at 70 °C. The AC-to-DC transition fails. The gas processing plant loses control — the compressor shuts down. $150,000 in lost revenue. There is no refurbished alternative.

What we provide as proof: OEM box photo, date code, a photo of the dual-input section, 3,000 VAC isolation test results, thermal chamber test data (8 hours at 70 °C), AC/DC transition test oscilloscope capture, and a full load test at 1 A on the +24 V output at both 120 VAC and 240 VAC.

Pricing context: Our price sits 25–30% below GE’s 2016 list — about $10,500 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.

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 80 W load at 70 °C: unit shut down after 2 hours — thermal shutdown at 90 °C.

AC input performance

• 120 VAC, 80 W load at 25 °C: efficiency = 80%.
• 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

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.

B&R 3NC154.60-2
YOKOGAWA CP451-10
A-B 2711-K6C8
GE VMIPCI-5565-110000