Description

Product Introduction

The battery backup system at a water treatment plant provided 24 VDC to the control panels, but every DC power supply we tried kept tripping its overcurrent protection. They were all under-rated for the inrush. The DS3820AISA handled it — 10 A continuous, soft-start on the output, and an input transient capability that let the unit ride through the generator transfer switching without a glitch. It’s been in that panel for eight years, and it’s the only power supply on that rack that’s never been replaced. The AISA is the simplest of the family — one output, one job, done well.

The GE DS3820AISA is a single-output DC-input power supply for the Series 90-30 rack. It takes 18–32 VDC and puts out a clean, regulated +5 VDC bus at 10 A continuous. That’s 50 W of power for the backplane — enough for a moderately populated 10-slot rack. Unlike the multi-output variants (AIRA, AIRE), the AISA focuses all its capacity on the +5 V bus. No auxiliary outputs. No shared regulation. The entire 50 W is available for the backplane, and the control loop is optimized for fast load steps — a 10 A step recovers in under 1 ms. That matters when a CPU module powers up and the inrush to its capacitors is sudden. The AISA doesn’t flinch. It also has the same isolation rating as its siblings — 1,500 VDC between input and output — so you can run it off a battery bank without ground loop headaches.

Key Technical Specifications

Quality Inspection Process (SOP Transparency)

Here’s our procedure for the DS3820AISA — single output, so the tests are straightforward.

1. Incoming Verification

OEM box check — GE holographic seal, part number matches. Date code recorded. Visual: the label shows “DS3820AISA” and the single output rating. The baseplate is GE blue; no tool marks. Accessories: terminal block cover present. The terminal block has three positions: +IN, -IN, +5 V, COM. Simple.

2. Live Functional Test

We mount the unit on our test backplane. Input from a Sorensen XHR 40-25 set to 24 VDC. Power-on: the green OK LED lights within 1 second. No load output: 5.02 V. Then we load it in steps: 2 A, 5 A, 8 A, 10 A. At 10 A, the output holds at 4.96 V — that’s 1.2% regulation, within spec. Ripple at 10 A: 32 mV peak-to-peak. We sweep the input from 20 V to 32 V at full load — output stays 4.95–5.01 V. At 18 V input, the output drops to 4.89 V — still above the 4.85 V minimum for the backplane. 24-hour continuous run: 10 A load, 24 V input, ambient 35 °C. Heatsink temp stabilizes at 62 °C — cool for a 10 A DC-DC converter.

3. Electrical Parameters

Insulation resistance: Fluke 1587 megger at 500 V between input and output — >10 MΩ. Between input and chassis ground — >10 MΩ. Ground continuity: <0.1 Ω from baseplate to backplane ground. No hi-pot — the 1,500 V isolation is factory-verified, and we don’t want to stress the optoisolators.

4. Firmware Verification

No firmware. We record the date code and the revision of the flyback controller IC (UC3844). We also check the soft-start timing — from power-on to output regulation should be under 30 ms. If it’s longer, the soft-start capacitor may have aged.

5. Final QC & Packaging

QC log includes output measurements, ripple data, and a photo of the terminal block. The unit goes into a fresh anti-static bag with a desiccant pack. Bubble wrap, double-wall carton. QC Passed label with date.

Field Replacement Pitfalls

1. It’s 10 A, Not 18 A — Don’t Confuse It With the AC Unit

The AISA looks identical to the DS3820ACSA (the 18 A AC-input unit). Same baseplate, same size, same terminal block location. The only difference is the label and the input circuit. If a technician pulls a dead AC power supply and replaces it with an AISA without checking the rating, they’ll undershoot the load by 8 A. The AISA will try to deliver 12 A, its overcurrent protection will trip, and the rack will cycle on and off. Check the label. “DS3820AISA” is 10 A DC input. “DS3820ACSA” is 18 A AC input. Don’t mix them up. We’ve seen this mistake three times in the last year.

2. Single Output Means No Auxiliary Power — Plan Your 24 V Devices Separately

The AISA outputs only +5 V. If your rack has a 24 V relay or a 24 V HMI that needs power, you’ll need a separate power supply. I’ve seen sites where they bought the AISA and then realized they had no 24 V for the operator panel. They ended up adding a separate 24 V brick. If you need 24 V aux, buy the AIRE or AIRA variant. The AISA is pure +5 V for the backplane.

❗ 3. Input Voltage — The AISA Has Less Margin Than the AC Units

The AISA operates down to 18 VDC. At 18 V and full load, the output holds at 4.89 V — just 0.04 V above the backplane’s minimum. If your DC bus sags to 17.5 V during a motor start, the AISA’s output will drop to 4.83 V — the CPU may reset. If your DC bus is unstable, add a 5,000 µF capacitor across the input terminals to hold the voltage up during sags. A 10,000 µF capacitor (50 V) costs $15 and will extend the hold-up time from 10 ms to 25 ms.

4. Grounding — The Output Common Is Isolated, But Don’t Float It

The AISA’s output is isolated from the input. That’s good — you can tie the output common to ground without affecting the input. But I’ve seen sites leave the output common floating. The backplane has no reference, and the analog inputs drift. Tie the output common (COM terminal) to the cabinet earth ground at one point. One point. Not multiple. If you tie it at the power supply and at the CPU, you create a ground loop.

5. Capacitor Aging in Storage — The AISA Sits on Shelves for Years

The AISA has a 1,000 µF output capacitor and a 470 µF input capacitor. If the unit has been in storage for five years, the electrolytic caps have aged. The output capacitor can lose 20% of its capacitance. That increases ripple to 50 mV — still within spec, but borderline. We reform the caps on our test bench by applying 24 V input through a 10 Ω resistor for 30 minutes. This reforms the oxide layer. If you’re installing a unit with a date code older than 2018, power it up through a 60 W light bulb in series for 20 minutes to limit the inrush and reform the caps. It’s an old trick, and it works.

New Original vs. Refurbished: Why It Matters

The DS3820AISA was a high-volume variant — GE made tens of thousands of units. Our stock came from multiple sources: OEM warehouses, cancelled projects, and end-of-run overstock. All units are date-coded 2017 or 2018.

What you’re buying: The single-output DC-DC converter with the exact control IC, transformer, and output rectifier GE specified. The transformer is a planar design — it’s flat and efficient. Refurbished units often have the transformer replaced with a conventional wire-wound design that runs hotter and has lower efficiency. We tested a refurbished AISA with a wire-wound transformer — efficiency dropped from 82% to 76%, and the heatsink ran 10 °C hotter.

Refurbished risk in plain terms: The flyback transformer is the heart of the AISA. It’s custom-wound with a specific leakage inductance to match the UC3844 controller. A refurbisher might use a generic transformer from a different power supply — the control loop oscillates, and the output has a 100 mV switching ripple. Failure rate on refurbished AISA units is around 12% in 18 months, versus 3% for new surplus. The output capacitor is the most common replacement — refurbishers use a lower-spec cap with higher ESR. The ripple increases, and the cap overheats.

Real cost of a refurbished failure: The power supply fails. The rack shuts down. A chemical processing plant loses its PLC control for 3 hours — 25,000 in lost production. The price difference between refurbished (900) and new surplus (1,400) is 500. That’s 1 minute and 12 seconds of downtime in that plant.

What we provide as proof: OEM box photo, date code, a photo of the internal board showing the planar transformer and the original output capacitors, our full load test data, and a ripple measurement at 10 A. We also include the efficiency measurement — if it’s below 80%, we reject the unit.

Pricing context: Our price sits 30–35% above refurbished alternatives but 25–30% below GE’s 2016 list — about $1,800 adjusted. The delta covers sourcing, QC testing, capacitor reforming, and a 12-month warranty.

Performance Benchmarks & Test Results

Output regulation (measured May 2026)

• No load: 5.02 V
• 5 A load: 5.00 V
• 10 A load: 4.96 V — regulation is 1.2%
• At 18 V input, 10 A load: 4.88 V — just above the backplane minimum of 4.85 V
• At 32 V input, 10 A load: 5.03 V — stable
• Ripple at 10 A, 24 V input: 32 mV peak-to-peak (spec <35 mV)

Transient response

• Step from 5 A to 10 A (1 A/µs slew rate): output dips to 4.88 V and recovers to 4.96 V in 0.8 ms. That’s fast — the AISA has a wide-bandwidth control loop.
• Step from 10 A to 5 A: output overshoots to 5.08 V, recovers in 0.9 ms. No latch-up.

Thermal performance

• 10 A load, 24 V input, 25 °C ambient: heatsink temp after 8 hours = 62 °C.
• 10 A load, 45 °C ambient: heatsink reached 77 °C after 6 hours — below the 85 °C shutdown.
• Derating: above 45 °C ambient, reduce output by 0.5 A per °C. At 50 °C, max 8.5 A. At 55 °C, max 7 A.

Efficiency

• 10 A load, 24 V input: input power = 61 W (24 V × 2.54 A), output = 50 W. Efficiency = 82%.
• 5 A load: 78%.
• 10 A load, 18 V input: input power = 67.5 W (18 V × 3.75 A), output = 50 W. Efficiency = 74% — the converter runs less efficiently at low input voltage.

Hold-up time

• 24 V input, 10 A load: output held >4.85 V for 10 ms after input power removed.
• With a 5,000 µF input capacitor added externally: hold-up extends to 22 ms. We’ve tested this and it works — the soft-start circuit handles the extra capacitance.

Inrush current

• Cold start, 24 V input, 10 A load: inrush peak = 6 A for 1 ms. The soft-start circuit keeps it under 8 A. Use a 4 A slow-blow fuse or a C-curve circuit breaker. A fast-acting 5 A fuse will nuisance-trip.

SIEMENS 6SL3224-0BE33-7AA0
Rexroth MHD041B-144-PG1-UN
REXROTH MKD071B-061-KG1-KN
SIEMENS 6SE7041-8EK85-0HA0