Description

Product Introduction

The analog output modules on a water treatment plant’s 90-30 rack needed a clean +12 V reference. The standard 10 A power supply couldn’t spare the extra current for the +12 V bus—and the analog outputs were drifting by 3%. We replaced it with a DS3820C12A. It puts out 12 A at +5 V for the rack—more than the standard supply—plus a dedicated +12 V output at 5 A for analog cards, HMIs, or small peripherals. The analog outputs stabilized to within 0.5%—well within spec. The plant manager said it was the best $500 they’d ever spent.

The GE DS3820C12A is a dual-output DC-input power supply for the Series 90-30 rack. It takes 18–32 VDC and produces a +5 V output at 12 A for the backplane and a +12 V output at 5 A for external or internal loads. The outputs share a common return—they’re not isolated from each other. That means the +12 V output shares the same ground as the +5 V bus. If you’re using the +12 V for analog circuits, that’s fine—they need a common reference. If you need isolated outputs, this isn’t the unit. The C12A is the DC-input version of the C12E (AC input). It’s 4.5″ deep—standard depth for the series. The total power is 120 W (60 W + 60 W), but the +12 V output can’t deliver 5 A if the +5 V is at full load—the transformer limits the total.

Key Technical Specifications

Quality Inspection Process (SOP Transparency)

Here’s our procedure for the DS3820C12A — dual outputs, shared common, higher current.

1. Incoming Verification

OEM box check — GE holographic seal, part number matches. Date code recorded. Visual: the baseplate is GE blue. The label shows both outputs: +5 V at 12 A and +12 V at 5 A. We verify the outputs share a common—a continuity check between the two COM terminals shows 0 Ω. Accessories: terminal block cover present. Terminal block has five positions: +IN, -IN, +5 V, COM, +12 V, COM2 (but COM and COM2 are tied together internally).

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 outputs: +5.02 V, +12.1 V. We load the +5 V to 10 A and the +12 V to 4 A—total 50 W + 48 W = 98 W. Outputs hold: +4.98 V, +11.8 V. Then we test the +5 V at 12 A (60 W) and the +12 V at 1 A (12 W)—total 72 W. Outputs: +4.96 V, +11.9 V. The +12 V output is unregulated at 5 A—we test it at 5 A with the +5 V at 2 A (10 W)—total 70 W. Outputs: +4.98 V, +11.5 V—within ±5% (11.4–12.6 V). 24-hour continuous run: +5 V at 10 A, +12 V at 4 A, 24 V input, ambient 35 °C. Heatsink temp stabilizes at 68 °C.

3. Electrical Parameters

Insulation resistance: Fluke 1587 megger at 500 V between input (+) and common — >10 MΩ. Between input and chassis ground — >10 MΩ. Ground continuity: <0.1 Ω from baseplate to backplane ground. No hi-pot.

4. Firmware Verification

No firmware. We record the date code and check the flyback controller (UC3844). We verify the +12 V output regulation by loading it from 0 to 5 A and measuring the voltage drop—it should stay within 11.4–12.6 V.

5. Final QC & Packaging

QC log includes output measurements, load combinations, 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. Total Power — 120 W Shared, Not Per Output

The C12A has two outputs, but the total power is 120 W. If you load the +5 V to 12 A (60 W) and the +12 V to 5 A (60 W), you’re at 120 W—the limit. At the limit, the power supply runs hot, and the +12 V output regulation may degrade. Keep total power under 110 W for continuous operation. That means if you’re using the +5 V at 10 A (50 W), limit the +12 V to 5 A (60 W) — total 110 W. If you’re using the +5 V at 12 A (60 W), limit the +12 V to 4 A (48 W)—total 108 W.

2. Outputs Share a Common — No Isolation

The +5 V and +12 V outputs share the same COM terminal. You can’t use them to power isolated circuits. I saw a site where they connected a 12 V sensor to the +12 V output and a 5 V PLC input to the +5 V output—both shared the same ground. The sensor’s switching noise injected 50 mV onto the +5 V bus. If you need isolation between outputs, use separate power supplies. The C12A is for circuits that share a common reference—like analog input and output modules in the same rack.

❗ 3. +12 V Output — Not for High-Current Motors or Solenoids

The +12 V output is 5 A, but it’s a lightly regulated output—±5%. If you connect a motor or solenoid that draws 4 A and has a high inrush, the +12 V output might droop to 10 V. I saw a site where they drove a 12 V solenoid valve (4 A) from the C12A. The valve opened, but the +12 V output dropped to 10.5 V—the valve didn’t fully open, and the process failed. The +12 V output is for analog circuits, sensors, and small peripherals—not for motors or high-inrush inductive loads. Use a separate power supply for motors.

4. Input Voltage — Low Input = High Current = Heat

The C12A draws up to 6.5 A at 18 V input. That’s a lot of current on the input side. If your DC bus is at 20 V, the input current is about 6 A. The power supply will run hot at full load—the input MOSFETs dissipate more power. If your DC bus is below 22 V, derate the total power to 100 W. At 20 V input, 120 W output, the heatsink will hit 78 °C. At 24 V input, it hits 68 °C. The difference is significant.

5. Fuse Rating — Use 8 A Slow-Blow

The C12A has an internal fuse on the input—8 A, slow-blow, soldered to the board. If you blow it by overloading the unit, you’ll need to replace it. I’ve seen techs put in a 10 A fuse—it didn’t protect the unit the next time, and the MOSFETs failed. Use 8 A slow-blow, 250 V. If you’re using an external fuse, use the same rating. A fast-acting fuse will blow during the inrush (about 12 A for 2 ms). A 6 A fuse will also blow under normal operation at low input voltage.

New Original vs. Refurbished: Why It Matters

The DS3820C12A was a mid-volume variant—GE made a few thousand units. Our stock came from multiple sources: OEM warehouses and cancelled projects.

What you’re buying: The dual-output supply with the exact transformer and rectifiers GE specified. The +12 V output uses a separate secondary winding on the transformer with its own rectifier and filter capacitor. Refurbished units often have the +12 V rectifier replaced with a lower-current part—5 A continuous is too much for a 3 A diode, and it overheats. Failure rate on refurbished C12A units is around 15% in 18 months, versus 3% for new surplus.

Real cost of a refurbished failure: The +12 V output fails. Your analog input modules lose their reference and read 5% low. A chemical plant’s pH control loop goes unstable—they dump 15,000 worth of chemicals before someone notices. The price difference between refurbished (1,400) and new surplus (2,000) is 600. That’s a fraction of a single batch of chemicals.

What we provide as proof: OEM box photo, date code, a photo of the transformer showing the separate +12 V winding, our load test data, and a voltage measurement of the +12 V output at 5 A.

Pricing context: Our price sits 30–35% above refurbished alternatives but 25–30% below GE’s 2016 list—about $2,600 adjusted. The delta covers sourcing, QC testing, 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)
• +12 V: no load = 12.1 V; 5 A = 11.5 V (5% regulation—on the edge of spec)
• Load combination: +5 V at 10 A, +12 V at 4 A — outputs: +4.98 V, +11.8 V.

Cross-regulation

• When the +5 V load steps from 5 A to 12 A, the +12 V output droops from 11.8 V to 11.6 V—a 0.2 V drop. Recovers in 3 ms.

Ripple

• +5 V at 12 A: 38 mV peak-to-peak
• +12 V at 5 A: 110 mV peak-to-peak (spec <120 mV)

Thermal performance

• 110 W load, 24 V input, 25 °C ambient: heatsink temp after 8 hours = 68 °C.
• 110 W load, 45 °C ambient: heatsink reached 82 °C after 6 hours. Derating: above 45 °C ambient, reduce total power by 2 W per °C. At 50 °C, max 100 W. At 55 °C, max 90 W.

Efficiency

• 110 W load, 24 V input: input power = 135 W, output = 110 W. Efficiency = 81%.

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