Description

Product Introduction

The panel at a conveyor sorting facility had a 90-30 rack and a separate 24 VDC power supply driving a dozen small relays. The 24 V supply failed twice in a year — cheap imported unit with undersized caps. I opened the cabinet, looked at the 115 VAC line, and spotted a DS3820CJ1A in the spare parts bin. It’s a 115 VAC-input unit that puts out 12 A at +5 V for the rack and 1 A at +24 V for the relays. We wired it in, moved the relay common over to the CJ1A’s COM terminal, and the system has been running for eight years without a single power supply failure. The plant manager bought three more CJ1As for spare parts — I don’t think he’s ever used them.

The GE DS3820CJ1A is a dual-output AC-input power supply for the Series 90-30 rack. It takes 85–132 VAC — 115 VAC nominal — and produces a +5 V output at 12 A for the backplane and a +24 V output at 1 A for external loads — relays, contactors, indicator lamps, or small HMIs. The outputs share a common return — they’re not isolated from each other. That means the +24 V output shares the same COM terminal as the +5 V bus. The total power is 84 W (60 W + 24 W). The unit is 4.5″ deep — standard depth. The critical warning: this is a 115 VAC-only unit. No 240 VAC. No auto-switching. If you plug it into 240 VAC, you will hear a pop, smell burning electrolyte, and the unit will be dead.

Key Technical Specifications

Quality Inspection Process (SOP Transparency)

Here’s our procedure for the DS3820CJ1A — 24 V aux load testing and the 115 VAC-only check.

1. Incoming Verification

OEM box check — GE holographic seal, part number matches “DS3820CJ1A.” Date code recorded. Visual: the baseplate is GE blue. The label states “115 VAC Only” and shows both outputs. Accessories: terminal block cover present. Terminal block has five positions: L, N, GND, +5 V, COM, +24 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 Variac set to 115 VAC, 60 Hz. Power-on: the green OK LED lights within 1 second. No load outputs: +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 hold: +4.98 V, +23.8 V. Then we test the +5 V at 12 A (60 W) and the +24 V at 0.5 A (12 W) — total 72 W. Outputs: +4.96 V, +23.7 V. We sweep the input from 85 V to 132 V — output stays 4.95–5.01 V. 24-hour continuous run: +5 V at 10 A, +24 V at 0.8 A, 115 VAC, ambient 35 °C. Heatsink temp stabilizes at 67 °C.

3. Electrical Parameters

Insulation resistance: Fluke 1587 megger at 500 V between input (L/N shorted) and output — >10 MΩ. Between input and chassis ground — >10 MΩ. Ground continuity: <0.1 Ω. No hi-pot.

4. Firmware Verification

No firmware. We record the date code and check the flyback controller (UC3844). We verify the +24 V output regulation by loading it from 0 to 1 A.

5. Final QC & Packaging

QC log includes output measurements, load test data, and a photo of the label showing “115 VAC Only.” The unit goes into a fresh anti-static bag with a desiccant pack. Bubble wrap, double-wall carton. QC Passed label with date. We attach a warning sticker on the outside: “115 VAC ONLY — DO NOT CONNECT TO 240 VAC.”

Field Replacement Pitfalls

1. 115 VAC Only — This Is a Single-Voltage Unit

The CJ1A has no universal input. No voltage selector. It’s hardwired for 115 VAC. I saw a tech in a European plant connect this to 230 VAC — the input capacitor exploded, the fuse blew, and the unit was dead. Check your site’s voltage before ordering or installing. If you have 240 VAC, you need the C12E (dual-voltage) or the ATEA/ATMA. The label on the CJ1A says “115 VAC Only” in bold — read it.

❗ 2. 24 V Output is 1 A — It Can Handle Relays, But Not Large Contactors

The +24 V output is rated at 1 A continuous. 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) to the +24 V output — 1.6 A total. The output sagged to 18 V, the contactors chattered, and the power supply overheated. The +24 V output is for relays and small solenoids — not for large contactors. If you need more than 1 A, use the +24 V output to drive a solid-state relay that switches an external 24 V supply. Or use the CJ1A’s +24 V to trigger a contactor’s control input only — power the contactor coil from a separate supply.

3. Outputs Share a Common — No Isolation

The +5 V and +24 V outputs share the same COM terminal. I saw a site where they used the +24 V output to drive a solenoid valve and the +5 V output for the PLC input — both shared the same ground. The solenoid’s switching noise injected 100 mV onto the +5 V bus, causing the PLC input to false-trip. If you need isolation between outputs, this isn’t the unit. Use the C12AH21C (isolated 12 V aux) or separate power supplies. The CJ1A is for circuits that share a common reference.

4. Total Power — 84 W Shared, But the +5 V Takes Priority

The CJ1A has a total power of 84 W. The control loop prioritizes the +5 V output. If you load the +24 V to 1 A (24 W) and the +5 V to 12 A (60 W), you’re at 84 W — the limit. At the limit, the +5 V will start to droop. Keep total power under 80 W for reliable operation. That means if you’re using the +24 V at 1 A (24 W), limit the +5 V to 11 A (55 W) — total 79 W. If you’re using the +5 V at 12 A (60 W), limit the +24 V to 0.8 A (19.2 W) — total 79.2 W.

5. Input Fuse — 4 A, Slow-Blow, Replace with Exact Rating

The CJ1A has an internal fuse — 4 A, 250 V, slow-blow. If you blow it by overloading the unit (or by plugging it into 240 V), replace it with the exact rating. I saw a tech put in a 6 A fuse — it didn’t protect the unit the next time, and the MOSFETs failed. Use 4 A slow-blow, 250 V. If you’re using an external fuse, use the same rating. A fast-acting fuse will blow during inrush.

New Original vs. Refurbished: Why It Matters

The DS3820CJ1A 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 115 VAC-only, dual-output supply with the exact transformer and rectifiers GE specified. The +24 V output uses a separate secondary winding on the transformer. Refurbished units often have the +24 V rectifier replaced with a lower-current part — 1 A continuous is too much for a 0.5 A diode, and it overheats. Failure rate on refurbished CJ1A units is around 14% in 18 months, versus 3% for new surplus. The +24 V output is the most common failure.

Real cost of a refurbished failure: The +24 V output fails. Your relays drop out. A conveyor sorting line loses power and jams — 2 hours of downtime, 15,000 in lost production. The price difference between refurbished (1,200) and new surplus (1,800) is 600. That’s less than 5 minutes of downtime in that sorting line.

What we provide as proof: OEM box photo, date code, a photo of the transformer showing the +24 V winding, our load test data, and a voltage measurement of the +24 V output at 1 A. We also include the 115 VAC warning sticker.

Pricing context: Our price sits 30–35% above refurbished alternatives but 25–30% below GE’s 2016 list — about $2,400 adjusted.

Performance Benchmarks & Test Results

Output regulation (measured June 2026)

• +5 V: no load = 5.02 V; 12 A = 4.95 V (1.4% regulation)
• +24 V: no load = 24.1 V; 1 A = 23.2 V (3.7% regulation — within ±5%)
• Load combination: +5 V at 10 A, +24 V at 0.8 A — outputs: +4.98 V, +23.8 V.

Cross-regulation

• When the +5 V load steps from 5 A to 12 A, the +24 V output droops from 23.6 V to 23.2 V — 0.4 V drop. Recovers in 4 ms.
• When the +24 V load steps from 0 to 1 A, the +5 V drops from 4.98 V to 4.95 V — 0.03 V drop.

Ripple

• +5 V at 12 A: 38 mV peak-to-peak
• +24 V at 1 A: 140 mV peak-to-peak (spec <150 mV)

Thermal performance

• 80 W load, 115 VAC, 25 °C ambient: heatsink temp after 8 hours = 67 °C.
• 80 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 70 W. At 55 °C, max 60 W.

Efficiency

• 80 W load, 115 VAC: input power = 98 W, output = 80 W. Efficiency = 82%.

Hold-up time

• 115 VAC, full load: +5 V held >4.85 V for 22 ms. +24 V holds for 18 ms.

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