📝 Description
Used product. Studer Solar / Joker J-402 S inverter, identified on the nameplate as Joker J-402 S M04, designed for OFF-GRID / Stand-Alone photovoltaic systems with a 24 V battery. It is a pure sine wave inverter designed to convert the battery's DC voltage into 230 V AC power. The J-402 S model is documented as a 400 W / 400 VA, 230 V – 50 Hz off-grid inverter.
⚙️ Technical Specifications
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Type: OFF-GRID / Stand-Alone
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Technology: pure sine wave inverter
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Model: Joker J-402 S
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Visible marking: Joker J-402 S M04
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Battery voltage: 24 VDC
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Battery voltage range: 21–32 VDC
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Rated power: 400 W
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Apparent power: 400 VA
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Output voltage: 230 VAC
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Frequency: 50 Hz
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Phase: single-phase
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MPPT: not applicable; this is not an ON-GRID photovoltaic inverter with an MPPT tracker
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Internal fuse: nameplate indication Max. 15 A
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Manufacturing: Made in Switzerland
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Cooling: the enclosure has side openings for heat dissipation
The safety nameplate also clearly shows “U battery: 24V (21–32V)”, “U out: 230 V / 50 Hz” and “P out: 400 W – 400 VA”, together with the warning “Don't connect to public grid or generator”, confirming its intended use in autonomous systems and not for direct connection to the public electrical grid.
⚡ Function in the Electrical System
The Joker J-402 S converts the energy available from the 24 VDC battery into 230 VAC pure sine wave power at 50 Hz, allowing AC loads to be powered within a system isolated from the grid. The available power is 400 W / 400 VA, so it is primarily suitable for small loads and equipment compatible with its rated power. The product is classified as Off-Grid in the current commercial documentation for the model.
🏭 Construction and Installation
The construction is typical of Studer inverters from this generation, with a painted metal enclosure, black side protections and high-gauge DC connections already installed. The red (+) and black (−) battery connections and the AC output connection are visible. The device must be installed in a protected, dry and adequately ventilated environment, avoiding direct exposure to water and providing sufficient space for heat dissipation.
🌐 Applications
- Small OFF-GRID photovoltaic systems
- Stand-alone systems with 24 V battery
- Cabins, motorhomes and applications isolated from the grid
- Powering AC loads up to 400 W, always checking the starting current of the loads
- Solar systems where battery charging is handled by a separate charge controller
🛡️ Safety and Product Condition
The unit is used, with normal surface signs of use and handling visible on the paintwork. The original packaging shows clear signs of wear and deterioration of the cardboard. DC wiring with cable lugs, connectors and the original “User's and Installer's Manual” are included.
The nameplate explicitly indicates high voltage 230 V / 50 Hz and states that the device must not be opened before disconnecting the line and battery. Before commissioning, battery polarity, cable cross-section, protection devices and ventilation must be checked. It must not be connected to the public grid or to a generator, as directly indicated on the nameplate.
Operation cannot be considered verified from the photographs alone; for sale as a tested device, a test with a 24 V battery and controlled load is recommended.
📦 Package Contents
- 1 × Studer Joker J-402 S M04
- DC connection wiring present on the device
- Original Studer Joker manual
- Original packaging visible in the photographs.
🚀 Final Description
The Studer Joker J-402 S is a 400 W / 400 VA pure sine wave OFF-GRID inverter, with 24 VDC (21–32 V) battery input and 230 VAC – 50 Hz output. It is a device from the historic Studer/Joker range intended for small autonomous systems, featuring robust construction and pre-installed DC connections. Current commercial documentation identifies the J-402 S specifically as a 400 W, 230 V single-phase off-grid inverter.
