We take cryptocurrency — so the coins you hold can buy real hardware.Pay in crypto, spend it on real hardware. Free insured shipping worldwide over $399. Plain, unbranded boxes, sent from Germany.Free insured shipping over $399. Your rate is locked for 30 minutes once checkout opens.Rate locked 30 minutes. Every item sealed, serial-checked and covered by a 24-month warranty.Sealed, 24-month warranty.

Saved items Sign in
Small rectangular USB to RS422/485 converter, matte black plastic housing

Black Box Corporation

Black Box Corporation SP390A-R3 data converter

SKU CH-P99A-FB3JR MPN SP390A-R3

Converts USB to RS422 and RS485 with opto-isolation in a 3 by 1.7 by .8 inch TAA-compliant enclosure

  • USB powered converter with opto-isolation for reliable serial links
  • Connects USB to RS422 and RS485 devices through two ports
  • Compact 3 by 1.7 by .8 inch design fits tight spaces
  • RoHS WEEE certified and TAA compliant for regulated projects
  • Backed by a five year limited warranty for long term confidence

USB-to-serial converter for industrial links

The Black Box SP390A-R3 translates USB signals to RS-422 and RS-485 levels, adding opto-isolation to protect host equipment from ground loops and voltage spikes. Two ports share the USB bus so a single cable carries both data and power. The unit is TAA-compliant and RoHS-certified for regulated projects.

Low heat and silent operation

With no moving parts and a USB-only power source, the converter draws minimal current and produces no audible noise. The compact enclosure measuring 3 by 1.7 by .8 inches dissipates heat passively, so it stays cool inside cabinets or DIN-rail mounts without forced airflow.

Replaces basic non-isolated adapters

The jump is worth it when signal integrity matters over long cable runs or between buildings with different ground references. Builders who need more than two ports or a different physical interface should look elsewhere.

Highlights

  • USB powered converter with opto-isolation for reliable serial links
  • Connects USB to RS422 and RS485 devices through two ports
  • Compact 3 by 1.7 by .8 inch design fits tight spaces
  • RoHS WEEE certified and TAA compliant for regulated projects
  • Backed by a five year limited warranty for long term confidence

Specifications

BrandBlack Box
Shipping weight68.13 kg
Package size254 × 25 × 25 mm

Questions about this item

How do I install the SP390A-R3 USB to RS422 & 485 converter and which step is often missed?

Connect the unit to a USB port for power and data, then attach RS422 or RS485 devices to the two ports; the step often missed is confirming the opto-isolation links are intact before applying bus power.

What maintenance or replacement will the SP390A-R3 need over time?

The converter has no moving parts or user-serviceable components; if the opto-isolation barrier or USB interface fails after extended use, the entire unit would require replacement under the five-year warranty period.

What limit appears first on the SP390A-R3 during sustained high-throughput use?

The USB bus power budget and the two-port RS422/485 throughput ceiling are the first constraints; sustained heavy traffic on both ports can saturate the available USB current and aggregate bandwidth.

New to this? Which coin should you pay with — what to check, what it costs to pay, and what is never asked for.

Also in this aisle

People compared these

Same shelf, same checkout — eight coins and a 30-minute rate lock.